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J 
RY 
-istl No. XXX: 
REPORT FOR 1921 
LANCASHIRE SEA-FISHERIES LABORATORY 


THE UNIVERSITY OF LIVERPOOL 


SEA-FISH HATCHERY AT PIEL. 
Dp 


Proressor JAMES JOHNSTONE, D.Sc. 
Honorary Director of the Scientific Work. 


LIVERPOOL. 
Printep By C. Trytine & Co., Lrp., 53 VictortA STREET 


1922. 


REPORT ON THE INVESTIGATIONS CARRIED ON 

IN 1921 IN CONNECTION WITH THE LANCASHIRE 

SEA-FISHERIES LABORATORY AT THE UNIVERSITY 

OF LIVERPOOL, AND THE SEA-FISH HATCHERY 
AT PIEL, NEAR BARROW. 


EDITED BY 
Proressorn JAMES JOHNSTONE, D.Sc., 
Honorary Director of the Scientific Work. 


CONTENTS. PAGE 
Introduction. Jas. Johnstone... Soe ees AOC 5c sa8 1 
Classes and other Work at Piel. A. Scott doc 506 306 el 32 
The Plaice Fisheries of the Irish Sea. Jas. Johnstone, W. Birtwistle 
and W. C. Smith. (See separate contents) nbc 265 Sie 37 
A Biometric Study of Irish Sea Herrings. W. Birtwistle and H. Mabel 
Lewis ... ene wae wes nde HOS Sor bor LS) 
Chemical Composition of the Mussel, Tables of Results. R.J. Daniel 205 
Some Diseases and Parasites of Fishes. Jas. Johnstone sae Seon 
Appendix: Report on Ribble Mussel Beds. W. Birtwistle ... At end 
INTRODUCTION. 


The greater part of this Report consists of a summary 
and discussion of the results of two investigations that have 
now been carried on for a number of years: these are (1) the 
plaice research, commenced by the Committee in 1908 and then 
continued during 1919-21 as part of the work done under a 
special grant made by the Ministry of Agriculture and Fisheries, 
and (2) the biometric investigation of herring races, begun in 
1913 as part of an international research. We think it desirable 
that these routine observations should now be suspended so 
that it may be considered what are the results and what they 
indicate. For the opportunity of publishing the complete 
results of the plaice work we are indebted to the Development 
Commissioners, who have kindly allowed us to spend the balance 
remaining over from the grant made for directed fishery 
research in the Irish Sea. In addition to these two series of 
data there remain Mr. Scott’s numerous estimations of organisms 


2 


present in the fourteen years’ samples of plankton taken by 
Professor Herdman at Port Erin. These data are also being 
summarised and discussed, and it is hoped that the results 
may be ready in another year. It cannot be doubted that 
full consideration of the observations so far made will indicate 
new and fruitful lines of investigation, and it is probably 
inadvisable to continue working by purely routine methods 
without some interval of close criticism. 


The Plaice Report. 
This consists of :-— 

(1) A summary, brought up to date, of the measurements 
of Irish Sea plaice, made on the various fishing 
grounds, during the years 1908-1920, by the Officers 
of the Committee. 

(2) A complete summary of all the results of the plaice- 
marking experiments made during the years 1906- 
1913. 

(3) A summary of the results of observations made on 
board fishing vessels during the years 1919-1920. 
This work was arranged/ by the Oceanography 
Department as part of the scheme of “ Directed 
Research in the Irish Sea.” 

(4) A general discussion of all the results obtained made 
from the practical administrative point of view. 


The attitude taken up in the course of this work was that 
of the need for restrictions on seasons and methods of fishing 
should it appear that there is a progressive impoverishment 
of the Irish Sea plaice fisheries. The conclusions made from 
the work already done may be stated briefly (and rather 
dogmatically in the meantime) :— 

(1) Impoverishment of the Irish Sea Fishing Grounds. 

Nothing in the results obtained suggests that there has 

been such an impoverishment. There are ups and downs. 


3 


The causes of these fluctuations is an interesting, scientific 
problem, and one which may be solved—given sufficient 
resources for investigation. 


(2) Effect of War-time Restrictions on the Fishery. 

There is no evidence that the military restrictions, in 
operation in the Irish Sea in the years 1914-1918, had any 
observable effect on the abundance of the plaice there in 
1919-1920. 


(3) Size-limits for Plaice. 

There is no evidence that a size-lmit for plaice that may 
legally be landed would have any effect on the abundance of 
commercially valuable plaice on the Irish Sea fishing grounds. 

A word or two may be said about what we regard as 
“evidence.” Jf the Irish Sea plaice grounds are being 
impoverished by too much trawling ; 7f the military restrictions 
of 1914-1918 led to an accumulation of plaice in the Irish Sea, 
and ¢f a size-limit could be shown to be useful in preserving 
the plaice grounds from impoverishment. Then the practical 
outcome of these findings would be administrative restrictions. 
These restrictions would create new legal offences, punishable 
by fines or imprisonments. 

Therefore the scientific evidence that would justify us in 
making administrative restrictions and by-laws ought to be of 
the same nature, or just as convincing as would be the evidence 
required by the police courts for the conviction of a fisherman 
who would infringe these by-laws. We know what is the 
nature of the latter evidence, and we hold that the results 
obtained from these investigations have not the same degree 
of strength and ought not to be used for the establishment of 
new legal offences. 

But the results that have been obtained may be strong 
enough to justify a fishery authority in spending money on what 
may be called fishery development. We do not say that it is 


+ 


because we do not know that any schemes of development are 
in contemplation. Also if a period of much greater exploitation 
of the fishing grounds should come about in the near future— 
say, as the result of a condition of severe food shortage—then 
the results that we give here will make it all the easier to find 
the point at which we may be taking more from the fishing 
grounds than the recuperative powers of the latter can stand. 
But we hope that the tendency of these investigations, and those 
others that they suggest, will be in the direction of culture 
vand development. 


The Natural History Results. 

From the point of view of general marine biology the 
results indicated in the report raise very curious and fascinating 
(and perhaps economically significant) problems. The shallow 
sea off the Lancashire and Cheshire coasts, and the foreshore 
there, may be rather unattractive to the zoologist. The 
foreshore is mostly sand and mud; there is much pollution 
from the adjacent cultivated and densely populated land area, 
and the fauna and flora are commonplace from the point of 
view of the naturalist collector. But the entire region is one 
of extraordinarily high production because most of the organic 
matter, in the form of foodstuffs, that is consumed in the 
densely populated country draining into the Irish Sea off the 
coasts of Cumberland, Lancashire and Cheshire 7s again 
converted into organic matter. This enormous production of 
proteid, fat and carbohydrate that goes on in the sea, entirely 
from waste materials, is almost wholly beyond human control. 
Only in the case of the mussel transplantation experiments, 
made at Morecambe by the Committee, has there been any 
attempt at utilising this production from waste matters. The 
question of how still further to make use of the surplus pro- 
duction of the sea may well become one of prime importance 
in the future, and what appear now to be perfectly abstruse 
problems of pure marine biology may require to be studied 


5 


in order that we may usefully control these powers of production 
of organic substance. Many things that are apparent in present 
economic tendencies suggest that this control over the regenera- 
tive power of the littoral seas simply must be acquired. 

The conditions that we speak of result in a shallow sea 
densely crowded with marine organisms that have little or no 
economic value : mussels, cockles, and shellfish that are mostly 
unutilised ; small plaice, dabs, flounders, solenettes, sprats, 
etc., that are not caught ; “* sea-weeds ” that contain enormous 
stores of cellulose, chitine, and other substances that might be 
used, but are not—and so on. 

Here we are only concerned with the plaice. The quantities 
that come into existence annually in the sea from the Solway 
Firth down to the coasts of North Wales are probably illimit- 
able—in the sense that fishing operations, as at present carried 
on, do not appear to make any sensible difference in their 
abundance. Of all the plaice eggs that are spawned in the Irish 
Sea every year only a rather small percentage become trans- 
formed larve. A certain combination of conditions, tempera- 
ture of the sea, density, strength and direction of resultant 
tidal streams and wind drifts, certain food organisms that 
appear just at the right time and in the right quantity, intensity 
of sunlight, ete.—probably all these and other conditions must 
co-operate in a timed manner in order that a large proportion 
of the fertilised plaice eggs produced during the spawning 
period may develop into baby plaice. Then, just for the few 
weeks that these larval plaice are living on the very shallow 
sea bottom just outside tide marks there must be plenty of the 
right kind of food organisms in the sand and in the water 
immediately over the latter—it will be no use if this plentifulness 
of food occurs a few weeks earlier or later than the very few 
weeks when the little plaice come close to the shore. A certain 
small proportion of the latter, therefore, are well fed and survive 
for a couple of years to be caught by the inshore trawlers, who, 


6 


nevertheless, only catch a small fraction of the fish that are 
there. Further on, after the plaice have become about three 
years old, a small fraction of them migrate out into deeper 
waters, beyond the territorial limits, and are caught by the 
smacks and steam trawlers. Hitherto it is the fate of this 
latter fraction of a per cent. of the whole plaice population, 
annually coming into existence, that has been studied. Of the 
fate of the plus 99 per cent. that perish before they are big 
enough to be caught by a trawl-net we know hardly anything. 

A very few, then, of the plaice that can be taken in a 
shrimp-trawl migrate out to sea, become big, valuable fish, 
spawn, and are sooner or later caught. This fraction consists 
of individuals that have greater “ vitality,’ grow more rapidly, 
are more “restless,” and are more precocious in their assump- 
tion of sexual maturity than are the average fish. The mediocre 
individuals—which constitute by far the greater number—are 
less variable, and they tend to remain longer on the over- 
crowded nursery grounds, where they develop and grow slowly. 
How to assist them in obtaining better conditions of life may 
well be the great task of fish culture of the future, and all 
experimental and observational work and all practical trans- 
plantation operations help to solve this problem. Then there 
is the greater problem of the utilisation of surplus, ‘“‘ waste ” 
production. The substance of the hundredweights of plaice 
that die in the sea uselessly (in contrast with the ounces that 
are caught usefully) is not lost, but appears later in the forms 
of crabs, molluscs, worms, starfishes, sea-weeds, and a multitude 
of other organisms that have—as yet—no commercial signifi- 
cance for us: at the most we think about them as a possible 
form, or source, of manure! Fishery work of the future will 
probably be dominated by the impulse to utilise the waste 
production of the shallow seas, just as that of the past has been 
obsessed by the fear of depletion and has resulted in successive 
crops of restrictions of very doubtful value, This idea of 


ff 


making use of surplus production seem to us to be the one 
which must give the keynote to the scientific research of the 
near future and reconcile the administrators to investigations 
which, no doubt, seem abstruse and pedantic in the extreme. 


Further Work on the Plaace. 

Some other researches, which are not of a routine nature, 
have been made, or are in progress, but are not published here. 
A series of drift-bottle experiments and corresponding fish- 
marking experiments were made by W. C. Smith in the study 
of the Solway spawning grounds. These tend to show that the 
area of the Irish Sea, north from Isle of Man and St. Bees’ Head, 
is a self-contained one, so far as the plaice is concerned. Along 
with this an account of the Cumberland sea-fisheries in 1919 
has been prepared. Collections of small plaice were made on 
the Manx and Cheshire foreshores by W. Birtwistle and W. C. 
Smith, and the feeding of these has been studied by A. Scott, 
who has also identified the food organisms found in a large 
number of larval and post-larval plaice spawned and reared 
at Port Erin: the results of this latter investigation are being 
published elsewhere. Plankton is being collected from the 
spawning and rearing ponds at Port Erin, and this is being 
described by A. Scott, for comparison with collections being 
made simultaneously in the adjacent sea. It is hoped that 
some useful information as to the nutrition of larval plaice 
may thus be obtained. Some much-needed experimental work 
on conditions of metabolism of developing plaice eggs has also 
been commenced by Professor Dakin, but this research is still 
in the tentative stages. Finally, a study of morphological 
variability in plaice is also bemg made. 


The Biometric Investigation of the Herring. 


In 1913 the Ministry of Agriculture and Fisheries requested 
this Laboratory to take part in a general scheme of investigation 
into the various races of herring which were assumed to inhabit 


8 


North European Seas. It was previously known that herrings 
from the North Sea, Baltic, Norwegian coasts, etc., presented 
various peculiarities—mainly in the proportions of the parts 
of the body—and it was thought that these variations in form 
were good evidence in favour of the idea that each great sea 
area had a different ‘“‘ race” of herrings, and that there was 
little or no inter-mixture between these various races. The 
migrations and shoaling movements made by the fish were, 
it was thought, all local ones. It was assumed that by making 
large series of measurements certain bodily characters could 
be found which would serve to distinguish between these 
various races. The first series of measurements were made 
by Mr. W. Riddell in 1913 and 1914, and the research was then 
suspended until 1919, when it was resumed by Mr. W. Birtwistle 
and Miss H. M. Lewis. 

It was suspected that even in such a small area as the 
Trish Sea there would be more than one race of herrings. It 
is known, of course, that there are at least two such races : 
one which shoals off the 8.W., 8. and 8.E. Coast of Isle of Man 
sometime about May or June, and then spawns in August or 
September, when the shoals disperse. Another school of 
herrings shoals in Cardigan Bay sometime about October and 
November, and then proceeds to spawn. In this case the 
shoaling and spawning begin first at the southern extremity 
of Cardigan Bay and then takes place a little later in the year 
in Carnarvon Bay, and finally off the North Coast of Anglesey. 
This is the usual progress of the fishing, and what we know 
about it is derived from the catches made by the local boats, 
for we have never been able to make big fishing experiments 
ourselves. The herrings may, however, appear much earlier 
in the spring, off the Manx coasts, than May, when the com- 
mercial fishery usually begins, and it is quite possible that they 
are there from the beginning of the year, but their quality is 
so poor that it is not worth while catching them. 


9 


‘ 


Thus there appeared to be two “ races ” of herrings in the 
Trish Sea—the Manx summer and the Welsh winter spawners. 
But the conditions are not quite so simple as this. It has been 
known for some years that herrings may be caught by means 
of trawl-nets, and big catches were so made, before the war, 
by steam vessels working in the North Channel (between 
Scotland and Ireland) and in St. George’s Channel (off the 
Smalls). Some of these fish were examined in 1913 and it 
was found that they were different from those obtained from 
the Isle of Man and the Welsh Bays. Further, in 1921 quite 
unusual conditions were observed. 

At various times in the past there have been commercial 
fisheries for herrings off the coasts of Cheshire, Lancashire and 
Cumberland, where the fish do not occur in the same regular 
way that they are found off the Manx and Welsh coasts. 
In 1894 they appeared in Liverpool Bay, and the Morecambe 
vessels followed them, catching the fish with drift-nets in the 
estuary of the Mersey itself and up the latter to near the 
entrance to the Manchester Ship Canal. Quite big catches 
were made for a time and then the herrings disappeared. 
At various times in the past, even in the eighteenth century, 
the herrimgs are recorded from the Lancashire and Cheshire 
coasts, and there are many records of their occurrence in the 
Minutes of Evidence of the various Fishery Commissions. 
Long ago there used to be a fishery off the coast of Cumberland, 
and the “ Parton Herrings,”’ caught a few miles north of 
Whitehaven, had a great reputation and have left a kind of 
legend in that part of the district. For many years, however, 
there have been no herrings off the Cumberland, Lancashire 
and Cheshire coasts, or, at least, not nearly enough to give rise 
to a distinct fishery. Now and then, of course, a few fish may 
be caught almost anywhere along these coasts, and the young 
ones, of one year old or less, are always there. 

At the end of 1921, however, Morecambe Bay was reported 


10 


to be “ full of herrings,’ and about the same time they were 
being caught off the coast of Cumberland. Some small samples 
were obtained, but not regularly, for there was no drift-net 
fishery. (Quite big catches were, however, taken in the 
“baulks ”’ at Heysham.) The fish were exceedingly lean and 
were very poor eating. Most of them were spent though so 
many were found to be “full” that it seems probable that 
these fish were shoaling and spawning. Apparently they were 
present all along the coast from the Solway down to Great, 
Orme’s Head. 

Thus we have to consider (1) the regular summer herrings 
that spawn in the region between Ardglas, in Ireland, and the 
Isle of Man, and (2) the equally regular winter spawning in 
Cardigan and Carnarvon Bays : these two fisheries never appear 
to fail. Then there are irregular fisheries which occur off the 
Cumberland, Lancashire and Cheshire coasts after long intervals 
of time. 

When the biometric investigations were commenced it was 
thought that each of these regular or irregular fisheries was 
that for a distinct “race” of fish. In order to establish the 
characters of these races a large number of fish had, presumably, 
to be measured and studied. There is so much individual 
variability between fish and fish that many hundreds would 
have to be measured in order to get reliable average values 
for each of the characters taken as diagnostic of the various 
races. Also the measurements were rather delicate ones, 
subject to some considerable, unavoidable errors; the fish 
were not always in good condition when they were received ; 
even the examination of so small a sample as 50 was quite a 
long job; different measurers did not always get precisely 
the same results; Wwe were never quite sure what were the 
best “‘ characters’ to measure—in short, the methods were 
not perfectly satisfactory ones and it was thought 
desirable to suspend the routine collection of data for a 


et 


while and see what was to be made out of those already 
accumulated. 

Believing that there were only the two main “ races ”— 
the Manx and Welsh ones—we thought the best method was 
to spread the collection of measurements over several years 
and to “lump ” together all the samples obtained from Isle of 


‘ 


Man, irrespective of the month or year of collection. So also 
with the Welsh fish. In that way we hoped to get such big 
series of data that the averages, and other statistical functions 
deducible therefrom, would be fairly representative ones. 
Now this method may be quite wrong. 

Even with quite small samples taken in the same region, 
and after intervals of some weeks, there may be quite noticeable 
differences: differences as big as those obtained when we 
contrast the fish taken from Isle of Man with those taken from 
the Welsh coasts. This may, conceivably, be the case even 
if we hold that there are only the two main races. It may be 


¢ 


that in taking the sample this week we have “ accidentally ” 
included more of the herrings that vary from the average in one 
direction while, in the next small sample, we may have included 
more of the herrings that vary from the average in the other 
direction. If this is so there is a test, based by Professor Karl 
Pearson on the statistical theory of random sampling, which 
can be applied. 

But it is also possible, and some results of general biology 
make it quite likely, that there is another explanation. It may 
be that, instead of two main “ races ”’ there are really a number 


ee 


of “ sub-races,” or “ genotypes,” that is, strains of herrings, 
that are really permanent, or the same from generation to 
generation, except in so far as they may vary by inter-mixture 
with each other. This inter-mixture may, however, be regarded 
as rather improbable because of the tendency of the herrings 
to remain together as lonely aggregated schools. There are, 


then, a number of strains, or genotypes, of Irish Sea herrings 


12 


differing from each other in those shapes, or proportional 
lengths of parts of the body which we call morphological 
characters, and those differences which we can observe in 
studying samples obtained month by month from the same 
fishery region may be due to the successive appearance of 
the various genotypes, or to the predominance of one or more 
of them in the samples. Further, the various genotypes may 
respond differently to the nature of the environment, the 
temperature and salinity of the water, or the reaction or some 
other physical condition. In the course of the Manx summer 
fishing, for instance, these physical conditions change markedly, 
and so there may be successive immigrations of different 
herrings—something like this is really what the fishermen appear 
to think is the actual case. If so, then, it will be wrong in 
principle to adopt a method of “lumping” together data 
obtained from the same region in order merely to get the big 
samples, which appear to be necessary from the statistical 
point of view. 

It is with these considerations in mind that a critical study 
of the methods and data of the herring race investigation has 
been attempted by Mr. Birtwistle and Miss Lewis. 


Shellfish Investigations. 


Two troublesome questions arose in the course of the 
administrative work of the Committee: (1) the alleged over- 
crowding of some of the cockle beds in the neighbourhood of 
the Dee, and (2) the pollution of the mussel beds in the estuary 
of the Ribble. ‘The former difficulty originated im complaints 
made by some fishermen that the cockles on certain beds were 
so small that most of them passed through the legal gauge. 
This was probably the case, but the matter was not to be 
remedied by reducing the legal size and so enabling a few men 
to glut their customers with small cockles fetching a much 
smaller price. In such circumstances the remedy must lie in 


13 


transplantation. The beds were examined and counts made of 
the numbers of cockles present in a square foot of sand on various 
parts, but the investigation was not pressed since it had little 
interest except where associated with some other shellfish 
research, which we have not yet been able to start. It has 
now been shown by the past work of the Committee that 
conditions of local overcrowding and stunting of growth, both 
with regard to cockles and mussels, can easily and profitably 
be remedied by transplantation. The difficulties are adminis- 
trative ones and are only to be removed by a rational system 
of control over the foreshore fisheries. 


The Ribble Mussel Fisheries. 


In 1921 the mussels taken from the Ribble Estuary again 
came under suspicion and several inspections were made by 
Messrs. Scott and Birtwistle, with the cordial assistance of the 
Harbour Authority. I saw this district in 1913, when there 
was also suspicion that mussels growing there were communi- 
cating typhoid fever. Very marked changes have occurred 
and these are due to the extension seaward of the training walls 
built in order to establish the new channel leading up to the 
Port of Preston. Charts marked then and in 1921 show these 
changes very clearly, and the altered conditions must be taken 
into account. The fact is that an almost continual revision 
of the charts representing the conditions of the mussel and 
other shellfish beds, channels and sewer outfalls is quite 
necessary in order that this question of sewage contamination 
may be studied in a really satisfactory manner. Every case 
that arises demands renewed local survey. 

There are two implicated regions in the present case : 
(1) the mussel beds on the foreshore, adjacent to the St. 
Annes-Lytham shore, and (2) the mussels growing on the 
training walls, much further away from the primary sources 
of pollution. The precise locality under (1) in question in 


14 


1921 was that known as “ Church Scar,” and this is subject 
to recent and significant sewage pollution. The adjacent shore 
is the locus of a good, residential population, and it is a well- 
known holiday resort, so that the contamination of the sea 
in its vicinity cannot be said to be free from danger. It is a 
place where people may go to recuperate after illness, and so 
there is always the chance that convalescent typhoid patients, 
who are still in the infective stage, may be temporarily resident 
there. The distance between the mussel beds and the sewer 
outfalls is short, and so quite a small period of time may elapse 
between the discharge of dejecta into privies ashore and the 
fouling of the mussels with the resultant sewage, which is 
quite untreated. There has actually been a barge (with a 
privy on board) moored on the Scar and inhabited by workmen, 
but we are inclined to regard this contributory source of pollu- 
tion as less objectionable than that resulting from the much 
better-off population living in the St. Annes-Lytham district. 

The case is rather different with regard to the pollution 
of the channel adjacent to the training walls. Much of this 
must have its origin at Preston and the distance is therefore 
considerable and the pollution remote in pomt of time. 
Bacteriologically there is little difference between the two 
regions (1) and (2), but the strong impression made on Messrs. 
Scott and Birtwistle in 1921 and on myself in 1913 was that the 
bacteriological evidence might safely be neglected so far as 
the training wall mussels were concerned. Thus we disregard 
the bacteriological evidence, though the latter shows that the 
contamination both at Church Scar and on the training walls 
is gross in its degree. It is fair to say that the conditions on 
Church Scar are such that closure is to be urged, but this 
conclusion we are reluctant to make in the case of the other 
locality. 

Something must therefore be said as to the general question 
of shellfish pollution by way of justifymg these findings and 


15 


also because this matter looks like again becoming one of 
public importance. 


Enteric Fever and its Incidence. 


It is instructive to notice the very remarkable way in which 
the mortality from enteric fever has diminished during the 
period of modern public health administration. The following 
figures have been extracted from the Report of the Registrar- 
General for 1919, and the decrease is most obvious :— 


Death Rate, per Mullion Persons living in England and Wales, 
from Enteric Fever during the last 80 years. 


1838-1842 ... ee 058 1891-1895 ... sev DTA 
1847-1850 ... we ol246 SIO L900 an, a lno 
1851-1855 ... noon heb 1901-1905 ... ceey ) tS 
1856-1860 ... bout Oe 1906-1910 ... dais 70 
1861-1865 ... Shed asp re 1911*1915 ... uae 47 
1866-1870 ... jth 2O00) 1916 as ae 30 
1871-1875 ... yee ole 1917 fe wale 28 
1876-1880 ... arene AUT 1918 as as 26 
1881-1885 ... sap, oil) GS) es ass 16 
1886-1890 ... 179 


It is to be noted that the statistics from 1838 to 1870 
include enteric fever, typhus fever and pyrexia, these diseases 
not being distinguished in the above data for the period in 
question. There can be little doubt that the contribution 
made by the two latter causes was considerable during the 
first half of the nineteenth century. The conditions due to 
the rapid development of the modern factory system, the 
overcrowding and insanitary housing of that period, unemploy- 
ment and general malnutrition among much of the artisan 
and labouring classes during the “hungry forties ’—these 
were, no doubt, responsible for the “ destitution disease,’ which 
we now know typhus to be. About 1870, however, enteric 
fever became distinguished, and it alone appears in the table 
for the years subsequent to that date. During the latter half 
of the nineteenth century typhus fever practically disappeared 


16 


from England—the result of better housing and nutrition, 
and plain, commonsense methods of sanitation. 

But even when we take account of this qualification of the . 
meaning of the table it is plain that the mortality from enteric 
fever has steadily diminished throughout the whole period, 
and this is so even during the war years 1914-1918 (for which 
years the death rate is calculated only for the civilian popula- 
tion). One might, at first sight, have expected some relaxation 
of public health administration during those years of strain, 
but this has not been the case—the rate of decrease is even 
creater than it was in the preceding decade. The entire record 
is a remarkable and very creditable one, and it ought to lead 
to a renewed appreciation of the medical service as it is 
organised in this country. It does not, at first, occur to one 
to reflect that this is the only profession which, by perfecting 
its work, tends always to render itself unnecessary ! 

It would be worth while, if there were the opportunity, 
to examine into the measures by which this notable reduction 
in the mortality from typhoid has been brought about. It is 
probable that no one line of public health work is to be singled 
out—for instance, prophylactic treatment only came into 
general use during the war period and was applicable only 
in the war services. What we have to thank for the effect 
noted has been the consistently maintained and always 
improved public health administration and a general, all-round 
effort to do all that is possible to minimise the chance that 
any person whatever in the population might contract epidemic 
disease, because with modern means of intercommunication 
the risk of infection has always tended to become greater, and 
class-distinctions tend to have no significance in this connection 
—it is all the same to the public health administrator what is 
the social standing of the patient: the labourer incubating 
for typhoid and using a privy on a barge moored on Church 


Scar has just the same “ epidemiological value,’ neither more 


17 


nor less, as has a Manchester millowner residing at St. Annes, 
if the latter also harbours Bacillus typhosus. This attitude 
has its significance: any person who is suffering from typhoid 
fever is a focus of infection ; the service is a public one, and its 
result has been the preservation of the health of the individual. 
And so, because of the existence of medical research, no one 
cause of dissemination of enteric has, for any great length of 
time, been over-estimated in value by the public health 
administration ; on the other hand fishery authorities have 
rather tended to become obsessed with the idea that mussels 
are the way in which typhoid is carried. It has been said that 
there still remains a persistent residue of the disease and that the 
cause is polluted shellfish, but in view of the now generally 
recognised fact that apparently healthy persons may be 
“typhoid carriers ” this view cannot be maintained. 


The evidence that Enteric Fever is conveyed by Shellfish. 


Without doubt the consumption of sewage-infected oysters, 
mussels and cockles 7s a cause of enteric fever, but a candid 
survey of all the available evidence does not convince one 
that this is even a prominent cause. It must be remembered 
that the role of shellfish in conveying the infection has only 
been attentively studied since 1894, when the late Dr. H. T. 


‘ 


Bulstrode made his well-known investigation into “oyster cul- 
ture in relation to disease.” Further, administrative measures 
designed to prevent communication of typhoid by this means 
cannot have been effectively applied until the first few years 
of the present century, yet a glance at the table on p. 15 will 
show that an enormous decrease in the mortality from the 
disease characterised the last decades of the 18’s. For this 
decrease we must therefore look to other action than that 
taken with respect to polluted shellfish, and the same kinds of 
action have doubtless continued to be taken,and with the same 


success, during the last dozen years or more. The statistics 
B 


18 


show that the residue of enteric is certainly not a persistent 
one, and one need not hesitate to conclude that some of it, at 
all events, is due to the existence of “carriers,” imsanitary 
dwellings, slums, locally defective drainage, open middens, 
ashpits, flies, etc. It is probable that far more stringent 
sanitation in the overcrowded quarter of big towns will be 
necessary to reduce the mortality to vanishing point, than has 
been necessary to arrive at the present rate. The residue is 
small, but the risk of any one person dying from enteric is still 
appreciable, while the risk of illness is, of course, much greater ; 
it is no consolation to the typhoid patient to reflect that his 
is only one of the dozen or two cases per million ! 

There is, of course, satisfactory evidence that typhoid 
fever is conveyed by means of polluted shellfish, yet it is very 
surprising to find that such satisfactory evidence is rather 
exceptional. If it were not for the well-known cases of 
epidemic illness following the two famous mayoral banquets 
at Winchester and Southampton (the cases investigated by 
Bulstrode) such evidence as is often adduced at the present 
time would lose a great deal of its force. These two classic 
investigations have, in fact, established a tradition which 
subsequent work can hardly be said to have maintained. It 
will be useful to quote some instances of the kind of evidence 
that has been regarded as proving the connection of typhoid 
fever and shellfish consumption :— 

(1) A ate steamed mussels on September Ist and fre- 
quently from then to November 29th. Then he 
ate a raw mussel and said to his wife that it was 
not good. He became ill on December 4th. His 
blood reacted positively on December 27th. He 
died on January 12th. 

(2) B ate cooked mussels on December 17th and he was 
ill seven days later. His blood gave a positive 
reaction on December 29th. He died on January 3rd. 


19 


He had influenza prior to November 24th. All his 
family ate cooked mussels on December 17th, but 
he was the only one who became ill. 

(3) C ate raw and cooked mussels at the beginning of 
December. Other members of his household ate 
cooked, but not raw mussels. C was ill on Dec. 12th, 
and on December 31st his blood gave a positive 
reaction. He died on January 27th. 

(4) D ate steamed mussels and a plate of oysters at a shop 
on December 21st. She was ill on January 3rd, and 
her blood gave a positive reaction on January 10th. 
She died on January 16th. Her three companions 
also had mussels at the same time, but they had 
had enteric fever about two years previously and 
they did not become ill. 

(5) E ate cooked mussels on December 21st and was ill 
on December 28th. His blood reacted positively, 
and he died on January 24th. A friend who was 
with him also ate mussels, but did not become ill. 

All the above are actual records and they may be regarded 
as quite typical of the kind of evidence that has been taken 
as establishing the connection between mussels and disease. 
“From a review of all these cases there appears to be little 
doubt but that the association between enteric fever and 
mussel consumption is something more than mere coincidence.” 
That was the opinion of most Medical Officers of Health, and 
may be so still, but nevertheless there have been other ways 
of looking at the facts. 

In 1910 there was an outbreak of enteric fever in the 
London districts of Bethnal Green, Stepney and Poplar. 
There are various criteria by means of which outbreaks due to 
personal infection, polluted water or milk can be recognised, 
and these criteria were applied by the London Health Officezs 
in investigating the origin of these outbreaks. A process of 


20 


‘hypothetical deduction ” applied during the enquiry showed 
that the epidemic was an “explosive one” (that is, a great 
number of cases occurred at the same time and not one after 
the other); therefore it was not due to personal infection 
(that is, the communication, by direct contact, from person 
to person). Further enquiry gave no reasons for supposing 
that contaminated water or milk were causes (in which cireum- 
stances the outbreak would have been “ explosive ”’). Two 
articles of food, however, were consumed by a “ considerable 
proportion ” of the patients durmg the month preceding the 
onset of illmess—these were mussels and fried fish—but further 
enquiry showed that the mussels might be disregarded. There 
remained, then, the possibility that fried fish were the means 
by which the disease had been communicated. 

The fish implicated were plaice which had been caught 
on the “ nursery grounds” of the North Sea, and, as a rule, 
they were poor quality fish. Plaice are very usually gutted, 
but it was suggested that, in this case, the process of gutting 
had been imperfect. These North Sea grounds are, it might 
be thought, very far away from sources of sewage pollution, 
yet it was concluded that the possibility of contamination 
“was not so remote as might at first be supposed.” Further, 
the fish were fried, and this process may be imagined effectively 
to sterilise small plaice ; nevertheless the contaminating germs 
assumed to be present in the tissues of the fish were also 
assumed to have survived the ordeal of boiling oil. 

Such enquiries as this, and the other ones quoted above, 
are usually very well done. There is a regular technique, and 
the investigators employed are well-trained men who are 
thoroughly conscious of the great responsibility of their work 
and who therefore do that work consistently well. Yet here 
we have, on the one hand, enteric fever occurring in a mussel- 
eating population and a causal association established between 
the mussels and the disease, and, on the other, a group of cases 


21 


occurring in a population consuming both mussels and fried 
fish, with the result that a causal association is set up between 
the fried fish and the disease. As a matter of fact the first 
population—that is, the one in which mussels were regarded 
as the cause of the disease—was also a fried-fish consuming one. 
We can hardly doubt that much the same conditions obtained 
in both populations and that there were various ways in 
which enteric fever might have been communicated, but that, 
in each case, the Health Officers took one particular aspect 
of the whole problem. In the first group they were influenced 
by the Bulstrode tradition, but in the other a spirit of 
scepticism with regard to accepted methods was allowed to 
gain force. 

It is quite fair to say that the evidence which implicates 


6 


mussels is ‘‘ coincidence.” A man eats mussels and, a week 
to a fortnight later, he shows that he is suffering from enteric 
fever. The typhoid germs require a week to a fortnight to 
‘incubate ”’ in the man’s body and cause the symptoms of the 
disease. That may be ‘‘ mere coincidence,” but all scientific 
proofs are based on just such associations, coincidences in regard 
to events that happen simultaneously or after a certain period 
of time. The probability of a causal connection between two 
such events is small, and it has to be strengthened by the 
establishment of a series of other coincidences such as, for 
instance, those that were observable in the cases of the out- 
breaks following the mayoral banquets at Winchester and 
Southampton. The strength of the evidence in the latter 
cases was due to the number of coincidences, and its weakness, 
in the cases A to H, on pp. 18-19, is due to their paucity. 
A certain shop sells mussels which are, presumably, all taken 
from the same contaminated shellfish bed, and a man buys 
and eats these mussels and then takes enteric fever a week 
to a fortnight later. But we ought not to overlook the other 
coincidences, which seem to me to have just the same value 


22 


as scientific evidence : a great many other people buy and eat 
just the same mussels, but they do not take enteric fever. 

It is quite easy to make an explanation of this apparent 
contradiction. Probably infection by organisms setting up 
typhoid, and other infectious and contagious diseases, is far 
more common than used to be imagined. Many of these 
organisms are ubiquitous, and modern conditions of life must, 
in many cases, greatly increase the chances of their distribution. 
In no case do men and women yield easily to infection for the 
defences set up by the normal healthy body are fairly strong. 
The infection may not “take” at all (and pathologists must 
encounter such failures, even in experimental work), and if 
it does “take,” it may successfully be resisted. There are 
many ways by which Bacillus typhosus may be distributed— 
by contaminated water, milk, vegetables and fruit, flies, carriers, 
shellfish, personal infection, and perhaps also fried plaice. 
Certainly some of these may be ruled out in many cases—water 
and milk in modern conditions of public health administration, 
for instances, but, as a rule, there must generally be more than 
one means. Further, it is probable that there are conditions 
which are necessary in order that the imfection may take. 
It is probable that the bodily “soil”? must be such that the 
pathogenic micro-organisms may grow: there may have to be 
symbiosis with some other organism; or a condition of 
‘‘ rundownness ”’ due to malnutrition, overcrowding, insufficient 
warmth or clothing, etc. ; or some set of environmental con- 
ditions which we do not understand. The progress of epidemics 
does suggest this: that a number of conditions must coincide 
and co-operate in order that the pathogenic organism (which 
is thus only the immediate “ cause ’’) may be enabled to operate 
upon the bodily “soil.” Thus public health practice, while 
it may not neglect these exciting, or immediate causes, may 
neither afford to neglect the essential co-operating ones. In 
short, the role of shellfish as a contributory cause of disease 


23 


cannot be overlooked, but it can greatly be exaggerated. It 
is probable that entire exclusion of mussels from the public 
markets would not greatly reduce the incidence of enteric fever, 
while it is also possible that a very highly perfected system 
of public sanitation, in the widest sense, might reduce typhoid 
to the status of typhus without interfering greatly with the 
use of shellfish as human food. 


The Administrative Procedure with regard to Contamined 
Shellfish. 

The above discussion will throw some light on the utility 
of the present administrative methods ; these date back only 
to 1915, when the Local Government Board made the “‘ Shellfish 
Regulations,’ under which action with regard to polluted 
mussels is now taken. Prior to 1915 little or nothing was done. 
Various Health Authorities were able to exclude mussels from 
the public markets under their control, and, apparently, they 
based their action on the inspectorial work done by their own 
officials (that is, they moved on the kind of evidence furnished 
by the quoted cases on pp. 18-19), or they took action on 
inspections made, and bacteriological analyses procured by 
the Fishmongers’ Company of London. Obviously they could 
only exclude mussels from the public markets, but could not, 
in general, prevent the sale of the shellfish by hawkers, or in 
retail fish shops. Attention was drawn to the matter, but 
it is not certain that much more than that happened. There 
was no closure of the polluted shellfish beds prior to 1915 
because no public authority possessed this power. 

The “ Shellfish Regulations ” conferred this power on the 
Local Health Authorities, and the Central Authority is now the 
Ministry of Health. The procedure is interesting: if the 
local Medical Officer of Health “is in possession of information 
that any person is suffering, or recently has suffered, from 
infectious or other disease attributable to shellfish, or that 


24 


the consumption of shellfish within the district is likely to cause 
danger to public health, he shall take such steps, etc.” The 
steps are the holding of a local enquiry at which the fishermen 
are called upon to show cause why the shellfish beds suspected 
should not be closed to ordinary fishing. This procedure, which 
apparently bears rather hardly on the fishermen, does not do 
so in reality, for its result must usually be to put the local 
fishery administration on their side: the latter does not appear 
to have any definite locus standi in the matter in the course 
of the enquiry. Here, too, it is quite relevant to ask for the 
definite results of such enquiries and closures that have taken 
place, for the making of an order closing a certain mussel bed 
is not at all the same thing as the prevention of taking mussels 
from that bed. Have the ‘Shellfish Regulations” really 
prevented the marketing of polluted mussels? We are 
enquiring into the causes of the decrease in enteric fever during 
recent years and so the question is a relevant one. 

The important thing in the ** Shellfish Regulations ” is the 
phrase attributable to shellfish. What evidence satisfies the 
Medical Officer of Health that any particular case of typhoid 
fever has been caused by eating, say, mussels. Study of the 
cases quoted above will show, I think, that there is no satis- 
factory legal evidence at all. A man takes the disease, and the 
investigators discover that he has, during the two weeks 
previously, eaten shellfish, bought at a particular shop or stall 
or barrow in the streets. There is no possibility of proving 
that these particular shellfish were competent to cause infection, 
because it is only sometime after they have disappeared that 
their association with a case of disease was suspected. Enquiry, 
however, shows that shellfish of the same origin are still being 
sold, and these are analysed and are found to contain evidence of 
sewage pollution. Thus the outbreak of disease is “ attributed ”’ 
to them. Now the association thus set up is so loose and 
unsatisfactory that we are impelled also to consider the fact 


25 


that just the same shellfish were eaten by a number of people 
without detriment, and this surely robs the original identification 
of the shellfish with the cause of the disease of much of its 
force. The proof cannot be regarded as satisfactory, and | 
think the ‘attribution’ of disease-conveying properties to 
mussels, in some such case, ought to be challenged in the 
Courts in order that some legal decision as to what constitutes 
the proof should be obtained. 


The Validity of the Bacteriological Evidence. 

Nor can the results of a bacteriological analysis find legal 
proof that the ilmess was the result of eating mussels that 
contained typhoid bacilli, because when the illness is being 
investigated its presumed material cause no longer exists. 
It must be remembered that it is a very uncommon thing 
indeed to find Bacillus typhosus in mussels taken from the 
foreshore. I have found it myself, on one occasion, but even 
then the identity of the organism was not beyond doubt.* 
What the bacteriologist does look for, and usually find, is the 
presence of what he calls Bacillus coli. This may be backed 
up by finding that various other organisms of the same category, 
Streptococci and B. enteritidis sporogenes, are also present. 
The occurrence of these organisms is held to prove, and usually 
does prove, that the shellfish in which they were contained 
have been living in sea-water which contains sewage organisms 
proceeding, via sewer outfalls and drains, from human dejecta. 
None of these organisms, of themselves, convey enteric fever, 
and all that is shown by the results of the analysis is that the 
mussels were living in such conditions that they would have 
taken up (and retained for a short time) typhoid bacilli had those 
bacilli been present in the sea-water in which they were living. 
The proof, from bacteriological analysis, is really this: had a 

* The biological characters were those of B. typhosus, but the agglutina- 


tion test was not a very stringent one and the further proofs were not 
attempted. 


26 


person suffering from, or convalescent from, or a carrier of 
typhoid fever been living in the area drained by the sewer 
discharging near the mussel bed, then the shellfish maght have 
become infected and persons eating those shellfish might have 
contracted typhoid fever. 

But the bacteriological evidence is really weaker than has 
just been indicated, and I may quote Bulstrode with advantage : 
The Report on “Shellfish other than Oysters,’ of 1909-10, 
says: ‘‘It was found during the enquiry relative to oysters 
that bacteriological investigations yielded conflicting results, 
and it cannot be said that bacteriologists are in agreement as 
to the standard to be adopted, and this seems to be the case 
whether regard be had to the total number of organisms 
present, the percentage proportion of certain organisms or the 
mere presence of certain organisms. It has also to be added 
that there are at present no tests which will serve to distinguish 
sewage micro-organisms of human origin from those of animal 
origin, and even if it were practicable or desirable to distinguish 
between the two it would be difficult to fix reliable standards 
when dealing with estuarial waters draining a whole catchment 
area, much of which might be devoted to grazing purposes. 

“Tt is necessary, too, to point out that the standards 
adopted by some bacteriologists would not improbably serve 
to condemn every shellfish bed round the littoral. Possibly 
the time may come when a standard of this nature may be 
regarded as desirable, but, in the meantime, a useful provisional 
standard is one based upon topographical and epidemiological 
evidence.” 

The above passage was written over a dozen years ago, 
but the matter remains precisely where it was then. The 
conditions at present are these :— 

There is no generally recognised routine method of identi- 

fying and enumerating the ‘ 
shellfish. 


‘colon bacilli”? found in 


27 


There are no certain means of distinguishing between 


bP) 


“colon bacilli’? of human and lower animal origin, 
when such are found in shellfish. 
All mussels are polluted by ‘‘ sewage bacilli’ to some 
degree. 
There is no standard above which one is justified in 
regarding the degree of pollution as noxious. 
In spite of the importance of the subject, the amount of 
administrative attention it has received and its susceptibility 
to scientific investigation this is still the case, as it was in 
1910, when Bulstrode completed his second report. 


So I do not recommend any action, on the part of the 
Committee, with regard to the mussel beds on the Ribble 
Channel training walls. The matter has been discussed at 
some length because it may again become very troublesome 
and analogous cases may have to be investigated. In such 
cases as that of Church Scar, where the pollution is gross, 
immediate, and patent, action may be taken, though, of course, 
it cannot be taken by the Fisheries Committee. In most 
other cases, however, the best policy may be for the Committee 
to oppose any further orders under the Shellfish Regulations 
should these be initiated in their District, unless the order 
carries with it an undertaking to provide facilities for cleansing 
the suspected mussels. If bacteriological evidence is adduced 
this should be controverted on the ground that there has been 
abundant time for investigation—which has not been made— 
and that without this investigation the methods of analysis 
at present practised are inadequate. A legal decision as to 
what is to be understood by the expression “ attributable ” 
in the Regulations ought to be obtained. 

It has been shown by Professor Klein in 1904, by experi- 
ments made by this Committee in 1906-12, and by the results 
obtained at Conway by the Ministry of Agriculture and 


28 


Fisheries, since 1914, that highly-polluted mussels can be 
cleansed. Provision for such cleansing process ought, then, 
to go along with any order made under the Regulations. By 
itself an order is merely a restriction leading to a legal offence— 
if it is enforced. If it is to be enforced then it is fair to the 
fishermen to insist that the evidence on which the order is to 
be made should have the same weight as that which would be 
submitted to a magistrate against a delinquent who is to be 
prosecuted under the order. 


OTHER INVESTIGATIONS IN PROGRESS. 
Hydrographic Research. 


The Liverpool] Laboratory has now arranged for the 
monthly collection of sea-water samples and the observation 
of sea-temperatures in the Irish Sea. This is part of the scheme 
of “ directed research ”? submitted by the Ministry of Agricul- 
ture and Fisheries. Three cross-channel steamship routes will 
be sampled: Fishguard to Rosslare; Holyhead to Dublin, 
and Liverpool to Isle of Man. It is expected that the work 
will begin in May. 


The Life-history of the Cod. 


This is also part of the scheme of directed research. 
Investigations have been going on since October. There are 
two main cod fisheries which go on during the winter and 
spring—oft the Cumberland coast and round Isle of Man ; the 
fish, of course, occurs nearly everywhere, but these are the main 
fisheries. The Whitehaven fishery this year was poor, but the 
Manx one was very good though the difficulties of transport 
were so formidable that the season has been an unprofitable 
one. The fishery, during the spring, both at Whitehaven and 
at Isle of Man is one for cod that come inshore in order to 
spawn, and by Easter the Manx fish had nearly all spawned. 
A very good series of measurements has been obtaimed by 


29 


Mr. W. C. Smith, and scales have been preserved for future 
study. A series of chemical analyses of the flesh and liver 
of Port Erin cod has also been made on samples obtained every 
few weeks, and it is hoped that these will fit into a bigger 
scheme of investigation of the seasonal changes in the meta- 
bolism of marine animals and plants in the Irish Sea area. 
The changes in general “‘ condition’ of the fish durmg the 
season have also been observed, and other lines of investigation 
will, no doubt, present themselves later on. 


The Chemical Composition of the Mussel. 


A preliminary study of the chemical composition of the 
common mussel has been undertaken by Mr. Daniel, and the 
results of this are published in the tables given on pp. 217-221. 
As this investigation has proceeded many interesting questions 
have been suggested—the nature of the substance which is 
called “‘ glycogen,” for instance. It cannot be doubted that 
this is not the same, chemically, as the glycogen of the warm- 
blooded animal, and difficulties and anomalies encountered in 
the course of the work suggest that an exhaustive research 
on the nature of the carbohydrates found in molluscs is very 
desirable and may be of economic value in view of the further 
utilisation, in some form or another, of the organic material 
found in mussels. The use of the molluscs as human food, 
in the fresh condition, has been decreasmg for years past 
because of the somewhat bad reputation they have now 
received from the Public Health Authorities, and, as things 
are, their total exclusion from the food markets seem only 
to be a matter of time. Year by year, for instance, an increas- 
ing fraction of the great Morecambe supply goes to the Kast 
Coast as bait for the liners, and until a good method of cleansing 
them from sewage pollution can be generally applied this 
tendency will continue. We have to reckon, then, on finding 
some new use for the huge supply of material which the 


30 


Lancashire mussel beds can provide without diminution, and 
some means of converting the flesh of mussels into a food 
commodity ought not to be impracticable. The so-called 
glycogen, for instance, may possibly be extracted by some 
fairly simple, large scale process and applied to some useful 
purpose: so much Mr. Daniels’ results seem to indicate. 
There are, of course, other purely chemical or bio-chemical 
problems that have arisen in the course of this research, but 
these must be left for more detailed work. In the meantime, 
and as a study preliminary to that more detailed work, this 
research on the seasonal variations in rough chemical com- 
position is of indispensable value. 

A good deal of histological work, dealing with the mode 
of distribution of fat and carbohydrate in the various tissues 
of the mussel, has also been done by Mr. Daniel. Here, again, 
all the methods given in the text-books and memoirs have had 
to be tried and varied to suit the particular nature of the 
tissue substances. Evidently we cannot speak simply about 
“fat? and ‘“‘ carbohydrate ” in “‘ molluscs ” and depend upon 
the application of any general method of fixation and tissue- 
staining, for it seems probable that the precise chemical nature 
of these substances may vary from group to group of mollusca 
and even in the different species. Only in this way can the 
anomalous results obtained be explained. A great deal of 
preliminary work has, therefore, had to be done, and the results 
of this, and further research on the histology and morphology 
of the mussel, must fall to be recorded in later reports. 

Other lines of work have been touched, but it is, perhaps, 
unnecessary to make reference to these in the meantime. 
The past two years have been a period of considerable difficulty , 
but it is to be hoped that they have also been preliminary to 
the complete re-development of the scientific work of both 
the Liverpool and Piel Fishery Laboratories. We have many 
pieces of research in contemplation—some of them having a 


31 


far from indirect economic interest—and it is expected that the 
near future may give us the opportunities for the full prosecu- 
tion of these researches. We acknowledge here, with much 
appreciation, the assistance given by the Development Commis- 
sioners and the Ministry of Agriculture and Fisheries, and look 
forward, with confidence, to the continued interest of these 
departments in the marine biological and fishery work, which 
has so long been carried on in the Irish Sea. 


JAS. JOHNSTONE. 
DEPARTMENT OF OCEANOGRAPHY, 


University, LivERPOOL, 
April, 1922. 


32 


CLASSES AND OTHER WORK AT PIEL. 


By A. Scott. 


Classes at Piel. 

Two classes in Marine Biology and Navigation for fishermen 
were held in the spring of 1921. The first one met during the 
period 7th to 18th March, and was attended by fourteen men. 
The second was held between 18th and 29th April, and was 
attended by thirteen men. 

The following are the names of the fishermen who attended 
these classes :— 

7th to 18th March.—W. Rimmer, Blackpool; Victor 
Houghton, F. Woodhouse, H. Woodhouse, R. Woodhouse, 
R. Gardner, J. Parkinson, Morecambe; Robert Burrow, 
Bolton-le-Sands ; Robert Burrow, Isaac Burrow, F. Dickinson, 
Grange-over-Sands ; Thos. Wilkinson, Baicliff; Thos. Butler, 
8. Benson, Flookburgh. 

18th to 29th April— J. H. Atkinson, Richard Wright (1), 
Richard Wright (2), Fleetwood; Fred Taylor, J. Baines, 
Bolton-le-Sands ; J. Dickinson, Silverdale; Frank Dickinson, 
Allithwaite; P. Benson, M. Cowperthwaite, Flookburgh ; 
H. Bayliff, W. Benson, Baicliff; Thos. Butler, Aldingham ; 
W. J. Edmondson, Rampside. 

Mr. R. J. Daniel, of the Oceanography Department, 
University, Liverpool, had charge of the whole of the teaching 
work. 

In the interval between the fishermen’s classes, Mr. R. H. 
Wardle, M.Sec., of the Zoology Department, Manchester 
University, brought a party of senior zoology students to 
examine the fauna and flora of the shore in the vicinity of the 
Laboratory. The following is the report supplied by Mr. 
Wardle at the conclusion of the visit. It gives an account of 
the work done and the facilities provided for workers. 


33 


Mr. Owen Hunt, one of the senior students, was unable 
to join Mr. Wardle’s party, but came later, 2nd July, and spent 
a week investigating the shallow-water fauna. 


Report upon Visit of Zoological Party to the Biological Station, 
Piel, Barrow-in-Furness, during April, 1921. 

The party under my charge consisted of the following 
eight students :—Misses MacGill, Allen, Comstive, Bishop, 
Dutton, Wainwright, Mr. Hopwood and Mr. Lean. 

The party left Manchester on Friday, April 8th, by the 
10.25 train to Fleetwood, were met at Wyre Dock Station by a 
member of the crew of the “ James Fletcher’ and conducted 
to the vessel. Upon this steam trawler an exceptionally 
interesting and instructive nine hours were spent as the guests 
of Dr. J. T. Jenkins, Superintendent to the Lancashire and 
Western Fisheries Committee. At a point 14 m. W. by N. 
from the Morecambe Bay Lightship an otter trawl was shot, 
was dragged for seven miles in a W. by N. direction, and was 
hauled at 5.30 p.m. A record was obtained of the 311 edible 
fishes caught, and the Invertebrate contents of the trawl] were 
set aside for further examination ashore. The party were 
landed at the jetty, Piel Harbour, at 9 p.m. 

Saturday was spent in examining the Invertebrate material 
and the tow-nettings obtained the day before. 

Monday.—A collecting expedition to Foulney Island was 
organised, under the guidance of Mr. Andrew Scott, in the 
morning. The material thus obtained was examined during 
the afternoon in the laboratory ; living plankton, obtained by 
tow-netting from the end of the jetty, was also available for 
examination. 

Tuesday : a hot, calm day.—The party, accompanied by 
Mr. Scott, boarded the police cutter at 10 a.m. and spent most 
of the morning and afternoon tow-netting in the Walney 
Channel, in charge of the Committee’s Officer, Mr. J. Wright. 
Cc 


34 


A beam trawl was shot and dragged for two hours, and the 
resulting catch examined and sorted out for examination ashore. 

Wednesday: cold and wet.—The morning was spent 
collecting along the foreshore west of the harbour, but little 
was obtained. 

Thursday.—The party went out in the morning under 
Mr. Scott and obtained a supply of Arenicola ; the rest of the 
day was spent in examination and dissection of this material, 
and in examination of segmenting ova of the plaice. 

Friday.—In view of the threatened railway strike, | 
decided to bring the party back to Manchester, and wired 
Dr. Jenkins to that effect. Otherwise, the party would have 
stayed until Monday, the 18th, and returned to Fleetwood 
on the “ James Fletcher.” During the morning a very interest- 
ing lantern lecture upon the Fisheries of the Morecambe Bay 
area was given by Mr. Scott. The party left Piel on the 
1.13 train. 


General Remarks. 


In spite of the unfortunate curtailment of our visit, a 
surprising amount of work was carried out, and the visit was 
in every way a success. The muddy and shingly foreshore 
is far more plentiful in variety of animal life than would appear 
from a cursory examination, and to the assiduous and 
experienced collector is not greatly inferior to a rocky coast 
such as obtains at Port Erin. 

Any inferiority of littoral fauna was, however, compensated 
for by the facilities afforded by the Fisheries Committee’s 
steamer. 

The laboratory facilities are equal to those prevailing in 
the University laboratory. There is bench accommodation 
for sixteen students, there are fifteen good Leitz microscopes 
and a Zeiss binocular, there is a plentiful supply of glassware, 
dishes, instruments, reagents, etc. In the adjoining fish 


35 


hatchery is a series of tanks and bell jars into which living 
material may be placed and kept under observation. We 
were thus able to observe fully-expanded specimens of 
Alcyonium, Actinoloba, various Hydroids, Nudibranchs, etc. 
Attached to the laboratory is an excellent library, and in the 
laboratory itself is a very complete collection of preserved 
specimens of Irish Sea fauna, which is available for teaching 
purposes. 

The success of the visit was undoubtedly very largely due 
to the energy and forethought shown by Dr. Jenkins and to 
the assistance of Mr. Andrew Scott, who sacrificed much time 
and trouble in conducting the party on collecting expeditions 
and in identifymg obscure or out of the way species. 


R. A. WARDLE. 


Dr. Stuart Thomson, also of the Zoological Department, 
Manchester University, who had carried on an evening class 
in Marine Biology in the winter, which was attended by 
members of the Manchester Microscopical Society, brought a 
party of thirteen members. This party was at Piel from the 
14th to the 21st May. The course consisted of lectures and 
demonstrations, examination of living material, shore collecting 
and photographing. 

A class in Marine Biology and Navigation for school 
teachers was conducted by Professor Johnstone and Mr. Daniel 
from August Ist to 12th, and was attended by the following 
eight schoolmasters :—A. KH. Morley, Scarborough ; P. H. Hall, 
Brightlingsea; A. V. Phaisey, A. HE. Johnson, E. D. Lowes, 
Swanley ; R. Fleming, R. 8. Cleator, E. V. Lawson, Fleetwood. 
Mr. A. Harris, Chief Inspector of Navigation Schools, inspected 
this class. Dr. E. 8. Russell, Director of Scientific Investiga- 
tions to the Ministry of Fisheries, also visited the laboratory 
during the teachers’ class and inspected the facilities for work. 


36 


Fish Hatching. 


A stock of large plaice were collected in Luce Bay in 
October, and in due course conveyed to Pie]. Adult flounders 
were trawled in Barrow Channel towards the end of 1920. 

The plaice and flounders both began to spawn on the 6th of 
March, eighteen days earlier than in 1920, and continued to 
produce eggs until 30th April. The last fry (plaice) were set 
free on 24th May. Altogether 1,150,000 plaice eggs and 
12,500,000 flounder eggs were collected and incubated; 
1,000,000 plaice fry and 11,000,000 flounder fry were hatched 
and set free. 


Re-survey of Shellfish Beds. 


The mussel beds of the Ribble, in the vicinity of Lytham, 
were examined by Mr. W. Birtwistle and myself in July and 
again in November, 1921. On the first date a topographical 
survey of the sewer outfalls and their relation to the mussels 
was made. On the second visit samples of the mussels were 
collected and examined for sewage contamination. Reports 
were submitted in each case and were published in the Report 
of the Superintendent, Dr. Jenkins, for the quarters ending, 
30th September and 31st December, 1921. 


37 


THE PLAICE FISHERIES OF THE IRISH SHA 


BY 


JAS. JOHNSTONE, D.Sc.; W. BIRTWISTLE 
AND W. C. SMITH 


CONTENTS 
PAGE 
PART I: Tue Pre-War PeEriop, 1908-1913 ae se sb 39 
Introduction ace é Sct aie si 50 S00 5c 39 
The area Sig etinated: p- 40; Nature and regulation of the 
grounds, 42; Distribution of the various species of fish, p. 45 ; 
Tables Land II, species of fish found, p. 46; Seasonal fisheries, 
p. 49; Migratory fishes, p. 50; Long period fluctuations in 
the fisheries, p. 52. 
Methods of investigation noc ee ee tas as was 53 
Treatment of the data ... dae ales si Ses iad as 55 
Statistical methods, p. 56; Pearson curves, p. 58; Summational 
curves, p. 60; Use of the same, p. 65; Measures of dispersion, 
p- 67. 
Lengths of the plaice caught ... Bie Tail 
Tables III to XIII, Length Ereeuerisied i on ae anes dite 
1908-1913, p. 73. Prevalent lengths, 85. 

PART II: Tue Lire-History or THE PLAICE ane Ae née 88 
The spawning grounds ... 506 50C 36h oe 306 506 88 
The hatching and transformation stages... ane Ss ah 93 
The first shore stages... Aa a ie a dis b3s 94 
Food of the larvae and transformed plaice ... 596 a M6 95 
Growth of the plaice during the first year ... pe ae re ee 96 
The nursery grounds and their conditions... 506 ace oes 99 
The rate of growth of the plaice aie 102 


Tables XIV and XV, length freqnediion, se age-groups O- IV, 
p- 104; Ratio of males to females, p. 107; Sizes at sexual 


maturity, p- 108. 


38 


CONTENTS—continued. 
PART I1—continued. 


Migrations of the plaice 


Plaice-marking experiments, p. 110; Age and the migration 
paths, p. 126. 


General remarks on the migration experiments 
Growth-rate of marked plaice, p. 131. 


PART IIL: Tue Pre-War AND Post-WaAR PLAICE FISHERIES 


Fluctuations in the Plaice fisheries in the North Sea, English Channel 
and Irish Sea ode te at 
Fluctuations in Lancashire Tana p- 136; aHiuetie: 
tions in the Mersey fishery, 1908-1920, p. 139 ; Table 
XVI, length frequencies on the Mersey grounds, 1908- 
1920, p. 140; Fluctuations in Liverpool Bay, 1909-1913, 1920, 
p- 143; The Northern plaice grounds, 1920-21, p. 145; 
Table XVII, length frequencies on the Northern grounds, 
1920-21, p. 146; Proportions of the age-groups in various 
years, p. 148 ; Table XVIII, length-frequencies for Age-group 
III, p. 148 ; Table XIX, length- frequencies for Age-groups II 
and III, p. 157; Composition of the plaice stock as regards 
groups, p. 150. 


Causes of the fluctuations 
Table XX, length-frequencies of Apes pie in aN ee 
trawl-net, Mersey grounds, 1908-1920, p. 154. 
The post-war fisheries, 1920 BC 
Tables X XI to X XVII, length- eas canes of sates seaaht on the 
various grounds in the year 1920, p. 156. 


The effect of the war restrictions on the fisheries 


PART IV: PracricaL ADMINISTRATIVE QUESTIONS 
The rate of exploitation 


The impoverishment of a fishing region 


Has there been impoverishment of the Irish Sea ann faienes ? 
p. 170; Is there an accumulated stock ? Does increased fishing 
tend ie make the plaice run smaller, p. 172; Did a stock of 
plaice accumulate in the Irish Sea during the war years, p. 173. 


The possible effects of legislative restrictions 


The protection of the spawning grounds, p. 174 ; The question 
of size-limits, p. 175; Effect of latter on smacks, p. 175; Effect 
on the steam-trawlers, p. 175; Possible effects on the fisheries 
of a size-limit, p. 176; The theory of restrictions, p. 178. 


Cultivation is Ree bee Boe ses see sme See 


PAGE 
108 


130 


133 


133 


155 


164 


167 


168 
170 


174 


179 


39 
PART Vi. 
THE Pre-War Periop, 1908-1913. 


(1) Introduction. 

This report is primarily a summary of certain fishery 
investigations carried out in the Irish Sea region during the 
years 1908-1920. Its object is to provide aseries of data which 
can be consulted for the purpose of assessing the usefulness of 
any practical legislative proposals as to size-limits or closed 
grounds. It also endeavours to provide a picture of the present 
condition of the plaice-fisheries on the fishing grounds men- 
tioned below. If we had such a picture for the period 1870- 
1890, the information so afforded would be of the utmost value 
in the discussions that are now going on with respect to 
questions of impoverishment, size-limits, etc. We think it very 
useful, therefore, to summarise here what has been the outcome 
of the investigations made by the vessels and officers of the 
Lancashire and Western Sea-Fisheries Committee during the 
last twenty years or so, as these observations will, at the least, 
record the present conditions and give a basis for comparison 
with those that may possibly be made some twenty or thirty 
years hence. 

The essential part of the report consists of the tables of 
measurements, etc., that are given on pp. 73-84. 

In addition to these we have added a summary of the results 
of a series of marking experiments and some additional observa- 
tions. In order, however, to present the general attitude 
adopted a rather full discussion of the methods used has also 
been written, and the general bearing of the conclusions reached 
are also discussed on pp. 167 and following. The impression 
obtained is that the time has not come for any legislative- 
restrictive action in this part of the sea. That impression is, 
however, personal to those of us who have been concerned in 
carrying out the investigations, and does not necessarily 


40 


represent the opinions of the Committee. The reasons for our 
opinion are given fully on pp. 167-179 of this report. 


The Area Investigated. 

The fishing grounds on which the observations and 
experiments have been made are as follows :— 

(1) The Solway Firth, including Luce Bay and Wigton 
Bay, and the fishing grounds between the Isle of Man and the 
coast of Cumberland. Permission to work on these regions was 
kindly given by the Scottish Fishery Board and the Cumberland 
Sea-Fisheries Committee. 

(2) “‘Morecambe Bay.’ This includes the territorial 
waters off the Lancashire coast, from the estuary of the Duddon 
to Formby Point, and the offshore region out to the Morecambe 
Bay Light Vessel. 

(3) “ Liverpool Bay.’ This includes the estuaries of the 
Mersey and Dee, and the adjacent sea out to the twenty-fathom 
contour line. 

(4) “Red Wharf and Beaumaris Bays.” This is the 
region situated just off the coasts of Denbigh, Flint, Carnarvon, 
and Anglesey, as far south as about Holyhead, and seaward 
to about the twenty-fathom contour line. 

(5) Carnarvon and Cardigan Bays. 

(6) The inshore waters round Isle of Man. Work was done 
there by arrangement with the Insular Fisheries Board. 

(7) The offshore regions in general, about and outside the 
twenty-fathom contour line. 

The various geographical terms are employed rather 
approximately and much in the same way as they are used 
by fishermen. The whole region investigated is quite a small 
one, but it is a typical, rich, inshore plaice fishing area of sea, 
and it is one about which more is known than any other 
similar region in the British fishing regions. The summary 
that we provide cannot, therefore, fail to be of much interest 
and practical importance. 


42 


Nature of the Fishing Grounds—their Regulation. 

Most of the region investigated lies inside the three-miles’ 
limit, and trawling by steam vessels is everywhere prohibited 
within this zone. In addition, trawling by any kind of vessel 
is prohibited in Luce Bay by the Fishery Board for Scotland. 
Trawling by motor-propelled vessels is permitted, by licence 
issued by the Lancashire and Western Sea-Fisheries Joint 
Committee, in Carnarvon and Cardigan Bays. There are 
regulations with respect to the size of trawl-mesh, which is now 
measured all round the mesh in the Lancashire and Western 
District and in the Cumberland District. Trawling by steam 
vessels is prohibited in the three-miles’ zone round the Isle of 
Man. Vessels fishing for shrimps employ a trawl-mesh of 
2 inches, and they are not supposed to retain any fish if these 
are less than 8 inches in total length. The mesh of stake-nets 
is also regulated, and is 7 inches measured round the four sides. 
There are no restrictions on the times of the year when trawling 
that is otherwise legal may be practised, and there are no 
restrictions on the sizes of fish of any species that may be landed 
and offered for sale. 

Most of the whole region in question is what is called a 
“nursery ground.” This is particularly the case in the Solway 
Firth, in the estuary of the Duddon, in Morecambe Bay, and in | 
the estuaries of the Ribble, Mersey, and Dee. Here there are 
enormous tracts of sand-banks, which are laid bare at each 
ebb-tide, and there are innumerable shallow channels through 
these banks. The water is rather cold in the winter on these 
shallow estuaries and rather warm in the summer—that is, 
the extremes of temperature are greater in the bays and 
estuaries than they are in the sea, just offshore. Sometimes 
there is considerable ice formation in Morecambe Bay. The 
higher temperature in the spring, summer, and autumn, and 
the lowering of the specific gravity of the water by that coming 
from the land are very favourable conditions, Water draining 


43 


down from cultivated land and from domestic sewerage systems 
carries essential food substances on which many lower 
organisms feed, and these lower animals and plants are the 
food of others, which are then eaten by the young fishes which 
inhabit the nursery grounds. 

The tidal streams are unusually strong and tend to run 
inwards to the Solway and Morecambe Bay from the channel 
between Ireland and Scotland. The tidal streams coming and 
going from St. George’s Channel also tend to and from the 
“ Liverpool Bay ” region—that is, the coast containing the Dee, 
Mersey, and Ribble estuaries. Off the mouths of these are 
extensive sand-banks, penetrated by shallow channels. Plaice 
and other fish spawn offshore and the eggs and developing 
larvae are carried by the tidal streams to the grounds that we 
have mentioned. 

The extensive sand-banks in the bays and estuaries are 
“alive ” with small Crustacea (Copepods), cockles, other small 
bivalve shellfish, and small worms. In the channels, and on 
the foreshores where the ground is rough there are enormous 
accumulations of mussels forming “beds” or “skears.” 
These animals, when young and small, are eaten by plaice, 
dabs, flounders, and other fishes, and their presence and great 
powers of regeneration are the principal reasons why the region 
in question constitutes one great nursery ground. The supply 
of fish-food, represented by bottom-living Copepods, worms, 
and small molluscs, is almost illimitable, and could doubtless 
support a much greater fish population than that actually 
present on the nursery grounds. This fish population itself, 
we have reason to believe, is only a small fraction of that which 
is theoretically possible of existence. 

In fact, such an area as that which we are now describing 
is certainly one of the most “ productive ” that exists, being 
capable of yielding far more organic food substance than any 
equal area of cultivated land. The annual quantity of mussel- 


44, 


flesh, for instance, that can be raised on a suitable Lancashire 
foreshore is greater by far than the quantity of beef or mutton 
that could possibly be raised on the same area of the best 
grazing land. 

This is the general nature of the North-west inshore fishing 
grounds, but some of the sub-regions differ from the above 
description. Luce Bay is such a nursery ground (in certain 
places), but it also contains large numbers of big plaice, up to 
over 60 cms. in length. Something in the nature of the Bay, 
and its water and food supply, may be associated with this 
remarkable distribution, but the main factor is preservation. 
The Bay has, for a long time, been closed against trawling by 
the Scottish Fishery Board, and the amount of other fishing 
(by “ gill-nets ””) that goes on is insufficient to deplete the area 
of the large fish. 

The fishing grounds of North Wales, lymg just off the 
coasts of Carnarvon and Anglesey, between Great Orme’s Head 
and Point Lynus (Conway Bay, Beaumaris Bay, Red Wharf 
Bay), are not nurseries to the same extent as are the grounds 
mentioned above. Here medium and big plaice are caught, 
principally during the months of October to January. There are 
nurseries in Carnarvon and Cardigan Bays, but not to the same 
extent as off the Cumberland, Lancashire, and Cheshire coasts. 
Medium to big plaice may be caught in the great Welsh Bays 
at the beginning of the year and in the summer and autumn 
months. 


¢ 


What we may conveniently call the “ offshore grounds ” 
are situated outside the twenty-fathom contour line on the 
English side and between this and the Isle of Man; also out 
from the same depths in “ Channel Course ”’* and St. George’s 
Channel, and between Cumberland, Isle of Man, and the South 
Coast of Scotland. Plaice occur over most of this region, but 


* «Channel Course ”’ is the sea in the neighbourhood of the general track 
followed by vessels entering Liverpool from St. George’s Channel. 


45 


in much smaller numbers than on the zone of sea within the 
twenty-fathom contour line. In fact, we may neglect most of 
the Irish Sea outside this limit as a plaice ground—though it 
would, of course, be difficult to give statistical data demonstrat- 
ing this. By far the greater part of the plaice caught come 
from the shallow water less than twenty fathoms in depth. 


Distribution of the Different Species of Fash. 

Even in such a small area as that which we are 
considering—it is all included within 3° of latitude and 2° 
of longitude—there are quite noticeable differences in the 
predominant kinds of fish present on the fishing grounds. This 
is Ulustrated by the following tables and graph, which represent 
the results of a number of fishing experiments made in the Firth 
of Clyde and Luce Bay (by permission of the Fishery Board 
for Scotland) as well as in the Irish Sea. The experiments 
were rather rough ones, being made at different times and by 
different vessels, so that the results are not precisely com- 
parable. Still, | have no doubt that very much the same 
general ratios would be obtained even by carefully standardised 
trawlings. 


46 


Table I. Results of Trawling Experiments carried on during 
the months of Feb.-May, 1898-1904 and Sept.-Nov., 1908-13. 


| West | | 
Firth from | Offshore} Cardigan | Liverpool | Luce 
Kind of Fish, | of | Isle of | grounds.) Bay. | Bay. Bay. 
| Clyde. Man. | | 
| | | 
Witchy ceteasevcesrectes: | 4,164 430 Tie eens see ra 
Blaicenecrsssasntecsccess | 1,093 27 | 346 1,203 | 3,544 4,548 
Dab pa eereccngoes eon | 354 Ome a deni 574 | 2,920 1,015 
Lemon Sole ......... 119 34 60 40 we 28 
Stolle)» Aeandceacosusssoec 116 10 509 411 18 ae 
Brillecsactsccecssecsss 33 | 1 42 42 | 7 21 
Mlounder y eececceeces: 14 | 638 36 107 PAT 
Meo rina aicecceeerscct 9 152 8 BH 
AIA Goonsnagsdoadoo 6 2 2 4 
Longrough Dab... 5a¢ 4 ee BE Bcc 
TBINGSIG KS  Seucnoobonee 1,121 65 1,427 we 99 
Hake sees ceeceiisesectilc 148 4 ae Spe 500 
NVI EIn ene esc aeecs 70 | 493 940 154 ie a 
(Olo%6 |e Sa smaendesooosdeoadc 41 13 141 2 116 70 
GLIMEAN codsacaosascode 42 4 ] 550 50 22 
IDTV soonocqonnp5b00n00> 8 4 3 50 
ollackwecenss-sccesse Soa | 4 1 iE ee 12 
Poor Cod Wa-ee.- 2-2 ame ALU 39 36 an ace 1 
Grey Gurnard ...... 759 466 519 115 101 30 
Red Gurnard _...... 47 | 27 190 7 ia 4 
Yellow Gurnard...... 1 9 34 27 16 20 
Gonmer tierce |) el ial es 1 2 
TER s. iGaeqnbdgndbdnodue: 347 123 434 761 669 610 
Sleaitetemerescccseacseras 10 6 130 20 108 3 
John Dory, | ences: 1 | ees =e 1 
AN AWAIT? gaoodbosnono|ce 300- |) 800 Doe 400 B00 1 
IBIGYTANEYE cooeopoonanoooe 508 me dot ee BOC 12 
No. of hours’ | 
1D RWAMUAYE?! srooecoae la) LOS 45 | 242 | ai 45 27 
Mean depth ......... | 22 32 | 21 12 | 6-5 7 
| = lice =a 
Total edible fishes 8,507 1,996 | 7,208 3,404 7,706 6,431 
| a 
No. of Species ...... 22 22 Ger 2oe| 14 | 12 | 19 


47 


Table Il. The same data as on p. 46, but expressed as numbers 
of fish caught per hour’s trawling (If less than one fish results 
from the calculation the species is omitted). 


| 
West 
Firth | from | Offshore! Cardigan | Liverpool | Luce 
Kind of Fish. of Isle of | grounds.| Bay. Bay. Bay. 
Clyde. | Man. 

All edible fishes... 83, | At 30 83 171 239 
\WAKWG 1). pcacndeodeocoodcoc 40 10 aes as eee sat 
IPIBNES. opedeanenbocaubscs 11 1 1 29 79 168 
Dalby isacccscsessesitesce 4 1 7 14 | 65 38 
Lemon Sole ......... i 1 ws 1 as 1 
SOI | Vasorieponsedcscoode WS cee 2 10 ae eee 
IBTUD Soe ccdesesaecases 500 AG is 1 adc 1 
IOUNG ET ser eceeeise 200 Spc 3 | 2 1 
Wigan) Gaceocs6ccosc0 so. 3 was ce 
[Haddocks \rse-cereece 11 1 6 aa 2 
FLBCON <.30--esncvecoess ie de : 
DWIRICIN Gos fcchssveceeee ee) eh 4 4 ie 
(Cio | Caen een | 1 3 3 
Woalfishin. ontscccccuer oo aes aE 5 | ot 1 
Grey Gurnard ...... eal 10 2 3 2 1 
Red Gurnard ...... oso | I 1 tae 
Yellow Gurnard...... Ato | cok sai 1 1 
TRAY, Jenescisvesdsescers c 3 2 19 15 23 
SKA bees ssse seems cose 1 1 2 
Mean depth ......... 22 32 21 1) 65 7 


The first of the above tables gives the actual numbers of 
hauls and hours of fishing, and the numbers of fish of different 
species that were caught. The second table simplifies the 
former one in that it gives the numbers of fish caught per 
hour’s trawling, in all the trials, and neglects all results in which 
less than one specimen—on the average—has been taken. A 
further simplification is rendered possible by the following 
diagram, which takes account only of about two-thirds of all 
the fish caught—that is, it gives us a fair idea of the prevalent 
kinds and abundance of trawl-fish present in our whole region. 


48 


as Pigee| Dab 


Hie. 2. 


Note, then, that whiting, gurnards, and witches are 
characteristic of the deeper grounds to the West and South 
from Isle of Man, witches, haddock, and plaice of the Firth of 
Clyde,* and dabs, haddock, whiting, and flounders of the 
offshore grounds outside the shallow coastal waters of Lanca- 
shire. We find plaice, rays, and dabs are characteristic of the 
fishing grounds in Carnarvon and Cardigan Bays, and plaice 


* That is, the Clyde between Stranraer and the South of Arran. 


49 


and dabs in Liverpool Bay. Luce Bay, it will be seen, is far 
more characteristically a plaice ground than any of the others. 

Some qualifications, with regard to this statement of 
distribution, will be found below. 


Seasonal Fisheries. 


The various fisheries are all seasonal ones. 

The great plaice fishery is that off the coasts of Lancashire 
and Cheshire in the summer and autumn months. Sometime 
about May or June plaice become abundant just off the mouth 
of the Ribble Estuary, and then this abundance becomes 
extended to the grounds North and South. About the begin- 
ning of August the fish usually appear in great numbers round 
about the banks off the entrance to the estuaries of the Mersey 
and Dee. By November these fisheries begin to fail. 

About the same time, or even earlier, plaice become 
abundant off the coast of North Wales, anywhere hetween 
Rhyl and Red Wharf Bay, on the north of Anglesey. This 
winter fishery ends about December or January, sometimes 
very abruptly. Then good catches of fairly big plaice may be 
obtained inshore in Carnarvon and Cardigan Bays. 

After that there follows a period when plaice are relatively 
very scarce everywhere. Some, of course, are always caught 
wherever there is trawling, but, in comparison with the well- 
marked summer and autumn fishery off the Lancashire coast 
and the equally well-marked North Welsh winter fishery, the 
plaice are very scarce. About the month of January medium- 
sized and big fish appear on the banks to the north-east of Isle 
of Man, and there may be a good deal of trawling there. A 
little later, however, these grounds may become “as bare as 
a bilhard ball.” Followimg that again the bigger plaice are to 
to be found on the ground called the “‘ Slaughter,” just off the 
mouth of the Solway. Here they spawn and the shoal disperses. 


Sometime about March and April, then, large numbers of plaice 
D 


50 


disappear from the Irish Sea fishing grounds, and there is always 
much speculation among fishermen as to where they go. There 
is little doubt that they ‘“‘ dawk ’”—that is, bury themselves in 
the sand in the channels offshore and among the sand-banks. 
Here they remain during the period of the year when the 
temperature is at or little above its minimum value, and when 
food has become scarcer than usual. Noting all these facts 
as to the seasonal nature of the plaice fishery, and comparing 
them with the results of the marking experiments—to be stated 


on pp. 110-132 of this report—we have little difficulty i 
making a general picture of the migrations of plaice in the 


Trish Sea regions (see p. 130). 
The Migratory Fishes. 


It will be noticed haddock are mentioned in the tables on 
pp. 46-7, though if a similar series of experiments were to 
be made at the present time this fish would be much scarcer— 
and it might not be represented at all in some of the areas. A 
number of species are migratory ones, entering the region we 
are considering and then moving away again. Some of these 
species come back every year with a certain amount of 
regularity and others only return after a more or Jess prolonged 
period. Although we are dealing mainly with the plaice in 
this report it may be useful to say a few words about these 
migratory species. 


Hake. 


Specimens of hake may be obtained now and then from 
most parts of the Irish Sea, but the fish is only (relatively) 
abundant to the west and south of the Isle of Man in the autumn 
months (usually July, August, and September). It migrates 
up from St. George’s Channel, in the South, with the rising 
temperature of the sea and moves southwards again when 
the temperature falls. The fishery is, however, not a very 
important one. 


51 


Sea-Perch (Labraz lupus) and Mackerel. 

So also with these fishes. They come into the Irish Sea 
at variable times, but generally about May or June, and they 
stay till about August and September. Thev also come up 
from the South and retreat back there again. Hake, sea-perch, 
and mackerel we may regard as southern fishes, and take their 
northern limit of distribution to be some particular isotherm in 
the sea. This isotherm, whatever it may be, changes from 
South to North as the summer advances and then changes 
back to the South as the sea temperature begins to fall, rather 
rapidly in September and October. 

Ferri ng. 

This is a well-known migratory species, but the conditions 
that rule the movements of the fish are very complex and are 
not clearly known as yet. There are two main herring fisheries 
in the Irish Sea area: (1) the Welsh winter, and (2) the Manx 
summer fisheries. The Welsh winter herrings appear in 
Cardigan Bay in October and the shoals gradually move to the 
North as the season advances, disappearing off the North Coast 
of Anglesey sometime in January. The fish are mature ones 
and are “ full’? when they first come on the coasts; later on 
they spawn, and by the end of the season they are usually in 
the spent condition. 

The Manx herrings are sometimes found off the coasts of 
the Island as early as February, but not in abundance. About 
May they begin to become abundant and are to be caught on 
the west, south, and east of Isle of Man. In July to September 
they spawn, and soon after that the shoals disperse and the 


fishery comes to an end. 


The Sprat. 


The sprat is found everywhere along the Lancashire and 
Welsh coasts and in the Solway, but during the summer months 
it is mainly immature fish that one sees. About October 


52 


mature sprats begin to shoal and are abundant enough to 
provide the material for a fishery. They are probably to be 
found all along the coast, wherever suitable gear may be used, 
but the only fishery is that prosecuted at Morecambe during 
the period October-March. The fish are mature ones about to 
spawn. Just before spawning they disperse and the fishery 
comes to an end. 


The Cod. 


Cod are found over all the region and generally at all 
periods of the year, but there are local fisheries where the fish 
is more abundant than elsewhere. About March fair catches 
are made off the coast of Cumberland and even further South, 
and about the same time there is a fishery off the West Coast 
of Isle of Man. In both cases the migration is a spawning 
one and the fish are full-roed ones. At the best, however, the 
cod fisheries in the Irish Sea are not of very much importance. 
The fish is a northern one, and this is near its southern limit 
of range. 

There are, of course, other migratory species of less 
importance—thus, whiting move about in much the same way 
as the cod. Large numbers of whiting, cod, and other species 
are to be found in the early stages on the nursery grounds 
during the summer and back-end. (rarfish (Belone) come in 
from the South during the summer and the long, rough dab 
(Drepanopsetta) comes down from the North in the early spring. 
The sole is, to some extent, a migrant, having its place of 
ereatest abundance to the south of our area. Some species 
of ray are also periodically migratory. 

Long-Period Fluctuations. 

Two species (at all events), the herrmg and haddock, are 

very capricious in their movements. The Welsh and Manx 


herring shoals are constant in their appearances and disappear- 
ances, but there have been other herring fisheries which come 


58 


and go. About 1890 and later herrings appeared off the coasts 
of Lancashire from Morecambe Bay to the Mersey Estuary, 
and were fished for, by drift-nets, in the latter area as far up as 
near the entrance to the Manchester Ship Canal. Before that 
time there was a fishery near the mouth of the Solway, and the 
“ Parton Herrings,” taken just north of Whitehaven, were well 
known and highly esteemed. Since then, and until last year 
(1921), these fisheries did not exist and only occasional herrings 
were taken. In the winter of 1921-22 the herrings came back 
to the Cumberland and Lancashire coasts in fair abundance 
and were taken at Maryport, at Morecambe, in Morecambe 
Bay, and all down the coast as far as Great Orme’s Head. 
Thus, there has been a period of about thirty vears during 
which the fish disappeared almost entirely. Before the ’nineties 
of last century there were other long-period fluctuations—thus 
somewhere about 1774, herrings were abundant in the estuary 
of the Dee—and doubtless elsewhere on the Lancashire and 
Cheshire coasts. In 1840, they appeared in the Mersey. No 
definite information is, however, now obtainable with regard 
to these fluctuations. 

Haddock came into Liverpool Bay in great abundance 
about 1890 to 1895. Since then they have been practically 
absent, only an occasional specimen being taken. 


(2) The Methods of Investigation. 


The work was begun in 1908 and the methods employed 
were, briefly, as follows : 

(a) Trawling experiments were made on the various 
grounds by the L.W.S.F. patrol vessels “John Fell” and 
“James Fletcher,” and also by some of the police cutters. 
All the plaice caught were measured immediately after the net 
was cleared. Lengths were recorded in centimetre groups, 
all fish which were over » and less than n+1 cms. being 
recorded as » -5 cms. The principal grounds sampled were 


5A. 


Luce Bay (in October, November, and December), the 
Cumberland coastal grounds, the ‘‘ Nelson Buoy” grounds, 
the “Mersey Estuary,” the “ Red Wharf-Beaumaris Bay ” 
region, Carnarvon and Cardigan Bays. 

(b) Trawling experiments were made continuously from 
1890 to 1920 by the sailing vessels employed on police work 
in the Mersey Estuarine area. All these experimental hauls 
were made by the same officer, Capt. George Hccles, a highly- 
experienced fisherman. Two series were made, one with the 
ordinary smal] trawl-net of 6-inch mesh, and the other with 
the ordinary shrimp-trawl net of 2-inch mesh. Some other 
similar series of bauls were also made in other parts of the 
District. 

(c) Comparative hauls with trawl-nets of 4-inch, 6-inch, 
and 7-inch meshes were made. 

(d) Samples of the plaice caught on the various grounds 
were regularly sent to the Liverpool laboratory. These were 
examined in detail : 

They were measured as above and sorted into groups of 
n to n+1 cms. 

The whole lot of fish in each group was weighed to the 
nearest gram and the total weight was divided by the 
number of fish. Average weights were so recorded. 

The length-weight coefficient “k” was then calculated 
(see Ann. Rept. Lancashire Sea-fish. Laby. for 1911, p. 17). 

Each fish was dissected; the sex was determined, as 
well as the stage of maturity ; the age was determined by 
inspection of the rings on the earstones and the food contents 
of the stomach and intestine were often identified. 

(e) Observations were made by the ‘ Fish-Measurers,” 
W. C. Smith, A. E. Ruxton, and G. Sleggs, on board steam 
trawlers, smacks, and _ half-decked trawlers. This work 
began in 1920. It was mostly restricted to the offshore 
grounds and to the shallow water area of the Solway Firth. 


55 


(f) Marking experiments were made. These began in 
1906 and were carried on until 1913. Twe areas were seen to 
be of much importance: the grounds off Nelson Buoy and 
those in Red Wharf and Beaumaris Bays, and most of the 
experiments were made there. In 1920 and 1921 the experi- 
ments were renewed and plaice were marked on the grounds 
between Isle of Man and the Solway Firth. In all cases the 
English form of mark was used ; at first the bone button and 
brass label, and later the vulcanite buttons and labels. 

(g) In 1921 the larval and post-larval plaice were 
studied. Catches were made by means of the Lancashire 
“push-net,” which is used to catch shrimps, being pushed 
along the sea bottom, in water of two feet or so in depth, by a 
man wading. The flat fishes collected in this way (from the 
Cheshire coast and the coast of the Isle of Man) were identified 
and measured and their food contents were recognised. Larval 
and post-larval plaice from the Hatchery at Port Erin were 
also collected and their food was examined. 

(h) Other investigations (Embryogeny, variability) were 
contemplated, but have not so far been adequately made. 


(3) Treatment of the Data. 


Not very much was to be made out of a direct comparison 
of the numbers of fish caught per hour’s trawling, on the 
various grounds, and at different times. The standardisation 
of the fishing gear and vessels and of the canditions under 
which the experimental hauls were to be made, were too 
difficult. In no case have we had, at our disposal, a vessel 
used exclusively for scientific research, and all the work had 
to be done on board the police steamers and sailing boats, or 
on board steam trawlers, smacks, and inshore trawlers. It was, 
of course, very gratifying that the L.W.S.F. Committee allowed 
us the use of their vessels, and we are also much indebted to 
the owners and masters of the commercial boats, whe allowed 


56 


the fish-measurers to go to sea with them and make records of 
the fish caught. Still in no case were we in control and fully | 
able to choose the grounds and times for the hauls. Scientific 
work on board the police vessels had, of course, to be dependent 
on the nature of the official duties that were to be performed. 
In the circumstances the results that were obtaimed are very 
satisfactory. 

One can, of course, make certain conclusions of value 
merely by comparing average catches taken at different times, 
and on different grounds, with each other. No doubt these 
experiments do give us rough general pictures of the abundance 
of fish from time to time and, so far as they go, they must 
represent the experience that an observant fisherman would 
acquire. Thus the tables on pp. 46-7, giving the relative 
abundance of the different species of fish on the various 
grounds, are certainly to be regarded as representing the 
natural conditions in an approximate manner. So also, the 
series of hauls made in the Mersey by Capt. G. Kecles, give 
some very valuable information. Too much, however, must 
not be made of the ordinary periodic trawlings on which the 
present report is based, as representing variations in abundance 
from year to year. 

What has been done has been to seek to get the information 
we require by a study of the measurements of the fish them- 
selves, rather than by mere counts of the numbers taken per 
haul. These relative lengths, ages, etc., are independent of 
the actual numbers of fish taken. It will be seen that they do 
give us valuable and, we believe, reliable data. Combined with 
the results of the fish-marking experiments and the information 
siven by the official statistics, they enable us to deduce 
conclusions that are of value for the administrators. 


The statistical methods employed. 


When the measurements of the fish sampled are arranged 
as follows :— 


57 


Mean length = 10-5, 11-5, 12-5, 13-5, ete., cms. 

Nos: caught = 2, 9, 133,46, ete: 
we obtain a series called a ‘* frequency distribution.” There 
are many ways of forming such distributions from the same 
data. The ‘ mean-lengths ” 10-5, etc., represent the middle 
points of the groups of measurements, that is 10 to Ilsems., 
11 to 12 ems., ete., but these groups might have been 10 to 12, 
12 to 14, 9 to 11, 11 to 13, ete., or they might also have been 
4 to 44 inches, 44 to 5 inches, etc., or even 4 to 5d, 
5 to 6 inches, etc. If we were to make such alternative series 
of measurements from the same sample of fish and then plot 
curves from the various distributions we should not get 
eraphs of the same form. Nor should we get quite the same 
averages and other statistical results. It is convenient to 
measure the fish in centimetre groups, but such a method has 
20 superiority over any other arrangement except its con- 
venience. 

If the series of measurements is a very big one—say 
several thousands of fish—it will not matter much what way we 
express the data. But every now and then small samples, 
50 or 100 fish, say, must be studied. Therefore we require 
some way of avoiding the errors which arise because of the 
alternative methods of grouping the measuremeats. 

This means that the crude distributions must be 
“smoothed”? in some manner. In general, a series such as 
the above one is irregular and these irregularities affect 
whatever form of average we adopt. Hf we calculate the 
latter an1 then re-measure the fish and arrange them in a 
new way we may get different irregularities which affect our 
averages (or other statistical conclusions) in different ways. 
Which results are we to accept? In social and_ political 
controversies we do all these things and then accept the 
results that are the most welcome ones! But this kind of 
statistics is that which “ can be made to prove anything,” and 
we must avoid it “like the plague.” 


58 


“Smoothing” might be effected by taking overlapping 
averagcs. Thus, instead cf the frequency, 5, at mean length 


2+5 ; 

11-5, in the above example we might take a = vss Ole: 

instead of 13, at mean length, 12-5, we might take 

5 + 13+ 46 
) 


some cases this method has an approved basis; it means that 


== 21:3 and so on, all through the series. In 


we are generally in doubt that any fish we measure is properly 
measured : it may really belong to the group in front, or that 
behind the group in which we have placed it. This is so with 
a number of fish in every sample. If one is very near 11 ems., 
say, it may be really a little less than 11, so little less that 
our necessarily hurried methods may not enable us to be 
sure. But it 1s only a few of the fish about which we are in 
doubt, in this wav. That means that we ought to employ a 
smoothing formula of this kind, 

(Bornes ee 

Qe 

where m is a small number, say 2 to 5. 


Pearson Probability Curves. 

The really scientific way to smooth such series as we have 
is to calculate a theoretical distribution and then use this instead 
of the crude series obtained by the measurements. Pearson 
curves are based on the theories of probability. The different 
results that are got in playing games of chance are explained 
by assuming that these results are due to the operation of a 
ereat number of small causes. The number of sixes one gets 
on throwing a dozen dice at the same time, or the number of 
heads we get when we throw a dozen pennies into the air, are 
chance effects due to a great number of small, mdependent 
causes, which are usually beyond our powers of control. The 
theory of probabilty enables us to calculate such chance results 
beforehand, and the calculated result agrees surprisingly with 


59 


the actually-observed result, when the number of trials is 
fairly large. Event when the chance results are due to the 
operation of a number of small causes, some of which can be 
controlled (say the “ loading ” of the dice, or the cutting away 
of the metal from some of the sides of a “* put and take ” top), 
the theory does not fail us. When the causes of variation are 
quite beyond our control we obtain a symmetrical curve of a 
certain mathematical form, and most biological variation 
curves approach more or less closely to this form (the normal 
curve of error). Human biological inequalities (sav variability 
in stature, or in the ability to pass an examination) come very 
close to this symmetrical form. On the other hand, social 
inequalities (say the annual value of the house a man inhabits ; 
the income on which he pays tax, etc.) are entirely different, 
for the curve of variability in such cases is an asymmetrical, 
* J-shaped,” exponential one. The meaning is that the causes 
of wealth and poverty have come under our contro], and that 
the control endeavours to bring about the observed form of 
inequality. 

In many of its applications (insurance and actuarial 
calculations) the theory is sound. When it is applied to the 
results of the study of organic variability it must also be 
regarded as sound. Obviously, when we apply it to finding 
out how much we are to qualify the results of taking a sample 
of something we are also on the right lmes. Now these observa- 
tions which we study here are samples. There are some 
millions of plaice on a certain fishing ground and we want to 
know their average length as well as the numbers that differ 
from the average by definite gradings above or below the 
average. We take a sample of, say, 1,000 plaice from this 
population and measure them and find the average and the 
variations from the average. But we cannot be certain that 
our sampling has been representative : some of the size-groups 
are always over-sampled and others are under-sampled. 


60 


Repeat this sampling again and the same misrepresentation 
occurs, but it is different groups that are under- and over- 
sampled. 

If this were all we could apply Pearson curves to such 
data as are here given. But the theory supposes that the 
population that is sampled is an homogeneous one in respect 
of the characteristic that we measure. One could not legiti- 
mately measure the stature of all the individuals in a crowded 
church, say, and then base a Pearson curve on the results. 
A number of the people are full-grown men, others are full- 
erown women, and others again are boys and girls of different 
ages. Thus there are groups in this church population, and the 
mode of variability from the average is not the same in every 
group. We ought to measure and classify the full-grown men 
separately from the women, etc., making a separate curve for 
each. The assemblage is an heterogeneous one. 

All fishery samples are, in general, heterogeneous, consisting 
of fish of one, two, three, etc., years of age. We find this by 
examination of a sample. It is, in general, quite impracticable 
to attempt to separate the sample of plaice caught and measured 
into its year-classes. Therefore we cannot (in general, again) 
apply the method of Pearson curves to treatment of the 
statistics, and this is fortunate, in one sense, because the 
arithmetic that is mvolved is “colossal.” Still there are 
samples in which one year-class may preponderate so greatly 
as to smother all the others. So some of the distributions in 
this report have been “ Pearsonified,’ with the object of 
illustrating this discussion. 


The Construction of Summational Curves. 

The method that has been adopted has been to smooth 
the observed frequency-distributions by making summational 
series from them. Then all the information required is obtamed 
from the latter curves. The methods actually used will best 
be described by an example. 


61 


Example : Table V, June, 1908-1913. 


| | 

(1) e | @ Qo Gi (6) 

Mean 

length. i Halts Sa Wee y Ly 
13-5 1 0-5 | 1000-2 ae 
14:5 iy 6-4 999-7 2-1 998-8 
15:5 39 20-7 | 993°3 21-6 996-7 
16°5 106 56-2 972-6 64:4 975-1 
17°5 205 108-8 9164 | 111-9 910-7 
18-5 304 161:°3 807-6 | 143-0 798:8 
19-5 263 139-5 | 646°3 149-9 655°8 
20:5 231 122-6 506°8 136-7 505-9 
21-5 228 121-0 | 384-2 112-6 367-2 
22-5 183 97-1 263-2 85:7 256-6 
23-3 124 65:8 166-1 61:3 170-9 
24-5 67 35-5 100-3 41-6 109-6 
25-5 45 23°9 64:8 27-1 68-9 
26:5 24. 12-7 40-9 17:0 40-9 
PA 5) 20 106 28-2 10-4 23:9 
28-5 9 4°8 17-6 6-2 13-5 
29-5 14 7:4 12:8 3:6 7:3 
30:5 5 2-7 5-4 2-0 3:7 
31-5 3 1-6 | 2-7 1-1 1:7 
32:5 *4 1-1 1-1 0-6 0-6 

1,885 1000-2 998°8 


The plaice have been grouped into one cm. classes, 13 to 
14, 14 to 15, and so on: Col. (1) gives the middle points of these 
class-ranges ; Col. (2) gives the actual numbers of fish measured 
and belonging to each class-range, and Col. (3) gives these 
frequencies expressed as numbers per 1,000. Thus all the 
series given in this report can be graphed on the same scale, 
and the graphs can be superposed for comparison. But the 
actually-observed frequencies are necessary whenever we 
require to find the “ probable errors,” so they must be stated. 
Col. (4), “ =f°/,.,” gives the results of the process of summa- 
tion: thus the entry, 17-6, opposite the length, 28-5 ems., is 
the sum, 48+ 74+ 2-7+ 1:64 1:1, of the frequencies 
opposite 17-6 and below the latter. In this case the summation 
begins at the bottom of the column, but it might as well 
begin at the top. The entries in Col. (4) are to be read in this 


62 


way: 1,000-2 °/.. fish are 13 or more than 13 ems. in length ; 
999-7 °/,, are 14 or more than 14 ; 993-3 °/,, are 15 or more than 
15 cms., and so on. Or, again: 263-2 °/,, plaice are 22 cms. 
or over 22 cms. in length and 506-8 °/,, are 20 or over 20 cms. 
long. Therefore 506-8 — 263-2 = 243-6 (that is, about one- 
quarter of the entire catch) are over 20, but less than 22 cms. 
long. 

Col. (5) in the table, “y,’ represents the theoretical 
frequencies as calculated by Pearson’s method of curve-fitting. 
Now let these theoretical frequencies be summed in the same 
way as Col. (3) has been obtained : we thus get Col. (6), “ Xy.” 
It will be seen that this is very similar to Col. (4), which gives 
the result of the summation of the crude frequencies. The 
crude Sf’s are more like the theoretical }f’s than the crude 
J ’sare like the theoretical f’s, and this is because, in the process 
of summation we have automatically got rid of the errors of 
random sampling—or, at least, to some extent. How this 
comes about is easily seen: if one class, say the fish of 18 to 
19 cms., 1s over-represented in the sample, then all the other 
classes will, on the average, be under-represented. Now in the 
summing we add together at each stage over- and under- 
sampled classes, and so the error of random sampling, apparent 
in the frequency series, tends to disappear from the summa- 
tional ones. Therefore, in graphing these various columns it 
will be seen (fig. 3) that the crude and theoretica] summational 
series are nearly the same. 

From the summational series, made in this way, smoothed 
frequency series can easily be constructed. First of all the 
summational series must be graphed on a fairly big scale. The 
curve must not be drawn free-hand, but by means of some 
device that enables us to lay a spline, or steel spring, evenly 
among all the points plotted. The curve should pass as nearly 
as possible to all the points, but without necessarily passing 
actually through any of them. It should be drawn by running 


63 


a pencil trace along the spline, and the trial curve so obtained 
must then be inspected. When the points are connected by 
short, straight lines it will be seen that there are a number of 
polygons, some situated above the curve and others below it : 


the combined area of the polygons above the curve should be 


equal to that of the polygons below the curve. If this is not 
so the curve should be redrawn. 


/20 


80 


Scale fer summational curve 


ce ie | bras. 


The changes of curvature should be as gradual as possible. 
We must first resolve whether the summational curve is simple 
or compound. Usually it is simple—that is, it should present 
one part which is all concave to the horizontal axis and another 
part which is all convex (as in Fig. 3). | There will be a portion 
which has no sensible curvature—that is, it looks like a straight 
line sloping in one direction or the other, according to whether 
the summation begins at one end of the distribution or the 
other. At the ends the summational curve is sensibly parallel 
to the horizontal axis. Sometimes there is a hump on the 
summational curve, formed by several pomts—say 3 to 6. 
When this is so the curve should endeavour to follow these 


64 


points, and in that case it will be seen that there are now 
two places where the summational curve is concave, and other 
two where it is convex to the horizontal axis. The frequency 
series from which the summation has been made must now be 
regarded as consisting of two simple, superposed series. 

In doing all this we are adopting a definite formula of 
interpolation. In making the smoothed curve pass evenly 
among all the plotted points we are making its total area equal 
to the total area of the polygon formed by connecting the 
plotted points by short, straight lines: in the Pearson method 
of calculating a theoretical curve we must first assume that 
the total unsmoothed frequency shall be equal to the total 
smoothed frequency. Further, the equation of the curve which 
is thus calculated by Pearson’s methods is graphically repre- 
sented by a certain form, and this form, for our smoothed, 
summational curve, is given by the line of gradually changing 
curvature, which is everywhere as near as possible to the plotted 
points. The elasticity of the spring (which we assume to be 
the same everywhere in it—not always the case, however, in a 
much-used one) confers on the curve this gradual, unforced 
change of curvature. 

The actual, smoothed curve, which is to be used further, is 
drawn with a ruling-pen filled with red ink, and obviously a 
fine trace is made. The points where the curve intersects the 
vertical scale lines of the graph paper are now pricked and the 
ordinates are read off on the vertical scale. These are written 
down to replace the unsmoothed ¥/ series. This smoothed 
series is next differentiated so as exactly to reverse the process 
of summation, as it was carried out on the unsmoothed / series, 
and the result is a smoothed, frequency curve. It is not quite 
smooth, however, because it is rather difficult to read off the 
ordinates very precisely on the vertical axis. There is never 
any difficulty, for all that, m drawing a smooth, frequency 
curve through the points found by this process, for we can 


65 


easily find three other important characters of the curve—its 
maximum and its points of inflexion. 

Very often the smoothed, frequency curve so found is very 
like the Pearson one which can be calculated but it is often 
significantly different in form. When this is the case the 
smoothed curve found graphically is, we think, to be preferred. 
Undoubtedly, there are plaice frequency series which do not 
give a Pearson curve with sufficient ‘‘closeness of fit” to 
satisfy the criterion proposed by the statisticians, and this 
may be the case even when the measurements are numbered 
by thousands. (Obviously the law of variability is not that 
stated by Pearson’s fundamental, differential equation with 
four constants.) 


Use of the Summational Curves. 

These curves can be used to obtain the numbers of fish 
between any two sizes. This is possible from the summational 
series themselves when the sizes in question are whole numbers 
of centimetres (or otherwise the numbers representing the ends 
of the groups or classes). From the curve, however, we can 
interpolate graphically and find the frequency between any 
limits whatever—the method is an obvious one and is illustrated 
onip: 69: 


The Mode or Maximum. 

This is the position of greatest frequency—the peak or 
hump of the frequency curve. It can be found graphically as 
follows :— 

A fine, straight line is scratched on a strip of transparent 
celluloid (a set-square, for instance) and the extremities of the 
line are neatly pierced by fine holes made with a needle. The 
set-square is laid on the graph, scratched line downwards, and 
then it is rotated, so to speak, on the curve. Where the latter 
changes from convex to concave there is a ‘‘ point of inflexion,” 


and here the tangential line will cross the summational curve. 
E 


66 


The set-square is now held in this position and ¢he apertures 
at the ends of the line are pierced so as to make points on the 
graph paper. The set-square is taken away and a fine line in 
red ink is ruled on the graph: this will appear to coincide with 


4. 


Hies. 4 and 5: 


that part of the summational curve which is sensibly straight. 
By inspection we find the points where curve and tangential 
line begin to diverge, and half-way between them we may take 
to be approximately the point of inflexion. This point is 
marked and a perpendicular is dropped from it to cut the 
horizontal axis. This latter point of intersection, read off on 
the scale of lengths, gives the abscissa of the mode, or maximum, 
of the frequency curve. 


The Poanmts of Inilexioen: 

Let the summational curve be supposed simple. There 
will be two places on it where its curvature is greatest, and these 
can be found graphically as follows :— 

Rule two parallel lines, about 1 cm. apart, on a transparent 
set-square and rule another line perpendicular to both at about 
the mid-points of the parallel lines. Graduate the lower line 
in mms. Rotate the ungraduated line on the set-square on 
the summational curve at the places of greatest apparent 


67 


curvature and find the point where the chord, as given on the 
graduated line, is of least length. This point is approximately 
the portion of greatest curvature. Drop a perpendicular from 
this to cut the horizontal axis and the point of intersection, 
read off on the scale of lengths, will be the abscissa of the point 
of inflexion on the frequency curve. 


Measures of Dispersion. 

There are a number of such measures—for instance, 
Standard Deviation, Probable Error, Interquartile Range, Semi- 
Interquartile Range, etc. We cannot properly speak about 
“the length” of the plaice inhabiting any sea area in any 
particular period of time for these lengths may be anything 
between the extreme lengths actually observed. But we see 
that all these sizes of plaice do not occur with equal frequency— 
for instance, the table on p. 61 shows that the plaice on the 
area in question, and at the particular time, ranged from 
13 to 33 ems. in length. Nevertheless, about 25 per cent. of all 
were over 20, but less than 22 cms. in length. Evidently, then, 
we attach importance to a limited range of lengths, the ends of 
which are situated somewhere on each side of the maximum 
of the distribution: this range gives us the prevalent length of 
the fish at that time and in that area. 

The commonly used measures of dispersion are con- 
ventional ranges of this kmd. The “ probable error ”’ and the 
“interquartile range ” are supposed to represent a short range 
of lengths near the mean length (or near the mode, or near the 
“median ”’), such that within this range are contained one-half 
of all the fish in the sample. The “ probable error” is cal- 
culated from the “ standard deviation,” which is calculated on 
the assumption that the frequency curve representing the 
distribution is what is called the “ Gaussian” one. It seldom 
is in any of the distributions that we have found. Therefore 
the use of the standard deviation and probable error has no 
theoretical justification, and, indeed, it may be very misleading. 


68 


The interquartile range is calculated by finding the 
“median” and “ quartiles.” The arithmetic is simple and 
easy. The method is applied to the crude frequencies and it 
is therefore affected by the errors of sampling and by the errors 
that arise from grouping. If different methods of grouping 
are adopted—in the cases of small distributions—different 
medians and quartiles are obtained, and any one of them, found 
by different methods of grouping, is equally probable. If we 
group only in one way we get only one interquartile range, but, 
obviously, there are other equally admissible interquartile 
ranges which we have not calculated ! 

What measure of dispersion is to be adopted? This 
depends on the plan of the investigation for the measure in 
question is only a means to some conclusion or other. Here 
we adopt the measure called the “ shortest half (or two-thirds, 
or three-quarters) range.” 


The Shortest Half-range. 
The total area of the frequency curve (or the sum of the 
frequencies) is taken as 1,000 (for we are converting the 


‘ 


observed frequencies into “ per-milles’’). We take the sum- 
mational curve figure and then take one-half of the total 
vertical scale (or 500) on a pair of dividers and, with this, 
measure off the distances aa', bb', cc', etc., along the vertical 
scale lines and from the points where the latter intersect the 
summational curve. Thus we get the points a', b',c',d', e', 
and then (with a “french curve”) we draw a smooth curve 
through them. 

Next, with a pair of dividers, we find the shortest distance, 
measured along some horizontal scale line, between the curve 
a', b', c',d', e' and the summational one. Perhaps there are 
several scale lines all sensibly the same in length and then we 
approximate by finding the middle one. The places are 
marked where this shortest horizontal line cuts both curves : 


they are g and! m Fig. 6. From g and /' perpendiculars are 


69 


Fic. 6. 


70 


dropped to cut the horizontal axis, and these latter points, 
read off on the scale of lengths, give the abscissae of the shortest 
half-range : the latter is about 18-5 to 21-5 cms., and within 
this range of lengths one-half of all the fish in the catch are 
contained. 

We now go further. From the point g'', on the vertical 
scale, 150 units are measured downwards getting the point h''. 
A horizontal line h'' h is drawn to cut the summational curve 
in h and a perpendicular hh' is drawn to cut the horizontal 
axisinh'. Between g' and h', that is, between about 21-5 and 
23 cms., another 15 per cent. of all the catch is contained. 
Next we prolong the vertical line, f'' f', upwards to cut the 
summational curve in f, and then a horizontal ff''' is drawn 
across to cut the vertical axis in f'''. From the latter point 
150 units are measured upwards on the vertical axis giving a 
point on the latter at about 1,000. Therefore a further 15 per 
cent. of the fish are contained within the range of lengths 
14 and 19 cms. 

Summarising we find : 

One-half of all the fish are over 19 and less than 
22 cms. in length ; 

80 per cent. of all are greater than 14 and less than 
23°D cms. in length. 

Obviously we can extend the method. We might repeat 
the above construction, using two-thirds of the vertical scale 
length, or three-fourths: these figures would give us the 
shortest two-third and three-fourths’ ranges. Or we may take 
the point 20 cms. on the horizontal scale, draw a perpendicular 
upwards to cut the curve and then a horizontal across to cut 
the vertical axis in the point 600. That shows that 60 per 
cent. of all the fish are 20 cms., or more than 20 ems. in length. 
Or, again, we may find the mode and then draw a horizontal 
across to cut the vertical axis. Stepping off 25 per cent. cf 
the latter scale on either side we get two additional points. 


(i 


From them horizontals are drawn to cut the curve, and from 
the points of intersection perpendiculars are drawn to cut the 
horizontal axis. The latter points are the two quartiles. 


It must be noted that the degree of accuracy of such 
determinations of the modes, points of inflexion, or measures 
of dispersion depends upon good draughtsmanship. This is 
not difficult to attain. There will be some personal differences 
in the results,* but we submit that these are usually smaller 
than any differences that ought to affect the conclusions that are 
to be made. These conclusions are to have certain probabili- 
ties: for instance, we lay it down that it is to be 2 to 1 that 
the fish caught on a certain area, in a certain month, and with 
a 6-inch mesh trawl-net, are (say) between m and m cms. in 
length. Then we find n and m, or we wish to find what fraction 
of the whole catch of fish are between n and m cms. long in the 
same area and in the same circumstances. Then n and m 
being postulated we find the corresponding probability. 
Extensions will readily suggest themselves. 


CHARACTERISTIC LENGTHS OF THE PLAICE Caucut DuRING 
THE PRE-WaR PERIOD, 1908-1913. 


We now give a series of tables, 3 to 13, which summarise 
the results of the trawling experiments made during the six 
years 1908-1913. These data are intended as a record of the 
condition of the plaice population on the eastern side of the 
Trish Sea during the years immediately preceding the war, and 
they will enable us to make a comparison with the condition 


* Analytical methods can always be employed to find the mode (dy/dx a 
maximum on the summational curve), and the points of inflexion (dy2/d22 
maximal and changing sign on the summational curve). We think such 
treatment would be pedantic. Measures of dispersion must be approximate 
so long as we do not know the equation to the frequency curve. 


72 


that followed the partial cessation of fishing which occurred 
during the vears 1914-1918. 

The arrangement of the data is as follows :— 

Tables 3 to 10 record the lengths of plaice caught in a 
trawl-net of 6-inch mesh, throughout the year, on the regions 
Luce Bay, Morecambe Bay, etc., Blackpool to Liverpool Bar, 
Mersey Estuary, Beaumaris and Red Wharf Bays, etc., 
Carnarvon Bay and Cardigan Bay. The actual frequencies of 
occurrence of each one-cm. group and the frequencies per 
thousand are given. 

Table 11 gives the same kind of data for plaice caught 
off the Mersey Estuary in a shrimp trawl-net of 2-inch mesh. 

Table 12 gives the same data for a number of hauls made 
with trawl-nets of 4-inch, 6-inch, and 7-inch meshes on the same 
grounds and at about the same times. 

Table 13 gives the dispersions, calculated by the methods 
indicated in the previous section of this report, for the distribu- 
tions of Tables 3 to 12. 


73 


Table lil. Luce Bay, Sept.-Dec., 1908-1912. 


el 
Ct Ov St Ot 


bok — 
SOP WNWHOODAATE WN HOOD 


wWwHwwwwwowrmbpdbddywerrprth 
AAAAaannnargana ana dc 


| 
Mean 
if bad es length if flee 
2 0-2 37°5 173 22:3 
6 0:8 38-5 155 20-0 
7 0-9 39-5 119 15-4 
9 1-2 40:5 91 11-7 
22 2-8 41-5 58 75 
79 10-1 42-5 66 8-5 
271 34:8 43-5 42 5-4 
372 48-0 44-5 51 6:6 
412 53-2 45:5 18 2:3 
523 67-5 46-5 PAT 3-5 
538 69-5 47:5 17 2-2 
454 58-6 48-5 13 1:7 
412 53-2 49-5 12 1:5 
380 49-1 50-5 5 0-6 
306 39:5 51-5 6 0:8 
290 37-4 52-5 3 0-4 
292 37:7 53:5 6 0:8 
257 33:2 54-5 2 0-2 
231 29-8 55-5 oars eis 
259 33:4 56-5 2 0-2 
239 30:8 57-5 1 0-1 
218 28-1 58:5 3 0-4 
276 35-6 59-5 aoe 
299 38:6 60-5 
264. 34-1 61-5 ae fis 
251 32-4 62-5 D2 0-2 
207 2 — 
Motals#sceeee 7,748 999-6 


74 


Table 1V. Morecambe Bay, &c., 1908-1913. 


Estuary 

MORECAMBE Bay. OF THE 

Duppon. 
June. July. | August. | March—May. 
fo eiales fem lea) of. ~\it coe 1 maka ee 

10-5 Bee Bae Beedle oe ES i 

11-5 e. Mee rl ee i no igi tes 

12-5 Tea its Pease es | Ae Pe aie is ane 
13-5 Se awilt eek oe | 1] 0-9 1 | 0-7 23 | 6:3 
14-5 9 3°8 | 3 2:6 5) || 3:3 82 | 38-2 
15-5 39 16-6 36 31-1 | 2) 13-7 205 75:3 
16:5 78 33:3 15: | 64-9 | 69 | 45:1 302 +°100-6 
17-5 171 729 | 135 116-8 101 66-0 390 117-2 
18-5 302 128-8 101 87-4 116 75:8 482 | 118-8 
19-5 305 130-1 | 147 | 127-2 128 | 83:7 413 111-1 
20-5 416 177-4 | 180 155-7 | 141 | 92-2 315 | 97-6 
21-5 345 147-1; lll | 96-0 NB || 89-5 221 | 81-9 
22-5 303 129-2 113 | 97-7 178 116:3 | 170 | 66-2 
23:5 183 78:0 65 | 56-2 157 102-6 178 | 51-7 
24-5 90 38-4 7 61-4 151 98-7 102 39-2 
25-5 50 21:3 42 | 36:3 123 80-4 84 | 29-0 
26-5 23 9-8 ay) 27:7 74 48-4 68 | 20-9 
27-5 18 7:7 18 15-6 | 67 43°8 44 14-6 
28-5 5 2-1 10 8-7 30 19-6 43 10-5 
29-5 33 1:3 7 6-1 16 10-5 32 6-9 
30-5 2 0:9 | 4 3°4 9 | 5:9 27 | 4-6 
31-5 1 0-4 | Seb WI eee nl 1-9 8 3-0 
32°5 1 0-4 i 0:8 | 2, 1:3 4 | 1:9 
33°5 I 0-4 3 | 2:6 a 0:7 4 1-2 
34:5 a re |) aes nae doe” Il Paes 4 0-7 

35-5 ESA lh 3-- i 0-8 | Ie 
2,345 | 999-9 1,156 999-9 | 1,530 | 1000-1 | 3,223 997-4. 


* Calculated frequency curve. 


70 


Table V. Blackpool to Liverpool Bar. 1908-1913. 
=; =e Te = we ae are ar es youw 
June. | July August. September. October. 
| 

i | Hi hes | f | f hee if | if ates f | f rien f if Ses 

11-5 a ae 1 1 eee eee eee | ' 
12-5 a Ds eae 6 | ; 1129 Reena 1 0-4 
13-5 1 0-5 1 Be DAN ae 9 39; 10; 40 
14-5 12 6-4 8 ee 57 | 3:8 34 12-1 19) Gad 
15-5 39 20-7 30 | 4:8) 131} 24-3) 111 31-9 75 | 30:3 
16-5 106 56-2 | 129| 29-7] 267| 55:9] 269 57-7 | 201 | 81:3 
17-5 205 | 108-8} 320 85-4 | 473 | 89-4 | 459 82:9 | 231 | 93-4 
18-5 304 | 161-3 601 | 139-3 | 740| 106-0] 517] 101-7 | 250] 161-1 
19-5 263 | 139-5 | 838 | 162-9 | 794] 114:0| 542| 111-2 | 196| 79:3 
20-5 231 | 122-6] 676 | 154-2] 839] 111-5 | 557} 111-3] 167 | 67:5 
21-5 228 | 121-0] 495 | 127-7/ 681] 101-8/ 506] 1036 | 152] 61-5 
22-5 183 97-1| 433 | 93-0] 57h | 882] 449/ 91-2] 160) 64:7 
23-5 124 65-8 | 320 69-4 | 444) 73:3] 339) 76:3] 164) 66:3 
24-5 67 35-5 | 254 47-9 | 338; 589] 311 Ci Vig | STG 
25-5 45 23-9 | 159 32:3 | 262) 460] 245 47-1 | 156) 63-1 
26-5 24 12-7 83 21-5 | 231 “35:2: 176 85-1 | 140) 56-6 
27-5 20 10-6 63 14-1 | 182)|, 926-4) 798 25-4 | 122 | ~49:3 
28-5 9 4-8 25 93 | 146 19-4 88 17-8 97 | 39-2 
29-5 14 7-4 22 6-1 86s «14 54 12-1 61 | 24:7 
30-5 5 2-7 6 4-0 63 10-0 34 8-1 37 | 150 
31-5 3 1-6 14 2-8 36 | 7-1 18 5-2 22 8-9 
32-5 2 1-1 15 18 34. | 5-0 18 3:3 8 3:2 
33-5 x 5 OE fee eA 3-5 4 20) ll 4-4 
34-5, an 6 0-8 | 21 | 2-4 6 13 | 5 2-0 
35-5 es 0-5 123) 1-6 5 0-7 | 4 1-6 
36-5 ile 0-4 Wed 1-1 6 04) 2 0:8 
37-5 3 0-3 3 | 0:8 1 O22 0:8 
38-5 h 2)] 0:28 |=. 0-5 1 O-1 | 1 0-4 
39-5 ses (Pt Ae ene | O:3) he io: Eta | a 
40-5 Te 0-2 1 0-4 
41-5 1 | 0-2 | 0-4 
1,885 | 1000-2 |4,516 | 1009-6 |6,492 | 1000-9 | 4,889 | 1003-7 | 2,473 999-9 


* Calculated frequency curves. 


76 


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LO I ¥:0 T £0 ie 9-0 Gc eee | eee L-0 1 wee see eee eee G-Le 
L-0 Ll | #2 G | #0 z ea ener IT | 30 € see Tile Ae i gescmellbites a lemeage 

eB peg L | 6-0 ¢ | 60 Lb | &0 9 | &0 z sn tas gS nee Uae eters 

ze AzOre Netgen || 8-0 6 | eT or | 2-0 = | £0 6 io =a ys | ope 
L-0 T -|ser | or | 81 Ol | 9% 6r | TT ie ec0 Ce \eLO) aula | el elaiee 

5 oa G&S SF L-¥ 9G 6-1 FI GG €1 8-0 ¢ GO I L-0 G G-6E 

7 ad FE IL i al | BG GG 9€ 6 0G Tel i €-0 € £0 | $ GHOé 

<9 sa 1-SP €6 9-¢ 1é Gas GG 8-9 Sf 9-T € F0 |G F:0 G G-0€ 
GT G L-9F C6 FEL FL FFI FOL 9-11 €L EG v 6:0 9 Gol € G66 
L-0 I 6-6F 601 9-CT | 68 G LT 9E1 0-61 8ST 8-€ él GT | € GS FI G-8G 
GP 9 8°87 IOI L-91 66 9-FG | LLI 9-6Z CCG 6G LI GG ) 8) UP 8I GLE 
L-9 6 VSP OOT L1é | OGT GLE | L6T LP 1S€ F6 8 GP | I €-8 FE G-9G 
6-F1 0G 8-0¢ SOT L-€€ LOT GI1é EGE 1-29 99€ FST €¢ (oz | PG C1 IL GCG 
€-GG 0& L:8& 08 | 8-8€& FIG 6-9§ G9 9-28 G9G GGG FIl GF 6¢ 6-LZ Té1 GG 
8-6 CE L:09 FEL 1-6¢ 9ZE GC: OF 88 8-LOL 119 GF 1G £96 | 601 8-8F CPG G-€¢6 
9-0G 89 L-69 PFI VOL | 1@P L19 SEP 0-LTT LIL 9-69 GIF VPP | 961 G-08 LOP GGG 
L8G 6L 8:L9 OFT S-9IL | #19 | 9-69 | 66F €-ZEL | 9F8 0-O1T FE9 8-FL €8E €O1l TFS GIG 
LOL G6 PSL GOT 6-FI1 ee9 «8 O19 8-LIT OL8 98ST | €08 8-LII 81g 98ST G89 G-0G 
6-9 Gs GEL ISI €-0€T SIL 9-9L OSS LTOT 89L L161 L68 6-991 109 8-PLI $98 G61 
FS01 6€T G-9OL 8ST 8-02I 999 8-16 6¢9 9-91 OS 9-ELT 8éL T-S6I GLL 0-SST 9GL G-8T 
F691 FIG FP9 €é1 G-68 | €6F L:SIL | 6&8 L-0¢ 16G L-€0r 60F L-PLI 199 G-LOL 667 GLI 
L- LOG 6LE L-69 6cl | L&6 | 91S 8-OFL | OLOT| 9-82 6ST 6-1F 8GE G- LOT OLD FP LG 9G G-9T 
0-0FT 881 €-16 Fr | OEE | L8T | S-66 | FIL G-E1 96 O-EL C6 FOF | imal €-61 raul GGT 
6:6¢ Ik a 2 | € | ¥:0 1G | €:9€ | 096 @eg 9¢ LS 6€ 0-6 | GF ¥8 6€ GF 
9-6I LI F0 I | 6:0 +S | LG | IP 9-T LI L-0 G tell 8 GG OT GET 
GT G as i G0 Il | TT 8 F-0 lee G0 G 1-0 — L-0 8 GEL 
1-0 I sto vee | ees | 2.9 Pe L-0 lots S06 eae a0 |Z e eT 
Paled Hy ale dh ooeae fh ee if oe of | f a Sa £ eee | if ie any i 

ae | ee “yy 3u9T 
“Iequ1900(T ‘IOQUIDAON =| “1q.0900) ‘loquteydag ‘qsnsny ‘Ane ‘aune “LV uvoyl 
"EL61-806L “Asenjsy Aosuaiy YO “IA 21geL 


(et 


Table VII. Beaumaris Bay, Red Wharf Bay, &c. 1908-1913. 
January. June. July. August. 
Mean 
length. a a 
ui UPTO i | Rie f Flo i Foo 

12:5 ae Sac Sco 2 1:0 2 1-0 
13-5 4 2-9 2 0-9 1 0-5 3 1:5 
14:5 9 6-7 3 1:5 3 | 1-6 3 1-5 
15-5 28 20-7 32 15:8 26 | 14-3 12 5-9 
16-5 43 32-1 92 45:3 43 23-7 5] 28:3 
17-5 63 47-0 213 104-9 124 68-4 145 Tlsg) 
18-5 81 60-4 261 128-5 207 114-0 231 114-6 
19-5 91 67-9 259 127-6 273 150°3 318 157-7 
20-5 70 52-2 237 116-8 255 140-4 282 139-8 
21-5 82 61-2 153 75-4 216 Ie 260 129-0 
22-5 85 63-4 113 55:7 156 85-9 170 84:3 
23-5 69 51:5 77 37:9 113 62-2 127 63-0 
24-5 60 44-8 75 36-9 86 47°3 105 52-1 
25:5 69 51:5 64 31-5 65 35°8 67 33-2 
26-5 78 58-2 47 23-1 42 23-1 50 24:8 
27-5 84 62-7 52 25-6 37 20-4 37 18:3 
28-5 67 50-0 56 27-6 36 19-8 34 16-9 
29-5 67 50-0 47 23°1 31 13-5 29 14-4 
30-5 68 50-7 44 21-7 23 12-1 26 12-9 
31-5 62 46:3 45 22-2 17 9-3 20 9-9 
32:5 44 32:8 56 27-6 18 99 15 7-4 
33-5 28 20-9 37 18-2 14 Wey 7 35 
34:5 34 25-4 19 9-4 7 38 6 2-9 
35-5 14 10-4 16 1-9 8 4-4 1 0-5 
36-5 16 Lg 8 39 5 2-7 3 1-5 
37-5 2 1-5 6 2-9 2 1-0 2 1-0 
38-5 4 29 5 2-4 6 3-2 2 1-0 
39-5 i) 3-7 6 2-9 Be abe 1 0-5 
40-5 3 | 2-2 5 2-4 os aR 1 0-5 
41-5 2 1-4 ot O00 1 1-0 aon 308 
42:5 1 0-7 ' a : ; 
43-5 1 0-7 : 60 ee 
44-5 1 0-7 5 
45:5 2 1-4 
46-5 1 0-7 | 
47-5 1 0-7 
48-5 1 0-7 

1,340 | 998-9 | 2,030 999-6 | 1,817 996-4 | 2,016 | 999-8 


78 


Table VIII. Beaumaris Bay, Red Wharf Bay, &c. 1908-1913. 


September. October. November. | December. 
Mean | 
length. | ———}-—,  —t- — -_ ——— aa 
PME eae 
11-5 3 0:6 26 see a a as 
12°5 8 1-6 3 0:3 oot 1 0-4 
13-5 20 3-9 14 1:5 5 | 0:8 2 0-8 
14:5 68 13:3 76 8-7 29 4-9 10 4-0 
155 | 158 31-0 421 48-4 146 | 24-5 20 7-9 
16-5 291 57-0 | 1,197 137-9 350 58:8 66 26-1 
17-5 438 85:8 | 1,493 In 7fler/ 413 69-4 94 37:2 
18:5 396 77-6 | 1,155 132-2 360 60-5 158 62-5 
195 | 430 84:3 802 92-3 343 57-6 175 69-2 
20° | 392 76:8 579 66-6 341 57:3 218 86:3 
21-5 319 57-0 502 57-7 362 60-8 201 80:5 
22:5 342 67-0 405 46-6 345 58-0 224 88-6 
23-5 | 296 57-9 310 35-6 339 56-9 211 83-5 
24-5 337 66-0 268 30:8 363 61-0 162 64-1 
25:5 299 58-6 261 30-0 349 58°6 154 60-9 
26-5 286 56-0 275 31-6 336 56-4 152 60-1 
27:5 278 54-4 219 25:2 312 52-4 Unven | 46:3 
28-5 217 42-5 215 24-7 361 60-6 120 47-5 
29-5 153 29-9 161 18-5 341 57-3 81 32-1 
30-5 131 25-6 107 12:3 272 45-9 109 43-1 
31-5 85 16-6 81 9-2 176 29-6 68 26-9 
32-5 59 11-6 52 5-9 137 23-0 59 23°3 
33-5 37 73 39 4-5 73 12:3 29 11-5 
34:5 22 4:3 22 2-5 60 10-1 28 | 
35-5 17 3°3 12 1-4 38 6-4 15 5-9 
36-5 7 1-4 12 1-4 30 5-0 12 4:7 
37-5 7 1-4 4 0-5 14 2-3 8 3-2 
38-5 3 0-6 4 0-5 8 esha 12 4-7 
39-5 1 0-2 2 0-2 14 2:3 10 4-0 
40-5 4 0-8 1 0-1 14 2-3 6 2-4 
41:5 es ae 3 0:3 6 1-0 + 1-6 
42-5 : : 50 aes 2 | 0:3 1 0-4 
43-5 2 0-2 1 0-1 ee of 
44-5 oe 2 0-2 Sa eee 
45:5 20¢ 4 0-4 
46-5 1 0-1 1 0-1 
47-5 Oe 
5,104 | 994-3 | 8,697 | 999-4 | 5,950 | 999-9 | 2,527 | 1000-8 


79 


Table IX. Carnarvon Bay. 1908-1913. 


June. July. August. September. October. 


<a | oe 


mee 


. 
— pee 


. . . 
a — oe ory 
. oe oe 


PET col 8 FAERIE tei aite leap 4 |iepsie amare lin elie 


|S allnetecees i) eat 4} 165) 5]| 20-2 
18 | 328] 11] 445 

25:8 | 75 | 156-3] 18] 72-9 
35 | 90-2| 50} 1066 | 28) 113-3 

89| 45 | 95:9] 16] 64-7 
72 | 171-0 | 78 | 118-7| 79| 204-1 | 52] 1109] 21| 85.0 
46 | 109-2 | 87] 1324 | 57] 147-:0| 35| 746] 23] 93-1 
38 | 90-3] 95| 1445 | 49] 1263] 32|) 682] 19] 769 
81-0 | 25, 101-2 


23- 8:3 13 27-7 11 44-5 
10 23°7 32 48-7 10 25:8 ll 23-4 ll 44-5 
12 27°8 26 39-6 3 7:7 14 29-9 1133 52:5 
6 14:3 19 28-9 2, 5-2 16 34-1 5 20-2 
2 4:7 6 9-1 1 2-6 22 46:9 8 32-4 
yy 4-7 6 9-1 Be 7 14:9 2, 8-1 
2 4-7 8 12-2 1 2-1 2 8-1 
4 9:5 6 9-1 5 10:7 2 8-1 
site ae 6 9-1 |° I 2-1 1 4:0 
I 2-4 4 6-1 ] 2+1 1 4:0 
De 4-7 2 3:0 | ase wes te oes 
oat 1 1:5 non 1 4-0 
I 2-4 1 1:5 Ane 2 8-1 
ews 1 1:5 1 2-1 Si aoe 
1 | 1:5 | 
i 15 | 
1 1:5 
421 | 999-8 | 657 | 998-5 | 388 | 1000-5 | 469 | 998-5 | 247 |} 999-3 


Table X. 


80 


Cardigan Bay, 1908-1913. 


Near NEw Quay Heap. NEAR 
| TREMADOC PATCHES 

Mean | Bay. Buoy. 
length. l 

Jan.—March.| April—May. June. July. 

Ff ON ehpeles | fan De jd ol eee eee id oe ee as eee) Chee |) ie leh ioe 

a ee a ae | a 

12-5 6 11:3 Hea ners BAe ll clio a6 ee 
13-5 i 13-2 See aco | wong she p 1 2, nee aoe 
14:5 9 17-0 1 Ory A 1:6 ae Hf: oak es ARC ee 
15-5 “te oe 5 3-6 1 1:6 Be a8 1 | 2 an ade 
16:5 8 15-1 5 3:6 6 9-7 1 1-4 3 | iS 1 4 
17:5 11 20:8 39 28-5 20 32°3 1 1-4 12 21 2 8 
18-5 11 20:8 | 108 | 78-8 22 35-5 10 14-4 20 35D 5 19 
195 | 5 9-5 | 100 | 72-9 28 45-2 13 18:7 25 44 1 4 
20-5 ili! 20-8 | 122 | 89-1] 54 87:2 36 51-7 48 84 2 8 
21-5 i 13-2 | 107 | 78-1 49 79-1 32 45-9 43075 3 11 
22-5 17 32-1 | 115 | 83:9 46 74:3} 55 79-0 48 83 il 25 
23:5 19 35:9 | 100 | 72-9 46 74:3 73 | 104-9 61 106 5 19 
24-5 18 34:0 | 128 93-4 | 40 64-6 90 | 129-3 55 96 9 33 
25:5 22 41-6 | 125 | 91-2 58 93-7 80 | 114-9 38 68 10 37 
26-5 29 54:8 | 102 | 74-4 ys) 85-6 81 | 116-4 37 | 64 19 70 
27-5 26 49-2 81 | 59-1 53 85-6 61 87-6 39 ~—s«68 13 48 
28:5 34 64:3 69 50-4 by || pale 50 71:8 31 54 22 81 
29-5 50 94-5 57 41-6 28 45-2 35 50-3 31 54 28 103 
30-5 36 68-1 40 29-2 NF 27°5 31 44-5 27 47 22 81 
31-5 34 64-3 25 18:2 9 14:5 21 30-2 I) | BR 20 74 
32:5 Tl 51-1 22 16-1 3 4:8 12 17-2 12 21 19 70 
33-5 29 54:8 9 58] 2 3:2 a 10-0 5 9 17 62 
34:5 19 35-9 3 2-2 | 1 1.6 2 2-9 3 5 11 40 
35:5 19 35:9 2 1-4 1 1-6 2 2-9 ay | 5 12 44 
36:5 | 13 24-6 2 1-4 1 1-6 Boe ee 3 5 7 25 
37:5 12 22-7 B26 se 2 3-2 1 1-4 1 2 8 29 
38:5 10 18-9 Bae ; 1 16 2 2-9 3 is 4 14 
39:5 8 15-1 3 | 2-2 . : 33 | 5 6 22 
40-5 2 3:8 ao] aac é 1 4 
41-5 5 9-5 | ld. Cee | 9) ao 8 
42-5 4 76 + | S80 EO Leon 1 4 
43-5 2 3:8 hi 1 1:6 | ais a 1 4 
44:5 6 11:3 | aoe a Sec ll eee 4 14 
45:5 6 11:3 | sais 25) ll | 2 4 14 
46:5 S 9-5 oe aie a ste a5 cee 
47-5 7 3:8 ewer — Pre a wie ae 
48:5 . sce an 1-6 | I 2 5x 19 

529 | 1000-1 |1,370) 998-7 619 | 99-95 696 | 999-7 | 574 | 1002 rill 999 

| | | i 
2 /s0nay Ie fylasy Ile Gypsy Ibs Cbs ILS (ilasy I 


81 


Table XI. Off Mersey Estuary, 2-in. mesh. 1908-1913. 


November to March. May to July. August to October. 
Mean 
length,.§<§ -——. J 
f Teles f Upttea af UES 
4:5 610 17-9 55 15:3 10 2-2 
5:5 4,796 141-2 71 19-8 172 38-6 
6-5 6,821 200-1 27 7-5 436 elias) 
7-5 7,123 227°3 37 10:3 418 93-8 
8-5 5,928 174:5 125 34:9 179 40-2 
9-5 2,527 74-4 289 80-6 153 34-4 
10-5 1,134 33-4 268 74-7 308 69-0 
11-5 1,104 32°5 304 84:8 415 93-2 
12:5 776 22:8 352 98-1 418 93-9 
13-5 583 17-2 368 102-6 535 120-1 
14-5 466 13-7 444 123:8 409 91-8 
15-5 471 13-8 327 91-2 402 90:3 
16-5 347 10-2 338 94-0 236 52-9 
17-5 235 6-9 213 59-4 131 29-4 
18-5 159 4:7 163 45-4 75 16-8 
19-5 111 3:3 101 28-2 52 11:7 
20:5 76 2-2 53 14:8 36 8-1 
21:5 4] 1-2 21 5:8 29 6-6 
22-5 26 0:8 12 3°3 17 38 
23-5 11 0-3 11 3-1 12 2-7 
24:5 18 0-5 6 IEG 10 2:2 
25-5 10 0-2 1 0:3 1 0-2 
33,973 999-1 3,586 999-6 4,454 999-8 


| 


82 


Table XII. Comparison of Catches made with different 
trawl-meshes ; Mersey Area. 1908-1913. 


4”-mesh. 6”-mesh. 7’-mesh. 
Mean 
length,.§ _ A), AJ a —____ 
if ii Pe f af niles fi f Wow 

10-5 1 0-2 i 
11-5 500 see 
12-5 16 6:3 7 3:7 Pi 
13-5 82 31:5 24 7:3 ‘3 
14-5 262 97-1 80 | 23-6 1 0-8 
15-5 420 144-2 ss 41:9 2 1-7 
16-5 418 141-9 222, 70-0 8 6-9 
17-5 342 106-9 388 126-0 29 24-8 
18:5 296 86:7 421 138-0 54. 46:3 
19-5 202 56-8 359 110-3 108 92-5 
20-5 234. 72:7 368 | 108-7 138 118-2 
21:5 220 62-4 300 | 82-9 113 96-8 
22-5 242 64-8 283 78-0 115 98-5 
23-5 186 43-6 209 54-2 119 102-0 
24-5 123 30:1 191 48-0 146 125-7 
25-5 102 25-1 125 32-1 110 94-3 
26-5 46 9-7 96 25-2 82 70:3 
27°5 37 9-1 68 20-9 63 54-0 
28-5 17 3:9 sui 10-4 35 30-0 
29-5 16 3:1 22 7:3 17 14-2 
30:5 al 1-4 11 4:3 al 6-0 
31-5 2 0-4 9 3:1 4 3-4 
32-5 4 0:8 3 1-6 11 9-4 
33-5 1 0-2 2 0-9 3 2-5 
34:5 ‘ 3 1-6 2 1:7 
35-5 sak * 
36-5 2 2 

Beare 999-1 3,361 1000-0 1,167 1000-0 


83 


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85 


Prevalent Lengths of Plaice on the Various Grounds. 


There is no need to consider the data of these tables in 
the present place—they are intended as a permanent record 
and can be used in many conceivable ways. Here we only 
point out some of the more obvious characters of the fish taken 
on the regions investigated. 


Luce Bay. 


One-half of all the plaice taken were over 21 and under 
34 cms. in length and another 15 per cent. were over 34 cms. 
and under 40-5 cms. These are the biggest fish taken in any 
inshore area on the eastern side of the Irish Sea. Why ? 

It is to be noted that observations were only made during 
the months of September to December. The hauls were made 
with the object of getting spawning fish for the hatcheries at 
Port Erin and Piel, and the Bay was fished by permission of the 
Fishery Board for Scotland. As we have no records for the 
other months it is impossible to say whether or not there is 
any marked seasonal variation. 

The Bay is well protected from 8.W. to N.W. winds, and 
' this may be a condition of importance. But we think that 
the reason why there are bigger plaice in Luce Bay than else- 
where in the district studied is mainly that the region is closed 
against trawling by al] kinds of vessels. Only a small amount 
of fishing, by means of gill-nets, goes on, and the plaice are 
protected. Luce Bay is a closed area, and it is interesting on 
that account. 


The New Quay Grounds in Cardigan Bay. 

Inside the three-miles’ limit, and extending to the N.E. 
for several miles along the coast of Cardigan Bay, are the 
New Quay grounds. Here also are relatively large plaice 
during the early months of the year. They are not so abundant 


86 


as in Luce Bay, for trawling by sailing vessels is permitted. 
The shortest half-range is from 25 to 34 cms., and 65 per cent. 
of all the fish caught were over 25 and under 39 cms. 


Beaumaris and Red Wharf Bays. 


This also is an inshore fishery, mostly inside the three- 
miles’ limit. The main season is in the late autumn—about 
October to January. We shall show later that this autumn 
fishery depends on a migration taking plaice from the regions 
to the N.E. The fish are bigger than on the other grounds in 
Liverpool Bay and off the Lancashire coasts, the half-range 
being from 19 to 28 ems. 


Carnarvon Bay, Mersey Estuary, Liverpool Bar 
to Blackpool, Morecambe Bay (inshore). 


All this area may be regarded as a single, natura] one. 
The fishery is carried on mainly by half-decked vessels, a few 
smacks, and an occasional steam trawler. It is mostly inside 
the three-miles’ limit, though there is also a considerable area ~ 
of plaice-ground outside this contour. The main fishing season 
is from ahout July to October. The whole ground may be 
regarded as a typical small-plaice one. 

The characteristic lengths of the plaice caught in the 
months August to October are : 


Carnarvon Bay ... ... 18 to 24 cms. 
Liverpool to Blackpool ... 18 to 22 ems. 
Mersey Hstuary... ... 20 to 24 cms. 
Morecambe Bay _... ... 20 to 25 cms. 


These are the shortest half-ranges, comprising 50 per cent. 
of all the fish caught. 


87 


There is a fairly well-marked seasonal variation in length. 
Thus, taking the Mersey Estuary, we get : 


May ... oF oe +. 18-21 cms. 
June... aN a ... 17-20 cms. 
sullivan ie es ee ... 18-21 cms. 
August ... vies oe ... 20-24 cms. 


These are also the shortest half-ranges. The differences 
are due to the natural growth of the plaice and also to successive 
waves of migration of small fish from the more crowded, very 
shallow waters, to the sea just offshore. This we refer to in 
the section dealing with migrations. 


The Nursery Grounds. 


These we refer to when dealing with the life history of the 
plaice in the Irish Sea. 


88 


PART Al: 


THe Lire-HIstory OF THE PLAICE. 


We next consider the available knowledge as to the life- 
history of the plaice on the eastern shores of the Irish Sea. 
There is, of course, much that has still to be investigated with 
respect to this: the embryology, the possible existence of 
local races, and the possible spawning-grounds in St. George’s 
Channel and the Welsh Bays. The information that is at our 
disposal, however, enables us to make such a general picture 
of the life-history as may be of use to the administrators. 


The Spawning. 

Plaice eggs are found in the plankton collected almost 
everywhere offshore, between the Solway and Cardigan Bay, 
in the months of February, March, and April. Exceptionally 
the eggs have been found in January as the result, we think, 
of the spawning of fish well to the southward in St. George’s 
Channel. Spawning occurs in the pond at the Port Erm 
Hatchery during the months of March, April, and exceptionally 
in May. ‘The fish kept in the tanks at Piel, Barrow-in-Furness, 
spawn a little later, usually about the end of March, in April, 
and in May. April is the best month for the fish in the tanks, 
but in the open sea March is perhaps the best month. There 
is, of course, much variation, from year to year, in the time 
of spawning, and this is to be associated mainly with the 
temperature of the sea at the time of spawning and during the 
previous months, when the reproductive organs are most 
rapidly developing. It also depends on feeding, as is shown 
by our experience in the hatcheries, where the fish must be well 
fed if the roes are to develop fully. A close study of the 
variations in the temperature of the water (both in the tanks 
and in the sea) and in the abundance of the eggs found would 


89 


be most interesting, but this calls for very exhaustive experi- 
mental and observational work. 

We think there are two sources of the plaice eggs that are 
found in the plankton of the Irish Sea: (1) somewhere to the 
S.W. in St. George’s Channel, and (2) the grounds near the 
entrance to the Solway Firth. The reason for attributing by 
far the larger share of plaice eggs to the St. George’s Channel 
grounds is the direction of the tidal streams in this area and 
in the Irish Sea. The flood-stream sets in a northerly direction 
in St. George’s Channel, with indraughts into Cardigan and 
Carnarvon Bays. It clings strongly to the Anglesey promon- 
tory and then sets towards the East, round into the Liverpool 
Bay area. Near a line crossing the Irish Sea from Morecambe 
Bay to about Ramsey the northerly flowing flood-stream 
slackens, and there is a general tendency for the drift of 
wreckage and other floating objects to be arrested on the 
North Lancashire and Cumberland coasts, between Morecambe 
Bay and about Drigg, in Cumberland. The ebb-stream runs 
in nearly the opposite directions, but there is also a general 
tendency to a drift from South to North, so that more water 
enters the Irish Sea with the flood-tide from the South than 
leaves it with the ebb-tide. Approximately the whole contents 
of St. George’s Channel and the Ivish Sea are changed every 
year, the water flowing out through the North Channel and 
entering by the South. 

Plaice eggs spawned in St. George’s Channel will, therefore, 
tend to drift slowly to the North and East, round Anglesey, 
into the shallow-water region between the North Coast of 
Wales and the “ head of the tide,’ between Morecambe Bay 
and Ramsey, in Isle of Man. 

Such a southerly spawning area is thus to be deduced from 
a knowledge of the effect of the tidal streams, but it has yet to 
be actually observed. The existence of northerly spawning 
crounds has long been asserted by the trawlers. It is said 


90 


that plaice spawn just offshore from Peel, in Isle of Man, and 
in the entrance to the Solway Firth. In 1920 we were able to 
investigate the latter ground. During the months January 
to April the Lancashire and Western Sea-Fisheries Committee 
allowed us the partial use of the s.s. “‘ James Fletcher,’ and 
about thirty hauls were made on the region between Ramsey 
Bay, in Isle of Man, and the entrance to the Solway Firth ; 
100 drift-bottles were set free, and 367 plaice were marked 
and liberated. The results of these investigations enable us 
to describe the northerly spawning ground under the conditions 
of 1921. 

It lies about eight miles to the west of St. Bees’ Head, in 
Cumberland, extending North and South for about eight to 
nine miles. Its bearings are: 

Centre, 7 miles W. by S. from St. Bees’ Head. 

Northern end, 9’ N.W. from St. Bees’ Head. 

Southern end, 9’ W. by 8. from St. Bees’ Head. 
Its depth varies from 15 to 20 fathoms. It is situated in nearly 
the coldest part of the Irish Sea (during February and March). 
There are several banks off the N.E. of Isle of Man (“‘ Bahama,” 
“ King William,” and the “Shoals”’). Between these banks 
and the fishing ground in the entrance to the Solway, called 
the ‘‘ Slaughter,” there is an interchange of plaice, such that 
the bigger fish tend to migrate from the “Shoals,” about 
February, over to the “ Slaughter,’ where they spawn. The 
spent fish then disperse, many of them returning to the Shoals’ 
area and to the South-west. 

In February of 1921 mature plaice were found between the 
“Shoals” and the spawning ground. In March they were 
found in greatest abundance on the spawning ground, and at 
the middle of April no mature fish at all were found there, but 
spent plaice were then to be taken on the “Shoals.” About 
March 21st the spawning season culminated, and by April it 
was practically over. 


ol 


The numbers of mature female plaice caught per hour’s 
- trawling* were as follows :— 


On the “ Shoals ” 
On the “ Slaughter ”’ 


On the southern part of the “‘ Slaughter ”’ : 
3-0; April, 6-3. 


South from the “ Slaughter ”’ 


: in February, 8:5; March, 5-2; April, 7-9. 
: in February, 8:9; March, 9-4. 


in February, 4:8; March, 


: in February, 5-9; April, 2-2. 


The proportions of the female fish taken in the mature 


condition on the various grounds were as follows :— 


(1) On the “Shoals”: February, 16 %; March, 31%; April, 64 %. 
(2) On the “Slaughter”: February, 86 %; March, 81%; April, 37 %. 


The sizes and ages of the fish dissected on board the 
vessel are given in the three following tables—which are of 
much interest :— 


Sizes and Ages of the Female Plaice Examined. 

Length (ems.). | IV V VI Wa |) \WAGHE || “1D-¢ x EXOT | eNCHT 

ZO-DO NM sacisecseniee: 1 

S335) ceananaaooo 2 1 

BO=4 0 Mseeceses: 7 U 7 

CM dN5). scncnaougae 1 6 9 3 2 

AG=DO) Weecrseeies 5 3 

ein eeeee eee 2 1 1 1 2 

BO60) fc -5.: | 

(NIEHS) Gonsoneso0 1 
Sizes and Lengths of the Male Fish Examined. 

Lengths (cms.). III IV V VI 

PREY soncdooscabopsaecoonpoor 1 1 

Ble318) cocomocposasbnocqc0a00Ge 1 

S150) Soonnonocasuencebdoadne 2 | 6 1 


* By an otter trawl-net of about 40 feet in spread. 


92 


Percentages of Mature Female Plaice at Various Sizes. 


Immature. Mature. | Percentage of 
| Mature. 
2530) cle. aaee 73 Pee | san 
DLedO ae wsccesesacesscestassecel| 25 ee. 47 65 3 — 
3O=40 Hoc wnswesarcwmecnactiaeee 3 92 | 96-8 
TTC ees eens ers, it 45 | 978 
| 


In general, female plaice were observed to be mature at 
about 33 cms. in length and at about Age-group IV. (IV, V, 
etc., mean over 4 years and under 5, over 5 and under 6, etc.) 

At the same time that these hauls were made a number 
(100) of surface drift-bottles were set free, the object being to 
ascertain in what directions the plaice eggs spawned on the 
“Slaughter ”’ grounds would be carried during the period when 
they, and the larvae hatching out, would be pelagic in habit. 
About half of these drifters were ultimately recovered and all 
of them were picked up along the South Coast of Scotland. 

This is what is to be expected, because the prevailing 
winds during the late winter and spring are from the 
South to West in this region. There were also some Hast to 
North winds, and these might have been expected to carry 
the bottles down towards the coasts of Isle of Man and 
Lancashire, but this was not the case. The tidal streams 
in the Irish Sea, North of the Ime joming Ramsey and 
Morecambe Bays, set in and out through the North Channel 
(between Mull of Galloway and the Antrim coast) and then 
North and South between Isle of Man and the Cumberland 
coast. Further, we see that there is a gradual, resultant drift 
of water, from the sea off the Lancashire coasts, up through 
between Isle of Man and Cumberland and then out through 
the North Channel. Therefore an unusual spell of North to 
East winds might, indeed, drive the drifters down to the 


93 


South of the “head of the tide,’ but, on the backing of the 
wind again to West and South, they would be carried back 
again into the Solway and South Scottish coast. 

It is reasonable to conclude, therefore, that plaice eges 
spawned on the Solway “Slaughter” ground will be carried 
mostly into the Solway Firth and into Wigton and Luce Bays 
(on the Scottish coast). The shallow water grounds here are 
pre-eminently “ small plaice ” 
as great an extent as are those off the Lancashire and Cheshire 
coasts (see the tables, “Solway Firth”). The northern part 
of the Irish Sea is therefore supplied with small plaice, which 


grounds, or nurseries, to at least 


are spawned and reared in the same sea region. 


Hatching and Transformation Stages. 


The plaice eggs found in the tow-nets are, from our 
experience, always fertilised. Now an unfertilised plaice egg 
will generally remain alive and buoyant, floating at the surface 
of ordinary sea-water for about a week. If they were present 
in notable numbers in the plankton they would certainly have 
been observed, but there is no doubt that such unfertilised 
plaice ova are very rare. It is fairly certain, then, that there 
is definite pairing in the sea, or at least that ripe males and 
females come together in the same local shoals, at the time of 
spawning. Thus we account for the absence of unfertilised eggs. 

The period of incubation varies from about three weeks, 
at the beginning of the hatching time, to about ten days, in 
April. The sea-temperature in the region between Morecambe 
Bay Light Vessel and the Lancashire coast rises about 4° C. 
(from 5° C. to about 9°C.) during the period Ist March to 
30th April. But the differences are considerable in the various 
regions: thus the temperature at lst March may be one or 
two degrees lower at the Solway Light Vessel and at least a 
degree higher at Carnarvon Bay Light Vessel. There are also 
considerable differences from year to year, and there are minor 


94 


differences even at places a few miles apart, at the same time, 
these latter variations being due to cold water ebbing back 
from the land (which is always colder at this time of year than 
is the sea). We cannot say, precisely, how Jong it takes a 
plaice egg to incubate in the Irish Sea because of all the above 
variations. The plaice at Port Erin Hatchery always spawn 
several weeks earlier than they do at Piel, in the Barrow 
Channel because of the higher sea (and land) temperature at 
the former station. There is a rather well-marked mathematical 
relation between the temperature and the incubation period 
of a fish egg: the higher the temperature, the shorter the 
incubation period. So far, however, we have not made 
experiments stating this relation exactly in the case of Irish 
Sea plaice. 

Neither has the time required for the later development 
been made out, though it is known that the baby plaice in the 
Port Eri spawning ponds have usually become transformed 
by the end of April. The fish hatches out from the egg as a 
larva, carrying a large yolk sac, and in the course of about 
two weeks this organ becomes very small, and then, later on, 
quite disappears. About the time of its disappearance the 
transformation (or metamorphosis) occurs; the body begins 
to flatten from side to side, and the left eye begins to show 
on the right-hand side of the head, because of the twisting 
(from left to right) of the bone between the mouth and the 
brain-case. In about a month from the date of hatching the 
metamorphosis has been completed and the fish is become 
definitely flat. At all stages between the egg and the fully- 
transformed larva, however, the latter can be identified as a 
young plaice, though it is very like the flounder and dab. 


The First Shore Stages. 


At about the end of May and the beginning of June, 
according to the nature of the season, the young plaice first 


95 


‘ 


come on to the shore as 
be seen in the shallow shore-pools left by the receding tide. 
They are very active, but can easily be caught. They must 
be present on the shores of Cheshire, Lancashire, and Cumber- 


‘sixpenny flukes.” They can then 


land at this time of year in enormous numbers. The mortality 
must also be very great at this stage, for the little, shallow 
shore-pools are apt to dry out as the tide recedes, or soaks into 
the sand, and when the sun is hot the larvae must perish. No 
precise observations have been made enabling us to state the 
time when the transformed larvae first come shorewards, and 
in what relative abundance ; but undoubtedly both conditions 
vary from year to year. It is certain, however, that it is 
nearly always about the same time (the very end of May) 
when the plaice first come on to the Lancashire shores, and it 
is probable that this is so even though there may be bigger 
differences, from year to year, in the dates of spawning and 
hatching. It is very likely that a certain combination of 
conditions (sea-temperature, sunlight, food) must be present 
in order to enable the baby fish to survive when they abandon 
their drifting, pelagic life, go to the bottom and seek the very 
shallow-water grounds close inshore. 


Food of the Larvae and Transformed Plaice. 


In general, the larvae first feed on algal spores (but this 
remark applies to observations made on the larvae hatched 
out and transformed in the Port Erin ponds). Later on they 
feed almost entirely on Copepods (Harpactids chiefly) though 
other organisms are, of course, eaten. A full report on the 
food of the larval plaice collected from the spawning ponds 
and from the shore has been prepared by Mr. Andrew Scott 
and will appear in a forthcoming part of the Journal of the 
Marine Biological Association. 


96 


Growth of Plaice during the First Year. 


This we were able to make out by measurements of little 
plaice reared in the Port Erin tanks. The results are as 


follows :— 
31-40 mm., 1; 61- 70 mm., 8 
41-50 ,, 3; (12 O0 ee 0 
D1-60 0 eaele 81-00" Tea 
91-100 d 


Thus, there is considerable variation between individual 
fish as one might expect. This variation continues, and even 
becomes greater in subsequent stages of the life-history. In 
1921 we made collections* of young plaice (and other flat 
fishes) in the shallow bays in Isle of Man, and on the Lancashire 
and Cheshire coasts. In May, the length varied from 13 to 
50 mm. in the case of the Manx fish. From now onwards the 
plaice grow rapidly, increasing in length about six or seven-fold 
by the end of the autumn. Precise measurements (averages) 
for Cheshire shore plaice are as follows :— 


June, 42-2 mm. ; July, 46-5 mm. ; 
Aug., 52:5 mm. ; Sept. 58-6 mm. ; 
Oct., 67-4 mm. ; Nov., 65-5 mm. ; 
Dec., 61:1 mm. ; Jan., 662 mm. 


These are all first-year plaice, for each was examined by 
inspection of the otoliths (or earstones). The latter are, of 
course, very small, but it can easily be seen that they consist 


‘ 


only of the central, opaque “nucleus.” Towards the end of 
the year this central white spot becomes surrounded by a semi- 
transparent ring, and thereafter an opaque white ring is formed 
during each summer and autumn, and a semi-transparent ring 


during each winter and spring. (Chemical tests showed that 


* The ordinary haul “ push-net”’ used by shrimpers in Lancashire was 
employed. The collector wades in water of about 2-feet depth and pushes 
the net in front of him. The fish can often be seen. The method is a very 
admirable one for the collecting of small shore fishes on a shallow, sandy 
coast. 


oT 


the substance of the otoliths was made up of the modification 
of calcium carbonate, known as aragonite. It contains about 
98 per cent of CaCOs;, the remainder being organic matter and 
water. ) 

During June the “ sixpenny flukes ” leave their foreshore 
and very shallow-water habitat and migrate further out to sea. 
In July and onwards they can be taken in the shrimp trawl-nets, 
and their abundance there has been, for a long time, the 
interesting feature in the life-history of the plaice from the 
point of view of fishery regulation. A great deal of attention 
has been devoted to this question in Lancashire: whether or 
not shrimp-trawling does more harm to the general fishing 
industry than it is worth? From the beginning of their 
period of control the Lancashire Sea-Fisheries Committee made 
many observations on the relative abundance of plaice and other 
fishes in the catches made by the shrimp-trawlers in their 
district. The late Superintendent, R. A. Dawson, devised a 
special form of the shank-net, designed to permit the capture 
of shrimps while allowing young, flat fishes to escape, but this 
instrument never became adopted. In 1899 the Committee 
applied to the Board of Trade (which was then the Central 
Fishery Authority in England) for confirmation of a By-law 
restricting trawling by fine-meshed nets in the important 
nursery ground off the estuary of the Mersey, but this measure 
was very seriously opposed by the local fishermen, and the 
Board refused to sanction it. Since then the question has not 
been raised again. 

Table 11, gives a summary of the results of the measure- 
ments of plaice made in the experimental hauls carried 
out by the officers of the Committee on the Mersey grounds 
during the period 1908-1913, and there is a detailed report on 
a series of observations made by Capt. + Kecles during the years 
1899-1920, which gives a very fair idea of the conditions on 
this nursery ground. First, as to the sizes of the plaice taken : 


G 


98 


this varies, of course, according to the time of year. During 
the wimter months, November-March, the fish are smallest, 
because then they belong mostly to those hatched in the 
previous year. The prevalent length is about 7 ems. (2? ins.), 
and 50 per cent. of all are between 6 cms. and 8 ems. in length 
(25 ins. to 34 ins.). During the months May to July there are 
three maximal lengths, or prevalent sizes: about 5 cms. 
(2 ins.), 9-5 cms. (32 ins.), and about 14 cms. (53 ins.). That 
means that a great number of the plaice caught in May to 
July are those that have been hatched in the same year (they 
are two to four months old). Then there are plaice that are 
one and two years older (that is, about 14 and 2+ years old). 
It is impossible to be more precise as to the ages of fish caught 
in the shrimp-trawl (on pp. 131-2 we discuss the general 
question of the growth rate of the fish), but the following 
results are useful: half of all the plaice caught during May to 
July are from 11} to 163 ems. long (that is, 44 to 63 ins.), and 
half of all those taken durmg the months August to October 
are from 11 to 16 cms. long (that is, 44 to 62 ins.). This will 
give a good idea of the kinds of plaice caught in the course 
of shrimp-trawling. 

Next, as to the numbers caught. A summary of the results 
of the Mersey experimental hauls is given by R. J. Daniel,* 
and this shows the actual numbers per haul, per hour’s fishing, 
etc., taken between 1898 and 1920. The number per haul 
varies between 14,697 (in 13 hour’s drag) and 0. The average 
number per hour’s fishing per annum varies between 1,197 
(in 1911) and 64 (1904 and 1916). There is a very evident 
periodicity in abundance of young plaice on this ground, and 
to this question we return Jater in the report (p. 136). 

The short statement made here will show, however, what an 
extremely heavy toll shrimp-trawling makes on the plaice 
population of the inshore nursery grounds in the Irish Sea. 


* Ann. Rept. Lancashire Sea-Fish Lab. for 1919 pp. 51-71. 


99 


Whether that amount of destruction of small fish is a thing to 
be restricted or prevented is not so easy a question to answer 
as it appears to be at first sight. To that again, we return in 
a later section of this report (see p. 167). 


The Nursery Grounds and their Conditions. 


These extensive shallow-water nursery grounds are of 
extreme importance to the fisheries, and it may well be the 
case that the attention of future fishery authorities will be 
directed to them far more than to the offshore regions, which 
at present almost monopolise investigation. From the natural 
history point of view they are of surpassing interest, and we 
feel that far too little research goes on here. They are by far 
’ zone of the sea, and that is, of course, 


b) 


the most “ productive 
the reason why they are fish nurseries. The conditions that 
make them productive are: (1) The drainage from the land 
carrying fresh water which brmgs down enormous quantities 
of organic substance, in solution or as a sediment (all of this 
is utilised by living organisms); (2) The low salinity of the 
water; (3) The relatively high temperature, and (4) The 
greater degree of sunlight. The sand everywhere contains 
abundant vegetable life in the form of Diatoms, Flagellates, 
and Dinoflagellates (microscopic plants and ** plant-animals ”’), 
and one can, nearly everywhere, see this as a yellow-brown or 
greenish scum on the surface of the sand. Beneath the surface 
the sand is, nearly everywhere, blackish in colour as the result 
of the action of sulphuretted hydrogen produced by the 
decomposition of dead organic substance. In the surface layers 
of the sand and in the water just over that layer there are 
numerous Copepods and small worms. Nearly everywhere 
there are very numerous shellfish—cockles, small mussels, 
Mactra, Scrobicularia, Nucula, etc. A minute fragment of 
zoophyte may contain dozens of small mussels about the size 
of a very small pinhead, and on some suitable bottoms the 


100 


zoophytes and polyzoa growing there may appear as if they 
were thickly dusted over with such minute mussels. Some 
counts made recently showed that extensive areas of sandbanks 
contained little cockles in such numbers as several hundreds per 
square foot, while the number of small mussels on a square 


? 


foot of suitable “ skear ”’ ground may run into the thousands. 
Such invertebrate communities are the feeding grounds of 
shrimps, crabs, starfishes, and young fish of various kinds 
(plaice, flounders, dabs, soles, cod, whiting, sprats, etc.). Here 
small plaice feed greedily upon Copepods, small worms, little 
periwinkles, and very small bivalve molluscs, while the larger 
fish eat the small Mactra, Scrobicularia, and cockles that are 
nearly everywhere present in the sand. In the spring and early 
summer months the temperature of the water on the nursery 
erounds rises several degrees higher than it is offshore; the 
tides run more strongly and so distribute the dissolved food 
substances used by the Diatoms, Flagellates, and Dinoflagel- 
lates. The sunlight penetrates to the bottom layers of water, 
overlying the sand, better than it does offshore, and this is 
favourable to the nutrition of the microscopic plants and 
plant-animals. The latter are then eaten by the shellfish and 
the smaller Crustacea and worms, which are, in their turn, 
eaten by the small fishes, large fishes, and invertebrates. As 
fast as the fundamental food substances in solution are taken 
from the water by the organisms that exhibit the vegetable 
mode of nutrition they are renewed by the drainage coming 
down from cultivated land and from domestic sewage entering 
the estuaries and then the open sea. The higher temperature 
on the nursery grounds accelerates the rate of growth of all 
animals living there. Further, the conditions, as regards 
temperature and density of the water, are more variable than 
they are offshore because of the more rapid tidal streams, 
freshets entering the estuaries, and the greater agitation of the 
water by wind action. This variability in external conditions 


101 


is itself a stimulus to growth and reproduction, and to the 
maintenance of a condition of health. 

The shallow-water grounds off the coast, between low- 
water mark and about 5 to 10 fathoms of depth, are therefore 
the place of origin of all the young fish in this neighbourhood. 
For about three years the plaice of the Irish Sea live here 
moving a little out to sea in the warm summer months and then 
returning inshore again for the period of the winter and spring. 
They roam about to a marked extent, making quite long, winter, 
longshore migrations, possibly in search of food and possibly 
just from the general “restlessness” that is a fundamental 
feature of animal life. In certain months, about December to 
March, there is an evident scarcity of the small plaice on the 
nursery grounds, and it is highly probable that they “‘ dawk ” 
in the sand at the bottoms of the deeper, inshore channels, 
covering themselves up so that only the mouth is visible. 
Respiration slows down, the fish cease to eat, and their functions 
are as nearly at a standstill as possible. The weight of the 
body, in proportion to the length, decreases. If we call w the 
body-weight in grams, / the total length in centimetres, and 
c a constant, then we get the following formula : 

100 73 
E= 
w 


Now when we find the value of ¢ for the various months 
throughout the year we see that it varies from about 0-8 to 1-2. 
When it is small, at the period of about lowest sea-temperature, 
the plaice is thin and in poor condition, and when it is large, 
at about the period of highest sea-temperature, in the autumn, 
the fish become plump. The decrease in the magnitude of c 
means that the fish does not feed and that the substance of 
its body is being used up to keep the heart and respiratory 
organs in action. Therefore there is a wasting of the body 
during the coldest months of the year. 


102 


The Rate of Growth of a Plaice. 

The age of a plaice is found merely by looking at the 
otoliths (or earstones). The sex is found by holding the fish 
up to a strong light and observing whether or not it has a roe : 
the latter is deeply pigmented and shows through the trans- 
lucent body and skin. The earstone has always a little opaque 
spot in the centre surrounded by opaque and translucent 
rings : thus— 

Nucleus alone—the fish is one summer old. 

Nucleus + translucent ring—one summer -+ one winter. 

Nucleus + translucent + opaque rings—one summer, 
one winter, one summer, and so on: a translucent 
ring is added during each winter and an opaque 
ring during each summer. 


The plaice in the Irish Sea are always hatched out m 
February, March, and April, but, for the most part, in March. 
Therefore, a fish caught in July, and having a nucleus only, is 
four months old, one caught in September, and with only a 
nucleus in its earstone, is six months old. So also, a fish 
canght in October, and having a nucleus, two opaque rings and 
two translucent ones, is two years and seven months old. 
Usually we called the plaice 0, I, II, III, etc., years old, meaning 
over 0 and less than | year of age, over | and less than 2, over 
2 and less than 3, and so on. For the first year we state the 
age in months, the number of the latter bemg the number of 
the months that have elapsed from the middle of March up to 
the date of capture. 

The growth, then, for the first year is as follows :— 


Up to middle of June... ... 42-2 mms. 
i. July... Sect EOD pias 
s August ... ses O2°Dy lies 
i September coh, DOOr es 


October ... 2 OWA, 


2) 


1038 


After October the growth ceases until the following April, when 
it begins rather slowly, increases up to about the middle of 
July, then falls off and finally ceases again about the middle 
of October. 

Now the growth is very variable. Even in the same season 
some fish of the same age grow more rapidly than others. 
Plaice reared in Port Erin tanks showed this to a remarkable 
extent, some (of the same year’s spawning) being actually 
twice as long as others: this is individual variability. There 
is seasonal variability: thus, fish of, say, two years of age 
may grow more rapidly in one year than do the fish of two years 
of age in another year. Finally, there are local variations : 
thus, the English workers obtained the well-known result that 
plaice grow about twice as long, in the same period of time, 
on the Dogger Bank than they do just off the Dutch coast. 

The following table (No. 14) gives the results of the 
measurements of 7,724 plaice, all caught on the nursery grounds 
and on the inshore grounds, and mostly within the territorial 
limits. The table, therefore, represents very well the kind of 
plaice to which regulations, restrictions, and prohibitions, of any 
kind, would apply. 

A few words of explanation are necessary : 

These are all plaice caught by shrimp-trawls (of 2-inch 
mesh) and fish-trawls (of 6-inch mesh). Now a shrimp-trawl 
will, in theory, catch plaice up to any length, but if it does take 
a fish of over about 25 cms. long, say, there is always the 
chance that the latter may swim out again through the mouth 
of the net : this is because there is not a very great “ draught ” 
of water through the very narrow and close meshes of a shrimp 
trawl-net. Therefore the latter tends to wnder-sample the 
larger fish that are on the ground over which it is dragged. 
On the other hand the 6-inch meshed fish-trawl will not catch 
many plaice less than 10 cms. in length, and this is because 
most plaice less than that length, and many of those between 


104 


Table XIV. Length Frequencies for Age Groups, O to IV, 


1908-1916. 


IHU | IV 


Mean Length. | O | I Il 

ZIG Spee ee aa nee igeee 20 

Ta) SR Se See eet 213 | 

Ge Diesen cetera 368 | 13 

TOS nes BOOC nan OOO SAT aC OOH 317 24. | : 

QDs teseneeseona eens 151 26 sue 

G5 sccibte aleiers s(sisisie ele eiarsteciare 65 56 | 1 
NOs Diaccsdcbapeeteesecnee 32 95 2 
Lilie ce cosveschecceeeecesce 20 151 | 2 
Haas Seaton coonéodanacnncccae 16 189 9 
Be aircarsiatcte slorsteletetewe'e s esicrees 6 258 | 45) 
A Sach ce see aniston wie astnais 3 | 276 | 17 
Stes aadacesweesecerenees wine 300 7) 
UG sia sevee nclcniensie oe come cles 22 165 seis 
Te bscassaccesenoccsenceres 256 | 278 1 
USB pac sncostecsaeuek sesres | ile? 428 3) 
NOs Dincrcnss cdeeocacnnwaets 118 | 479 19 
Dey eauscnranoe Yoeeoeacae ete 65 490 2] 

Wty T Aasins sass oeclsseeeeeess } 31 425 34 
DD Asiatic ware Sanielslosstenictce a 18 364 24 

DS Edimcicre sicislele'e slalslewiemresie sieves 13 280 22, 
DA Din ease wapeuseu ssa: | ac 8 207 32 
DF Dyes ect seeetat cede seeaee das 3 148 | 29 1 
Tete Anpe ey ett 28 Ke es 2. | 92 | 35 I 
Dl DicMeomateeaceaeemee sees 65 43 AG 
2S 5a aa aU ERS SOU IaSaec 39 36 2 
DOs tye EF se calcination tance De 38 6 
URS a onaneennebeTnoenaeccendc 9 29 5 
Bila aancamapacdceccchetEnen 1] 20 6 
BOT eee ests ene chan cerence see 5 24. 1 
SBD Msnctanses srenasecieescus 1 10 2 
8 LATS sopndcsousagauncostena 2 8 8 
32725) \awlooaie cersivleteinie siaisleisisveisios | 5) 7 
SG25 cchitenieceueascteeeesce 5 22 
BT caeamencioonons meter eals| 1 2 
SBUBe whan ee eeonesceetere 3 2 
BO Hats se sansstnenocsontsacos il 
EGS Roanucncoeaecocrnoranc ne 
(UNG) OUR PERS Sei mcs 2 
Notalssicssce- see csesconnes 1,211 2,385 | 3,638 442 48 
Mean Lengths ......... 11533 15:3 21-0 26:8 | 32-5 
Standard Deviations... 1:58 3:18 2-63 4:34 3-70 


Shortest Half-ranges.... 5-8—7:5 | 13-5—17°8 | 18-5—22-5 23-9—30-2 | 30-8—35-8 


105 


10 and 25 ems. in length, can escape out through the meshes. 
Thus the fish-trawl tends to wnder-sample the smaller fish 
inhabiting the ground over which it was dragged. 

We cannot allow for this by using both a shrimp-traw! 
and a fish-trawl at the same time, for we don’t know exactly 
how much time to give to each method. We cannot employ 
a compound net, that is, a small-meshed one laced round about 
a wide-meshed one, for the small-meshed net restricts the flow 
(or draught) of water through the large-meshed one and so 
impedes the action of the latter. Table 15 shows that we get 
a different result for the Age-group I, according as we use the 
shrimp-trawl or the fish trawl. Therefore we have added 
together the results of the fishing of these two instruments 
and then made some rather arbitrary corrections, which, 
however, are probably “ quite all right.” Thus we get the 
Column “I” of Table 14. 

Observe here that we are dealing with a characteristic 
“small-plaice ” area. We might sample Luce Bay, the Solway 
spawning grounds, Beaumaris and Red Wharf Bays, each at 
its appropriate season, and get much bigger plaice. Sfal/, in 
regard to the operation of any restrictions or prohibitions, 
Table 14 shows us what are the kinds of plaice which will be 
affected. 

It will be seen that a plaice of length of 25-5 cms. may be 
1, 2, 3, or 4 complete years of age—and this represents an 
apparently wide range of variation. But the table also shows 
that, in all, 181 plaice between 25 and 26 cms. in length were 
measured (that is, 181 out of 7,724 fish that were examined) ; 
that 3 of these belonged to Group I, 148 to Group II, 29 to 
Group III, and 1 to Group IV. Therefore, the chance that any 
plaice caught at random belongs to Group II are 148 in 181 ; 
that it belongs to Group I, 3 in 181; that it belongs to Group 
III, 29 in 181, and that it belongs to Group IV, 1 in 181. 
These are the “‘ odds ” in favour of the ascription of the fish 


106 


Table XV. Age Groups: Data for Group I, 1908-1916. 


Caught Caught | Formed by 


in in | completing 
Mean Length. 6” mesh. 2” mesh. | Total. last series. 


Tit eae Pes Cae AS 13 13 13 
Te ce te, ee 24 24 24 
tne Wea AR AREA 26 26 | 265 
LO ES eae eas een Sere ee are 1 55 56 56 
NO: ae se a | 4 91 95 95 
WIth tee diac) Seema 6 | 145 151 Pecpatar 
5 Pe ee en ae ere ll mags 189 | 189 
1 Deo cece eee ee 12 151 163 | 258 
CE Oi sh ae aan 6 136 162 276 
Lbea ices eer ee 91 | 89 180 300 

Gs Deeesaetes seca ee aeeneare 186 68 254. Dil , 
Weoeeteeeeeee er cea 215 40 255 | 256 
1 ee ee eee 193 | 20 213 | O13 
105 hoe eee 110 | 8 118 118 
yy ee ie? eG 65 ae 65 65 
DIRS 2 ek eee ee 29 2 31 31 
DO Ae ah Ae 17 1 18 18 
AH AALS es he en 13 | Me 13 13 
YS SE gant PERL 8 8 8 
SEs ONY cioerancie ie ons alaiesieeicerneeeries 3 3 3 
Matai gee em meee cake 990 | 1,047 2,037 2,385 

| "| oe Sr 
MGA Steiacaseerec cee cereal | 15:38 | 15-28 
| 3-405 2-142 


Standard Deviations...... 


to any particular group. Really the odds will be a little 
different when we apply certain necessary corrections, but we 
shall only do that when required by the administrators. This, 
then, indicates the way in which this (and the other) tables 
ought to be used practically. 

Fig. 7 is a graph of the results of Table 14. It shows the 
average lengths of plaice of Age-groups 0 to IV, and also the 
‘“ dispersions,’ so that some idea of the significance of the 
overlapping of the various group-lengths may be obtained. 
The graph is not a straight line, but a logarithmic curve of a 
kind, and to see how this is we must consider the sizes of 


ea he 


107 


plaice of each monthly age during the first year of life. So far, 
however, we have hardly enough data to enable us to do so 
b>] u fo) 


satisfactorily. 


Age. érovp AL) 
Age Grovp ME) 7 
ES Aes AéeCrop CAND) 1 


X = hositron of mean 


Gea 


The Ratio of Males to Females. 


We don’t know what is the ratio of males to females in 
the first year of life, but it is probably one of equality. This 
is also the case (probably) for any year group up to about HI. 
After that, however, a very curious thing happens ; the males 
diminish in number relatively to the females. This is shown 
by the following statement, based on the numbers of mature 
females and males over 23 cms. in length captured on the 
Solway spawning grounds and adjacent regions in the spring 
on IG PA 


Size in cms. fon) AE Ody OX, D7, IS Ot) BIOS Ble ie 33, 34, 35, 36, 37, 38 
Females... soe O, Oy “As 0, i yD WO fy Gh Ia, NOs Wy, Ga 1a 
Males eats olson 64. olor OOo 455 45, 43, 46, 44, 37, 30, 22 
Size in cms. ... 939, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53 
Females... Soe HIG BAO, AKG, PAS) A), Bia, BRE ER I BE ce Rh a) 
Males ane LOM Seo Some oe Ome OOS TO TO Os Ol O% #0 
Size in cms. ee ae «. 94, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65 
Females ... ate sy soo Oe BE Oe JOS Th WOR Oy O. Ohe ile Oe ol 
Males ... eRe eae sco OS @ Wn Os Os Wh Os © OO O, © 


Thus, the females caught are always bigger and older fish 
thanthemales. They grow alittle faster. Theinteresting thing 
is that the males apparently die off at a greater rate than do the 
females, and this probably represents a general law among the 


108 


marine animals. Hverywhere the female is the dominant sex : 
usually bigger in body, longer-lived, and predominantly the 
more actively metabolic animal of the two. This is so in such 
fish as the plaice, sole, turbot, etc., where the mass of material 
converted into sexual products by the female is always much 
greater than in the male. The ovaries in most fishes are bigger 
than the testes. The herring, however, may be an exception, 
for here the two “ roes,” hard (or ovaries) and soft (or testes), 


are of the same size. 


The Sizes at which the Plaice become Sexually Mature. 

Not so much has been done on this point as we would like, 
but some observations will be found on p. 92. The smallest 
mature female found was 26 cms. long and the largest immature 
female was 42 cms. long. <A general Jimit may be taken at 
33 cms.: above that the majority of Irish Sea plaice are 
sexually mature, while below it the majority are immature. 
As to the males we are still rather uncertain, but the general 
size at first sexual maturity (puberty) is less than in the case 


of the females. 


The Migrations of the Plaice. 

Migratory fishes fall into several general types :—(1) Stur- 
geon or shark, which roam over wide regions of ocean in an 
arbitrary way. (2) Herring, mackerel, hake, sprat, etc., which 
migrate at fairly regular intervals, the latter bemg determmed 
by sea-temperature, density of the water, and possibly other 
physical events. The migrations may occur yearly, as in the 
case of most herring fisheries ; or after longer periods of time, 
as in the case of the Irish Sea winter herring fishery (30 or 40 
years) ; or after periods of over a century, as in the case of 
some of the winter herring fisheries off the Swedish coast. 
(3) Plaice, sole, etc., where the migrations are small and occur 
seasonally, the fish following fairly regular paths according 
to the depth, nature of the sea-bottom, coast line, ete. 


109 


The causes of migration are intrinsic ones (that is, they 
depend on something in the organisation of the fish itself), or 
extrinsic (when they depend on the nature and order of the 
events that occur in the sea,in the atmosphere, ete.). Intrinsic 
causes are, for instance, the ripening of the eggs in the ovary 
or the sperms in the testes. These changes produce “ internal 


b) 


secretions,” which get into the blood-stream, are carried over 
the body and stimulate the latter in many ways. Thus the 
changes in the bodies in boys and girls that occur at the age 
of puberty are caused by substances that originate in the 
developing testes and ovaries and are then carried through the 
body by the blood-stream. Restraint of sexual development 
is the result of secretions elaborated in the pineal gland (in the 
brain); acceleration of sexual development comes from 
production of an internal secretion by the brain structure called 
the pituitary gland ; extreme under-production of the secretion 
of the thyroid gland leads to dwarfing and a form of idiocy ; 
over-production of the secretion of the thyroid leads to general 
excitability and other well-known effects, and so on. Changes 
in “ temperament ”’ and “ personality ” accompany the above 
physiological ones. It cannot be doubted that such causes 
operate also in fishes—thus, an American zoologist stated, long 
ago, that the internal secretion from the ovaries caused a certain 
‘ auto-intoxication,”’ which was the immediate stimulus to the 
migration of the salmon into fresh water. 

Added to this there is a general “restlessness ”’ in all 
animals, expressing itself in undirected, random movements. 

The extrinsic causes are chiefly the changes in the tem- 
perature and salinity of the sea-water. In every animal there 


b} 


are certain “optimum ” conditions, that is, certain external 
circumstances which suit the make-up of the animal’ better 
than any others. Thus a fish, like the mackerel, does best in 
water of much the range of temperature of that off the 8.W. 


Coasts of Ireland, or outside the entrance to the English 


110 


Channel. In the summer the temperature to the North (say, 
in St. George’s Channel) rises and approaches that which suits 
the fish. Its general restlessness then Jeads to it enlarging the 
region of its movements into the new zone of water of suitable 
temperature, so that it migrates up into St. George’s Channel 
and the Irish Sea. 

“Feeding migrations” are a consequence of external 
causes. Plaice, for instance, are always “on the move” 
during spring, summer, and autumn. Let there be a certain 
region of rough ground on which there is no “feed ’’: plaice 
doubtless cross this in various directions, but don’t stay there. 
If, however, there is a “ strike ” of small mussels on the region 
the plaice which cross it will tend to stay there to eat the 
shellfish, and so there will appear to have been a migration 
on to this region from the surrounding ones. Old fishermen 
know these conditions very well and expect migrations when 
they foresee a strike of mussels. 

“ Spawning migrations ” are the results of the development 
of internal secretions. In some way or other these cause the 
fish to ‘prefer’? water of a certain depth (pressure) and 
temperature. It is unlikely that a plaice which is ripening 
sexually for the first time knows where to find these conditions, 
but its general restlessness leads to its exploration of the 
whole region in which it lives, and having found the agreeable 
conditions it stays among them. 

‘“Shoaling migrations.” The causes that lead one fish 
to seek certain conditions also impel others, thus we get shoals. 
Probably fish are not “gregarious” in the sense that they 
want each other’s society : the shoal is brought about by the 
occurrence of external conditions that affect all mature plaice 
at the same time. 

Plaice-marking Experiments. 

Much has been made out as to the movements of plaice, 

and other fishes, by studying their sizes and density on different 


gia 


grounds and at different times. The same kind of results can, 
however, be obtained by making direct experiments. Plaice 
were marked in the Irish Sea in small numbers, the region 
itself beg a small one, and there were two principal series of 
experiments, in the area just off the estuary of the Ribble and 
in Red Wharf and Beaumaris Bays. The numbers of fish 
marked are as follows :— 


(1) Offshore from the Ribble Estuary (“ Liverpool Bay ”’) : 


13th July, 1905 = 31 plaice. 
12th June, 1906 Le ao 40 ,, 
9th July, 1906 er an, HORE. 
3rd July, 1907 us PU hehe 
5th June, 1912 ar Soh EOS 
ord October, 1912 _... ele ice 
3rd June, 1913 es ne oa maar 
17th July Soe. . ae GR 
17th September, 1913. eh OO ee ese 
otal ... 1,129' plaice. 
(2) In Red Wharf and Beaumaris Bays : 
12th Nov., 1904 he te 42 plaice. 
12th Nov., 1904 ai as uy 
Ist Feb., 1906 es: a 44, 
21st Feb., 1906 a ie Sa 
19th Sept., 1906 re — 2 
6th Feb., 1907 ds ae Ope es 
24th Oct., 1907 ee elon 
20th Nov., 1913 ans hog eO a 
Total =. ... 616 plaice. 


The methods employed were those adopted by the English 
investigators. The mark was a bone button on the white side 
of the fish and an oval, concave, hard brass disc on the coloured 
side. These two marks were connected by a silver wire passed 
through the body about 4 inch below the edge of the fin on the 
dorsal margin. Fixing the mark was very easy, and we were 
unable to trace any serious injury to the patient. Later on 


112 


the label in use now was employed, that is, a button of vulcanite 
above and below instead of the bone and brass discs. It has no 
advantages over the old mark, and is more expensive. Details 
of all these experiments, and of most of the fish recaptured, 
have been given in various reports of the Lancashire Sea- 
Fisheries Laboratory, but all the data are now summarised 
for the first time and unnecessary detail is avoided. 


(1) The Liverpool Bay Kxperimen te. 

It was soon noticed that the results of the experiments 
repeated themselves from year to year. Therefore they are 
all combined and are regarded as one. All the Junes are 
thrown together, and the recaptures from these experiments 
are all recorded in the same way. Then all the Julys are 
combined, and the recaptures of plaice taken in July (in 
general) are made to give us the migrations of the fish liberated 
in June and July, and so on—the details will become easily 
grasped by studying the charts given hereafter. The places 
of recapture for any one month (which are rather approximate, 
of course) are plotted on a chart and then a contour line is 
drawn round about these positions. This method of treatment 
was suggested to me long ago by J. O. Borley, and it is a very 
convenient one. 

Note, first, the sizes of the fish hberated and recaptured :— 


Mean | Numbers Numbers Mean | Numbers Numbers 

Lengths. Liberated. | Reported. | Lengths. | Liberated. | Reported 
16:5 | 4 0 28-5 17 12 
17°5 18 0 29-5 5 14 
18-5 31 1 30-5 2 a 
19-5 | 89 2 31-5 0 4 
20:5 250 12 32-5 3 2 
21-5 200 aie 33-5 1 5 
22-5 183 39 34-5 1 4 
23°5 97 39 35:5 ] 1 
24-5 96 33 36-5 0 1 
25-5 47 | 25 37-5 | 0 2 
26-5 38 24 38-5 | 0 0 
eo 23 | 21 | 39:5 | 0 1 
| | | | 1,116 281 


113 


(A few cases where the lengths of liberations, positions of 
recapture, etc., have obviously been mis-recorded are omitted.) 


Condensing this table we get :— 


Ranges of Lengths. Numbers Numbers 
Liberated. Reported. 
| = 
oO /O 
ILeess) Uelmein IG) CHANEL, —-Gaaqaosoanensoncodoocaducos 5 | 0 
5 LLU epee eerie oer er 13 | 1 
mB Pall, py | PoguddbboonoodenEDcbanbecDoc 34 | 9 
oo 2) 65. © soubeoupsposesodooquonedade 54 | 16 
AD GO 28} OHNE Gonoagenapcoceooanoopoonbpocooacd 50 400 
PGi OMmeeae WME Safenistes Savers ccsicto a ctclnlew’s Siceiets's 5s ue 50 


This means that the smaller fish do not stand the marking 
operation well (and, of course, that they grow between the 
time of liberation and that of recapture). The two lower lines 
of the last table are read as follows : Half of all the fish liberated 
were between 20 and 23 ems. in length and half of all those 
reported were between 21 and 25 cms. in length. 

One must remember that the position of recapture reported 
is always approximate, for the skipper cannot tell, to a mile or 
two, exactly where he is, and also the fish may have been 
caught anywhere on a ten to twenty-mile drag. We have no 
reason to suspect any misleading information as to the places 
of recapture: on the other hand skippers were always most 
willing to give full details, and very often eager to know where 
the fish had been marked. We assume, generally, that the 
plaice moved straight from where they were set free to where 
they were caught, but this must hardly ever be the case : 
the fish, doubtless, ‘‘ backs and fills” in its movements. For 
small periods of a month, however, it is quite permissible to 
assume that the migrations path is directly from the one spot 
to the other. 

Phe June-July Migrations. 

The data from which these are to be deduced are given 

in the following synoptic chart :— 


H 


115 


The following explanation will serve for this, and the 
other charts illustrating the migrations. Hach recapture is 
indicated by a black dot, and the number underneath the latter 
gives the length of the fish, as recaptured, in centimetres. 
The area where the fish were liberated is outlined by a broken 
line enclosing the words “ area of liberation.” An irregularly- 
curved contour line, marked “ June and July,” is drawn round 
the places of recaptures in these two months so that we may 
understand that the fish liberated have spread out, in all 
directions, from the “* area of liberation ” to the area enclosed 
by the “ June-July ” boundary line. During June and July, 
plaice previously inhabiting the shallow-water region 
immediately offshore are migrating out to the West, North-west, 
and South-west from shallower into deeper water, and from a 
warmer into a colder region of sea. 

Certain temperature contour lines are drawn on the chart, 
but these will be explained later on. 


The August Migrations. 
It is fair to assume that all the plaice caught and liberated 


¢ 9 


on the “ area of liberation’ in June and July have now left 


that region and have migrated outwards as just explained. 


¢ 


No recaptures are reported from the “ area of liberation ”’ in 
August, though there was plenty of fishing going on there, 
and this means that during June, July, and August there is a 
continual streaming out of plaice from the Ribble Estuary, 
and all the adjacent nursery grounds. As the plaice grow up 
to about 20 ems., or thereabouts, in the summer months, they 
abandon the nurseries for the more open sea offshore. The 
chart shows an irregular area marked by the dotted line 
“ June-July ”: this was the region where the marked fish 
were recaptured in those months. A number of black dots 
are seen in this area and to North and South of it, and 
these are the positions of recaptures in August. Therefore the 
plaice, which were within the “ June-July ” boundary in those 


118 


‘ 


months and which had come from the “ area of liberation,” 
tend now, either to remain where they were, or to move to 
North and South, still remaining offshore and in water of much 
the same depth. Note also a very interesting feature: the 
water is warmer inshore and colder offshore, and it is still 
rising in temperature, but it is rising more rapidly inshore than 


it is rising offshore. 


The September Migrations. 

As before, the boundary line marked “ August”? shows 
where the plaice caught in June-July, on the “area of 
liberation,” were in August. Only a very few fish were caught 
in September on the latter area, but it will be seen that large 
parts of the August region of recapture are also vacant. The 
marked plaice are now evidently drawing in from the extensive 
region mostly just outside the ten-fathom contour line and are 
tending to move back inshore again. This is the plain meaning 
of the chart. 


The October Migrations. 

Clearly the inshore retreating movements observed in 
September continue during October. The boundary line 
marked “ September ” surrounds the region where the marked 
fish were in that month, and it will be seen that the inshore 
migrations from the September region is very well indicated. 
The “area of liberation’ is now obviously invaded, but in 
addition plaice are spreading both to the North and South. 
There are two main trends in this North and South migration 
which are more clearly shown in the November and December 
recaptures. 


The November Migrations. 

There are now three distinct migration paths :— 

(1) Inshore directly to the “ area of liberation ” and to the 
other shallow-water grounds in the Bays and Estuaries 
(Morecambe Bay, the Mersey and Dee) 


Se a ea A ae me 


' 
' 


j « : IN \ 
1 ie: \ 


ee 
2) 


‘ a, ae 
OD / \ 
\ JN fr 

ey! 


he December Migrations. 
Clearly there were three main regions where the fish were 


December. 


122 


ten- and twenty-fathoms’ contour lines. From regions (1) 
and (2) the plaice are still moving closer inshore, and from 
(3) they are moving down into the Red Wharf-Beaumaris Bay 
area. A new path is clearly indicated—that from the grounds 
just offshore from the original area of liberation up to the 
banks offshore from Ramsey Bay, in Isle of Man. 


The Autumn and Winter Migrations. 

We may now summarise the results obtamed so far: these 
are represented in Fig. 14 in a very general way. Each arrow, 
tipped with a black dot, represents the approximate position 
of an actually-recaptured marked plaice, while some other, 
untipped arrows on the chart merely suggest the general 
directions of the migrations. All the marked fish recorded as 
recaptured in this chart were liberated in the region indicated 
as the “ area of liberation ” in Figs. 8 to 13: this is the 
region in Fig. 14 where the tipped arrows are most densely 
crowded. 

First, then, we have the summer offshore migration. 
The plaice, of sizes about 20 to 25 cms., stream outwards from 
the Lancashire coast to the 8.W., W., and N.W., and by the 
end of August they have come to occupy a region of sea, just 
outside the ten-fathom contour line and extending from about 
Morecambe Bay Light Vessel down to Liverpool N.W. Light 
Vessel. There is an active plaice fishery all over this region, 
while outside it and up to the N. and N.W. there is also an 
active fishery for soles. This offshore migration, then, is the 
first half of the total migratory movement of Lancashire shore 
plaice. 

Next, there is a retrograde movement, and this reversal 
occurs about the time when the temperature of the sea, having 
attained its annual maximum, is now beginning to decrease 
‘ again. The retrogression is indicated by the successive contour 
lines—‘‘ September-October,’ “‘ November-December,’ and 


b) 


“ January-February.” Each of these lines is a boundary, 


123 


showing the region into which the marked plaice have spread, 
from the region occupied during the previous two months. 
We see, then, that there are three directions of migration: 
(1) The retrograde one back to the “area of liberation’ and the 


Fic. 14. General synoptic chart showing the migrations of marked plaice 
uring the months August-December. 

similar regions to North and South of the latter—this is very 

evident in the months November and December, and it still 

continues during the months January and February. The 

plaice are seeking the shallow-water regions just off the 


124 


estuaries, and they are preparing to adopt a semi-hibernate 
habit for the remainder of the winter months. (‘* Winter” in 
the sea means the months January, February, and March.) 
(2) In addition to the retrograde movement there are, however, 
two others. Some plaice are migrating up to the N.W. towards 
the extensive, late winter, fishing area, between Ramsey Bay, 
in Isle of Man, and the entrance to the Solway Firth, while 
others are migrating to the 8.W. towards the “ back-end” 
plaice fishing region, just off the coasts of Anglesey and 
Carnarvon (Red Wharf, Beaumaris, and Conway Bay regions). 
The S.W. migration begins in September and October and 
culminates in December, while the N.W. movement begins in 
November and December and culminates in February. Here, 
then, we have a continued offshore migration in direct contrast 
to the retrograde one mentioned above. To elucidate it further 
we must now look into the sizes of the recaptured, marked 
plaice. Fig. 14 shows that the prevalent lengths (shortest 
half-ranges) of the latter were :— 


o 25:5 ems. on the inshore region in October to December. 
to 26-5 cms. on the N. Welsh region in November-December. 
5 to 29 cms. on the Manx region in January-February. 
27 to 30 cms. outside the Irish Sea in the following year. 

This latter point is one to which we return later. A 
certain number of the larger plaice leave the Irish Sea altogether 
and do not return. They are recaught in St. George’s Channel 


and elsewhere. 


Further Recaptures. 

So far we have only considered the recaptures reported 
during the months July to February, immediately following 
the months of liberation—that is, the eight months or so after 
the times of the experiments. Further, we have combmed 
the results of experiments made in different years—a deliberate 
policy. When we take the various experiments separately we 


125 


see that just the same results are obtained as when they are all 
combined, though the data are, of course, fewer in number. 
The fact that, year after year, we get the same general results 
leads us to attach the greater importance to the summaries 
with which we have so far dealt. 

Something must be said about the recaptures reported 
in the years following those of liberation. The marked plaice 
may be recaptured even after three years, but in very small 
numbers, of course. Now all those taken during the months 
January, February, March, and April in the year following 
that of liberation have been put on a separate chart (not 
reproduced here). There are three main regions in which the 
recaptures occur: (1) Round about the “ area of liberation,” 
and in Morecambe Bay, the Mersey, and Dee; (2) On the 
“Shoals,” that is, N.E. from Isle of Man, and (3) In &t. 
George’s Channel. None were taken off the Anglesey and 
Carnarvon coasts—an interesting result to which we refer 
presently. The fish taken on the Lancashire coast are all 
small (the extreme lengths are 20 to 26 cms.); those taken 
off Ramsey Bay are larger (24 to 33 cms.), and those taken 
in St. George’s Channel are also large (25 to 32 ems.). In 
January to April, that is, durmg the winter months, the 
migrations that were described as occurring in December to 
January still continue: the small fish are returning to the 
nursery ground and the larger ones are migrating offshore. 

If, further, the recaptures reported during the months 
May to September and then from October to December in the 
year following that of liberation be considered, we see that 
the results of the months immediately following those of 
liberation are repeated. The plaice recaptured are all a year 
older, and a few cms. longer, of course; but the offshore 
migration in the summer, the retrograde one in the autumn, 
and the continued offshore migration to N.W. and 8.W, are 
-all to be traced. 


126 


Age and the Migration Paths. 
Fig. 14 and the followmg table show how the migration 
paths depend on the age of the plaice :— 


Marked Plaice liberated on the Ribble area and recaptured at the 
various grounds mentioned in the headings. 


Central | Ribble | More- | Mersey | Beau- | Off Isle | Else- 
Length. Area. | Area. | cambe and = maris | of Man. | where.* 
| Bay. Dee. | Bay. | 
| | 
E385) Sosooonesne Sen. ele. toad 306 EO) ieee a 
19 Di esacesscecss | 1 roee | Le ip ass 60 oC 
PADS)“ Spacnacos000 2 4 Ac Bap doe att Sc 
Mallolss Saaccooconee 3 i} 3 2 1 586 - 
22:5) veesseesesee a} 12 4 2 3 a ed 
PB3H5) ‘copaosn00 f) is3 2 4 4 1 «a 
DU Been ceenecess 4 |} 5 2 2 a 1 oes 
3) “Saqodcnescade 2 5 500 300 4 2 2 
(8) GspouecedoGe 2 6 2 2 2 2 Sac 
PAIRS Eoadeacnoun’ 2 3 1 1 2 3 1 
DBDs ensenerecees 1 1 1 2 bas 1 1 
PAY HDY. cinqnoancnece | 2 a06 1 oor 1 
SOS Sadcocssnode Seats, Al) @ a0 : ee 50 
BUCH saceomagases : 2 
GPA) “Goooseagneds 1 1 1 
32519)" aancodan5o0 | 1 5¢ 
BAT ac Sach save ly ae ~ 
35-5 ee ceecceccee | aoe 
36-5 steer eeeweee | see 
DUCD, eacteasreeer | 1 
28 | 64 15 IEP Ws 13 8 


* Outside the Irish Sea. 

We see from the table that the smaller fish are those that 
have been recaptured in the central area limited by the August 
boundary line in Fig. 14, and those taken im the bays and 
estuaries of the Lancashire coast during the few months 
immediately following the date of liberation. In these fishes 
the prevalent size (shortest half-range) is about 22 to 25 cms. 
Those taken on the grounds off the N.E. Coast of Isle of Man 
and in the Red Wharf Bay Estuary are a little bigger, 23 to 26 
and 25 to 29 respectively. This means that there is a tendency 
to segregation according to the stage of maturity. The latter 


oe 


127 


is only indicated approximately by the differences in length, 
for there is a considerable variation in the sizes (or ages) at: 
which plaice become mature. The meaning of these differences 
in the migration paths taken by the fish is therefore this : the 
plaice that are approaching the stage of sexual maturity move 
offshore, into deeper water, and towards the spawning grounds 
in St. George’s Channel and in the Solway, while those which 
are still in the immature condition migrate back again to the 


nursery grounds. 


(2) The Red Wharf-Beaumaris Bay Experiments. 


Looking at the results of the marking experiments con- 
sidered so far we see two rather singular things: (1) Year 
after year a certain fraction of the plaice that have migrated 
offshore from the nursery grounds in the summer return there 
again in the autumn and winter months; (2) Year after year 
a certain fraction of the plaice that have migrated from the 
nursery grounds into the Red Wharf-Beaumaris Bays region 
also return in the winter months. What becomes of the plaice 
that do not so return? This question was investigated by 
marking and liberating several lots of fish on the grounds 
near Red Wharf Bay during the course of the back-end fishery. 
These experiments were :— 


12th Nov., 1904 ae se 42 plaice. 
Do. A Bi 49. 
24th Oct., 1907 ae ge Vals ae 
DVTHUNG yp EOI uN ees te 290 
Total... ... 431 plaice. 


First, we take the experiments made in October and 
November: 431 plaice were liberated, and 106 of these were 
reported as recaptured on the same grounds as those on which 
they were liberated—that is, within a line drawn straight from 


128 


Point Lynas, in Anglesey, to Great Orme’s Head, in Carnarvon. 
After December no more of the plaice liberated were caught 
until a year later. The mean length of those taken on the 
same grounds immediately after liberation was 24-5 ems., and 
the mean leneth of those taken on the same grounds a year 
later was 28-8 cms. The difference represents the mean 
4-3 ems. Those fish that were caught a 


erowth in one year 
year later on the ground where they were lberated had not 
stayed there during the interval: we know this because there 
is always some fishing in this area and there were no reports 
of recaptures during the interval. Further, some of the 
plaice marked in the Red Wharf-Beaumaris Bays area were 
actually recaptured on the fishing grounds to the N.E.—five on 
the nursery grounds, and having a mean length of 24 cms., 
and three on the central region bounded by the August contour : 
these had a mean length of 30 ems. 

Of the plaice to be found on the grounds off the coasts of 
Anglesey and Carnarvon in the back-end of the year, some 
migrate to the nurseries on the coast of Lancashire, and then 
they move from there out into deeper water in the summer 
months : these are the smaller fish. The rest of the plaice, that 
is, the bigger ones, go elsewhere. Where they go is indicated 
in the followmg statements, which account for the recaptures 
during the three years following the date of liberation :— 


(1) Into Carnarvon and Cardigan Bays. 


There were reported : 


In Jan. to March, the year after, 3 fish of mean length = 23-1 cms. 


,, April to June, Be 14 55 3 20 Onmiee 
», July to Sept., oe 3 a + = Nor) a. 
, Oct. to Dec., PP 1 53 Le San) x 


April to June, 2 years after, I ~ $5 = 88H) = 


3 


129 
(2) Into Bristol Channel, St. Georges Channel, the English 
Channel. 


There were reported : 


In April to June, the year after, 2 fish of mean length = 29-0 cms. 


,, July to Sept., %3 4 _ + == ORG 
,», Oct: to Dec., 5 1 Pr A = 29 ih ais 
,, July to Sept., 2 years after, 1 0 + = 8 og 
,, April to June, 3 years after, 1 a = =) BO 


(3) To the EF. and S.E. Coasts of Ireland. 


There were reported : 


In April to June, the year after, 3 fish of mean length = 28'5 cms. 


» Oct. to Dec., a 1 oC 33 =o) A, 
,, July to Sept., 2 years after, 1 1 os = Giles) 
, Oct. to Dec., re 1 PP 5 = at (0) a5 
,, July to Sept., 3 years after, 1 ae - = 38:6 ,, 


Thus the large (that is, the more nearly mature) of the 
plaice inhabiting the grounds between N. Anglesey and 
Carnarvon migrate down channel into the great Welsh Bays, 
St. George’s Channel, the Bristol Channel, the 8. and KE. Coasts 
of Ireland, and the English Channel. Of the plaice liberated 
on the N. Welsh ground and recovered, 28 per cent. had been 
recaptured on the same grounds or had gone back into the 
Irish Sea; 5 per cent. were recaptured in Carnarvon and 
Cardigan Bays, and 4 per cent. were recaptured in St. George’s 
Channel, the Bristol Channel, on the 8. and EH. Coasts of 
Treland, and in the English Channel. 

Where do these plaice that are taken on the N. Welsh 
srounds come from ? The Liverpool Bay marking experiments 
answer this question. They come from the nursery grounds 
on the Lancashire coast. Of the plaice that migrate out from 
those grounds in the summer months, a considerable fraction 
of the larger ones go down to the Red Wharf-Beaumaris Bays, 
where they form the material of the fishery that sets in during 
the back-end. 


I 


130 


General Remarks on the Migration Experiments. 


The spawning grounds of the plaice are in the water of 
15 to 20 fathoms in depth, off St. Bees’ Head, in Cumberland, 
and somewhere in St. George’s Channel. The eggs produced 
in the northern spawning ground drift mostly into the Solway 
Firth and into the Bays on the 8. Coast of Scotland to replenish 
the nurseries there. The eggs produced in St. George’s Channel 
drift to the N.E., round Holyhead, and are reared on the 
nurseries just off the Cheshire and Lancashire coasts. The 
drift of the eggs and larvae is a passive one, due to winds and 
resultant tidal currents. 

The baby plaice live on the nursery grounds until they are 
about 20 ems. in length and about three years old. Then they 
begin to migrate. 

They move out to deeper water off the coast during the 
summer months. The more vigorous ones continue to migrate 
to the grounds off the N.E. Coast of Isle of Man, or to the 
North Welsh grounds. Most of the others return back again 
to the nurseries during the months September to December. 
Next year these latter plaice migrate offshore again and 
probably succeed in moving away altogether from the nurseries. 

The grounds off Ramsey Bay (Shoals, etc.) and those 
between the N. Coast of Anglesey and Carnarvon are in the 
nature of “relays” in the plaice migrations. The fish remain 
there for some time and then reassume their migrations. By 
the end of January all the plaice have usually left the Red 
Wharf-Beaumaris Bay region, and they can be traced down 
into Carnarvon and Cardigan Bays. Later on they go offshore 
somewhere in order to spawn. During January and February 
the plaice tend to leave the Shoals region and they probably 
migrate over to the Cumberland and Lancashire coasts. 
The larger ones from the Shoals area, and possibly mature 
fish from the Solway Firth and the South Coast of Scotland, 


EE Ee 


131 


migrate on to the Solway “Slaughter ”’ area in March in order 
to spawn. 

Temperature changes in the sea are closely associated 
with the plaice migrations. The long contour lines on the 
charts (Figs. 8 to 13) were drawn with the idea of elucidating 
this relationship. They are called “ Isoanomalous lines,” and 
indicate the rate at which the sea-temperature rises or falls 
(according to the season) between the coast and the sea offshore. 
But we have yet far too few data to allow of this subject being 
pursued. One thing, however, may be noted’: in their migra- 
tions the small fish of the Imsh Sea tend to move across the 
isotherms. Obviously one impulse in the migrations is that 
of the fish to tend to remain as much as possible in water of the 


same temperature. 


The Growth-rate of Marked Plaice. 

First we consider the general growth-rate of plaice as it 
has been found by the methods indicated on pp. 102-7 and in 
the data of Table XIV. (See Fig. 7.) These results show that 
the mean rate of growth of Inish Sea plaice, males and females, 
taken from all the regions is about 6 cms. (= 22 inch) per year. 
That is fish up to five complete years in age. Taking the Age- 
groups II, III, and LV, the mean increase in length per year 
is 5-75 ems. (= 24 inches). 

How fast does a marked plaice grow? This is easily 
found by making measurements of plaice marked and liberated 
before the beginning of the spring and then recaptured after 
the end of autumn. Sometimes measurements can be made 
on plaice that have undergone two or even three complete 
seasons’ growth. These results are fairly constant and they 
show a mean rate of growth of marked plaice of 3 inches. 
Sometimes the yearly increase may be much more than this, 
and it 1s generally greater in the case of marked plaice that 
have made long migrations from Liverpool Bay into St. George’s 


Channel. 


132 


Why does a marked plaice that has migrated grow faster 
than those that can be fished on the ground of liberation ? 
One is apt to say that growth depends mainly on the supply 
of food, and that is true to some extent. But females grow 
faster than males, and then, after a certain age, the males 
seem to die. Therefore there is an intrinsic growth-factor 
which is different in its “strength” in different imdividuals. 
We must assume (in order to attempt to explain the difference 
in rates of growth of marked and unmarked fishes) that this 
erowth-factor is associated with, or may be the same thing, 
as the intrinsic factor that urges one plaice to migrate sooner 
in its lifetime, and to farther distances, than another one. 
Looking, then, at the general results of the marking experiments 
we can distinguish between an “ ordinary ”’ plaice population, 
growing sluggishly because of the low intrinsic growth-factor, 
and another fraction of the general population, growing rapidly 
and migrating sooner for the opposite reason. Therefore a 
(probably large) fraction of the plaice population off the 
Lancashire coast is a residual population, the more vigorous 
individuals migrating to outside areas. And so, it would appear, 


b) 


‘“ protection ” of this residual population may not be of any 


practical administrative value. 


133 


PARE ik 
THE PRE-WaR AND Post-WaR PLAICE FISHERIES. 


With the resumption of sea fishing, on the great scale, in 
1919, the question arose: had the restrictions that were put 
in force, as military measures, led to an increase in the pro- 
ductivity of the sea fisheries. The question was directed chiefly 
to the plaice because this fish had been studied more completely 
than any other in the dozen, or so, years preceding 1914. 
It was known that there had been a very marked falling-off 
in the quantity of plaice landed from the North Sea grounds 
during the years 1907 to 1913—a falling-off which was particu- 
larly evident in the medium-sized and larger fish ; this falling-off 
was to be traced not only in the total quantities landed, but 
also in the quantities caught per hour’s fishing. Naturally the 
change became associated with the great expansion of steam- 
trawling since the end of last century, and it was generally 
believed that the plaice stock in the North Sea was a stock 
which was being depleted by the intense fishing that had been 
practised. 


Fluctuations in the Piaice Fishery. 


When trawling was resumed in the offshore regions of 
the North Sea in 1919 it was seen that a considerable change 
had occurred. The landings of plaice rose, as did the quantities 
taken per hour’s fishing. The following graphs show this 
change very well. Fig. 15a represents the North Sea landings, 
and it shows that the total quantity taken and brought ashore 
by British fishing vessels fell from about 650,000 ewts. in 1907 
to about 475,000 cwts. in 1913. Then follow several years 
when war restrictions prevented the full exploitation of the 
fishing grounds, and when the fishing was resumed the quantity 
landed was found to have increased—until, in 1920, it exceeded 


134 


| | 
: | : (nee 
ak Chann 


| 
| | | | : oe 


e/ 


| 
| 
| 
| 
( 


| 
| 
| 
L 


| 


Fie. 15. Graph showing the change in the plaice fisheries in the North Sea, 
English Channel, and Irish Sea. Based on official statistics. 


135 


the quantity landed in 1907. Not only so, but very consider- 
able measurements of the plaice caught aboard trawlers showed 
that the size of the fish had also increased in a notable manner. 
So much for the results obtained by the English investigators 
in the North Sea: similar conclusions were made both by the 
Danish and German workers. 

Fig. 158 represents the total landings on the West Coast, 
while Fig. 15c is a graph of the same data for the English 
Channel. Even when we take the quantity of plaice landed 
per day’s fishing the same general result is obtained. There 
is a marked drop in the catches from the year 1911, in the West 
Coast and Enelish Channel data, to about 1914-5, and then 
there is an equally marked rise to about 1918-20. In so far 
the experience of the southern and western fisheries is similar 
to that on the Kast Coast, but there are other features of the 
graphs representing the latter regions that call for comment. 
In the case of both the West Coast and Channel there is a 
rise in the quantities landed from 1906 till 1911, and then 
follows the falling-off. The latter, it has been noted, com- 
menced, in the North Sea, in 1907, but we must remember 
that we do not know as accurately what were the landings 
in the years immediately preceding 1907: it may be that they 
had gradually been rising, just as were those from the West 
Coast and Channel. Further, the still more important informa- 
tion as to the quantities landed per day’s fishing, per vessel, 
are not known. 

So long, then, as we do not know what was the statistical 
history of the North Sea plaice fisheries prior to 1907, it is 
not quite certain whether the changes noted were of the 
nature of those due to a reduction of the stock by over-fishing, 
or to a natural fluctuation that might have occurred no matter 
how the intensity of fishing varied (within reasonable limits, 
of course). 


In 1918 everything pointed to the conclusion that greatly 


136 


increased fishing would deplete a natural stock of fish. So it 
must, of course, provided the increase is great enough ; but 
the question we have here to consider is whether the increase 
of fishing in the North Sea trawling fleet did actually lead to 
the diminution in the catches which was observed in the year 
following 1907? We anticipated, as everyone then did, in 
1915-8 that the great decrease in trawling must have an effect 
upon the fisheries, and such statistics as were then available 
for the North-west of England were examined with that question 


in mind. 


Fluctuations in the abundance of Plaice on the Lancashire 
Fisheries, 1892-1920. 

From the year 1892 onward and till the present time the 
condition 0° the inshore ground, or nursery, just off the estuary 
of the Mersey, has been regularly examined. Experimental 
hauls, made with a beam trawl-net of 25 to 30 feet in breadth 
and having meshes of 6 inches, have been made several times 
every month. Similar hauls with a shrimp trawl-net, of 
2-inch mesh, were also made: all these experiments were 
carried out by Capt. George Eccles, a highly experienced 
fisherman. Taking them critically one sees that the methods 
were not always strictly comparable, but this does not affect 
the broad, general conclusions that are certainly to be drawn 
from the data. The latter are recorded and are fully discussed 
by R. J. Daniel,* and the numerical results need not be given 
here in full. But a graph is necessary in order to see where 
they lead. 

Fig. 16, then, is such a graph. Two series of “ averages ”’ 
have been plotted: first, the average catch per annum 
(smoothed by taking three-yearly averages yearly, and second, 
the “ half-ranges ”’ calculated as in the following example :— 


No. of plaice caught ina haul ... ... 0 to 50, 51 to 100, 101 to 150, ete. 
No. of times such a catch was made ... 13, 6, 1, ete. 
Sums of the above frequencies not SH] 24, 18, etc, 


* Rept. Lancashire Sea-Fish. Laby. for 1919. 


a i i 


ee ee 


137 


That is, there were 13 hauls in this vear that contained 0 or 
less than 51 plaice, 6 that contained 51, but less than 100, and 
so on. The lower line is to be read as follows: there were 
37 hauls in the year, and in all of these either no plaice or some 
plaice were caught ; there were 24 hauls in which either 51 or 
more than 51 were caught; there were 18 hauls in which 
either 101 or more than 101 were caught, and so on. When 
we plot the figures of the last line we get a J-shaped curve 


400 


/00 


ESE IR SSK es SS oS tore 


~ 


inal Q 
ad a 
tS =~ 
~ 


Fic. 16. The continuous, angular line represents the average catch 
per hour’s fishing with a trawl-net of 6-inch mesh. The individual annual 
averages are “smoothed” by taking three-yearly averages yearly. The 
catch for the period 1895-7 rises to 895. The series of columns represents 
the results of the other method described in the text. | Several years’ records 
are lost. 


(or exponential). Then we take half the area of this curve 
on the steeper side and note what is the range of frequencies 
covered by the half area. Such ranges are represented by the 
columns of Fig. 16. 

This kind of average gives us the nearest approximation 
to the experience of the fishermen. The latter would say 
“we usually got about 100 fish per haul,’ or so. This kind 


138 


of graph is, therefore, the best general expression of the whole 
experience. 

But it does not matter whether we take the results of the 
trials with the fish trawl-net, or those made with the shrimp 
trawl-net. Nor does it matter whether we take the average 
catches per year, or the smoothed average catches per year, 
or the half-ranges of the summed catches. Whatever way 
we deal with the data the same result comes out: there is a 
periodic fluctuation between 1892 and 1920. There are two 
periods :— 

(1) There are maxima in 1896-7 and about 1910. 

(2) There are minima about 1905 and about 1915. 
(« 
(4) There appears to be a maximum about 1920-22. 
(9 


) 
) 
3) There must have been a minimum about 1890. 
) 
) 


5) When the fish-trawl and the shrimp-trawl data are 
examined it is seen that the minimum for the 
former occurs about two years after the mimimum 


for the latter. 


Here, then, we have actual observations that point directly 
to a national, periodic fluctuation in the abundance of plaice 
on a certain ground—the Mersey nursery area. The evidence 
is experimental, but the same results also come from examining 
the variation in the quantities of plaice landed from year to 
year. Allowing for various sources of confusion this same 
periodic fluctuation is seen in the quantities of plaice landed 
at Morecambe—a typical inshore fishing port. It is also to be 
seen in the total landings from the English Channel and from 
the West Coast. One cannot doubt that we have here evidence 
of a natural periodic variation in the abundance of plaice on 
the West Coast. Every ten or twelve years the fish becomes 
unusually abundant. There was a minimum of abundance 
(several lean years) just about the date of commencement of 
war, but this cannot be more than a coincidence, 


139 


Fluctuations in the Size of Plaice taken off the Lancashire 
Coast : 1908-1920—Mersey Estuary. 


We now consider the variations from year to year in the 
sizes of the plaice landed from the Lancashire inshore waters. 
The data are not so abundant as we might wish and the results 
are rather inconclusive. But since they may fit in, afterwards, 
with the results of other investigations it is advisable that they 
should be recorded. There are measurements of plaice caught 
on the various grounds and these are summarised in tables. 
There are, however, no records for the war years 1914-1918 
for most of these grounds: only one series of trawlings was 
maintained all through the period 1908-1920, and that was 
those taken on the Mersey nursery ground. The two best 
months here are, on the whole, September and October, and 
these are, therefore, combined as the series of length-frequency 
distributions of Table 16. Here we have measurements of the 
plaice caught in those months by a beam trawl-net of 6-inch 
mesh used from a sailing boat. 


140 


Table XVI. Off Mersey Estuary, Sept.-Oct. Trawl Net, 6-in. mesh. 


1908. | 1909. 1910. | 1911. | 1912. 
Mean | 
Length Sa al 
ee £% ij £% if ive | JF % Hi liv’ 
| 
15. | 1 0-02 ae - ‘ : | wee 
12°5 4| 0:07 5 0-21 ae a {ae 
135 | 38 0:68 7 0°36 a i 1 | ona 
145 | 249 4-47 28 1:22 ca : bes 4 | oma 
15°5 833 | 14:97 54 2:36 - ne 2 0°25 12 | 1°31 
16°5 331 | 23°88 127 5°55 1 0:16 | 20 2:49 | 34 3°71 
17°5 919 | 16°51 271 | “11:86 10 1:62 | 30 3°74 | 52 5°66 
18°5 600 | 10:77 3274) daegit |) 722 3°58 | 29 3:62 | 77 | ease 
19°5 378 6°77 265 | 11:59 | 38 618 | 25 311 | 129 | 14:05 
20°5 325 5°83 961 | 11°37 | 51 8:29 ll 1:34 | 99 10°78 
21°5 253. | 4:54 221 9-66 69 11-23 13 162 | 121 | 13:18 
22°5 215 3°86 | 180 7:92 | 43 699 | 31 3°86 | 87 | 9:47 
23°5 146 2°62 | 123 538 | 41 666 | 45 566 | 72 7:84 
24°5 81 145 | 109 ATT 61 9:92 | 57 711 57 | 621 
25°5 79 1:41 | 86 | 3:76 | 54 8°78 | 74 9:22 | 34 3°71 
26°5 40 0-73 | 76 3°32 50 8:13 | 85 10°61 36 3°92 
27°5 31 0°55. | 50 | 219 | 48 7:80 | 98 19:29" | 22400 ee2ot 
28°5 18 0:32 | 40| 1:75 | 41 666 | 96 11:97 13 | 1:42 
29-5 12 O21 | 24] 1:05 37 6:02 | 82 10°22 15 1°63 
30°5 3 005 | il 0-48 17 2°76 | 36 4:49 15 1-63 
31°5 2 0-04 9 0°39 12 1:95 | 26 3°24 8 | 0:87 
32°5 2 0-04 3 0-13 10 1-62 18 2°24 4 0:44 
33°5 2 0-04 | 2 0:08 6 0:97 9 1:12 9 0:98 
34:5 | 1 0-02 4 0°17 es ie 8 0-98 4 0:44 
355 | ra eal) Spee 2 0°33 4 0-49 | 6 0°65 
365 ae _ 1 0-16 1 O12 | 1 0-11 
37:5 2 0-04 l 0-04 1 016 | 1 012 | 2 0-21 
385 | 2] 0:04 % a SE oo eel O-L1 
39°5 1 0-02 1 0-04 1 O12 5a 0-11 
40°5 ae: ie ates ice 
5,568 99°95 2,285 99°96 | 615 | 99°97 | 802 99:96 (E 99-98 
| | | 


141 


Table XVI—Continued. 


Mean 
Length. 


AAT Whore 


UH TU CUA UT TTT SUH 


SNMNWNWR Re RRP RR Ree 
Se OO CO 


wnwwwbh bt 
OMAP UKE Wt 


1913. 1914 1915. 1916. 
i omen Nd Yo. | ae et cate % 
is a s I |g 02ers a 
- 2 O17 45\0 GO;008 meee i. 
ce - 9| 062 | 33| 0-76 | 3 | 0-48 
Somos 240 2-09 | 159 | 3:67) 9s 1-29 
TON ROOPe | oo 453 || S17) | 7320s oP i210 
89)|) 3:13. | 115) 10-02 | 540 | 1247 | 13 | 2:10 
307) 1078) | 1899) 1221 || 549) 12-67. | 26°) 4-20 
522 | 18:34 | 91) 7:94 | 385| 880 | 42 | 6-79 
633 | 1872 | 94] 820 | 365] 843 | 587 9-21 
BI4eWe 18061! 4865) 750 | 315 | 727. Var |) W244 
BA sigs" || 70) 6:10) | 347°|  S:01 |) 63 fh 10-17 
216 | 97:59 | 59’) 513 | 307] 709° | 78 | 12-60 
TAG 7e) | 62) 549 || 313) - 7239 64 3) 0:34 
68| 2:30 | 55 | 480 | 226| 5:22 ) 41 6-62 
SOP esas BOR eros, e185 | 4-27) i soe 
Pm eOdo | 74) G46 (109) | 2:75. \esPeale bil 
TON), 0:35.) 404) 33:58 |) 75.) 1-73) 19) 13:07 
Sie 0:28) |), 44) S84 yest) O72 Ip 242 
De OOTe) 220 O28) 21) O48 | Ton 249 
So OL 15 | 1°31 10| 023 | 6 | 097 
aa Ould in 96 G3) 0:21, aay 1:13 
1005s) (a tO en O;S7 nigel, 0-07), ypmeamiimO:32 
2| 0:06 Ty) 009) ye 5) O12) || aaa ee0-48 
i) REE! 1| 0-09 Te -0:02) i |eaee Be 
“ mM 2 O17 2) 0:05 
1| 0-03 Qi) 0°17 Zi\) 0:05 
: arias PU eer ale, (0:0. 1) ses 
Te 0-036 | ie 0709) a!) 2a) 0 O05" 0: 
1| 0-03 Sil O26/019 <2. ‘: e 
Te liga 703. ate) Baas | : oe is 
z a : a ot De en 32 
ae ie 1) 0-09 1| 0-02 l 0-16 
1} 0-03 1} 0-09 | Pc0026" |b eee me 
1| 0-03 a a se 
1, 0:09 
2,846 | 99-95 |1,147 | 99:80 | 4,330 | 99°98 | 619 | 99°97 
| | 


1917. 1918. 1919. 1920. 
Mean 
Length. a = 
if f% A L% uf £[% f f% 
115 Seat Al Mache we li moneeles well’ piece 
125 ats See i) © eBul BOR3S ae 13| 0-53 
13°5 2| 0:03 18 0-99 4| 08 7 | 0:29 
145 79 | 2-22 43 2:36 43) |) 322 91| 3-76 
15°5 190 534 123 6°75 77| 5°75 266 10:99 
16°5 297 | 8:54 195 | 10:67 109 | 815 | 307] 12°68 
17°5 382 | 10°73 | 193 | 10°58 133 | 9:94 | 211] 8-72 
18°5 436 | 12-24 | 174| 9:54 126 9-92 185 | 7°64 
19°5 446 | 12:52 | 169 9:27 144 | 10-76 190 | 7:85 
20°5 334 9°38 169 9:27 145 | 10-83 165 | 6-82 
21-5 334 9:38 117| 642 | 126| 9-42 160) 6-61 
22-5 299 8:40 | 156 | 856 | 111] 8-30 166 | 685 
23°5 224 6:29 130 713 | 83] 6-20 101 | * 4:17 
24°5 | 184 5:17 79| 433 | 61] 4:56 107 | 4-42 
25°5 | 100 | 2:81} 60/ 320 | 45 3:36 | “937) “3:84 
26°5 78 2-19 28 154 | 32] 2:39 53 | 2-19 
27°5 45 1:26 38 2:08: | 23 1-72 60 | 2-48 
28°5 27 0°76 34 187 | 22] 1-64 59 | 2-44 
29°5 | 21 0°59 21 115 | 15) 1-12 49 | 2-02 
30°5 17 0:48 27 1:48 11 | 0-82 36] 1:49 
31'5 | 14] 0-39 ll 0-60 3) 0-22 23] 0-95 
32°5 15 | 0-42 4} 0:22 11 | 0-82 21 | 0°87 
33°5 7 0:20 5 | 0:27 1) O07 | 19°0k078 
34:5 6 O17 2] Oll 21) 0:15 16. 0-66 
35:5 i Mea 30517 31 0-16 2) O15 6 | 0:25 
36°5 | 4{ O11 27) 0:11 2) W015 4) 0-17 
37°5 3 0:08 5 | 0:27 3 | 0-22 A O17 
38:5 1 0-02 1 0:05 e ee 1} 0-04 
39°5 2 0:03 3| O16 | 1! 0-07 >| 2013 
40°5 2) 0:03 31 O16 | 1| 0-07 2| 0-08 
415 l 0-02 1 0:05 | 5 rn oe 
42:5 1 0:02 ely on 1| 0-07 1| 0-04 
43°5 fs ee ye 1 0-04 
44°5 - 1 0:05 1| 0-07 - a 
45°5 1 0:05 1} 0-04 
46°5 | ee ; a 
475 | a, 
48°5 ie 
49°5 2 0:03 | 
50°5 0:02 = hs | 
515 er 1 005 | ... | 
3,560 | 10004 1,823 | 99°92 1,338 99:96 2,421 | 100-01 


143 


The results of Table 16 are studied by making shortest 
half-ranges from the various yearly distributions. 


30 


Fie. 17. Variation in length (shortest half-ranges) of plaice caught 
on the Mersey nursery grounds, during September and October, 1908-1920, 
by a trawl-net of 6-inch mesh. 


The figure represents the prevalent sizes of plaice on the 
above grounds. The lengths of the columns, read off on the 
scale on the left-hand side, give these prevalent sizes. Now 
the latter certainly increased regularly from 1908 to 1911 
(which latter year was about the time of a maximum in plaice 
abundance), but after 1915, when there should be a minimum, 
the prevalent size of the fish does not increase towards another 
maximum about 1920, as one might expect. Perhaps, to expect 
so much would be foolish for we may have to reckon with 
the fact that the migration periods that we noted above may 
be variable—and here we have studied two months only. 
In fact, this question of variation in length is very complex, 
and we are still without the knowledge that would enable us to 
deal with it satisfactorily. 


Fluctuations in the Size of Plaice—Liver pool Bay. 


Next, we take another region, Liverpool Bar to Blackpool 
(mostly within territorial waters). All experimental fishing 


144 


was suspended here for the period of the war and we have 
only the years 1909, 10, 11, 12, 13, and 1920 for comparison 
with each other. The distributions considered are those for 
August and September (the best ones), and the data are taken 
from Tables 5, 23,24. What we can compare is the pre-war 
period, 1909-13, with the post-war one, 1920, and it is to be 
noted that we know nothing of the years 1914-19: possibly 
1919 was a year in which the plaice here ran bigger than they 
did in 1920. Now which of the pre-war years ought we to 
set over against 1920 ? 

The last pre-war year, 1913, is the one with which we 
naturally compare the first post-war year, 1919 (or 1920, for 
we have no data for 1919). But we see, from Fig. 16, that 1913 
appears to have been a year of minimum abundance of plaice, 
while 1910 was situated near a maximum. It is well, then, 
to see if there are differences between the prevalent sizes of 
plaice as they occurred on the Liverpool Bay grounds, and so 
Fig. 18 was prepared. 

Evidently, if we compare 1920 with 1913, we find that 
the post-war plaice ran bigger than did the pre-war ones ; 
but if we compare 1920 with 1910 we find that there is little 
(if any) significant difference. I{ we take the average lengths 
for the years 1913-1909 we shall find that the plaice of 1920 
are, on the whole, bigger than in the years immediately pre- 
ceding the war ; but it would be wrong to associate the increase 
so indicated with the restrictions on fishing of the years 1914-18. 
It is necessary to consider also the deviations from the average 
of 1909-1913, and we see that the good year 1920 is not any 
better than the best of the pre-war years with which it is 
contrasted. The fact is that these length-frequency data are 
very difficult to interpret in some cases: to make the best 
use of the information that they give requires also a knowledge 
of the migrations. We should want to know, rather closely, 
in what months the crises of the migrations occurred, because 


145 


we are comparing a definite period (August-September) in all 
the years, and it may be the case that large plaice had left 
Liverpool Bay, in greater proportion, and in a certaim month, 
in one year than in another. 


ail | eee — = = Saree ys eee = ee 
[ELMS DOD AORTA ENDS. IST I IS OT 27. | 


trawl-net on the Liverpool Bay grounds in the months August-September 
during the period 1909-13, 1920. Summational curves, from Tables 5, 23, 24. 


The Northern Plaice Grounds in 1920 and 1921. 


There is material for an interesting comparison in the 
data obtained on the northern grounds in 1920-1921, when 
investigations into the spawning of the fish were made, and 
when we were able (by permission of the Fishery Board for 
Scotland) to trawl in Luce Bay. The Table 17 gives the 
leneth-frequencies tor the months of January to April, and for 
the ‘‘ Shoals ” and “ Slaughter ”’ grounds (the latter being that. 
on which spawning fish were found). Fig. 19 is a graph of these 
data, and also the results of the hauls made in Luce Bay in 
1920-21. 


K 


146 


Table XVII. Northern Crounds, 1920-21. Length Frequencies. 


** SHOALS.”” ‘* SLAUGHTER.” SoLway SPAWNING | LucE Bay. 
GROUND. 
| | | 

I ie | TV. Pe ne.) TV. | 9) ae ave S208 eiaoee 
15°5 a 2 aT as 6* eee Saleen 6 
16°5 Dale Pi eee. eS i 2 2 3 pA) Ts 
17°5 PST NBs Rita a ANAS 1090) 7 6 3 | 47 
18°5 Be S28 al) ul meee 4|/ 5/ 4 Sr a3 5 9 Pa at oS: 
19°5 2 aes © fas fe nents oe Meese Sel ol pst 6 | 46 
20°5 12| 30| 6 Oe POel er Grl s P1e 2S |e a ete 4 Balaeal 
21°5 10°), 30) 104)" Se 29. Si) 755) Os Se elo eee 6| 14 
22°5 127) 034 en 2 Selle 2 1S) eS aeeG 8 5 | 15 
23°5 AD ST 6 934 Sale 185) 6.) aI Sa ees : 17 
24°5 D1 S29 Rea jane 2 7 S|) 2 2) lees 6 4 6 
25:5 DO AG Gat Doin aT a rales 5 1h Sea etna a4 3 | 15 
26°5 133), 135) as 5 | 155) 20 2) 131) S62 ls 5 6 
27°5 SA Sa eal weet a) eS 1 OP Ser lmees 7 tae! 
28°5 (a by, 7 aeties |pe ts 57) 3 | 8b" ean 22 S40 
29°5 al Te) | Sallie ae ee 1 2" 49) 728 9 3513 
30°5 3 5 Qi By agk | ae 4 || 3) 255) 18a) ie 6 | 10 
315 3) 8 Br) lt jee Fi ike ShaleasOniy 24s | 110) 4) 93 
32°5 Selheals api ily) Pies) ile ies. erooey) 10 8 5| 18 
33°5 Pad a0) aah fea al ee se Sal 2s) 387) 14 8 7 las 
34:5 2 9 Tse alee Greek Wl Oey pa S|) @25. eee 
35°5 3 81 2 i wees Selena eos 1 623 S| 1O"les 
36°5 6 6 An 2 9 3 | 30 | 12] 12) W923 
37°5 Re ER eal biceps ele | 3) | 34) 15 | 10 on eat 
38°5 2 Sule at eal 5 | 10 2 2) 20 9 6 | 2saeay 
39°5 Weyer seael | a. 33 Bal US| Cee een cool: 0 9 | -10)) a 
40°5 5 4 3 fi 6 2 13 7h 9)| 12 
41°5 a eee 6 7 1 13 6 2) 125 arG 
42°5 ey ak Bia ces 7 8 1 |) 26.) 10 BRL y -7/ 4 
43°5 een, soe wl aT 8 5 1 14 5 3.) atl 4 
44°5 1 35)" 1 9 8 1 algae: 6 5| 6 3 
45°5 Fs gees ie 1 6 8 1 lly 2 7 4 3 1 
46°5 5 1 1 1 7 2 1 3 3 
475 3| 4 1 2 8 | Ged 2 mu 2 
48°5 Sil hic eee es eee Ball eee | tkneee 3 1 
49°5 Bi gee 1 3 1 5 1 1 3 
50°5 1 1 1 ih 2 D . 2 
515 aeons 1 1 1 1 2 ; 1 
52°5 eee 3 1 | 5 1 as 1 
53°5 1 1 1 3 2 1 
54°5 : Pe 1 
555 1 1 1 2 
56°5 1 + 
515 a | 2 
58°5 1 | 1 
59°5 Sats ons 
60°5 | ae 
61°5 | as 
62°5 ; 
63°5 1 Wy : 
65°5 ; | A eae WAH soe Ts) pee eg Gee hd) eee 1 

133 | 449 185 | 70 | 313 | 367 | 77 | 133 | 927 | 469 | 279 | 194 | 558 


147 


These results represent the biggest plaice caught anywhere 
in the Irish Sea area. Here we are concerned only with the 
Luce Bay figures. The graph shows a fairly well-marked 
difference between 1920 and 1921 for this region, the plaice 
taken in 1921 being considerably smaller, on the whole, than 
those taken in 1920. Now a somewhat similar decrease in 
size in North Sea plaice, in 1919 and 1920, was held, by the 


= PS 


oS x ~. 
Vig 
(e) Ah 


Summed | x ry \Y 


Northern Plaice Grounds 


I9LO-21 | 


Length. cms. 


Fre. 19. Graphs of the length-frequencies of plaice caught in a 6-inch 
mesh trawl-net on the northern grounds in February-April, 1921, and in 
Luce Bay in September, 1920 and 1921. Summational curves from Table 17. 


English workers, to point to the first results of the renewed 
intense fishing of the North Sea. That explanation is difficult 
to extend to the Irish Sea area, for there is comparatively little 
fishing in these northern grounds, and Luce Bay is, of course, 


148 


a preserved region, where all forms of trawling are prohibited 
by the Scottish Fishery Board. 


Relative Proportions of the Age-groups of Plaice in the various 
years. 

Hitherto it has been rather suggested that plaice are 
bigger or smaller im one year than in another because they grow 
more or less rapidly. No doubt there are differences of such 
a kind in various years, and, no doubt also, these differences 
depend on a greater or less food supply. Just yet we have 
very little information about variations in the food supply : 
the subject is a very important one and it is being investigated, 
for the North Sea, by the English Ministry of Agriculture 
and Fisheries. What we have to point out here, however, 
is that the differences in prevalent length between the plaice 
of a certain ground from year to year (such differences as are 
represented by the length-frequency distributions given in this 
report) depend principally wpon the composition of the shoals 
of fish as regards the age-groups. This is the argument, worked 
out very ingeniously by Dr. Hjort, for the Norwegian cod 
fisheries. 

Consider, first, the lengths of the plaice belonging to 
Age-group III (over three and under four years old) and taken 
in Liverpool Bay in the years 1908-15. The sexes are not 
separated, and the numbers of fish measured in each of the 
months June to November (the Roman numerals at the heads 
of the columns) are given separately. The mean lengths of the 
plaice in each month are given at the bottom of the columns, 
and we see that this increased from 23-0 cms. in June to 29-5 
ems. in November. Thus we have a mean increase in size, 
during the growing season of the year, of about 7 cms. (for we 
must suppose that there was some growth in April and May, 
for which months we have no data). 


149 


Table XVIII. Lengths of Plaice of Age-group Ill, ¢ 9° : 
Liverpool Bay, 1908-1915. 


Mean | | | 
Length. | VI Arai VIII 1D x XI 
| | fra 

Go | 5p Sac ae 
175 | 3 ns a 1 af | 
18°5 4 | 4 1 pe nt 
19°5 7 6 ne 1 na 
20°5 16 | 2 4 1 1 1 
21°5 16 5 10 1 1 
22°5 10 i 7 7 4h | ies 
23°5 18 10 7 11 an | 1 
24°5 7 9 7 8 i as 
25°5 a 9 8 6 1 | as 
26°5 5 7 9 10 ae 4 
27°5 4 6 6 4 3 oe 
28°5 2 4 4 5 2 | 1 
29°5 2 1 6 3 2 3 
30°5 1 ts 3 2 | 3 
31°5 1 4 4 1 
32°5 nae l 1 2 
33°5 a 1 
34:5 1 1 aes 
35°5 1 1 
36°5 1 

Totals ...... 104 74 Gir 67 11 19 

Means ...... 23-0 23°9 25°4 25:9 | 27:3 29°5 


Relative abundance of Groups II and [11—Liverpool Bay. 


II Il Ratio of II to IJ 
1908-16 500 pod 3,638 442 100: 12 
1914-16 556 563 630 73 100 : 12 
T9207 ea: ne sae 928 802 100 : 86 


Next, we take the year 1920, for which we have better 
data. Table 19 gives the results of measurements of plaice 
caught in Liverpool Bay during the months June to December, 
distinguishing the sexes and stating the measurements for each 
month separately. Also Age-groups II (over two and under 
three years old) and III (over three and under four) are distin- 
guished. Now it is obvious that the data for the months 
June to August in the case of Age-group II are incomplete, 


150 


and this is because the trawl-net employed (one of 6-inch mesh) 
did not sample the fish of lengths 10 to 20 adequately, many 
of the latter escaping through the meshes. If we had had 
representative samples of plaice of Age-group II of this range 
of lengths the mean lengths for June, July, and August would 
have been reliable: as it is they are not reliable and have 
not been stated. (This selective action of the nets used is a 
troublesome source of error far too frequently neglected in 
discussions such as this.) 

Age-group III, male and female, are, however, more 
adequately sampled and perhaps we can depend on the mean 
lengths. Allowing, then, for a certain growth m May (not 
given in the data) we may conclude, from inspection of these 
tables, that the mean growth-rate for Age-group HI was about 
7 cms. There is no reason for supposing that there is any 
trustworthy evidence that plaice of Age-group III grew any 
faster or slower in 1920 than they did in 1908-1915. If there 
are distinct differences in the prevalent lengths of plaice 
inhabiting Liverpool Bay in the period 1908-1915 and in the 
year 1920 this cannot be said to be due to different rates of 
growth. 

Composition of the Plaice Stock as regards Age-groups. 

Now we consider the relative abundance of plaice belonging 
to Age-groups IL and III in all the fish measured, from the 
Liverpool Bay region, in all the months, during various periods. 


Sex is not distinguished. We have 
Age-group II Age-group III Ratio of IT to IIT 


1908-1916... 306 3,638 442 100 to 12 
1914-1916... nee 630 73 100 to 12 
US PAD) oac 36C eee 928 802 100 to 86 


All these plaice were taken in the 6-inch mesh trawl-net and so 
were the following ones, caught during 1909 and 1911; Age- 
eroup I being also included in this series of measurements :— 
Age-sroup I Age-group II Age-group III 

52 46 


1909 ces Ras 2 per 100 fish, 
1911 sie ick 11 68 21 a 


151 


Table XIX. Lengths of Plaice of different Ages and Sexes : 
Liverpool Bay, 1920. 


AcsE-Group IT, MALE. | AGE-GrouPp II, FEMALE. 
Mean | 
Length. “Fe Pyrite we ae ees = iin el ae iy ree all 
Vile avarie VAL ING |e XX HOD) WP) WEL. | VERE |, 1X D-Mnd.T Ne o.41 
16°5 4 1 2 x ae a ads 4 re a 2 Fae l 
175 ky us 33 2 3 3 eae 19 | 9 6 1 3 1 at 
18°5 22 10 7 4 5 | 2 1 tO nets 8 6 4 2 1 
19°5 VS7|7 <0 6 10 ll 5 2 12 LT 7 14 9 5 nis 
20°5 9 4 14 24 16; 10 ] 5 5 4 16 8 3 2, 
21°5 1 4 5 16 18 | 9 3) } 2: || 4 4 19 8 14 3 
222i 1 | 6 22 14 | 18 6 Sill meee 6 12 7 11 4 
Qe | 1 20 Wie eo 4 | Te) 1 1 10 16 zi Z 
24°5 1| 14 EO aS 7 | awe : 5 5 19 2 
25:5 one if ei a ae 3 | : 2 10 ui 2 
26-5 ee aoe are a a & 4 | =| 2 1 5 Bae 
27-5 | | 6 fit 3) | 5 1 a ; 
28°5 Salar ett pack en, eH) 2 
29-5 Pe eea ages 
Totals... 69 | 32 | 45 | 124 | 105 | 100 30) eo 2 een 36 92 74 97 19 
IMe@amsices\) ce ||| eae Son || PZB) || PPLE || 2283877 1 CBG} 28) 2220) 23:8) 22-9 
Acs-Group III, Mate Aas-Group III, FrmMae. 
Mean 
Length | ; a ] 
WAL |) WO WANT) IDs |) ox DML |) STL WAL fh WADE |) WAU B26) Oe || a2ar I) sant 
16:5 OM Nace : a Al ee 
ils) 1 3 : \ Panes 2 es é - ae ae ; 
18°5 8 5 ae peers u 4 oy 52 1 ees ; 
19°5 16 4 4 aie tie 1 a 6 1 1 1 1 Ae 
20°5 18 ZU 5 ae 5 1 14 6 1 sist 1 ] 1 
21-1 10 55 2 8 PAA Msg 2 8 4 3 2, 1 és te 
22:5 i a 2 enon nee 2 — 13 4 tad 9 4 son SRE 
2320 2 18 4 4! 8 8 33 53 ll 3 8 5 3 1 
24°5 7 14 11} 10} 4 | 5 3 19 4 al 3 4 4 
20°) 1 8 3 11 | 3 Tn 8 ae 10 Ti 7 3 5 2 
26°5 aoe 9 Age 19 | 7 8 | 1 ey 1 6 4 3 2 
Disb ses 10 2 VE (a) j) JL 3 9 2 9 | 8 4 ee 
28°5 8 1 2 8 6 2 4 2 3 5 4 5 
29°5 5| 1 Teens) | * i ae le Borie 2 
30°5 3 sea. 5 2 3 te 5 8 Uf 
3311955 aisle } 4] 1 | 4 2 bas 4 1 5 2 
32°5 os 4 | DAI Saelh ede : 3 ise 2, 1 
33:5 3 aale Bibi ee aera michael Sore I hepetil saine Ah eee 
34°5 Mts | ey |e | Aa see ae ae 1 1 aide 
Totals... 72 | 106 29,0 ai | 67 | 62).|, 28 59 | 89] 28 64 | 44] 50 27 
Means ...| 20°8 | 24°8 | 24:0 | 26:1 | 26-1 | 27°3 | 26°8 || 21-1 | 22°8 | 25-4 | 261 | 26:1 | 28-1 | 28-0 
! | | 


152 


Now Fig. 18 apparently shows that the plaice caught in 1911 
were markedly bigger, on the whole, than the plaice caught in 
1909, and one might incautiously infer that the rate of growth 
was greater in 1911 than in 1909. But the comparisons of the 
composition of the shoals, both in the periods 1908-16, 1914-16, 
1920 (Groups II and III), and in the periods 1909, 1911 
(Groups I, II, and III) show clearly that the prevalence of 
bigger fish in some years is due to the fact that older (and therefore 
bigger) fish are more abundant in those years. 


Causes of Fluctuations in Abundance and Size. 


Why, then, are plaice bigger, on the whole, and on a certain 
ground, in one year than they are in another? It is because 
there are more older fish in the shoals in those years when the 
plaice run bigger, not because there is a greater rate of growth. 
No doubt the rate of growth varies to some extent, but not much 
—not enough, we think, to account for the differences that are 
to be observed from year to year. 

Why are plaice more abundant on a certain ground in one 
year than they are in another? It is because more fish have 
passed successfully through the critical periods of metamor- 
phosis and have managed to settle down on the nursery 
grounds, there to grow rapidly and safely. If there are more 
plaice of three years old on the Liverpool Bay grounds in the 
summer of 1920 than there were in 1919 (say) it is because 
more little fish came on to the nurseries in the summer of 
1916. And so with each age-group. 

The abundance of plaice of any particular age-group, on 
a fishing ground, depends, then, on a number of conditions, 
all of which have, by some happy chances, been in existence 
and have been correlated. 


(1) There must have been, so many years previously, an 
unusually large production of spawn. 


(2) An unusally large proportion of the larvae hatching 
out from this spawn must have metamorphosed 
successfully. 


153 


(3) The larvae must have found suitable food in the plank- 
ton on the sea area where they metamorphosed. 


(4) Suitable wind-drifts, tides, etc., must have brought 
them to a nursery ground and not to some unsuit- 
able part of the coast. 


(5) There must have been plenty of food on the nursery, 
with other suitable conditions. 


To test all these conditions is quite possible—and_ it 
would be the most fascinating kind of research imaginable. 
Just vet the resources for such investigation do not, of course, 
exist and so we cannot offer any data. But even the inadequate 
material we do have at our disposal may carry us some way 
and so we have prepared the following Table 20. There are 
marked differences between the prevalent sizes of plaice taken 
in the shrimp trawl-net in different years, and these we are 
considering. We have included all the measurements of plaice 
caught in hauls with such nets (of 2-inch mesh) in the months 
October to March of 1908-9, 1909-10, 1910-11, and so on. 
By October the fish have ceased to grow, and it is April of the 
following year before growth begins again. Therefore we can, 
from a study of the relative abundance of very small plaice 
taken during the winter months, endeavour to obtain a measure 
of the numbers of plaice spawned, successfully metamorphosed, 
and transported to the nursery grounds. Thus we have 
prepared Table 20 in order to make such a measure of the 
productivity of the various years for which we have data. 

Looking at the length-frequencies recorded in Table 20 
we see two kinds of distribution: that of the years 1908-9, 
on the one hand, and that of 1914-15, on the other. Small 
plaice of less than 8 cms. largely preponderate in winters of 
which 1908-9 is the type, while in the other kind of winter, 
such as those of 1915-20, the small plaice are much less frequent 
in the catches. It is hardly necessary to examine the small 
fish taken in the shrimp trawl-net in order to find what is 
their approximate age, for we can be pretty certain that 


1éG 99F'T 8L0°E 1&9 SIé‘T GFL‘G 828% | SSL‘E SLE°SE| sPre’e 960°F 6686 


wee tae eee eneeeeee 


wee see Stee eee eeene 


eee we wenee 


teen ee ewes 


te eee eeee 


Stee w en eeee 


| PE 
G If GP LT SOT €LI 9G | 68 
8I FL gg 89 gel terete) GE | 966 | at 
€¢ LO | §&I SII O&T StP OF | 9&€ 6G | GOL 86 06 ae ae 
&@ OST 891 6e1 18 G88 IP gig | Vel G0G T6 GL eile a 
1G L8T EPG G8 €8 1¢0'T 8L 0g FIG OGG 60T 611 pales ads 
GG LOG CFG IL TOL 9GL 99 609 | ILzé Ilé Sol Shi ok ae 
09 [0G HIG 8é v8 O8P 9L (pale CbG CEG VEG FOG pa a 
GL. 691 | GGE 9 L& | 9&P 901 O00OG | FEST GLY LOF 90a baie 
; | 666 PIG Sol | 0067 FIG 809 COCs alictaeons 


i 
ioe) 
= 
4 
ioe) 
| td 
No) 
— 


q 


UD UD UD UD UD UD UD UD 1D UD 19 1 UD 


wD 


1 14 1 


1d 1) UD 


ONO HINO DODO ANA O H 19 OE OS 
Oe Se Oa ee Sa fot ala ok Ga ON CN IGWIAN GlICN CN CWE 


lo 


sD 


08 GL CPG 61 OP 06G €G¢ | SLT | €éPr6 FES 819 COUT ales t cs 
Cie) 88 n08 |= 8e8'- | 6. | 9LO'OT\/c9c6, | ono)” | -eeeia tes 
7G ¢ Me fon 68 ora | s89 | sob | ool | ori | ceo | corn 
G SI OZ | 8 een | SIP ILZ R89 eCZ |eceeeeeee AO 


1 1G UD 1 


Jose oe Seas 


‘0G GIGI | “6-SIGT | “S-LIGI | “L-9161 | ‘9-SI6I | “S-FI6T PSIGL | “E-CIGT @LIGL ; “L-O16L |OL-606T | 6-806T 


"Bary Aassail > 0361-806! ‘Y2ARIN-"}90 SULNP JON-|MUAL duAYS UI pYSNeD edIeid “XX GUL 


155 


about 90 per cent. of al! those that are less than 8 cms. in 
length belong to Age-group O. This arbitrary limit has 
therefore been taken in Table 20, and the proportions of 
plaice of less than 8 cms. long have been calculated and regarded 
as giving us a good idea of the relative abundance of young 
fish resulting from the spawning of the months March and April 
immediately before. In this way Fig. 20 has been made. 


40 


1908 1909 1910 19/1 19/2. 19/3 10/4 1QIS 19/6 19/7 19/8 1919 192.0 1921 


Fie. 20. Graph showing the productivity of the spawning seasons 
during the years 1908-19. The heights of the rectangles are proportional 
to the numbers of plaice larvae reaching the nursery grounds. 


We see that 1908-11 and 1913 were good years in that 
large numbers of young plaice came on to the nursery grounds. 
The years 1912, 1916, and 1918 were bad ones—years in which 
there was an unusually small production of young plaice. 

It would be unprofitable to pursue this matter further, 
for hardly any data exist, just yet, which would enable us to 
look for the reasons why some years are better than others. 


Tables 21 to 27 now follow: these give the results of 
measurements of plaice made in the Irish Sea during the 
year 1920, and they are intended to provide the data for more 
minute comparisons with the pre-war period than we have 
now the opportunity to undertake. 


156 


Table XXI. June, 1920, Irish Sea: Plaice taken in Fish Trawl. 


HU OUT UU OUT SUAS AU UU 


SWWWWWWWWWNNNWNWNW hb bo 
PADUA OWA SSHISUR EIS 


INSHORE GROUNDS. OFFSHORE 

GROUNDS. 

Length. LIVERPOOL MERSEY NortTH | CARNARVON Via, Vis. 

Bay. ESTUARY. WALES. Bay. 

f ges fiw lee if Piles f Folge if Seales 
ane 19 | 15:5 Bs coe sea | ce 1 2°4 

ae oe 70 Byeil |) il 4 1 9°8 me Ae 
11 L225 164 134:0 1 4 2 19°6 Ih 2°4 
24 PAL BY | AKet#) 154°2 3 1 5 | 49:0 33 eZ, 
119 135°4 | 186 151-7 9 36 1 9°8 3 die, 
170 193°4 | 196 159°9 21 84 1 9°8 12 28'8 
166 USS:Siaa lesa 04:4.) 18 Te 4 39°2 6 14°4 
14551) 65:0 84] 68°5 31 | 124 5 49-0 6 14°4 
81 92°1 | Oomltose 30 120 7 68°6 10 24:0 
48 | 546 46| 375 | 19 | 76 7 686 | 16 381 
45 51-2 | 23 18°8 17 68 12 EG 15 35°9 
30 34:1 25 20°4 17 68 10 98-0 15 35°9 
16 18:2 15 2s, ily 68 8 78°4 22 52°8 

9 10:2) 1) 107) 81 10 £0 al? 117°6 28 67°1 
1 | 33 | 2°4 10 40 12 117°6 40 95°9 

3 3°4 6 49 | 10 40 7 68°6 32 76°7 
2 2B} 2 16 7 28 1 9°8 37 88°7 
a. Le 6 24 3 29°4 35 83°9 
2, 2°3 4 Geel: 9°8 23 55:2 
: Ade } 3 | 12 Bae ae 30 71:9 
. er | 4 | 16 2a 50°4 
: Ba howe | 8 ape 14 33°6 

2 23 (Paes Rr | 4 1 9°8 15 35°9 

1 | iMeali | i | 4 1 9°8 11 26°4 

dé eae 4 vas 5 12:0 

i } 1 4 ee 8 19°2 

| 2 23 fa » 4 9°6 
owe ne. 8 | sae A wd 4 ah 1 2-4 
l IPI 1 Or8r ii sce aa Pe 2 48 

1 Veil i 08 ul 4 il 98 1 2H. 

3 12 
| 879 | 999°8 1,225 | 999°3 | 250 |1,000 | 102 999°6 | 417 | 999-6 


Table XXII. July, 1920, Irish Sea: Plaice taken in Fish Trawl. 


157 


Mean 
Length. 


ID CUR Co hor 


SNM RR Re Re Re Re Re Re 
ICs Tt He CO RIES S 
UC OU OU OUST SUSU SUC SUSU SUS OUT OU 


bo bo kD by by bo 
SSHAANEWNHE 


INSHORE GROUNDS. 


OFFSHORE 
GROUNDS. 


LIVERPOOL MERSEY | NortH | CARNARVON Ville 
Bay. ESTUARY. WALES. | Bay. 
ii th des f aaiiae i ES if ial os J ine as 
ge | Spats Th eo. | - ds sn 
ee ee 35 | 28°6 | 4 Se a A ae 
cm eee 102 83-4 2 1:6 anes “ a 
if al 1:8 144 | 11777 | 17) 1874 = 1 0-8 
8 14:7 187 | 152°9 51 40°3 1 54 6 4-5 
52 958 140 | 114°5 86 | 67:9 ce ae 25 18°8 
67 123°4 83 67°9 123 97:2 l 54 49 | 368 
39 71°8 65 531 117 92:4 2 10°8 100 | 75:0 
33 60°8 54 44-1 | 112 88°5 3 16:2 135 101-2 
20 36°8 BL | ALT. | 395 75:0 9 48-6 145 | 108-8 
25 46:0 44 36:0 118 93:2 iva bod 160 120-0 
37 68:1 61) 49:9 | 125 98°7 19 102°7 108 ~— 81-0 
44 81:0 39 31:9 110-869 16 86°5 126 94:5 
39 71-8 42 | 343 | 83! 65:6 | 23 , 1243 78| 585 
51 | 92-9 20 | 163 59 | 46-6 25 135°1 84 63:0 
$8. | 70:0 25| 204 | 41 32:4 16 86°5 67 50°3 
32 58:9 29 2377) 40, | 3204 33 178°4 53 | 39:8 
16 29:5 19 15°5 25) 19°7 11 59-4 47 | 35:3 
14 258 8| 65 10/ 79 8 43-2 32 | 24-0 
5 9-2 TQ eo Selre' 9 | er 7k 3 16:2 39 | 29°3 
8 14:7 GON fez | 7| 55 2 10°8 29 21:8 
7 12°9 5 4-1 12} 95 2 10°8 17 | 12:8 
2, 3°7 8 65 8 6°3 ie 19| 143 
2 3:7 OF Tt Gap 27 E 6 45 
1 18 4A (33 4| 32 1 0-8 
1 18 3 pr ee | Bee 1 0°8 
ne ae 1 0-8 | 2 | 1°5 
ee . ah 57 ae 1} 0o8 
an aS 5 4] Ee Tol) Os 
l 1:8 2 | 16 en 2 2 
14 ae 1; oO8 1 0:8 - 
ie 2 1:6 | : ae 
. ee eee | eee 
1 0°8 ae 
1 08 oe 
£ as 4 1 0:8 
| eels 
| | 
543 999°7 1,223 | 998°5 | 1,266 1000-0 
| 


185 999°7 | 1,333 , 1000°5 


158 


Table XXIII. August, 1920, Irish Sea: Plaice taken in Fish Trawl. 


Mean 
Length. 


O00 VSS QUES CSRS F210! S31) G3 Gu HX 09 RS 
CULOLOU SUSU OL OU SUSU CUCU CE OU CUCU OL OLA A OT OA OT I 


WWWWWHWHWWWNNWNNNNNNNNR Re ee 


SASHA WYSSSHO1 


INSHORE GROUNDS. 


OFFSHORE GROUNDS. 


LIVERPOOL | 

Bay. | 

Se odaee 
1 0'8 

9 ices 
Sono led 
102 | 83:0 
123 | 100-0 
162 | 131°8 
TSS W222 
108 | 87:9 
110 89°5 
87 70°8 
73 | 59°4 
55 | 44°8 
49 | 39°9 
57 | 46°4 
38 | 30°9 
31 25°2 
20 16°3 
9 83 

7 5:7 

4 Si} 

3 | 2-4 | 

1 0°8 | 

il 0:8 

2 16) 
1,229 | 999°8 


| 


MERSEY Nort CARNARVON VIII... Vile 
~ Estuary. WALES. | Bay. 
f | F loo if Hiehioe if i Fan bs ij ries | f Jouine 
| | 

Tn 54 me = » e 

37,| 28°8 1 132 ae ee es 
147 | 114°3 se 2] 100 tos 
163 | 126-7 : 2) 100 ce! ; 
133 | 103-4 7 85 4 200 2 2°8 | x 
122 | 94-9 45 | 54:9 2" | S100 157) 20°F <: 
117; 91:0] 96 | 115-9 3| 160°) ) 2aeieare7 Shite 
71 | 55:2} 99 | 120-7 1/ 50] 53} 741] 26 

82} 63°99) 79 | 963| 2) 100) 64) 89:5) 51 

59 ©45°9| 69] 84:1 2/ 100! 62] 86:7| 80 

40 | 31-1 77 | 94:0 1 50 63 | 881 94 

540) "42-0)| 58) |) 70-7 | 1! 50 56 | 783] 92 

Sia e28'Sii, eo oe | eG4cGil ee 69 | 96:5] 105 

34| 264] 45] 54:9] BI) 713) 07 

34 | 264] 30] 36°5 | 61 | 85:3] 87 

42 | 32:°6| 37) 45:1 42 | 58:7] 94 
26 | 20°2| 36] 43:9 34 | 47:6| 65 
16 || 12:4) 20 | 24-4 26 | 364] 52 
25 | 194] 20] 24-4 125) 16 Sees 
LOM © TS 15) 1456) 154) 20:5 14 

127) 9:3 13 | 15:8 |) 5 15 

6) 46 4] 49] | 9°8 10 

i 0-8 7 8:5 Sal) ps2 1 

31) 2:3 7 8:5 16 | 22:4 4 

14) 40:8 3| 3:6 6 8:4 1 

eel 1 1-2 2 2°8 | 1 
See GIN oe 1 1:2 3 4-2 | 1 

1) OS): eee ss 3 CED A eke 

1 0:8 1 1:2 1 iA 
Wiens a 4 56 1 

s | 1 1-4 1 | 
re | | 1 fe er 
1 0:8 | | 
| | 
1,286 | 999°9| 820 | 999-6} 20 | 1,000 715 | 999:°0| 919 


159 


Table XXIV. September, 1920, Irish Sea: Plaice taken in Fish Trawl. 


INSHORE GROUNDS. 


Mean 
Length. LIVERPOOL MERSEY Nortu | 
Bay. Estuary. WALES. XCAe IXs. 
ij | if We J f Wee 1G ' i Wen | I Hj Ghee J | ih Thee 

10°5 | Tie roe 
115 | 1 18 Fl aes 
12°5 ’ 10 18-0 1 0-6 
13°5 : te ae 25 45:1 4 | 2:5 
14:5 2 0-9 5 6:7 | 29 52° 10 6-1 
15°5 10 4:7 10 13:3 SR 56:0 18 11:0 
16°5 6 2°8 26 | 34:7 29 52:3 4 | 2°5 
17°5 Be gaye 46 61:4 i nee 46 82:8 45 |» 27°6 
18°5 74 | 34:7 43 57°4 6 27:0 49 | 884 lll | 67:5 
19°5 139 65:2 58 77°4 11 49:5 | 59] 106°5 178 | 109-2 
20°5 203 95°3 70 93°5 24 | 10871 87 | 157-0 200 | 122-7 
21°5 246 | 115°4 64 85°5 23 | 103°6 58 | 104°6 179 | 109°8 
22-5 274 | 128°6 77 | 102°8 21 94-6 26 | 46-9 151 | 92:6 
23°5 239) |) 12-2 56 74:8 17 76°6 28 50°5 100 | 61-3 
24°5 191 89°6 56 74:8 17 76:6 9 16:2 78 | 47:9 
25°5 154 72°3 48 64-1 15 67-6 LS ie 82-5 63 38:7 
26°5 114 53°5 31 41-4 2D 99°] || BOR Z/ 51 | 31:3 
27°5 90 42-2 33 44°] 17 76°6 12 21°7 54 33°1 
28°5 96 45:0 34 45°4 12 54:0 7 12:6 40 | 24:5 
29°5 75 35°2 26 34:7 15 67°6 5 | 9-0 46 28-2 
30°5 51 23°9 14 18:7 11 49°5 3 54 42| 25:8 
31°5 37 17°4 7 9°3 4 18:0 3 | 5-4 49 301 
32°5 28 13°1 ll 14:7 2 9-0 | 33 20:2 
33°5 37. | 174 9) 120 2 9:0 ie 46 | 28-2 
34:5 14 6:6 10 13°3 2 9-0 2 3°6 337 |e220;2 
35°5 5 2°3 3 4-0 - 30 18:4 
36°5 5 Oe 1 1:3 l 45 14 86 
37°5 1 0°5 4 5:3 18 | 11-0 
38°5 1 0:5 I 1ic33 | 8:0 
39°5 : 2 2°6 | 5 all 
40°5 ie 1 1:3 2 1:2 
41°5 Daleme Ors a . 3 1-8 
42°5 Me 1 1:3 aoa ; 
43°5 l 1:3 (eres 
44:5 | oe 10 PO:6 
45°5 1 1:3 3 | 1:8 
46°5 see we 
475 1 0°5 
48°5 
49°5 | eM ec 
50°5 1 0°6 
51°5 | ae 

2,131 | 1000-0 749 | 999-7 222 | 999-9 554 | 999°3 1,630 999-1 


Mean 
Length. 


CO OI ON I ON OO I ll cell cel 
CRU SU SUSU SUSU SUSU SUSU THT UU SUSU 


HKESOHDADARWNESHSHAANKEBWNHSOHAIBDUEWNIHOS 


PRP WWWWWWWW WWI h 


Table XXIV—Continued. 


OFFSHORE GROUNDS. 


1 


60 


IXc. 
| if haeias | 
| ha est hekees ox 
| 1] 526 
3 157°9 
iI 52°6 
2 105°3 
2 105°3 
3 157°9 
1 52°6 
| "3 | 157-9 
| 2] 105°3 
|} 1| 526 
19 1000°0 


IXp. 1X34. TXs,. TX43. 
Go flee) | Flee. | 0 Nace eerie) mea 
| wae | eee . on 
| 8 10:0 2 375 30 200 ot : 
| 29 36°3 1 Loy 2 | | goat 1 1-9 
57 71°3 6 10-4 7 20-4 8 15:5 
59 73°8 18 31:3 21 60°3 21 40°8 
69 86°3 31 53°9 37 | 106:3 45 87:4 
| 74 92°5 51 88:7 22) (63:2 63 | 122°3 
| 59 72°8 41 71:3 20 57:5 81 | 157°3 
74 92°5 52 90-4 22 63-2 74 | 143-7 
56 70:0 47 81:7 29 | 83:3 ol 99:0 
55 68°7 61 | 106-1 29 | 83:3 60 | 116°5 
63 78:9 58 | 100-9 32 | 92-0 46 89°3 
47 58°8 62 | 107°8 30 86:2 25 48°5 
43 53°7 45 78:2 16 46:0 16 31-1 
| 36 45:0 43 74:8 21; 60°3 14 27:2 
| 27 33°7 23 40-0 Use) S17 3 58 
| 25 313 20 34'8 15 | 43:1 2 3°8 
| 9 11°3 6 10-4 yi) api 3 58 
| 8 10°0 1 7-0 9 25:9 l 9 
|) al 13 2} 3-5 3| 86 _ 
hoe 13 1) 47 ei 86 Wess 
ren ‘ Dill) 16:7 i 
| 33/17 .8-6r 1} Oe al ee 
| . a 1] 19 
on . see o- aoe 
38 sibs 
| l | ioy/ 
| | 
| | | 
800 | 1000°5 575 | 999°8 348 | 999-7 515 | 999-7 


161 


Table XXV. October, 1920, Irish Sea: Plaice measured. 


Mean 
Length. 


=) 


ee SS 
GO 1S? OTH OS tS 


9 NO) 5S COUT S9) OU HO BO) Onc 100) AS OU CR SS) 
CU OU St SU GU US SUSU TC STU STUOUOTU SU TUT HTT TUT TU 


ee Oo OO OO OO OOO 
OAS oS w eOowe 


oe 
Iie) 


Liverpoon Bay. | Mersty Estuary. 


Ue are F Loo 


5 | 13 
a5) 7 
3 86 

5 256 

ifs 281 

33 +O 165 
6 9:9 142 
19 314 132 
29 479 95 
51 843 96 
65 107°4 89 
67 110°8 45 
sl 133°9 51 
64. 105-7 45 
47 TTT 22 
$75) 57:9 Dal 
yy 52°9 25 
22, 36°4 23 
19 31°4 22) 
32 52°9 16 
9 14:9 10 
11 18°2 10 
4 6°6 6 
3 5:0 3 
2 33° 3 
3 50 
1 ie7/ 1 
1 

605 1000°2 1,672 


NortrH WALES. 
holes i Peles 
| 
eA Wiel oak ; 
4:2 | 1 ii} 
51:2 eis was 
153-1 iT 13 
1679 | 8 10°5 
987 | 19 24:8 
84:9 | 62 81-0 
| 189 | 125 163°4 
56:8 74 96°7 
57:4 80 104-6 
| 53°2 41 53.6 
26°9 49 64-0 
30°5 38 49°7 
26°9 47 61:4 
jess 53 69°3 
161 41 53°6 
15-0 36 47‘0 
13'8 33 43°1 
13:1 15 19°6 
9-6 8 10°5 
| 6-0 11 14-4 
6:0 ai 91 
3°6 4 5:2 
18 8 10°5 
18 3 39 
Ss 1 “3 
06 
0'6 

999°8 


999:4} | 765 
| 


162 


Table XXVI. November, 1920, Irish Sea: Plaice measured. 


INSHORE GROUNDS. | OFFSHORE 
GROUNDS. 
Mean | ie. 
Length. | LivERPOOL | MeERSEY Nort SoLway 
| Bay. | Estuary. | WALES. Firtn. Xo. 


Hh, ales | ij Tlb6 if fe oo | i i Slee f | f oles 


| | 

11:5 a sa hel ae 
12°5 1 0-5 | 4 | oe 
136 ies wir, MS 12:3 | | 16) ay 
145 | 1 Ls 49 263 21| 62 
155) | a 1 18 161 864 24 71 
16°5 2 0-9 ar cf i 18 | 282 |) [bia Ws Sito 
17°5 18 7:9 1 15-4 12 S11 | “272 P1460 ee 86 
18°5 60 26°4 1 15°4 22 40-1 184 98-7 55 | 163 
19°5 li 48°8 4 615 44 80°3 202 | 108-4 82 24°3 
20°5 167 73°4 a mi 48 876 | 144 173 93 27°5 
215° )'229)) 97:6 6 92°3 49 89:4 | 145 778 149 44°] 
22-5 255 | 112:1 4 | 61:5 55 | 1004 | 106 56:9 | 212 62:7 
23°5 294 | 129-2 3 4671 26 47°4 100 53:7 | 288 | S38 

24°5 | 290 | 1274 | 3 | 461 S5 ep Ooser|) | bal 38°] |) so27 96°8 
25°5 236 -103°7 11 | 169-2 36 65:7 43 231 | 352 | 104-2 
26°5 143 62-9 2 30:7 31] 566 | 16 86 | 322 95°3 
27°5 100 44-0 3 46°1 31 566 | 14 75 280 82°9 
28°5 93 40°9 3 46:1 2 530 | 18 97 | 225 | 66:6 
29°5 82 36:0 7 | 107-7 24] 43:8 7 38 | 210 62:1 
30°5 59 259 4) 61:5 19 34:7 4 21 181 53°6 
315 40 176 3 46:1 10 18-0 6 3:2 126 37°3 
32°5 36) 15:8 | ss 15 | 27:4 1 05 | 92) (272 
33°5 30 iS Srie | 2 30:7 16 29-2 4 21 77 22-8 
34:5 7 Spe) l 15-4 4 73 2 11 57 16-9 
35°5 19 8:3 1 15°4 7 12°83 | 2 el 50 148 
36°5 2 0-9 ; 7 12S 3 16 | 35 10°3 
37°5 2 0-9 1 15-4 5 971 f F 16 47 
38°5 1 0-4 2 30:7 5 9-1 25 Pall 12 36 
39°5 be oat 3 55 1) O35 6 1:8 
40°5 ie 1 15-4 | 4 7:3 a 5 15 
41-5 0-4 | 1 154 | 1 18 2| 06 
42°5 1 0: ee 4 7:3 1 0:3 
43°5 4 ik 1 18 I 03 
44:5 : | : l 0:3 
45°5 2 3-7 | 1 0:3 
46°5 oe | . eee 
475 a aK 1 15:4 |... ta) ate sax) pee 
48°5 os, bbs a ti Ah cee3 ote. 1/12 gees ile) aise eed 03 
49°5 a ae F: 2S he re oe ee te oe $ 

2,275 | 999-8 65 | 999°5 | 548 999:1 | 1,863 | 999°8 | 3,379 | 1000-2 
| 


Table XXVII. 


163 


December, 1920, Irish Sea: Plaice measured. 


Mean 
Length. 


~ 
is . . . . . . . . . . . 
TST Ot Or Cr Ot Ot Ot Ot ST St Oc St St Gr Gr Gt Ot Ot Ot Gr Or 


SS 
“ 


ee 
: AL 
Or Dr Ot Ot St St St Oi Or 


| LIVERPOOL 
Bay. 


Re WOR OO 


Cre soe Ole ST 


to 


SMOMMWA-TI-I1¢ 


~ 


999°7 


MERSEY 


NortTu SOLWAY 
WALES. FIrtHu. 
i alee i | bieal er 
2, | 1-9 
Si) aRe7 
42 | 40-2 
76 72:8 
2 1-6 128 | 122°6 
BY 152 | 1456 
_ : 182 | 1743 
10 8-0 129 | 123°5 
27 216 87 83°3 
29 23:1 73 69°9 
42 | 33°5 59 56°5 
40 | 31:9 40 38°3 
44 | 35-1 30 | 28:7 
62 | 49°5 Hd eatiss: 
58 | 463 15 | 14:4 
70) 560 4 3°8 
75 | 59:9 4 3°8 
HUST 30072 Dee 
108 86-2 1 1:0 
113 90-2 e 
105 | 839 
82 65°5 are 
59 47°] 1 1-0 
54 | 43-1 | 
35 | 27°9 
32 | 25-6 
18 | 14:4 
12| 96 
8 6:4 | 
9 2 | 
7) 956 
3) 2-4 
6 4°8 
7| 56 
4 a2 
1 0-8 
2 | 16 | 
3 2:4 | 
6| 48 lee 
3 2°4 : 
1 0°8 | e 
2 16 = 
252 | 999°8 | 1,044 | 999°8 


— 
. 


164 


The Effect of the War Restrictions on the Fisheries. 


It will be seen, then, that the results of the Irish Sea 
investigations give little evidence that the restrictions that 
were in operation during the years 1915-18 had any very marked 
effect. Now we must not assert this conclusion as holding 
for any other fishing region than that studied here: There is 
evidence that the war restrictions had an effect in the North 
Sea—although this evidence is not entirely convincing. So 
far as it goes, however, it suggests that during those years in 
which the ordinary intensity of fishing (that characteristic of 
the pre-war years) was in operation, there was a gradual 
falling off of the quantities of plaice landed, as well as in the 
average quantities caught per day’s fishing. This decline 
persisted throughout the years 1908 to about 1914. Then 
followed about five years during which the existence of mine- 
fields, and other conditions, greatly reduced the area over which 
steam trawlers and smacks could fish. When it became possible 
to resume trawling on a scale comparable with that of the pre- 
war years it was seen that the quantities of plaice landed per 
day’s fishing had increased. At the same time measurements 
made at sea aboard the fishing vessels showed that the plaice 
were, on the average, markedly bigger than they were in, say, 
the year 1915. The natural conclusion was that the reduced 
fishing in 1914-1918 had allowed the plaice, that would 
otherwise have been caught, the opportunity to live and grow. 
In 1919, therefore, there was an “* accumulated stock ” on the 
North Sea grounds, the results of a period of ** protection.” 


Now when the same argument is applied to the Irish Sea 
grounds the same conclusion follows. There was evidence of 
a decrease in the abundance of plaice during the pre-war 
years and there was a marked restriction in the intensity of 
fishing during the war years. In 1920 the size of plaice had 


165 


increased, and, on the whole, better catches seem to have 
been made. But the evidence brought forward in this report 
also shows, we hold, that this variability in the size and 
abundance of the plaice inhabiting the Irish Sea is something 
that happens, “ of itself,’ that is, quite apart from the influence 
of the fishing fleets. Throughout the period 1892-1920 there 
is good evidence of a natural fluctuation m the abundance of 
plaice, some series of years being very good, while others 
are relatively very bad. The evidence we refer to is all 
experimental, but it is backed up by what we do know about 
the fluctuations in the quantities of plaice landed by the 
steam vessels and other trawlers working in the Irish Sea 
area. Further, the conditions in the English Channel seem 
to resemble those obtaining in the Ivish Sea. 

If there had been no war, and no restrictions on fishing 
in the Irish Sea, the result to have been expected would have 
been just that which we actually observe—the progress of a 
natural fluctuation in the abundance of plaice. If only the 
measurements and other data which we give here, or which 
are otherwise obtainable, were at our disposal, and no knowledge 
that there had been a state of war during the years 1914-1918, 
we should have been quite unable to deduce the latter. All 
we should have known would have been that, for some reason 
or other, vessels did not go to. sea so frequently in 1914-8 as 
they did in the year previous to 1914. 

These results obtained from a study of the West Coast 
fisheries naturally make us cautious in accepting, without 
reservation, the conclusion that the effect of the war restrictions 
was an increase in the stock of plaice inhabiting the North 
Sea. The natural fluctuation which, we believe, characterised 
the Irish Sea during the years 1892-1920 may, quite reasonably, 
be supposed to have characterised the North Sea also : it 1s to 
be noted that the statistical information relative to the latter 
area is very defective for the years before 1908, and between 


166 


that and 1914 is only a very short period. The conditions, then, 
that have been observed in the North Sea are consistent with 
the belief in a natural fluctuation as capable of explaining, 
to a certain extent, the variability, from year to year, in the 
productivity of the fishery. 

“To a certain extent ” only, we may add. Probably the 
Trish Sea is a more productive area, as far as plaice is concerned, 
than the North Sea. The “ productivity ” depends on the 
existence of the shallow-water nurseries. Just because the area 
of such grounds is greater in the Irish Sea, relative to the 
total area of sea, so we expect a greater production of plaice. 
Probably the exploitation of the North Sea, that is, the amount 
of trawling per square mile, per year, is greater than it 1s in the 
Irish Sea. If that is so then the natural fluctuations that we 
are assuming would be more easily noticeable in the eastern 
than in the western region, particularly if, as may be assumed, 
the exploitation in the North Sea is pressing closely on the 
recuperative power of the nurseries. 

It is quite unlikely that the data exist which would enable 
us to answer the questions suggested above. ‘The fishery 
statistics are too imperfect prior to 1908; the work of com- 
parison of the productivity of the fishing grounds before and 
immediately after the cessation of war was not thorough enough, 
in any British fishing ground ; we have no available knowledge 
of the extent to which military restrictions actually prevented 
fishing in the various regions ;_ no detailed classification of the 
‘plaice fishing grounds ” that is of much use, and, of course, 
not nearly enough knowledge of the life-history of our species 
of fish. It is regrettable that the opportunity for studying 
the very remarkable conditions that the war-restrictions 
afforded was not taken full advantage of in 1918 and 1919 
by any European fishery authority. 


167 


BARE IV, 
PRACTICAL ADMINISTRATIVE QUESTIONS. 


One reason why these researches were undertaken was to 
provide information that would be of use to the administrators. 
It was assumed, to begin with, that there might be an 
impoverishment of the Irish Sea plaice fisheries, and that 
something might have to be done to arrest this. In the past 
that “‘ something” has generally been a legislative restriction 
or prohibition—-that is, the fishermen have been forbidden to 
do this or that at one time or another and have been prosecuted 
when they insisted on doing whatever was forbidden by 
by-laws or statutes. Lately, the tendency has been towards 
constructive administration—scientific research, the dissemina- 
tion of intelligence or the promotion of schemes of development, 
but so little successful has this kind of work been in England, 
that it may be regarded as rather alien to the traditions (such 
as they are) of fishery administration. Here, therefore, we 
are obliged to suggest in what directions the results of investiga- 
tion pomt—those directions being assumed to be restrictions 
of one kind or other. We assume that such questions as these 
are beimg discussed—the prohibition of fishing in certain 
places or at certain times ; size-limits below which plaice may 
not be legally captured or landed ; prohibitions or restrictions 
of the operations of vessels propelled by steam or internal 
combustion engines ; restrictions on the dimensions and forms 
of trawl, or other kinds of nets, etc. Now a full discussion of 
such measures can only be attempted when there are definite 
proposals, and so we can only indicate, in the most general 
kind of way, how the data summarised in this respect are to 
be used. We begin with the question—/s there an impoverish- 
ment of the Irish Sea plaice grounds ? 


168 


The Productivity of the Fisheries. 


By “ productivity ” we mean the total quantity of plaice 
which grow up, in a definite region, to a certain size, in a 
certain period of time. It is necessary to specify the size 
because it is only when the fish become so large that they 
become commercially valuable, and so become commodities. 
That means that the idea of productivity must necessarily 
include the idea of commercial profit. 

Suppose that plaice only become commercially valuable 
when they have attained the size of about 20 ems., and the 
age of about three years. To convert a hundredweight of 
13 em. plaice into 2 ewts. of 20 em. plaice will require a certain 
quantity of production in the sea and this will be much the 
same as the production necessary to convert 1 ewt. of 20 em. 
plaice into 2 ewts. of 25 cm. plaice. Yet the latter production 
will have more commercial significance than the former quantity 
because 25 cm. plaice have more value, as commodities, than 
20 cm. plaice have. Production, in the scientific sense, means 
the origin in the sea of plaice substance but, in the commercial 
sense, it means the origin of plaice of the range of size that 
sells in the markets. What the industry want is plaice of this 
range of sizes and if such fish decrease in numbers the 
‘“ productivity ” of a fishery region decreases. 


The Rate of Exploitation. 


The total quantity of plaice that are landed annually 
depends not only on the productivity of the region in question, 
but on the degree to which it is fished. If there is an increase 
in the catching power there will generally be a corresponding 
increase in the quantity of fish landed. To find whether or 
not there is any change in a fishing region we require to know 
whether there has been any change in the catching power 
employed, and this is always a very difficult question. Plaice 
are caught by steam vessels, motor boats, smacks and _half- 


169 


decked sailing vessels; by trawl-nets, seme-nets, stake-nets, 
trammels, etc., and so we must have some idea what all this 
variety of catching power means when it is reduced to a 
“common denominator.” A steam trawler will catch more 
fish per day than a smack and a smack will catch more than a 
half-decked sailing boat. But does the steam trawler catch 
more fish per unit of man-power, or per £ invested in her 
maintenance than does a smack? And which rate—the rate 
of catch per day, or per man, or per £ ought we to adopt ? 
The ratio of steam vessels to smacks that work on a certain 
fishing ground is not always the same and we cannot, usually, 
neglect the fishing by half-decked sailing vessels and motor- 
boats. What, then, is to be the “common denominator” ? 
We may calculate how many small trawlers are equal in 
catching power to one smack, and then how many smacks 
equal one steam trawler. Thus we can express the catching 
power in ideal vessels, or “fishing units,’ or we might try to 
calculate the number of hauls made per week or day and then, 
knowing the average size of the trawl-nets used, calculate the 
number of square miles of sea bottom swept per day. Any 
sort of calculation made in these ways would be a rough one 
since we have not much exact knowledge of the conditions. 
In practice, what is done is generally to calculate the average 
quantities of plaice caught, per day’s absence from port, of 
an average steam trawler or smack. If this decreases we say 
that the productivity of the fishing grounds worked also 
decreases—noting all the while that our quantity of fish 
caught is fish of a certain, chosen range of sizes. Obviously 
the results are rough ones in any case and too much strain 
must not be put on them. Whatever changes in the results 
of fishing we observe must be big enough to be much the same 
(that is, to show much the same tendencies) in whatever way 
we estimate the change in catching power. Thus the quantity 
of plaice annually landed in England, from the North Sea 


170 


grounds, diminished from 1908 to 1913, and so did the average 
quantity of plaice caught per day’s absence from port of the 
average steam trawler. 

Of course the whole question is a rather academic one : 
what the owner of a steam trawler has to consider is the 
average cost of catching the average cwt. of fish and then the 
average price obtained when it is sold. 


The Impoverishment of a Fishery Region. 


For the moment we deal with plaice of a definite range 
of size—say, 20 to 25 cms. (small plaice). Suppose that the 
productivity of a certain fishing region is “ indefinitely great,” 
no matter how many plaice are caught there would still be 
plenty left—that would be what we mean by “ indefinitely 
great.” So many small plaice are produced that a certain 
fraction must die from want of food: now if, say, 1/LOth are 
caught by the fishermen that would mean that about the 
same number would not die, but would survive to take the 
place of those that had been caught. Probably some localised 
fishing regions are like this—they are “‘ overcrowded ”’ grounds. 
On the whole, however, such an area as the Irish Sea is not 
an overcrowded one, where the productivity is indefinitely 
ereat, for the fact that the abundance of plaice undergoes 
periodic changes shows ether that the quantity of plaice food 
changes, or that the quantity of baby plaice spawned, hatched, 
and transformed changes. Probably the latter is the case. 


Has there been an Impoverishment of the Irish Sea Plaice 
Grounds ? 

To answer this question we have to consider both the 
commercial statistics and the results of experimental trawlings. 
The quantity of plaice landed from year to year depends on 
the catching power and the natural productivity of the grounds. 
The statistics of catching power are not very accessible (if they 
exist), but it is probably the case that it has not decreased 


171 


of late (except during the war years). The number of steam 
vessels working from Fleetwood has increased, and though 
most of these vessels fish outside the Irish Sea region it is 
likely that much about the same fraction of all of them trawl 
on these grounds each year. The number of smacks working 
from Fleetwood and Hoylake has steadily decreased since about 
1890, and there are no indications that the number of half- 
decked sailing boats has increased. But the increase in 
number of the steamers probably makes up for the decrease 
in the smacks and the decrease (“if any ’’) in the small boats. 
Probably, then, the catching power is approximately uniform 
or has increased. 

So far as the commercial statistics go they show that 
there are marked ups and downs in the quantities of plaice 
landed from the Irish Sea. There was a maximum in 1911, 
a minimum about 1915, and another maximum about 1920. 
Thus there is no definite tendency one way or the other, so 
far as these data enable us to discuss the question. 

So far as the experimental trawlings go the same conclusion 
is to be made. There are ups and downs, and these are nearly 
the same as the changes revealed by the commercial statistics. 
In fact these two series of data support each other to a certain 
extent and indicate that there have been actual changes in the 
natural productivity of the Irish Sea grounds during the period 
1908-1920. 

When we deal with the measurements of lengths of plaice 
caught on the fishing vessels (steamers and smacks) and caught 
experimentally there is rather more trouble, because there are 
so many ways of going wrong in our deductions. “* Lumping ”’ 
of the various grounds in even such a small region as the Irish 
Sea is fatal. In the winter of 1920, for instance, a fairly large 
number of plaice were measured on the Solway grounds and 
these were all rather small fish (see Tables 26, 27). Also 


2,275 plaice were measured on board a steam trawler working 


172 


just outside the territorial limits in Liverpool Bay (Col. 1 of 
Table 26), and these fish also were unusually small. Now 
these grounds were not worked in the corresponding months of 
any of the previous years, and so (just because of this difference 
in the sampling methods) the size of plaice on the “‘ North-west 
Coast region”? would have appeared to have diminished in 
1920 as compared with previous years. Therefore we must 
distinguish, to a rather fine degree, between the various grounds, 
and we must compare, with each other, only rather small areas. 
Kven then there are “accidental” variations that might 
mislead us. Thus a good breeze of wind may make a 
perceptible difference in the kind of plaice found on a ground 
in the course of a few days. We have seen, however, 
that it is not the difference in the rate of growth that 
makes the fish on a ground appear to be bigger in some 
years than in others, but rather the varying proportions of 
older and younger plaice. That means, then, that more fish 
are spawned, transformed, and reared (one or all) in some 
years than in others, which means, again, that some years are 
more productive than others. So there is a good deal to be 
made out of the length measurements—if we are critical. 
If only we had had good series of plaice measurements in 1889 
(when the regulation began in Lancashire) the questions pro- 
pounded now would have been more easily answered. Perhaps 
this is the most convincing argument for the future utility of 
the series of measurements recorded in this report. 


Is there an “ Accumulated Stock” ? Does Increased Fishing 
tend to make the Fish run smaller ? 


An “accumulated stock” of plaice means that the fish 
grow old more rapidly than they are caught. There is no 
accumulated stock in Liverpool Bay because the plaice migrate 
out from this region as they grow old. But even if the natural 
conditions were such that plaice of five or more years of age 


173 


preferred to remain in Liverpool Bay they would probably 
not be any more numerous than they are at present. There 
are fewer fish of six years old than there are of five, fewer of 
five than there are of four, and so on, and therefore trawling 
affects the abundance of larger fish more than it affects that of 
the smaller ones. There is so much trawling in Liverpool Bay 
that the abundance of these larger fish would be kept down, 
even if the grounds were natural ones for such plaice. 

On the other hand we do seem to have an accumulated 
stock of plaice in Luce Bay. We have reasons for believing 
that fish that have spawned on the northern grounds migrate 
into the Bay when they become spent. They are protected 
there because trawling is effectively prohibited by the Fishery 
Board for Scotland, and the other methods of fishing that are 
practised are probably quite insufficient to bring down the 
numbers of the big plaice (up to 65 cms.) that are found there. 


Did a Stock of Large Plaice accumulate in the Irish Sea during 
the War Years ? 

We have discussed this question in the preceding pages 

and find that there is no very good evidence that such an 
accumulation took place. 


Our conclusion is, therefore, that there is no reliable 
evidence in favour of the conclusion that there is an impoverish- 
ment of the plaice grounds of the Irish Sea due to over-fishing. 
But it may be said that the plaice there “run rather small” 
and that they might get bigger and so become commercially 
more valuable if there were size-limits, or restrictions of other 
kinds. This further question must briefly be considered. If 
We could, by any means, raise the prevalent size of plaice from 
(say) 23 to 30 ems. the same total weight of fish landed would 
be more valuable. If, further, we could so legislate that the 
same numbers of plaice would continue to be caught, but that 


174 


the prevalent size of these fish would be 30 instead of 25 cms., 
the fisheries would become still more valuable. Apparently 
it is some such ideas that are at the bottom of any suggestions 
for size-limits, ete. 


The Possible Effects of Legislative Restrictions. 


The only kinds of restrictions or prohibitions that seem 


b) 


to be “ practical politics” are (1) the closure of spawning, or 
nursery grounds, and (2) the imposition of size-limits. One 
may ask, first of all, whether it is practicable to enforce such 
restrictions or prohibitions. Of course this is no business of a 
scientific investigator any more than it is the business of the 
Central Authority (which has, of course, no power of actual 
fishery regulation, but is only responsible for the approving, 
or initiation, of policies). Still the whole affair, that is, the 
initiation, approval, and enforcement of legislative proposals, 
ought to be one, and any person that recommends a policy 
ought to be prepared to consider whether or not it is practicable. 
He ought also to consider in what way it is going to affect 
the existing fishery customs and populations. It must be said 
that a fair amount of actual contact with the fishermen of this 
coast, and some experience of the difficulty and enforcing highly 
unpopular restrictions does not encourage us to regard anything 
of the kind with much favour. 


The Protection of the Spawning Grounds. 


Should we add significantly to the number of marketably 
valuable plaice in the Irish Sea by preventing the capture of 
spawning fish on the Solway grounds? Any measure of this 
nature would mean the closure of a fairly well-defined area, 
and the employment, therefore, of an efficient police. It is, 
further, an “international” question since the area is mostly 
outside territorial waters. We are not certain, in any Case, 
that it is the eggs and larvee of the plaice, in the Irish Sea, that 


175 


ought to be protected should we have to admit that there 1s 
progressive improvement of the grounds. Evidently, then, this 
question need not be further discussed in the meantime. 

The Question of Srze-linuts. 

First of all one asks how any specified size-limit would 
affect the various classes of fishermen on this coast, and what 
is to be the size-limit? Those that have generally been 
discussed are 20 and 22 ems. (8 and 8? inches). Such a 
restriction would mean that a certain fraction of all the plaice 
caught by the inshore trawlers (the few smacks, the half- 
decked sailing vessels and the stake-net fishermen) would have 
to be returned to the sea. The length-frequency distributions 
tabulated in this report for the various areas and seasons enable 
us to state approximately what this fraction of rejected plaice 
would be. If the limit were 20 cms.—and still more if it were 
22 cms.—the fraction would be so great that the restriction 
would interfere, in a most serious degree, with inshore fishing 
on the North-western Coasts. It would be most strongly 
resisted by a class of fishermen who are, by no means, 
inarticulate. The question, however, may be deferred until 
definite proposals have been made. 


How would it affect the Smacks and Steam Vessels ? 


There are now so few smacks left that the question has 
little significance (except for the few smacksmen, of course). 
At any rate the Imish Sea smacks fish in the summer mostly 
for soles, and small plaice on the sole grounds are not very 
numerous. <A size-limit of 20 ems. (or even one of 22 cms.) 
would make little difference. 


How would it affect the Steam Trawlers ? 


Col. 1 of Table 26 represents the catches made by a 
steam trawler working on a small fish-ground. Even a size- 
limit of 22 cms. would obviously mean that a large proportion 


176 


of the total catch made would have to be rejected. But a 
useful answer to our question hinges upon information as to the 
extent to which such small plaice grounds ave generally worked 
by local steam trawlers, and we do not know whether or not 
that information is obtainable. 

Also, we must consider whether small plaice caught in 
the large trawls—and long drags—of smacks and steam trawlers 
can be returned to the sea alive. Undoubtedly the business of 
trawling could be so conducted as to allow most of the small 
plaice to be put back alive into the sea. Without doubt the 
nets could be so made as to allow small plaice to escape through 
the meshes (when valuable soles would also escape, in the 
case of the smacks). But all this depends on the willingness 
of skippers to work regulations which could hardly be enforced 
upon them—as things are. For one must never forget that 
it is of little use to discuss such proposals as these without also 
considering their obvious consequences—which are a much 
more elaborate (and expensive) system of fishery police than 
exists at the present time. 


The Possible Effect on the Fisheries of a Size-limit. 


Merely to prevent the trawlers from catching—or selling— 
plaice of less than 20 or 22 cms. in length means nothing but a 
restriction: we have to investigate what would be the effect 
on the Irish Sea Fisheries as a whole. The restriction might 
be expected to deter the steam trawlers from fishing on the 
small plaice grounds (always supposing that they do fish there 
to an appreciable extent); if they do go to these grounds 
they go to make money by getting marketable plaice. and if 
they are prevented from getting them there they will have to 
go further and so spend more money in catching the same 
value of fish, for otherwise they would not go to the small 
fish areas in preference to going to the more distant grounds. 
We are expected to convince them, therefore, that it will be 


ft 


more profitable to refrain from catching small plaice near the 
territorial limits because these small fish will become big ones 
a year or so later, and then the big fish can be caught on the 
more distant grounds. The argument runs thus: Small plaice 
of about 25 ems. migrate out from the shallow-water grounds, 
and they grow more quickly when they so migrate. Thus an 
hundredweight of plaice of 25 cms. in length will become 
about 14 ewts. of plaice of 30 cms. long as the result of a year’s 
erowth. Better then not to catch the fish until they are 30 cms. 
long, for then they are worth much more in the markets. 
And certainly the data given in the foregoing pages do 
seem to lend some support to the kind of argument indicated 
above. Out of every 100 plaice marked and liberated on the 
Nelson Buoy grounds in the summer months about 2 migrate 
into the Red Wharf-Beaumaris Bay region in the latter months 
of the year. These are the bigger fish and their mean size is 
about 25 cms., whereas the mean size of all the fish when marked 
on the Nelson Buoy grounds is about 21 cms. Next we mark 
and liberate plaice caught on the Red Wharf-Beaumaris Bay 
grounds, and we find that out of every 100, 9 are caught on 
the southern grounds—in Carnarvon and Cardigan Bays, in 
St. George’s Channel, in the Bristol Channel, and on the 8.E. 
Coast of Ireland. These also are bigger plaice than those that 
were marked: their mean length is 30 cms. as against 24 cms. 
Therefore about 75th °% of the percentage of the small fish that 
inhabit the nursery grounds in Liverpool Bay can be shown to 
migrate and grow up during the two to three years following 
the date of liberation into medium and large fish. Protect a 
large quantity of the small plaice from being caught on the 
nurseries and we therefore get a small, additional quantity on 
the offshore grounds, where the fish run much bigger in size. 
This, we take it, is the argument for the imposition of size 
limits. 
M 


178 


The very Theory of this Argument implies Differential Legislation. 


Obviously one robs the fisherman, Peter, in order to benefit 
the other fisherman, Paul! In order to increase the quantity 
of medium and large plaice on the grounds frequented by the 
smack and steam trawlers we deliberately restrict fishing on 
the grounds frequented by the small sailing vessels. We must 
contemplate, if our policy is to be effectively carried out, 
curtailing the earnings of the poorer class of fishermen m order 
to increase those of the owners of the smacks and the industrially 
organised steam trawling fleets. Now this may be “ quite all 
right.” It may be expedient that the small, unorganised, 
individualistic, inshore industry should be sacrificed in order 
that the highly industrialised and capitalised industry should 
continue to make progress, and that all the world and his wife 
should have abundant (if rather stale) plaice. It may (and we 
like to think that it will) be the case that an organised steam 
fishing industry should assimilate itself to the “ State ” in some 
way not yet specified very clearly—tfor obviously differential 
legislation that boosts the big industry, employing State services 
for this purpose, ought to expect a quid pro quo. Now the 
scientific calm of this discussion would evidently be broken up 
as the result of a further development of this line of thought, 
and so wedropit. Itis sufficient to have pointed out that some 
policy or other must be clearly stated and adopted before the 
question of size-limits can be resolved. 

Finally we can look at the matter from a rather sordid 
(and, therefore, thoroughly practical) pomt of view. Some 
steam-trawlers fished just outside Liverpool Bar, and up 
towards Nelson Buoy, in November of 1920 and caught 
considerable quantities of quite small plaice. It is also said 
that they made a lot of money.* If they had not trawled 
there, and so avoided catching the small plaice, they would 


* See Quarterly Rept. of the Superintendent, Lancashire and Western 
Sea-Fisheries Joint Committee, December, 1920, p. 5. 


Lu7it8) 


have had to go further afield, spent more money, and caught 
less fish. (For that, we may take it, is why they fished where 
they did.) But the year after, or the year after that again, 
they might have caught the small fish (which they had refrained 
from catching in Liverpool Bay im 1920) when these fish had 
grown to be much bigger. Now, knowing all this, would the 
skippers have voluntarily consented not to exploit the small fish 
grounds ? Would the legislator who suggests the restrictions 
on sizes have done so had he not been a legislator, but the 
owner of the steam trawlers? If not, then, it is certainly very 
unfair to advocate restrictions on the inshore fishermen that 
have the same objects and are enforceable only by making 
them penal offences. 


Cultivation. 


It is because of the difficulties suggested in this section of 
the report that cultivation seems to be a much more promising 
field for research and application than are legislative restrictions 
and prohibitions. We do not refer here to the artificial 
hatching and rearing of plaice because that is still a matter of 
polemics. But the now well-known suggestions of Captain 
Douglas and the experimental proof of these by the trans- 
plantations carried out by the Marine Biological Association 
on the Dogger Bank certainly open out a broad track along 
which cultivation methods may develop. This does seem to 
be the line which scientific and practical fishery work will 
follow if and when it becomes clear that the productivity of 
the fishing grounds is diminishing under the reign of lassez- 
faire, as established by the strictly modern steam-fishing 
industry. 


180 


BIOMETRIC INVESTIGATIONS ON THE HERRING. 


By W. Birtwistle and H. Mase. Lewis. 


When this work was originally planned the intention was 
to accumulate three series of data, on (1) the Manx summer 
spawning herrings, (2) the Welsh winter spawning herrings, 
and (3) trawled herrings. It was only possible to deal with 
rather small samples, and it was intended to add together all 
samples belonging to each of these three groups and so make 
three large distributions. But it was found that samples of 50 
fish taken from the same place but at different times, appeared 
to be more different from each other than was expected on 
the assumption that they were samples of the same race. 
When these small sub-samples were added together the 
frequency distributions of a single character became rather 
irregular, suggesting that the material was heterogeneous in 
respect of the character studied. This was not always the 
case, but it was so often enough to cast doubts on the propriety 
of adding together small sub-samples taken from the same 
locality but in different months (to say nothing of different 
years) to form one big sample. 

Scale readings suggested also that the herrmgs invading 
Manx waters in (say) June differed from those in (say) August. 
This, too, is what the local fishermen appear tothink. Theidea 
suggested itself that we have not to deal with a single “ Manx 


b) 


summer race” of herrings, but really with a small number of 
sub-races or “ genotypes.” In some weeks the shoal may 
consist predominantly of fish of one genotype, but at other 
times predominantly of fish of another genotype, or perhaps 
of a mixture of several. It is possible that seasonal conditions 
may favour now one genotype and at another time another. 
Therefore it would appear that it might be necessary to 


measure big samples taken at the same time. But even then, 


181 


such would be expected to differ from big samples from the 
same locality at another time—if the physical conditions had 
changed. At all events it was necessary to test this. 

First of all we have taken all the herrings measured so far 
and have (as a rule) taken them sample by sample and not 
lumped them. The characters D, V, A, l.cp.l., and K, only 
are dealt with. A separate frequency distribution was made in 
each case. In each case the independent variable is D, etc., 
expressed as a percentage of 7'.cd. The classes of D, etc., 
change by 0:25 %. In the tables “ 50-25,” “ 50-50,” “50°75,” 
etc., must be read as “50-25 to 50-49,” “50-50 to 50-74,” “50-75 
to 50-99,” ete. The dependent variable is, of course, the numbers 
of cases of D, etc., falling within the classes 50-25 to 50-49, ete. 

The conventional signs indicating the various characters 
are as follows :— . 

T. = Total length from tip of snout to the tip of the dorsal 
lobe of the caudal fin. 
T.cd. = Total Jength to base of tail. 


D. = Length from tip of snout to beginning of dorsal fin. 
V. = Length from tip of snout to beginning of pelvic fins. 
A. = Length from tip of snout to anus. 

l.cp.l. = Lateral length of head. 

K, = Number of keeled scales between anus and pelvic fins. 


In order to investigate the matter further we have assumed 
that all Manx herrings belong to the same “race.” Thus the 
samples of June and September, 1920 (Table XI1), for instance, 
although they are rather different in respect of the distribution 
of frequencies of values of D, are assumed to represent the 
same “ population ” or “xzace.” To what are the differences 
due ? 

We assume they are due (1) to errors of measurement and 
(2) to errors of random sampling. Errors of measurement are 
then reduced somewhat by grouping the classes. Thus we 
take, say, 50-00 to 50-49, 50-50 to 50-99, etc., instead of 50-00 


182 


to 50-24, 50-25 to 50-49, 50-50 to 50-74, 50-75 to 50-99, etc. 
The range of the classes is now doubled, and so the risk of 
mis-measurement is minimised. 

There may also be errors due to distortion (as the results 
of bad condition, icing, freezing, etc.), but we do not consider 
that this source of error is considerable. 

The error of random sampling is the greatest, and it cannot 
be avoided except by making very large series of measurements 
and on big samples taken from the same locality at the same 
time. This is, in general, impracticable. The method used is 
based, therefore, on the study of small samples (50 or there- 
abouts). These are subject to errors of measurement, 
distortion and sampling. All this has to be considered in making 
conclusions as to the existence of “ races.” 

In the following pages use has been made of Pearson’s 
method of “ goodness’ of fit” (see Biometrika, Vol. VIII, 
pp. 250-254). We make the hypothesis : 

All Manz fish belong to the same race and the differences 
between sample and sample are due to errors of random sampling. 

This hypothesis is now to be tested. 

Let there be two samples taken at the same place, but at 
times a month apart. For instance (Table XII, D) :— 

D = 51-:00—51-25, 51-25—51-50, 51-50—51-75, etc. 

(= 23 , 24 : 36 , ete. (June). 

= 14 ‘ 12 , 21 , ete. (July). 
Consider only the frequency, 24, corresponding to the class- 
range, 51-25—51:-50. 

Suppose that, instead of only one sample for June, we had 
had five samples: then, instead of the one frequency, 24, we 
might have had (say) 19, 23, 24, 26, 28, or some such numbers— 
in general, we should have had about as many different 
frequencies as there were samples. This is because the range 
of D = 51-25—51-50 is only one part of the whole range, 
which is about 46 to 59, and our methods of collecting are such 


183 


that we cannot, in general, always take the same proportion of 
fish from this range in every sample. We assume that the 
divergence of any one frequency from the mean in our series of 
samples conforms to the normal law of error (given by the 
Gaussian curve). We might get 19, 23, 24, 26 or 28 in any one 
sample, but there would be a tendency for the majority of these 
frequencies to cluster round the mean (say round 24). 

Next take the series for July, when the frequency for 
D = 51:25—51-50 is 12. If we had had a number of samples 
instead of the single one we would have found f= 9, 10,12, 14, 15 
(or some such numbers) and these latter frequencies would also 
have tended to cluster round their mean (say round 12). If we 
reduce the two series of frequencies to percentages of the 
totals and then replace them by theoretical ones and draw 
curves we should get some such figure as Fig. a. Here there 


4 
Observed frequency 
of D por The range 


SAG Se) 


/ Observed 
7TEG UE 7ey of D 
for the range I+-25 — 51-50 


is very little doubt that the two series represent the same 
conditions but, again, in such a case as that of the Manx 
summer herrings of 1914 compared with those of 1920, the 
superposed curve would be more like Fig. 6. Here we have 
little doubt that the two samples represent different conditions 
or populations (with regard to the character D). 


184 


If, then, we always had a series of samples for each place 
and time of sampling, we might be fairly certain whether or not 
the population had changed in its character. But we have, 
as a rule, only one sample for each place and time of sampling, 
and that is generally all that is practicable in routine work. 

Thus, considermg only the frequency of occurrence of 
character D for the range of values 51-25 to 51-50, we find that 
it is 24, or 7:3 % of the whole, for June, and 12, or 6-3 % of the 
whole, for July. The problem is this: does the difference 
between 7-3 °% and 6-3 °% represent a “ real” difference in the 
populations of June and July, or is it only a difference due to 
random sampling? No answer, admitting of no doubt 
whatever, can be given to this question, but we can say yes or 
no, and assign a rough degree of probability to the answer. 

Fig. c represents the curve that might be calculated 
giving a large number of samples taken at the same time in June 
and at the same place. The central ordinate gives the observed 
frequency of our single sample, that is 7-3.%,, and we assume 
that this is the mean of the theoretical series that would be 
given by our hypothetical series of samples. Ordinates drawn 
on either side of this central one give the divergences of the 
frequencies from the mean one that are due to errors of random 
sampling. We now take the observed frequency for the 
July sample: it is 6-3 .%, or 1 % less than the mean of June, 
and there will be another ordinate 8-3 °%, which is 1 % greater 
than the mean and which we must regard as equally probable of 
occurrence. We draw these two ordinates in the curve, one on 
either side of the mean. There is a block of frequencies greater 
than 8-3, and another block less than 6-3, and we calculate their 
combined area. Then we divide this by the whole area of the 
curve and the quotient represents the probability that diver- 
gences from the mean greater and less than 1 % on either side of 
the mean will occur as the result of the error of random 
sampling. 


185 


But that is only for one class-range of D, 51:25 to 51-50, 
and we must do the same for every range. This will give some 
idea of the mathematical reasoning involved. It is not the 
observed frequencies that we must deal with, but the relative 
ones, and so each is divided by the total frequency, thus f/n is 
taken instead of f. Obviously the samples are of different size, 
and this is necessary. Also the negative divergences (less than 
the mean) must be added to the positive ones (greater than the 
mean) and so we have to square the relative frequencies, so that 
all of them will be positive. Finally, we calculate the sum :— 


Sum kK -£y i = 6 
enue 


fand f! are the two series of frequencies and n and n! the 
two total frequencies. Having obtained s we calculate 
y2=sxnxn'. We look up y? and also the number of 
classes in our distributions in Pearson’s Tables for Statis- 
tacians and so get a value, P. This gives us the probability 
that the two distributions that we compare are both 
- representative of the same population and that the differences 
between them are only due to errors of random sampling. 
When P = 0-1 the chances are 1 in 10 that differences as great 
or greater than those observed are due to random sampling ; 
if P is 0-01 the chances are 1 in 100, and so on. Let, for 
instance P = 0-1, then once in every ten times, or samples, 
random sampling would give differences as gieat as, or greater 
than, those we observe. 

Elderton, in Frequency-Curves and Correlation, p. 144, 
paragraph 7, says :—“ The only other point to which reference 
is necessary is the actual value of P at which a good fit ends 
and a bad one begins. It is impossible to fix such a value. We 
have merely a measure of probability for the whole table, and if 
the odds against the graduation are twenty or thirty to one 


186 


the result is unsatisfactory ; if they are ten to one the graduation 
is not unreasonable, but the exact value when a result must be 
As, however, it 1s clearly impossible 


discarded cannot be given. 


to imagine any test which can fix an absolutely definite 
standard, there is no reason for objecting to the particular 
method because it fails to do so.” ; 

The results of these calculations of P are tabulated below :— 


TaBLE I.—Calculation of P on sub-samples of Manx herrings 


taken during 1914, on characters D and l.cp.!. 


CHARACTER JD. 


1914. | 
June June July July Aug. Oct. 
138. | 265. 9: 31. Pall 2. 
June ses 0-003 0-116 | 
June 13.0.0... 0-052 | 
June 25.0.0... ae | | 
July 9 veeeseeee 0-215 | | 
diet ailt Goocdseen 0°66 
ANTIG, PA eeacadaee 
Sept so cese. | 0-684 
CHARACTER l.cp.l. 
1914. —— 
June June July July Aug. Oct. 
13. 25. 9. 31. 21. Pe 
JUNE Sie eccscess 0-001 0:044 
DUNG WO secs: 
TUTE, AB sos5ccqcn 0-072 vetted 
Anti 8) descennse 0:008 
dfilby Si meeesoane 
ANuhes (All -canboodc 


Loy 


TaBE IT.—Calculation of P on bulk samples of Manx herrings. 


June, 1914 


July, 1914 


Summer 
Season, 19 


CHARACTER D. CHARACTER J. CHARACTER l.cp.l. 
rt =) =] 
4 | da | 2 4 | oa | 3 4 | oa | 2 
Qo = D = coal 
Ssetnas | S | eS las |.2 | 82 | ac 
2 >>| 83S g >| 3S * el aN 
parents We Ps Bo lat lee ee 
mH |a4o]8 mS |4O/8 mH |}qO|¢g 
= 3 3 
N a) 2) 
0:095 | 0-199 0°34 | 0:98 0-027 | 0-067 
Hee 0°785 0°57 0-000 
14 0-000 0-000 0-000 


Taste I1I.—Calculation of P on bulk samples of Welsh herrings. 


Winter, 1913 


Winter, 1914 


CHARACTER D. 


CHARACTER JV, 


CHARACTER L.cp.l. 


| Winter, 
1914. 


Winter, 
1921. 


0-000 0-000 


weet eet wees 


0-000 


seers eee eeee 


Winter, | Winter, 
1914. 1921. 
0-000 0-9 
0-000 


Winter, | Winter, 
1914. 1921. 
0-000 0:05 
0-000 


TaBLtE IV.—Calculation of P on bulk samples of trawled 
herrings from the Smalls. 


October, 1913 


CHARACTER D. 


October, 1914. 


0-00008 


Peer trees eeeee 


CHARACTER J. 


October, 1914. 


0:0008 


CHARACTER L.cp.l. 


October, 1914. 


0-099 


188 


Dealing first with the small sub-samples of Manx herrings 
taken during 1914 (Table I), the general result based on 
character D supports the view that the differences are most 
likely due to errors of random sampling, except in the two cases 
where June 3rd is compared with June 13th, and June 13th 
with June 25th. In these two cases the odds against the 
differences being due to random sampling are 333 to 1 and 19 
to 1. In all the other cases they are less than 10 to 1. 

Comparing these results calculated on D with results 
calculated on lcp.l., we find confusing discrepancies. The 
lowest odds against the differences being due to random sampling 
are about 14 to 1, in the case of June 25th compared with 
July 9th. This is becoming unsatisfactory; and they even 
become as high as 1,000 to 1 when June 3rd is compared with 
June 13th. So that, with the exception of June 3rd and 
June 13th, the result based on character D is negatived by 
that calculated on l.ep.l. 

The lumped samples are next compared (Table ITI) and the 
three characters, D, V, and l.cp.l. taken. Only in one case 
out of four, the summer season of 1914 compared with the 
summer season of 1920, do we get agreement on all three 
characters, the odds against the differences bemg due to random 
sampling being more than 1,000 to 1, as computed on each of 
the three characters. 

In the other three examples D and V show odds of 10 to 1 
or less against the differences being due to random sampling, 
yet l.cp.l. shows these odds to be so increased that they are 
either in the region of doubt or improbability. 

The examination of the Welsh herrings (Table III) reveals 
a high probability that the differences are due to reasons other 
than random sampling. But one confusing result occurs which 
is unexplained. Winter 1913 compared with Winter 1921— 
character V gives odds of 1-1 to 1 against the differences bemg 
due to random sampling. On l.cp,.!, for these same samples 


189 


the odds against are 20 to 1, and on D over 1,000 to 1. The 
samples of Winter 1914 compared with those of 1921 agree on 
all three characters, with odds of more than 1,000 to 1 against 
the differences being due to random sampling. 

The trawled herrings from the Smalls (Table 1V)—October 
1913 compared with October 1914—show somewhat conflicting 
results. D and V suggest that the differences are due to 
causes other than random sampling, but l.cp.l. shows much 
lower odds against—about 10 to 1—whereas in the other two 
cases the odds are over 1,000 to 1 agaist. 

It is difficult to explain these anomalies. We consider 
the most reliable character to be /.cp.l. from the measurer’s 
point of view and would regard it with more confidence perhaps 
than any other character. It is clearly defined and does not 
suffer from the effects of distortion due to bad. condition, 
freezing or softening, as might D, V, or A, and in nearly all 
cases P, when calculated on this character is low. In the one 
case only—that of the Smalls, October 1913 and October 1914, 
does this character give any value of P which indicates any 
approach to a “ good fit.” So that the bulk of the evidence 
inclines to the theory that there is no racial homogeneity in the 
samples compared. 

It seems pretty clear that the herrings inhabiting the 
Irish Sea are a mixture of sub-races, or genotypes, and 
that one of these predominates at one time, and another at 
another time. For the chances that the differences observed are 
due solely to errors of random sampling are, very often, far too 
smal! to allow of any other conclusion. Further complications 
are the choice of the diagnostic character, or whether we should 
not, preferably, choose a combination of characters, or whether 
some other character than those studied must be sought ? 
Evidently the question of races is not so simple a one as has been 
thought and some further investigations, as to what characters 
are truly germinal ones and what are environmental only, must 


190 


obviously be undertaken. Meanwhile we hope that the 
records given in the frequency distributions may serve for 
comparison with other sea-areas. 

The possibilities of a shifting with growth of any one of the 
characters investigated should also be considered. That this 
actually happens in the case at any rate of young herrings of 
from 30 mm. to 60 mm. is very clearly shown in Table V. 
This is a series of measurements of young herrings from North 
Wales made by Mr. Andrew Scott and examined by Professor 
Johnstone. The distance D is expressed as a percentage of 
T (total length) and correlated with 7 as tabulated, giving a 
coefficient of correlation of —0-9696. This is almost absolute 
correlation. The form of the table shows at a glance how the 
dorsal fin is gradually moving forward as the young herring 
is growing. 

This investigation of the shifting of characters was 
extended to the sprat. Measurements were made by Mr. Scott 
and tabulated by Professor Johnstone. Tables VI and VII 
show the results. Table VI is a correlation between the 
position of the dorsal fin and the total length. The result 
shows that this character does not vary in any regular way with 
imcreasing length. Table VII is a correlation between the 
position of the ventral fins and total length. This shows a 
somewhat irregular tendency to move forward as the fish grows, 
but not so definite as in the case of the dorsal fin of the young 
herring. 

Unfortunately, in the case of the samples of larger herrings 
examined by us, time did not permit of more than four 
correlations being made. Three of these were based on 
character A, and one on character D. The results were 
inconclusive, as Tables VIII to XI show. There is little or no 
evidence of correlation in any case investigated. 


191 


TaBLE V.—Correlation between length and position of the 


dorsal fin in the Herring. 


Total 
length. 


31-33 
34-36 
37-39 
40-42 
43-45 
46-48 
49-51 
52-54 
55-57 


Distance of dorsal fin from snout: °% 


Totals | 


/O 
ae Es Totals. 

43-44 45-46 47-48 49-50 51-52 53-54 

EY aa fe ee ee 

1 Ph) el 24 

a00 isle an 9 42 8 59 

Sas “ies 1 3 33 1 58 

She 3 5 22 1 F 31 

1 7 19 1 28 

4 22 2 28 

1 4 1 6 

4 6 ae 10 
ioe ese s6 | 79 «| «631 || ae 
r = Coefficient of Correlation = — 0°9696 + 0:0005 


TasLe VI.—Correlation between length and position of the 
dorsal fin in the Sprat. 


Distance of dorsal fin from snout: % | 
Total | Totals. 
Length. = 
41-42 43-44 45-46 47-48 | 49-50 
30- 49 4 37 106 45 12 204 
50- 69 anc 17 100 77 18 212 
70- 89 14 90 83 12 199 
90-109 as 12 154 99 4 269 
110-129 3 a 73 U 380 90 
130-149 see ae 9 5 ee 14 
Totals ...... Tease acne eicn es), 460 <|) tose. 
r = Coefficient of Correlation = — 0:0945 + 0°0205. 


TasLe VII.—Correlation between length and position of 


the pelvic fins in the Sprat. 


| Distance of pelvic fins from snout: %. 
Total 
Length. i 
40-41 42-43 44-45 46-47 48-49 
30- 49 1 8 107 62 19 
50- 69 3 46 97 46 9 | 
70- 89 10 79 84 24 6 
90-109 2 109 148 8 
110-129 1 47 40 2 | 
130-149 4 5 4 3. | 
Totals ...... 21 294 480 142 34 | 


r = Coefficient of Correlation = — 0°5005 + 0-015, 


| Totals. 


192 


TaBLe VIIT.—Manx Herrings, 1914. Character D. 
Correlation between T7'.cd. and D expressed as a % of T.cd. 
Be : 
48— | 49— | 50— | 51— | 52— | 53— | 54— | Totals. || Means. 
48:9 | 49°9 | 50-9 | 51-9 | 52°9 | 53-9 | 54:9 | 


| 


| 
| | 
180-189 onc 200 1 Zia wl Alen are 17 | 52°44 


2 

= 

23) 190-199 | ... |... A> |. 35 6:10 3 67 5225 
g 3 200-209 ie 3 27 58 fil |) Uy 3 159 51°88 
a8 210-219 |... 2 38 96 1 | 47 3 228 ~=||:«#51°82 
EE 220-229 1 1 19 45 44 27 3 140 || 52-09 
8 B+ 930-239 |... Gs 6 15 17 | 9 2 49 | 52-21 
Hale AQ E40 a zee dle ole meen eel eee 32. feelers 3 || 52°50 
2 |——— | | a 
| & | Totals ...... 1 6 | 95 | 243 | 219 | 85 | 14 | 663 || 

r= eee , Si See 

= (Means ...... 225 | 211-6 | 214-26| 213-15 213:40) 214-18] 213-57 


, = Gaomoens of Goren - 0:000499. 


TaBLE [X.-—Welsh Herrings, 1914. Character A. 


Correlation between T.cd. and A expressed as a % of T.cd. 


| | 
| 73— | 74— | 75— | 76— | 77— | 78— | 79- | 
73°9 | 74:9 | 75°9 | 76°9 | 77:9 | 78:9 | 79:9 | Totals. || Means. 


| 

fo. 1802189 | jhe SoC an eeLGo, MO Cranes 35 | 75°78 
= 190-199 | 4) 2 eG | aels es ae 45 || 75°50 
2 200-209 | 0 4], 4a ise ide a 1 29 || 76-26 
5 10-310 |) 25. Phar aaa cies (ele eT 1 | 47 Neos 
B's) 920.090 | 1 | a oe ape ns |e 85 || 76-38 
Be) 2° 6280-280) 2.7 | 3 BE il UT Ga 2 | ei) Rome mnee 
Feil G20 249.011 sw 1 cecenn ae gea el ee a 4 | 76-00 
5B | Totals...... 6 || 86 (See 550 ieace ein i ere 
oO 
= 


| Means Bence 201°6 | 205-1 | 209°5 | 215°7 |216°7 | 218 215 | 
| | 


r = Coefficient of Correlation = 0-267 (-+ 0°047). 


Actual measurement of T.cd. 


Actual measurement 
of T.cd. 


193 


Taste X.—Welsh Herrings, Winter, 1921. 


Correlation between 7.cd. and A expressed as a % of T.cd. 


/O 
Seas ste fs tk! era | 
Rees tae TG Tr 1 7T8— Wo |80 
| 739 | 749 | 759 769 | 77-9 | 789 | 79:9 | 80-9 | Totals. | Means. 
| | | | | | 
190-189 | ... ; 1 | i | Poe ttel a en ee ya lve 27 77°50 
190-199 | 1 | 1 ey Ole Tome dae MON Or Nace enna 
200-209 | 1 | 1 | 3 SS) eae) 4 55 «| «77°50 
| 210-219 | Meeec5oe abt |) t15, 6 | 4 42 | 77:26 
220-229 | re ad) | ekO}. aed 2 19 | 77°76 
230-239 | 2 fs\tOnt |) 12 ] 29. aaa 
J BE a ee ree 2 5 7 ler afi aoe NTS:06 
250-259 |... Te eee hy ss, i i ere re feet am 76:00 
SOCOM Pei liicee! | ce || psn: ee eee 75°50 
Totals ...... 25) 5 13) 950%), (997 | 60 | 18 1 | 248 
Means ...... 200 | 211 | 210-38' 207 | 210-15 214-3 |211-11) 195 
| | | 


r = Coefficient of Correlation = 0-094, 


Taste X1.—Manx Herrings, June, July, August, 1914/20. 
Correlation between T.cd. and A expressed as a % of T.cd. 


| | ] 
tlre lis aie ain renee (|e. Ps ; 
| 73— | 74— | Jo— | 76— | 77 — | 78— | 79— | 80— 


73:9 | 74:9 75:9 | 769 | 77:9 | 78:9 | 79°9 | 80-9 | Totals. || Means. 
: | gee 
Ge EOAWTOn Wala. leva ||, fl ys 1 (il cere tee Bl) aavelley 
TSGstO glee) 26 Se] “4G 6 Saas | 1 | 25 76°54 
RAO OOM 2p 12 NES esis soe 4 |) 2) 2 | 188 76°65 
200-209 | 3 19 | 46 68 46 30 6. i 2 220) ||) We:59 
210-219 | 2 | 13 | 33 | 55 46 \4 a || | 170 || 76:68 
J 220-229 .. | 1 | 10 | 14 | 29 | 15 4 | 74 Ts 
230-239 1 meee 3 7 3 2 17 77°68 
| Loe en ee ee 
Rotalees-s aS | aol lly welss eT |, 80 * |) 21 7 | 642 
| | ad 
| Means....... 208°75 203°24 206°32 207-35, 209-33) 208-75) 214-05 206-43 | 


r = Coefficient of Correlation = 0°152. 


194 


REMARKS. 


The mathematical investigation of these data can scarcely 
be regarded as giving very satisfactory results ; many of them 
are conflicting and in some cases one result completely annuls 
another. The reasons may be sought in many directions, some 
of which under present circumstances would be difficult to follow. 
We might get more trustworthy results from weekly samples 
of herrings and by dealing with them immediately. This, 
however, would necessitate the abandonment of some other 
equally important work during a very critical time in a marine 
laboratory programme. Methods of measurement might be 
improved and additional characters investigated, including the 
counting of the vertebrae. 

The grouping of the data according to scale markings has 
been considered. That is, instead of giving a range of per- 
centages of T.cd. of any one character and lumping together 
all the fish of a sample irrespective of their ages, as we have done 
in the present report, the fish would be selected according to the 
scale markings and each age group treated separately. This, 
however, has the great disadvantage of reducing the present 
dats. to many groups with much smaller frequencies and would 
consequently necessitate much larger samples. The samples 
would at least be homogeneous as far as age was concerned, and 
any peculiarities due to a possible shifting of any character 
might reasonably be expected to be confined to the particular 
age group under consideration and to be evenly distributed 
among the varying length frequencies. 

Our examination of scale markings of the various samples 
considered reveals great heterogeneity as regards age. A sample 
generally contains fish with from two to six scale rings. In 
some cases one special ring group will predominate, in another 
perhaps three groups will be equally represented and form the 
bulk of the sample. 


195 


We do not consider the keeled scales (K,) to have any 
particular significance and they seem to show very little 
variation. For this reason we have not investigated them 
mathematically. 

Our indebtedness to Professor Johnstone is acknowledged. 
He drew up this scheme of investigation and supervised its 
carrying out. Thanks are also due to Mr. Smith and 
Mr. Fleming, who have helped in the measuring and examin- 
ation of all the samples. It should not be overlooked that the 
measuring and examination alone of a sample of 50 fish is a full 
day’s work for two operators, and the greatest care must be 
exercised. Scale reading takes up a great deal of time and 
becomes very trying. The results of scale readings of the 
samples will be the subject of another report. 

The analysis of all samples received from the commence- 
ment of these biometric investigations in 1913 to the present 
time are appended. See Tables XII to XX. 

“Range” of a character im the Tables means the per- 
centage of the measurement 7’ cd. occupied by the measurement 
of the character under consideration. The material is divided 
into sub-samples, which appear under the heading of locality, 
month and year. The final column for each year is the total of 
these sub-samples and forms the * lumped ” samples data. 

Table XX. Character K,. The “range ” of these data 
are not percentages of T.cd. but absolute numbers of the 
keeled scales as counted. 


TABLE ex): 


196 


Range of D. 


46°00 
46°25 
46°50 
46°75 
47°00 
47°25 
47°50 
47°75 
48°00 
48°25 
48°50 
48°75 
49°00 
49°25 
49°50 
49°75 
50°00 
50°25 
50°50 
50°75 
51:00 
Dd; 
51°50 
61-75 
52-00 
62°25 
52°50 
52°75 
93°00 
53°25 
53°50 
SAEED 
54:00 
54°25 
54°50 
54:75 
55°00 
55°25 
55°50 
55°75 


bot 


~ 

= 

— 
On one a) 


—_ 
Ne = oc © 
WwWwods 


ae 


+ oo 
— — 
D> | & 
_— = 
Jo 
be | oe 

s. |< 

a | 8 
— — 
= | & | 


5 
ell OO Od 


re 


et 


~ . . . . 
2 | Sapsaeales ie 2 
Wee es] eS cea I et 
o (on) — — ia! ea (=>) 
— “ n~ n” Cy —/ 
jos Ss Oo © or) a n 
| 3 Sal Tetest ape maker liege acs 
" = - ol a a 
4#iS S/8is la is 
< fa i — — = x 
= Sate Nee 
— 
= 
! 
| i l 
| 
» G3 
res ea 
1 1 
| 
| | 
| | 
eee leas 
| 5 | i 1 eee | 2 
Pak 1 Bed) es 
| | il 1 


2s 5 1 | 
4 I gaan | 

Bot [reDea 

5 

5 | 

| 

| 


—_ 
ae? 


a et SO OS DS 01 GS OS Tb bb: 
ees 
> et OU SUIS OH Ge SD GS 


RWW RUA WTIR eo: 
Or 
ye 


—. 
— 
-I 
— 


bo: 


ars 


Eat 
eee bobby: 


mT O10: 


Manx, 3, 1921. 


Manx, 5, 1921. 


ee On 


We PRUIKROWwW oP BP: 


Manx, 8, 1921. 
Manx, 1921 


es 


—_ 
as 
w 


to 
—_— 
bo se we 


mee OOHRS e: 
— 
be 


328 190 


| 
i 


149 667 
| | 


60 |153 | 60 [181 454 | 


| 


49 


24 |120 


(PABEE OP — 7)! 


. me = a al . . 
5 Reals ce ees eee esi le Ss 
a =r) fon] | Co inn =r) =r) 
S oa) eels at as = a z 
S st | rm i . en & cy 
i ae fe Sh ee ee 
| eo { = 
48-00 
48:25 
48°50 ee 
48°75 rs Ee l + i: | Ae cet 
49-00 oe Poca (Rohe a er Be 63 l 
49°25 1 3 1 1 ay ae 
49°50 2 4 1 | | 
49°75 | 5 oe oY a 2 
50-00 4 26 2 Sa | 3 vr 4 
50°25 eer, 26 1 I 2 l 
50°50 9 20 4 l 5 2 se 
50°75 aniiee oll 4 2 6 2 4 
51:00 10 in eens 1 2 16 5 i 
51-25 21 33 13 6 | 20 5 9 
51-50 15 34 19 4 2: els 
51°75 10 Waele y| 1 25 5 9 
52-00 10 19 17 2 a 19 ia 12 
92°25 15 20 17 7 I 25 12 18 
92°50 10 11 21 9 5 35 11 11 
52°75 3 4 10 4 1 15 17 5 
53-00 on 3 15 Gil 33 19 8 
58 5) 5 6 5 4 15 12 ll 
53°50 l i 5 2 14 14 2 
53°75 4 5 4 9 7 2 
54:00 3 l 4 9 13 12 1 
4-25 4 2 6 2 1 
54°50 1 2 5 7 2 l 
54°75 2 2 2 
55°00 1 L 2 ns 
55°25 3 3 2 
55°50 | l 
55°75 ie I I 2 
56°00 
56°25 
56°50 | | 
56°75 
57-00 


141 | 280 | 185 | 61 | 48 | 294 | 150 120 
| | (eerteslea Eos § mul 


| 
| 


198 


TABLE XIV.—YV. 


“i _ | | | | 

. Pe ss. eee 
= ealal~lS eiSl/Sl(SlalSlalSja 
B ele Hal) al een ee eo ay fo) SS 
= S eh st a) Se ec los | o> | -. | oS | am |) od = 
Et) ~ ~ oS w : . o o ial * a * Last 
PI 4 mn S va | ee hy IER || %S 4 4 4} <4 

a\e| 4 lz \/Slelel"\s\sis 

| = | | | 

48-00 me i i 
48°25 a oe 25 
48°50 i 1 1 
48°75 ay ata 2 
49-00 pe Seale | 1 
49°25 wi eh pe 1 j 
49°50 BY wales. oe » 
49°75 ee el ee 1 ; 
50°00 es eae * | os - 
50°25 EN, [ek Weer Meee at me 
50°50 eb ee Oe lt elie Ey 
50°75 SU ean ee a | eats aa 
51-00 LO bie poet ee ota | es 4d, 
51:25 TWAS Deed Wee | (ea fae ca Pe en Salven a 
51°50 iia feces | a | ee fc Ly eee eat 1 
51°75 Tea eee eon) Fa, Pet 1 eee |e we 
52-00 xecep l|eB | gel mee a cx ea eee | ee alien: shan! ah 
52°25 1) se Re a a eT: Sul eerie 
52°50 BF NMR eR OT ea a een ta a 
52°75 Beetles el Sa Oana S| a OST al) ees eee sn 
53°00 Gileaal eetaliaia OSS Fay 2 6) ca |e | eee 
53°25 19)! VEU ga eos) el 7 oe Oe 
53°50 184) 2-83) 8-949) Sel 104) 24 ee) ea) ee 
53°75 9g 19) V4.1 549) “3°! 10°) 6 | 2.) 18 |) eae 
54:00 59 90) ieee) 2 18)| 7) eo | ee ee 
54°25 Deal a0) | 8s, 46.) 16-110) 4 | 98. 29.1) Se ee 
54°50 99 | Ist 53.) 27] 19) 8 | “70)-96'| “Ue oueeo alee 
54°75 99 | 17 19)| 51) 4113) 41) 95 96) Sona 
55°00 41| Sesh isst | 6 112) 7 SSG) 65 aire ails 
55°25 99°) Fo 11 145 | 6 | 4) 62°) 1071214) 35) on ea ee 
55°50 F716 Ti | 54.) 4) 6" V4) 16 eS ee ee 
55°75 16) 12.) 7 35) 41 Sel 1 1 20 NS eee ieee 
56-00 Wl 2) 8199! 11 -6-| 1) 10s) Tse) ey eee 
56°25 13°) 8 17 1-28)| ea) 3), 22172031295 4) Ga eee eaten 
56°50 7) Oil 4407) | 2.) 25 eGelaa a So ee ee 
56°75 Bi) oO Sa) Ft) 3c Seas eas ee ee | eee 
57-00 Tie Peso | Om feta eee 197 1G | il eee 2 
57°25 Soul soul. ill well 14 IS ee o 2 
57°50 Same loreal 73) wl al cred 16 aN oe nl 
57°75 id | ocr hay 2D ibe ee al nasa ool 1 
58-00 aul 3a 7 haley |e 1 
58°25 l ee ee ate 1 
58°50 ot a Nae | Oe ee a 
58°75 ae 5| 5 ee 
59-00 Real 2| 3 
60-00 1 i lee 
61-00 Kees feed l 

329 |190 [149 [668 60 [152 | 61 es fe | 47 | 49 | 24 |120 


a 


199 


TABLE XV. 


—V. 


“s eee fe | ae ah Ss See 
: ee eo | ae lean 
8 mee le oe oe 
a = = Se | Sa a & 
48-00 | | | | 
48°25 | 
48°50 ee: | 
48°75 nee 
49-00 aft 
49°25 | ies 
49°50 | Whee : 
49°75 tp ee 355 | | 
50-00 | eee leecale | | 
50°25 f a. Wenn sae ||| 
50°50 a ” pant le | 
50°75 tes ne roe Be 
51-00 1 ee lesen ey ‘ 
51-25 1 St | i oo 
51°50 a 1 | ian vs 
51°75 in a ee |p ae if aes 
52-00 ae Me ye ie ey ih Bele wa I 
52°25 ee 9 ce cit we a | hee 1 
52°50 i 4 - 1 TEP ea | eee es 
52°75 a | ae 7 1 3 Sei) Geile Bae wis 
53-00 2 i 9 4 5 os Oliva: 2 
53-25 4 16 4 1 a Bat 5 
53°50 6 18 8 1 De LS ee 4 
53°75 2 28 9 2 a Tia Ble at 5 
54-00 5 25 8 4 Pe aioe es 8 
54°25 9 29 10 ll 7) 95" les 5 
54°50 11 28 15 6 se 21 || 10 12 
54°75 16 | 29 19 4 1 24 || 17 12 
55°00 13 19 15 8 1 94 | i 13 
5525 15 28 28 6 2 360 |) 10; ol 28 
55°50 11 7 11 Pala esi ae) 1) a 
55°75 11 11 13 3 2 189) Pero 4 
56-00 9 3 10 aw 6 16 || 10 15 
56°25 7 2 | 15 3 4 22 || 6 7 
san! 9 Bee | sat l 3 ae ny) 
56°75 2 eo 4 9 | 9 n 
57:00 1 ees | 9 Gers l 
57°25 2 (Pao 6 8 5 1 
57°50 Dees late 1 ee Te hoes ee 
BT15 Pi ike Al) ed eee Doli ately. 
58-00 1 cee are ane eee oe | 
58°25 ae fl 2 Be Wetec 
142 | 285 | 183 | 61 | 49 | 293 || 149 - 120 
| } 


TABLE 


: ~}al/afi/ai/= oilbhS Smile Ite Pe | aial|. 
x i eee | os. see Meal es Sree. Meee cee- | ped Ges | uoeal lees 
oo | el tl 4 3 2 ee a head = =— = | = = 
r= 4 | K SO Ela ee || si eh || iz 4 A 8 wo | al |e 
CI ea |< i ash |i 2 oF a | 8 I et Wek i) Siti ics 
pe E a@i\e/e|/e|a| s | S |S) See lS Se slae 

yt ee eee a vee aes = a S| = ee re 
| 

73°00 1 il 

Hetedse Ae heal ees Be s& 

73°50 | 1 feat | Sah 2 a 
WOT Bs | wae | leer [lee 2 3 he 
74:00 | Sale 4| 2 4 6 | ules 
74:25. | 2.| ... 2 | 7 8 1 
74:50 | 4-|. 1 | 3. | 5 3 6 9 

FAs | eecst) 6 | oh erie 3 8 11 

TsO en ele loge bbe se) 2H it 9 163) ese =i 
Tips | eS ale ell ese) eee sl meen ALS 1 VB | sell ce ce LGM ean cere 
75°50 eae lea meat ree nea | 12 Bh. Gy) AG a eas 
7576+ | 151.971 3) eas 1) 29 3 6 1 TOmh oo ee 4 
76-00 $1.10] 5| 1] 31/27 3 14 AAR eae 44 Wal eee aes 
16200) L6s\= 9) 42) 2a 43> 5 9 AL | GY | Bl Di} Al & 
76:50 | 17 | 14}... | 3 | 1) 35 6 16 Dit isce al dar|) V2 aell Cea 
76°75. | 21:),100) <b | 1D 38 5 6 Bobo. | ltl 64s alte a 
T7700" | T2125) 24) 7 | 38 4 7 5 Sled AB al ea 
T7125 | -2el20.) 985), oasis e581 e:. 5 2) 9 | 16); Ta esa elie 
77°50 | 18 |-16| 4| 10} 4] 52 3 8 Sb 9) 295) es 2 eens 
by Far ssp Wad Wea fa Ne fe Del Pine Se eee | | 4 Ty) | OS 2| Fe asa eae ea 
78:00 Oa STs Soe 26 l 4 Z| 1S) 300, Weeds eel 
78:25 a eo se Re IST Mie 5 Bal Aa Sl OS Sula 
78:50 Gil 64 oreo ee eo 1 2 PWD AT. Ce el aS a ed 
78°75 Sa ell aed eed eee lt LO) 2 By) i OX Sy | 7 
79-00 Oy St FOS! Dae eae ek eS Bt, Male anal 2 
79:25 By 2 eee el 9 dpe. 1 Le sgn os ipall 3 
79°50 | } 2 | -67-0/0...1 ipa) |e 4 
79:75 2 EE AL 6 

ef la PG as 


80-00 
80°25 
80°50 
80°75 
81°00 
81°25 
81°50 
81°75 
82-00 


a 


=e be: 


a 


Ialiec cs! pen et 
| | 6) Tees 
| | 6/8-00).. 
6|8-25 |. 
mee | 7/1:50 |. 
see) | 
200 190 | 50 | 49 | 50 [539 


60 


(154 


466 | 


47 


TABLE, XViil——A. 


201 


Range of A. 


73°00 
73°25 
73°50 


76°50 
76°75 
77:00 
MWE2Zo 
eo) 
Wiladko 
78:00 
78:25 
78°50 
78°75 
79:00 
M9225 
79°50 
79°75 
80-00 
80°25 
80°50 
80°75 
81-00 


| Welsh, 10, 1914. 


pees 


BPN Rew: NNN hw: 


ae 


. 
melo: 


| Welsh, 11, 1914. | 


Welsh, 12, 1914. | 


Welsh, 10, 1921. | 


Welsh, 1, 1922. 


Welsh, 1921-2. 


«,° oo: bo: 


yt 


~ 


bo OO 


bos 


bos 


woo whys: 


aC wo 


—_ 


bo. 


CO ae 


=r) 


202 


TaBLE XVIII.—Il.cp.l. 


sag Soa) ee estes (eS. |. |, Sepa te eee 
SlelselelelSisiSiSlSlSislSisisia 
~s ee Tl _ eae y = _ [on — = =p _— _ _ S 
a NG Nod: cop Sameera es os |S |) Se alco linea ae 
© lagi | eel ae el el eal oe | oe al ea ea 
qe 8 8) Bl sues eee | | 8 sl Saas 
e |slielseiais Sse Ss | si Saas 
19:00 | . Ey Sotal e shi| a6 Re aliecce Misses 4 Alter E ee 
19°25 ae sass Seseiil urea cdl mere Bere Wetcee | [one ace 3 4 5 dee, ieee llvecter 
IRE PEO | Soc Lee ee Se alone 1 tee 1 1 5 0 dliineeea lire 2; 2 
19°75 Si edeo l eceall seen lmace 3 1 | eerie 1 2 2 Ne sell poe 1 1 
DO 00K tees 8 “EW seo || 1 |} 83 2 1 8 ay || yi 1 1 4 6 
20°25 9 6 4 Dae eral caters 1 5 SoU aly cecal meee 1 1 
20°50 (hl) dal 7 2 | Ab S| AA7/ 2 LOM PM 28a ee. 1 1 8 
20°75 | 19 | 13 5 6 1 | 44 2 9 By) ils} |) 3¥ | 1 1 3 5 
D009) 24) U1 | 7 2 2) 846 6 9 | 10 9 | 34/| 4 1 1 6 
21°25 | 44 | 12 6 8) 4 74 Ay Aa AS 2 | ed 1 1 9 
21°50 | 44 | 30 4 5 41 87 AW LT) 2d) | 24 | 50 | 7 4 Delile 
OA br(ss || zal |) 333 5 6 25a 1e80 sya) bel 1 | 16 | 39 4 2, 2 8 
22°00 | 46 | 13 5 oP ers 6) 12 BN 13 | Bye | 3 Galesce 9 
Dees i DE IY | aos 6 9 | 61 GS a ee ele Sl aS 5 11 
22°50 | 24 | 13 1 4 5 | 47 6 | 16 2 9 | 33 6 5 Wal 
22°75 | 16 OM e 3 Siow Omiela a. 8 | 28 4 4 8 
23°00))) 1) a2 1 2 2 | 28 5 1 15 1 TN Dees) we Uf 9 
23°25 7 3 Tl eee sell ty | fe ee 3 on ay jf deh | 2 9 11 
23°50 5 Wall ane : 1 8 1 3 A) ell es 2 2, 
23°15| 1| 3 ela ole) Alas si an 
OX ETO Goo || ane aac ltee, tlllceee pacwell- aces . Lis 
BAS || nec an 4 earn ll| wees aoe 
24°50 1 1 
328 1189 | 50 | 49 | 50 |666 | 60 1153 61 |181 |455 | 47 | 49 | 24 |120 


TaBLeE XIX.—1.cp.l. 


203 


~ 2 | 38 
i <i 4 
on = = 
E|2 
jaa 
| 

19-00 [18°75 
19°25 on cae 
19°50 Rea nee 
19°75 6 a 
20-00 3 6 
20°25 8 113: 
20°50 14 9 
20°75 14 23 
21:00 14 30 
Dee ty 19 31 
21°50 13 37 
21-75 7 45 
22°00 9 26 
22°25 8 24 
22°50 6 19 
22°75 4 12; 
23°00 4 6 
23°25 3 Abe 
23°50 5 
23°15 aes 
24:00 ee 
24°25 
24°50 

137 282 


Welsh, 10, 1921. 


BS OUCUG me Go 


185 


Welsh, 12, 1921. 


= : 
OQI1K1w: bw: 


H= Ol G9 Gd GD « 


a 


60 


ACs 
[o>} o 
cl ion) 
: 5 
2/8 
PLS ore 
sot 3 
: 3 
6 
8 
10 
S06 13 
3 23 
2 29 
1 25 
1 36 
5 29 
4 | 2 
3 15 
10 22 | 
7 19 
5 16 
3 4 -| 
4 8 
1 2 
30C 1 
49 | 294 


Smalls, 1913. 


| 150 


Smalls, 1914. 


| 119 


AG a “GEBL ST 
TG) Cs xUehe a ce licn ‘aq urRdaIO]Y 


“CEBI ‘T 


“ 


204 


IDABLE NO Ne — he. 


"1261 ‘¢ “sue | TW RAAN ils | 10d Arey 
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205 


SEASONAL CHANGES IN THE CHEMICAL 
COMPOSITION OF THE MUSSEL (MYTILUS EDULIs). 
(Continued). 

Bye). DANTEL, B.Sc: 


The investigation into the seasonal variations in the flesh 
of Mytilus edulis, which was referred to in last year’s Report on 
the Lancashire Sea Fisheries Laboratory, has now been con- 
cluded, and covers a period of two years. Observations show 
a marked annual reproductive cycle which, on the whole, 
repeats itself in each of the two years. The discrepancies are 
probably due, in the main, to the unavoidable errors of 
sampling. 

The data obtained from examination of the samples, 
tabulated in various ways, 1s shown in the attached tables. 
It is not possible just yet to publish the results obtained from 
microscopic sections, stained to show the distribution of fat and 
glycogen in the tissue, but since the information obtained from 
these latter investigations is closely bound up with the fluc- 
tuations in chemical composition, it will be necessary to refer 
to it im passing, 

The samples sent from Morecambe are to some extent 
selected ” mussels. They have been gathered in the same 
manner as the fishermen pick them for food, only those greater 
than two inches (5-1 ems.) being taken. This is not altogether 
a disadvantage ; it lessened the irregularities with regard to the 
_size of the mussels, and allows of results which are comparable 
with the shellfish that are actually put on to the market. 
Most of the mussel samples showed an average length of 


6-0—6-5 ems., and only five of them averaged so low as 
5:5—6-0 ems. There were one or two samples which were 


obviously not in the “ general” run. For example, the mussels 
received on August 16th, 1921, were small, and with very 
dark shells ; they were procured from a bed near to Morecambe, 


and not from the usual Skears. On the other hand, the 


206 


sample for December 17th, 1920, was composed of mussels so 
large and well-nourished that they must have enjoyed the most 
favourable conditions on the Skear, from which they were 
obtaimed. Although such samples cause irregularities in the 
tables showing weights and percentages, they do not obscure 
the general trend of the figures. 

The methods of dealing with the shellfish in the laboratory 
have already been described.* The selection of six mussels at 
random from the whole sample, for the drying and subsequent 
analyses, has been successful, within limits, as may be seen by 
examination of Table I. The figures for the average weights 
of shell and of flesh for the six mussels, and the corresponding 
ones for the rest of the sample, do not show differences which 
alter the main conclusions. For instance, a graph plotted for 
the average weights of wet flesh for the rest of the sample 
shows fluctuations, but the curve does not differ fundamentally 
from a corresponding curve for the six mussels. 


Differences in Weight. 


The weight of wet flesh in both years rises from May, 
with variations, to December, and then maintains a relatively 
high value until there is a rapid fall to almost half the maximal 
value in the April 01 May of the following year. 

The series of weights given by the dried flesh show the 
same sequence in a more marked manner. It will be seen that, 
during one part of the year, it is possible for the mussel beds to 
yield two-fold the amount of foodstuff that they offer at 
another time. 

The proportion of water to dry flesh is least from August 
to October, and shows an increase before and after spawning in 
the Spring. There is no doubt that all these differences of 
condition are connected directly with the reproductive cycle of 
Mytilus. In May the mussels were in a spent condition. The 


* Report on the Lancashire Sea Fisheries Laboratory, 1920, pp. 74-84. 


207 


reproductive products, which invade and cause to swell enor- 
mously the mantle, and also every part of the body which is not 
occupied by organs or muscle, had been extruded, leaving 
behind a thin, watery, and semi-transparent animal, so 
emaciated in appearance in the case of the older mussels that one 
is almost led to wonder how they survive. The “fat” 
condition of the molluse which forms such a contrast to this 
state of emaciation, is dependent upon the amount and 
conditions of the sexual products ; this is ‘‘ common” know- 
ledge to the fisherman, and a closer examination of the 
reproductive phases during the two years under consideration 
bears it out. 

The spawning time of the mussels in the Morecambe Bay 
area has received some attention in the past. Herdman and 
Scott* record that in 1894, mussels matured about the middle 
of May and that spawning continued until the middle of July. 
Scott} confirms, two years later, that the mussel reaches 
maturity about the middle of May. So far as the Morecambe 
Skears themselves are concerned, Mr. Edward Gardner, 
Honorary Bailiff to the Lancashire and Western Sea Fisheries, 
has kindly given information drawn from his long experience, 
and which may be summarised as follows :—The main spawning 
time is about the middle of April, but the actual date varies 
shghtly according to the weather. Some beds seem to ripen 
before others, and there may be a spawning at the back end of 
the year which never comes to very much and seems to be 
due to the younger mussels which recovery more rapidly than 
the older ones. 

Certainly there is other evidence for this spawning later in 
the year,t but so far as the evidence of the two years under 


* Herdman and Scott. Lancashire Sea Fisheries Laboratory Report, 
1894, p. 40. 


ft Scott. ibid., 1896, p. 5. 


+ Johnstone, Lancashire Sea Fisheries Lab. Report, 1898, p. 36; 
Ascroft, ibid., p. 81. 


208 


consideration goes, if was centred round the month of April. 
The fall in weight in the October and November of both 
years might suggest sporadic spawning during these months, 
especially as in one or two cases the mantles showed little 
difference in thickness from those of a spent “ fish ”? (0-7—0-8 
mm.). This thinness, however, was due to poor condition; the 
mantle consisted of connective tissue, and a few immature eggs 
or sperm sacs, and did not show the typical collapsed con- 
dition containing but a few residual ripe reproductive elements, 
which one associates with a spawned mussel. 

The differences in the weight and condition of the samples 
for April and May in 1921 show that a short and thorough 
spawning had taken place between these two months. The 
spring of 1922 exhibits a less well-defined spawning period. 
One or two mussels of the March sample ran with spawn when 
being handled. Millions of fry had settled on the Morecambe 
Skears in mid-April, which (if the estimation that it takes 


about a month for the larvae to settle down* is reliable) 
suggests spawning in March and possibly in February. 

The April sample also showed a condition where some 
mussels were full and others not, and it was only after 
examination of some shellfish sent in May that one felt sure 


the spawning period had come to an end. 


Proteid. 


The amounts of proteid have been obtained by multiplying 
the Kjeldhal nitrogen values by the usually accepted factor 
6-25, This assumes molluscan proteid to be the same in 
empirical composition as that of the higher animals, and must 
therefore be adopted with some reservation. Factors obtained 
from the amount of nitrogen in fat-glycogen-ash-free substance 
give somewhat higher values, but they vary, and the experi- 
ments cannot be regarded as definitive. Whatever factor is 


* Johnstone, ibid., p. 38. 


209 


used will not alter the relative values of the proteid throughout 
the year, but is certain to affect the amounts of carbo-hydrates 
obtained by difference, and may explain, in part, the higher 
percentages of carbohydrates so obtained, and the corresponding 
glycogen estimations, in those samples where the latter were 
taken. Undoubtedly the percentage of nitrogen in mussel 
proteid is not constant. 

The amount of proteid rises throughout the season from 
the spawning time in early spring, until the eve of the next 
spawning. There is a slight depression about February in 
both years, which seems to occur, however, in conjunction 
with a fall in general body weight. There seems little doubt 
that, on the whole, there is an increase up to the time of 
spawning. 

From May the proteid percentage in the dry-ash-free 
substance slowly falls until September and October, and then 
rises again to a maximum in the following March. Since the 
actual amount of proteid is increasing when the percentage 
depression shows itself, this increase is obviously not pro- 
portional to the rest of the tissue during September and 
October, when there is a rapid formation of carbohydrate 
material. 


Carbohydrates. 


The carbohydrates differ materially from the proteid and 
fat as regards their variation throughout the year. There is 
a slow but steady rise up to the months of September and 
October, a tendency to form a second maximum in December 
of both years, and then a rapid decrease until March. The 
percentages of carbohydrate in the dry-ash-free substance 
shows essentially the same variations, and in the first year 
the percentage value rises again up to the spawning in April. 
The relative abundance and stability of glycogen in the mussel 
have been referred to in the previous paper, and the conclusions 
0) 


210 


have been borne out by subsequent observations. Water 
extractions carried out in a Soxhlet apparatus upon mussels 
which had performed the railway journey from Morecambe, 
and subjected to the Mohr-Bertrand method of volumetric 
estimation for glucose, after precipitation of the proteids in the 
solution with basic lead acetate, gave no reaction. Yet the 
water extraction is fairly effective, as is shown by the fact that 
in the sample for April 1922, the solution, after inversion, 
gave a glycogen return of 0-862 °% on the wet substance, 
whereas a glycogen estimation by Pfliiger’s short method gave a 
value of 0-992 °4 which is not much higher. In this connection 
it is interesting to compare the results of glycogen estimations 
made from the wet flesh, and then from the dried powder of the 
same sample: the following results are expressed as_per- 
centages on the wet substance, and were obtained by Pfliiger’s 
method except where otherwise stated. 


The percentage of Glycogen in the wet substance— 


Calculated from wet flesh. | Calculated from dry powder. 


June 23, 1921 ...... 4095 2°733 
INOver li LOZ earns 3°844 0°704 (water extraction) 
Dec. 16, 1921 ....... 2-699 ree 


(| 1:252 (water extraction) 


Extractions from the dry material of these samples were 
also carried out by stirrmg with 0-4 °%% hydrochloric acid and 
repeated decanting through filter paper. The solution 
obtained failed to reduce Bertrand’s solution. This suggests 
that the glycogen may be broken down into other material 
than glucose. 

The question of variation in the quantity of glycogen 
seemed of such importance that, in spite of the labour entailed, 
estimations were performed for the later samples. Pfliiger’s 
method was adopted, and after inversion the glycogen was 
estimated as glucose, by the Mohr-Bertrand, or Benedict’s 
method. Both of these give results which are strictly com- 


211 


parable, but the former was found to be the shorter, and easier 
of manipulation. The results obtamed are given as percentages 
in Tables III and IV, and in all cases but one fall below the 
corresponding figures for the carbohydrates calculated by 
difference. These differences cannot be due entirely to the 
wrong use of a constant (such as the proteid 6-25, or that of 
0-927 used for calculating glycogen from glucose) because they 
vary in amount. 

As seen above, there is no sign of the discrepancy being 
due to inversion into glucose, before the samples were tested 
for glycogen, and this is borne out by sections, which show 
great quantities of glycogen, even when the tissue is not fixed 
until it arrives at the laboratory. It may be that there is some 
non-nitrogenous, organic matter present which exists in other 
forms than glycogen and its inverts. This is at once the most 
interesting, but, so far, the least conclusive part of the whole 
investigation. One fact which is of importance, however, 
emerges from the data, and that is that both the relative 
amounts of glycogen and carbohydrates by difference are 
at a maximum, on the whole, about October, and then decrease 
rapidly to immediately before the spawning time. This 
decrease in glycogen before the time of spawning is of additional 
interest when one studies its distribution in the tissues of the 
animal. MacMunn* was’ unable to discover glycogen in 
sections of the digestive gland of several invertebrates, cluding 
Mytilus edulis, and the study of sections of one or two mussels, 
fixed in absolute alcohol on the mussel beds, as well as that of 
many sections made from mussels after having been received at 
the laboratory, has led to the same conclusion. In all sections, 
whether from mussels fixed directly or after they have been 
on a railway journey, it has been possible to detect glycogen by 
staining with iodine and Best’s Carmine after several fixatives, 
in changing quantities throughout the year, in the connective 

* Phil. Trans., 1887, part I, p. 257. 


21% 


tissue of the body and mantle, in the muscle, and even the 
labial palps and gills, yet it has not been possible to get the 
same staining reactions in the “liver” itself. This means 
that if there is glycogen present in the organ, it is either there in 
such a form or in such minute quantities that methods which are 
successful for the demonstration of it in other parts of the body 
are unable to detect it in the liver. 

In this concentration of glycogen in the connective tissue, 
as well as in the slowness of inversion in the body, Mytilus 
seems, to contrast markedly with the oyster. Mitchell* states 
that in the Jatter mollusc, glycogen is found mainly in the Jiver 
region. In the Report of the Government Chemist for the 
year ended 31st March, 1921, page 24, it is stated that deter- 
mination of the glycogen in oysters was “ carried out with 
difficulty owimg to its rapid change to other carbohydrate 
matter immediately after opening the oyster.” 

In the light of this evidence it is interesting to compare 
the seasonal variations in carbohydrates of the mussel] described 
above, with the quantity of glycogen present in samples of 
oysters examined throughout the year by J. A. Milroy.f 
Speaking of the percentages of dry glycogen in the moist animal, 
Milroy says: ‘‘ As regards seasonal variations there is a 
gradual rise in the percentage from the beginning of August 
until the middle or end of October. This is succeeded by a fall 
which reaches its mimimum about the middle of December. 
From that period onwards the percentage rises until it reaches 
its maximum some time between the begmning of April and 
early in May. The percentage then falls until it reaches its 
second minimum early in August.” 

According to Bulstrode,t oysters in British waters spawn 


* Mitchell, Bull. Bureau of Fisheries, U.S.A.. XXXYV., 1915-16, p. 483. 


+ Milroy, “‘ Seasonal variations in the quantity of Glycogen present in 


samples of Oysters.” Dept. of Agriculture and Technical Instruction for Ireland 
Fisheries Branch Scient. Investigation, 1907, No. IV. 


{ Bulstrode, 24th Annual Report of Local Govt. Board, 1894-95. Supple- 
ment, ““ On Oyster Culture in relation to Disease,” p. 8. 


213 


between May and August, so that from Milroy’s results, the 
percentage of glycogen rises from December to within a month 
or two of spawning. Mitchell* obtaimed glycogen in American 
oysters in quantities which he states to be similar to those of 
Milroy, and he also gives the spawning time as July and 
August. The rise in glycogen in late summer is similar in the 
oyster and mussel, but from December the variations in the 
two animals do not show agreement. For several months before 
the oyster spawns, the glycogen content of the animal is steadily 
rismg and, although a decrease sets in before the spawning 
takes place, the minimum is not reached until this season is over. 
With Mytilus there is a rapid fall of glycogen from December 
to March, and then a tendency on the whole to a rise until the 
time of spawning in April. It is of the greatest interest to 
examine the sections stained for glycogen during this period. 
In September, although the mantle may be comparatively 
thick (2-4 mm.), there is no sign of reproductive products in 
the connective tissue; mantle thickness is not necessarily an 
index of increasing sexual maturity. The glycogen is seen as 
solid lumps lying in the connective tissue cells. From October 
onwards, the egg and sperm sacs ramify through the tissue, 
increasing apparently at its expense, and grow until they almost 
impinge one upon the other. The glycogen, along with fat 
globules, is seen to be wedged into the surrounding tissue. 
Apparently one reason why there is less glycogen now is because 
the sperms and eggs take up the space occupied by the former. 
It is to be expected that such rapidly-growing tissue requires 
nutriment, and there is little doubt that they obtain the latter 
at the expense of the fat and glycogen; but whereas the 
former becomes incorporated into the reproductive products, 
so far as micro-chemical methods are to be relied upon, there is 
no conclusive evidence that this is the case with the glycogen, 
as such ; it is apparently converted into some other substance. 
* Mitchell, loc. cit., p. 481, 


214 


The eggs are quite as large a month or two before spawning 
as when they are extruded, and during this time when they are 
maturing it may be that nutrition is no longer necessary, and 
would explain the rise in glycogen just before the spawning 
period. This, along with the apparent absence or slowness 
of a diastatic enzyme suggests that the glycogen stored up 
by the sea mussel is made direct use of in the extraordinary 
reproductive activity of this animal. 


Fat. 


The amount of fat, as we have already seen, is small, and 
shows a steady increase up to the time of spawning. The 
accumulation of fats throughout the year is well shown both in 
frozen sections stained with Sudan III, and in tissue fixed in 
Fleming without acetic acid. Sections in October show fat 
only in certain liver tubules, and intestinal epithelium. This 
increases In amount, and by November the fat is beginning to 
show in the growing reproductive products in the body and 
mantle. From December onwards there is an accumulation of 
fat about the sperm sacs of the males, and in the eggs of the 
females, and this condition obtains until the spawn is extruded, 
after which time the fat again seems restricted mainly to the 
liver. 


Enterochlorophyll. 


The greenish yellow pigment extracted from the digestive 
gland of several molluscs by MacMunn*, and named by him 
Enterochlorophyll, is very evident in frozen sections, and 
also attracted attention during the extraction of fats in the 
Soxhlet apparatus, by giving to the carbon tetrachloride a deep 
green or brown colour, until the apparatus had siphoned over 
several times. It was noticed too that after a Pfliiger glycogen 
estimation the pigment showed itself in the filtered liquid, 
and had therefore apparently resisted digesting on the water 

* MacMunn, loc. cit., p. 235, 


215 


bath with 60 % caustic potash. The frozen sections show that 
the colour and intensity differ from month to month, although 
the years do not repeat entirely the same conditions. The 
liver is a lighter green about September, and it is certain that a 
dark brown colour, much more intense than at other periods of 
the year, appears in March and April, the months which cover 
the reproductive period. 

MacMunn concluded that the colour was secondary in 
nature and derived from the diatoms taken in food. List* and 
Dastre and Florescot have shown that the liver can be colour- 
fed. This organ of Mytilus certainly shows most colour 
during the period of the plankton maximum and when the 
spores of algae are abundant. It is interesting to note that 
the amount of ash steadily increases up to the two months in 
question; since the amount of ingested sand and mud must 
affect considerably the ash estimation, this also suggests 
a vigorous feeding in the early spring. There is evidence that 
the time of most active feeding is from January to April.t 


Composition of the Mussel Shell. 


Estimations for calcium carbonate and iron were carried 
out on shells ground to a powder in a mortar, from various 
samples. The water percentage was estimated from the 
difference in the weights of a sample of powder before and 
after drying to constant weight in an electric oven at 100°C.; this 
was carried out immediately after the grinding down of the 
shells. To obtain the amount of calcium carbonate present, 
a sample of approximately 0-5 grammes of shell powder was 
taken, and dissolved in dilute hydrochloric acid, after the organic 
matter had been removed by ignition in a crucible. The 
solution was made alkaline with ammonia, and then acetic acid 


* List, “Die Mytiliden,” Fauna und Flora des Golfes von Neapel, 
XXVII, 1902. 


+ Dastre and Floresco, C. R. Ac. Sc. Paris, T. 128. 
t Herdman and Scott, loc, cit., p. 41. 


216 


added until there was a slight excess. After heating, a boiling 
solution of ammonia oxalate was added, and the precipitated 
calcium oxalate allowed to stand overnight. It was then 
washed carefully with boiling water to remove any excess of 
ammon. oxalate and received on to a filter paper. The paper 
was pierced and the precipitate washed into a measuring 
flask with boilmg water and warm dilute hydrochloric acid ; 
sulphuric acid was then added to dissolve the precipitate 
completely, and to get the oxalic acid into solution. After 
making up to 250 cc., the solution was titrated against »/10 
potassium permanganate, and from this titration the amount of 
CaCo; found. 

From several estimations which were made in duplicate 
it would seem that the method of sampling was not to be 
trusted. The chitinous covering of the shell, and also its 
organic matrix, probably did not allow of a homogeneous mixing. 
It has been thought as well to give the results in Table V, with 
the results of a second estimation, when these were taken, in 
brackets. 

The same error of sampling would of course apply to the 
iron estimations. Here 0-5 grammes of the powder was 
ignited, dissolved in HCl, and then the iron present was 
converted into the ferric state by careful addition of potassium 
permanganate to the solution. 

The estimation was carried out colorimetrically with the 
aid of potassium thiocyanate, against a standard solution of 
ferric iron.* 


* See Sutton, Volumetric Analysis. 


217 


TABLE I, 
AVERAGE WEIGHT OF| AVERAGE WEIGHT OF || AVERAGE WEIGHT OF 
SHELL AND FLESH. SHELL. Wet FLESH. 
Date. - - 
Rest of Rest of Rest of 

6 mussels. | sample. | 6 mussels.) sample. | 6 mussels. | sample. 
1920 
May 21 13:1 130 6:9 6:9 671 61 
June 10 15°8 16°4 10-0 lf) wis 58 56 
July 7 | 12-0 12°5 62 | 74 59 ol 
July 26) 158 14:2 9°9 | ae 5:9 ake 
Aug. 20] 18:3 18°3 10°8 | 10-4 45 78 
Sept.13 | 18-0 17°4 10-4 9°6 76 ‘7:8 
Oct. 8| 17:0 15:0 79 69’ 9°1 81 
Oct. 29 17°6 18°9 9°4 9°6 8:2 9°3 
Nov. 25 16:0 7/58 8-0 8-2 8-0 9°] 
Dec. 17 20°8 20°4 8-4 8:6 1223 11°8 
1921— 
Jan. 13 19:7 7/27 9°2 79 10°6 9°8 
Feb. 5 19-0 20°6 8:3 9:2 10°7 11°4 
Mar. 2 18°7 15°8 9°5 8:2 9:2 76 
Mar. 24 | 22:4 20°5 Hite 10°6 is? 9°9 
April 22 18°9 18°6 9°5 9°6 9°5 9-0 
May 20 14:8 last 8:7 8:7 61 6:9 
June 23 19°8 19°5 11:2 Tiles} 8°6 8:2 
July — 906 50 ee aoe Bb ae 
Aug. 16 14:4 16°5 871 9°6 6:3 70 
Sept. 15 21°4 17°1 10°9 8:9 10°4 8:2 
Oct. 18 14:7 14:3 6:2 6:4 8:4 79 
Nov. 17 ps3 16:1 6:3 15) 9-0 10°6 
Dec. 16 Wea 18°5 7EU 79 10:0 10°6 
1922— 
devil, ie 19:9 159 10-2 81 9:7 isd 
Feb. 17 17:0 15s les | 6:5 9°6 86 
Mar. 15 20°0 23°9 10-0 | _aliles: 10-0 12°6 
April 20 14°3 1st 6:8 6:2 105; 6°9 


19 


April 22 


218 


TABLE II, 


Weights of six mussels from each sample. 


21— 

Jan. 13 
Feb. 5 
Mar. 2 
Mar. 24 


May 20 
June 23 
July — 
Aug. 16 
Sept. 15 
Oct. 18 
Nov. 17 
Dec. 16 


22—— 
Jan. 17 
Feb. 17 


Mar. 15 | 


April 20 


May 13 


Weight of 


94° 
109°7 
107°9 
101°6 
105°7 

96°0 
124°6 


118-4 
1140 
112°2 
134°5 
113°6 


88°6 
118°7 


86°4 
128°1 
88-0 
DIES 
106°5 


119-4 
101°7 
120-0 
85°8 
82°9 


| Weight of 
shell and flesh. | 
| 


shell. 


OAS 


BR onl rHOUOpE 
IA: SO] CHNWMES 


ope rE 


Weight of 
wet flesh. 


“1 OTP BW OO we 
Bea SSH OU CUCUCUHS OS 
KOR Oke LD +10 


Weight of 
dried flesh. 


i 
COOP S SAAMI 
ORWO WOR Te bo 


—_ 


—— 
: AS [he Uae NS) 
NNO’ Or He Ww Oh © 


a 
SSH: oar 


Weight of 
water. 


OS Soe 


PPP RO Bw] Roo 
20) ire : ; 
moomnon* ow wwodn 


ww SSS: 


219 


TABLE III. 


Percentage composition of the wet substance. 


| | Ones || Carbo- | 
Date. Water. Dried Proteid (Carb. Ash. hydrate | Glycogen 
| flesh. (N 6:25). | tetrach. | (by (Pfliiger). 
extract). difference). | 
1920— | 
May 21 85:9 141 8:2 0°6 09 | 4-4 
June 10 85-4 14°6 | 8:5 0-5 1:2 44 
July 7) 83:9 Lo 5) 86 (Ey | BR 4:5 
July 26 80°1 19°9 10°8 1-2 | 15 6°4 
Aug. 20 | 78:0 22:0 118 15 16 7 
Sept.13 | 76°5 23°5 12°5 15 7 | 78 
Oct. 8 | 80°1 19°9 9:7 1:3 a 68 
Oct. 29 | 79:0 21-0 11:0 14 one 6:7 
Nov. 25 | 80:3 19+7 10°8 16 1:9 5°4 
Dec. 17 82°4 17°6 SPI 11 1:8 56 
1921— 
Jan. 13 811 18°9 We 15 0:2 5°5 
Feb. 5 82°6 17-4 10:7 13 18 3°6 
Mar. 2 81:8 18-2 Leys 15 2°4 2°6 
Mar. 24 83°3 16°7 10°9 16 271 271 
April 22 80:0 20:0 12:0 21 2°4 3°5 
May 20 | 85-4 14-6 86 0-7 2:2 371 ae 
June 23 83:0 17:0 86 1121 2°7 4°6 4°1 
July — 50 ane Se sae oe 308 bot 
Aug. 16 80°1 19:9 10°6 16 19 58 ce 
Sept. 15 80-1 19°9 9°8 13 LST 1 2°5 
Oct. 18 80°3 19:7 10-1 1-0 2°5 61 6°6 
Nov. 17 81:2 18°8 9:7 1-2 2°4 55 3°8 
Dec. 16 | 81°4 18-6 10:2 1°5 1°9 50 dl 
1922— 
Jan. 17 84:2 15°8 9°6 10 18 a4 113 
Feb. 17 84°6 15-4 9°6 1:2 2°2 2-4 05 
Mar. 15 81-1 18°9 119 1-2 3°5 2°3 0-2 
April 20 83°2 16°8 9°8 1:3 3'8 1-9 1-0 


220 


TABLE IV. 


Percentage composition of the dry, ash-free substance. 


Date. | Proteid. Oil. Carbohydrates Glycogen 
(6 x 25) (Carb. tetrach. | (by difference). (Pfliiger). 
extract). 

1920— 
WEN PRL Saccce 62°3 47 33°0 | 
June 10 ...... 64:1 3°9 32°0 | 
AEN? 2) sane 62°4 | 5°2 32°4 
July 26 ...... 58°7 68 34°5 
Ang, 20h) | ors ip 35:0 
Sept. 13 ...... | 57°3 69 35'8 
Oct) 8 cace0. 54°6 7:0 38-4 
Ole PAD sconce 57:7 | 75 34'8 
INOWs) 25) seca 60°5 9°3 30°2 
Dectaliieeccss 57°6 | 7:2 35:2 

1921— 
Jans) 1Si tees: 62°3 78 29:9 
INS occa 68°7 81 23:2 
Mars 2) sss. 74:1 9:7 16:2 
Mar. 24 ...... | 74:2 10°7 151 
April 22 ...... 68°1 12:1 19°8 
Maiyie20 ee. 69°3 54 25:3 
June 28 ...... 59°7 74 32°9 28°5 
July — ...... 568 3 50C eee 
USS Giwoce est 58°7 9:0 32°3 alte 
Septilote.cs 54:0 6:9 39°1 13°8 
Oct wI8¥-52-2- 58°5 6:0 35°5 38°6 
INOWe Uae ccs: 58°7 75 33°8 23°4 
Decy Gees. 61:2 9:0 29°8 1671 
22 
rig INE Geaene 68°8 74 23°8 9-2 
1Slsy LZ couse 73°0 89 18:1 4:3 
Mary 15) cess. 77:0 76 15°4 1:4 
April 20 ...... 75°7 10:2 14:1 76 


221 


TABLE V. 


Percentage composition of the shell. 


1920— 
Oct. 29 
Nov. 25 
Dec. 17 


1921— 
Jan. 13 
Feb. 5 
Mar. 2 
Mar. 24 
April 22 
May 20 
June 23 
Aug. 16 
Sept. 15 
Oct. 18 
Nov. 17 
Dec. 16 


1922— 
Jan. 17 
Feb. 17 
Mar. 15 
April 20 


UNDRIED SHELL. 


DRIED SHELL. 


Water. 


1:07 


ee 
Oo 
“11 


HOH WSSoSoooo 
wor 710 0O+1 
KEOCORRWHaIRWOR 


So -1to 


Sass, 
o bd 0 
oo 19 


95°31 
95°35 (98°39) 


| 95:31 (96:69) 
| 94:90 


95°31 


| 95°74 


96°90 


| 98-06 (95°43) 


95°79 
99°38 
98-05 (96°29) 
98°22 


97°31 


| 99:26 
| 98-25 
| 97°27 


Fe. 


0-08 (0:06) | 
0:07 (0-07) 


0-08 
0-04 
0-02 
0-05 
0:04 (0:05) 
0-007 
0-002 
0-007 
0-007 
0-01 


0-02 

0-008 
0-007 
0-003 


Organic matter, ete. 


BY 222, 


DISEASES AND PARASITES OF FISHES. 
By JAS. JOHNSTONE, D.Sc. 


CONTENTS. PAGE 

Septic Ulcers in Cod; Malnutrition of North Sea Fishesin 1921 ... 222 
Various Fish Tumours— 

(1) A Benign Tumour ina Plaice ... aes wa ik fea, PAT 

(2) Sarcoma in a Haddock ... Se aes ast nis ao) lh 

Cestode Degeneration Cysts in a Trout ... iss ae ace .. 230 

The ‘‘ Oyster Parasite,’ Gasterostomum gracilescens... ar seg | BI) 

A Myxosporidian in a Hake 406 50¢ Sa abe oe ZOD 


Septic ULcers In Cop AND OTHER MARINE FiIsuH: 


MALNUTRITION OF NortH SEA FISHES IN 1921. 


Between September, 1921, and March, 1922, a number of 
specimens of diseased cod and other marine fishes were received : 
all of them were taken in the 8.W. part of the North Sea. 
The sendings were: 27th Sept., 1921, codling; 24th Oct., 
cod; 27th Oct., cod; 4th Nov., cod; 7th Nov., cod, 2 plaice ; 
17th Nov., 2 plaice, codling, haddock; 24th Nov., cod; 
28th Nov., plaice, sole ; 20th Jan., 1922, cod; 14th Jan., cod. 
All these fish were taken inshore, or at a greatest distance from 
the land of about 60 miles. 

The same general affection was displayed by all these 
fishes. There were large, shallow ulcers on the surface of the 
body, destroying the skin and eating down into the flesh to a 
depth of about one quarter of an inch. In most cases there 
were several ulcers, or sores, and usually on both sides of the 
fish. In several cases there was healing—this I refer to later 
on. Sometimes there were red, highly-inflamed patches on 
the skin, without erosion of the latter. In other cases there 
were places where there was no ulceration, but where the scales 
were apparently raised up and swollen, and with swellings in 
the skin below the scales. 

Usually the fish were in “poor” condition, or were 


223 


> and in several cases there was extreme emaciation. 


* slinks,’ 
This was especially characteristic of one of the plaice—where, 
however, there was healing of the ulcerated sores. In some 
of the cod the emaciation, particularly on the head and 
shoulders, was very great. In two cod there were other 
malformations, a shortening of the length of the fish relative 
to its girth. This was due to a twisting of the backbone, the 
latter having a slightly spiral shape. 

The general appearance of the ulcers is, of course, highly 
variable. Sometimes they are little more than inflamed spots 
on the skin, but as a rule there is complete destruction of the 
latter over a greater or less area. When this occurs there is 
a typical “sore,” the boundary of the ulcer bemg rather 
sharply marked and its floor being formed by the underlying 
body muscles, the skin being completely destroyed. Thus 
there is a shallow cavity of irregular shape, partially filled with 
pus and products of necrosis, including much blood. The 
ulcer is never very deep, though occasionally there are small 
pits going down into the muscles. Generally the edges are 
highly inflamed, and the inflammation often extends over the 
whole floor of the shallow cavity, though sometimes the colour 
of the latter may be yellow-white. Beneath and round the 
eroded area there is always a margin of inflamed skin or 
muscular tissue. 

In the plaice examples all stages of healing were observed. 
One fish was very greatly emaciated, the skin, in some places, 
‘‘ clinging to the bones.” There was an ulcer of about 3 inches 
in diameter on the coloured side, but the greater part of this 
had healed over and there had been regeneration of tissue. 
Near the centre were the remains of the ulcer, as a cavity 
about an inch in diameter, at the bottom of which several 
vertebre, with their hemal species, only very lightly covered 
with colourless connective tissue. The whole area was thus 
skinned over, and the greater part of this new skin was 


22.4 


pigmented quite normally. In another plaice the process had 
gone still further and, though the ulcerated cavity had not 
completely filled up, the edges had smoothed down and the 
pigmentation had, except for two small white spots, been 
completely restored. This was on the coloured side of the fish : 
on the colourless side was a patch of skin about an inch and a 
half in diameter where there had been an ulcer. This was 
level with the rest of the skin and of the same colour. In all 
these cases of healing it is notable that there was no regeneration 
of the scales. It would appear that, once destroyed in a fish, 
these structures are not formed again. 

Often the first indications of the lesion are the apparent 
swellings of the scales. Underneath a small patch of the latter 
there is an obvious thickening, and the margins of the scales 
become loosened so that their outlines are the more easily 
seen. Each scale lies in a sort of dermal pocket and is covered 
over with epidermis, and all these structures share in the 
general disintegration of tissue which is the result of the 
inflammatory process. 

On the whole, then, the sores are very obvious, very 
familiar, in a kind of way, and are so repulsive that they are, 
of course, sufficient to ensure the instant rejection of the fish 
as an article of food. 

Sections were made of various parts of the ulcers, including 
the edge, and other lesions where the surface was unbroken, 
but where there was a region of inflammation beneath the 
skin. Smears from the pus on the open sore were made and 
stained, and these showed numerous bacteria, which had, of 
course, infected the sore after the latter had been formed. 
Staining of the sections so as to demonstrate the presence of 
bacteria had very variable results: in some cases the latter 
could not be detected. -What was seen were only abundant 
leucocytes, blood corpuscles, and broken-down tissue in 
general. Round the margin of the ulcer there is a kind of ring 


225 


of connective tissue crowded with small, round leucocytes and 
containing an abundant blood supply. That is all that can 
sometimes be found. In other sections, however, even when 
the surface of the skin is not eroded, but where there is only 
inflammation, the presence of micro-organisms can be seen. 
There are apparent spaces in the sub-dermal or dermal tissues 
filled with small bacilli, very evident when the section has been 
stained only with carbol fuchsin. Except for these, and a richer 
blood supply than ordinary, there may be no evidence of a 
pathogenic condition. In other cases there are plenty of 
bacilli lymg among the leucocytes in the marginal parts of the 
sores, even although none may be found in the pus in the 
central parts. Evidently, then, we have to deal with infections 
—the ulcers may be regarded as generally septic ones in spite 
of the condition that, in some cases, the micro-organisms are 
difficult to detect. There was no opportunity for making 
cultures, or for studying the living fish. This kind of investi- 
gation demands an amount of time and special training which 
we are, as yet, unable to give to the work. The only special 
tests that were made were those for acid-fast bacilli, and in no 
case were such successful. 

The interest of these specimens of ulcerated cod and other 
fishes was increased because of various circumstances. The 
number of diseased fish occurring in the North Sea arrested 
attention during the last winter. Thus: “ The skippers report 
that they have never known such a year as the present one for 
poorness in the quality of fish and the number of fish seen with 
sores. They report that the sea is extremely dirty at all 
places. It may be of interest to you to know that the herrings 
landed this season at Yarmouth are all of very poor quality, 
having the appearance of being starved.” Again, ‘‘ The general 
condition of the cod caught in the deep water has been extremely 
poor. The majority of the fish are poorly furnished and are 
termed ‘ slinks ”.” 

2 


226 


The North Sea herrings were also abnormal in quality in 
1921. Thus a packer of tinned herrings of high grade says: 
“This year’s pack has something the matter with it. The 
flesh of the fish is grey to brown instead of light, like a chicken. 
The liquor in the tin is watery and dark and bitter instead of 
light, thickish, and pleasing to smell and taste.” These defects, 
it must be understood, were comparative ones, for even this 
1921 pack of herrmgs were, to the ordinary person, of very 
high quality. Nevertheless, to the trained eye and palate the 
result of the packing operations was inferior to that of 1920. 
Why ? 

What one heard about was, on many sides, the “ still and 
dirty ’’ water (which meant unusually large quantities of plank- 
ton organisms). The abundance of oil was also blamed, and 


‘ 


the mines and dumped explosives which were “ exuding their 
filthy, deleterious chemical compounds to the detriment of the 
plant life upon which the little animals forming the herring’s 
food, feed.” 

It is, of course, quite impossible to say, with the information 
that we have, whether the general poverty of nutrition charac- 
terising many fish, at certain times of the year, was due to any 
one, or several of the suggested causes. The ulcerated cod 
which are described here may have been such because of some 
form of poisoning due to the presence of products of decom- 
position of explosives. Not all these sores were septic, and 
in some there was little indication of organisms in the pus. 
It is possible to produce a septic pus by the local action of 
various chemicals, such as mercury and copper and their salts, 
and so some of the ulcerated fish may have become so by such 
means, Still other sores were certainly septic, so that, on the 
whole, it is not possible to state definitely what were the causes 
of the lesions. 


07 
Various Fiso Tumours. 


(1) A Benign Tumour in the Plaice. 


A plaice of 164 inches long, a female in very fair condition, 
was sent to us by Mr. King, the Collector of Statistics at 
Yarmouth. The fish has a very typical tumour on the dorsal 
fin, on the coloured side. The growth is about 33 cms. in 
diameter, and is raised up from the general surface of the fin 
about 3 cms. It is nearly spherical, except that it is a little 
flattened in the same plane as that of the fish. It is pigmented 
very much in the same way as the fin and there are several 
very noticeable blood vessels running just beneath its surface. 
It is firm, but elastic. It has all the appearance of a human 
“wen,” such as one sees sometimes on a man’s neck, except 
that the fish tumour has a rather narrow attachment to the 
part on which it is situated. 

Sections show the structure to be that of a typical fibroma. 
At the periphery there is no proper skin, resembling that of 
the fish: whatever cuticle there is is rather transparent. 
Beneath the surface there is a layer of strong elastic tissue 
and on the surface itself this merely becomes rather more 
compact than it is in the deeper layers. There is a very definite 
“capsule? made up of this dense elastic tissue, and below 
this, and occupying the central part of the tumour, there is a 
loose connective tissue, the fibres of which are wavy, but run, 
on the whole, in lamine concentric with the surface. Here 
and there are a few small blood vessels and capillaries, and 
sometimes a few rounded, connective tissue cells, but otherwise 
the histology presents no remarkable features. 


(2) Sarcoma in a Haddock. 


The specimen described here was sent to me by Mr. F. 
Stokes, Port Sanitary Inspector at Grimsby. It was a haddock 
of large size caught by a Grimsby codman and landed at that 
port. It is of some interest because very much the same 


228 


kind of affection has been seen in several cod, and it is important 
to ascertain whether or not such conditions are of exceptional 
occurrence. 

The fish was much emaciated, so that, as might be expected, 
the presence of a large, malignant tumour has a considerable 
influence on the conditions of health. In such cases as this 
we may expect some diffusion, through the body, of the products 
of the growth. This, I take it, is the justification for the 
condemnation, as articles of human food, of fish suffermg from 


bd 


malignant, “‘ cancerous ”’ growths. 
The growth in question is situated on the top of the head, 
above and behind the eyes. It is represented, about half 


natural size, in Fig. 1. There are two principal tumours, or 


Fig. 1. 


centres of growth, and these have run together. Cutting down 
into them we find a general softening, or necrosis, and this 
has gone so far as to lead to a breaking through the surface 
at the top of the foremost growth. There is a peripheral zone 
of firm tissue, but internal to this the tumour is semi-liquid 
in consistency. 

The histology is represented, under a magnification of about 


10 diameters, in Fig. 2. The figure represents a section taken 


Malignant 7/ssue 


Degenerating, S 


A 
‘ 


eee 


, 


Fie. 2. 


at the margin of the tumour, that is, at the growing part. 
The skin is shown diagrammatically, with several scales in 
position, each in its epithelial pocket. Below these is the 
dermis, here a rather thick, fibrous layer. To the right of the 
part represented in the figure this dermal layer thins out and the 
scales disappear, though the ordinary pigmentation of the skin 


230 


remains. At the central part of the tumour the integument, 
so altered, becomes very thin and finally breaks through at the 
region where the internal part of the tumour is undergoing 
necrosis. 

Cutting down into the latter, along its middle line, we 
find this general liquefaction, and the necrosed contents rest 
directly on the bones of the skull. In the firmer parts we have 
the fibroid type of structure—fine fibres running in various 
directions and, here and there, a few round cells. The latter, 
however, do not characterise the histology, which is of the 
nature of that seen in fibromata rather than in sarcomatous 
growths. The malignancy is evident, however, when one looks 
at the growing margin. On the left-hand side in Fig. 2 are a 
number of isolated muscle fibres, here cut obliquely: in a 
section of this region in a normal fish there would be a thick 
layer of muscle bundles running in various directions. Here, 
however, these are degenerate and are represented only by 
detached fibres, becoming fewer as the tumour is approached. 
The malignant tissue is represented by fine stippling in the 
figure, and this is seen infiltrating the muscle tissue, intruding 
between the fibres. It is, as in all other fish sarcomata that 
I have seen, this intermuscular connective tissue that takes 
on the conditions of malignancy and gives rise to the sarcoma- 
tous tumours. 


CESTODE DEGENERATION Cysts IN TROUT. 


The viscera of a 10-lb. yellow trout were sent to me by 
Mr. J. Ritchie, of the Perth Natural History Museum. These 
structures contain a number of cysts which are so very remark- 
able that a description may be interesting even although the 
parasites responsible cannot now be identified. 

The peritoneum over the liver and pyloric ceca bear a 
number of little oat-shaped bodies which look almost like seeds. 
They are about 4 or 5 by 8 to 10 mm, in their lesser and greater 


231 


diameters. They have a kind of papery lustre and are hard. 
Some of them appear to be embedded in the liver, but they 
can generally be separated, when it is seen that they are 
attached to the peritoneum by slender pedicels. 

They are easily cut. Fig. 3 represents a transverse section 


through one of them. At first sight the appearance is very 


Fie 3. 


puzzling, but on dissecting a cyst one finds that a firm nucleus 
can easily be “ shelled out.” Then the nucleus can easily be 
dissociated into two or four collapsed thin-walled cysts that 
were evidently spherical when they were in their original con- 
dition. So Fig. 3 shows four of these cysts, crumpled together 


232 


by mutual pressure and fitting into each other, so to speak, 
in the way shown in the section. 

The outer wall of the whole cyst is fibrous in structure 
with a thin, external serous layer, and among the fibrous layers 
there are a few blood vessels. This part, therefore, belongs to 
the host. The fibrous layers send inwards a few trabecule 
between the secondary cysts, but apart from this there are no 
other tissues. The internal, secondary cysts have walls of quite 
a different nature, these consisting of an apparently homo- 
geneous substance (it is represented by the thick black bands 
in Fig. 3. It may be called “ elastic tissue,” though it is not 
exactly like this. It is yellow in colour. Within these 
secondary cysts there is nothing but an unrecognisable cell 
debris containing much oil, which tends to coalesce in droplets 
when the cyst is opened and scraped out. No remains that 
can be ascribed to known parasites can be identified—no hooks, 
spines, or calcareous corpuscles. This is rather a difficulty in 
assuming that we have to deal with a degenerate cestode larvee, 
for the hooks and spines are very persistent. Still, the parasite 
may not have had any skeletal structures and the calcareous 
corpuscles may have been dissolved for the specimen had been 
kept for nearly two years in spirit and part of it was fixed in an 
acid preservative. 

A taxidermist who had the fish supposed that the cysts 
were ova that had been eaten by the fish, but this is obviously 
not the case. Nor are they ova that have not been extruded 
for there is no trace of egg structure. It is exceedingly likely 
that they are really small groups of Plerocercoid larvee which 
have degenerated. In many fishes there are collateral life- 
histories for the contained Cestode and Trematode parasites : 
that is, there is an infection arising by the fish eating some 
animal which contains the larve of the Cestode. Now the 
latter has usually “ definitive’ hosts, one which contains the 
larvee and which is eaten by the definitive final host, where the 


2338 


Cestode comes to sexual maturity. If, however, other fishes 
than the definitive final host become infected the life-history 
of the Cestode cannot be completed, and the larve develop 
no further than the Plerocercoid stage, which finally dies and 
degenerates. But in so doing there is some reaction on the part 
of the collateral host. That is, there is often some kind of 
covering laid down by the tissues of the host and this may 
take extraordinary forms, as for instance, when typical pearl- 
like bodies are formed round the unrecognisable remains of a 
parasite of some kind. This is what has, no doubt, happened 
in the specimens we have. Plerocercoid larve of tetrarhynchid 
tapeworms are very common in many teleost fishes, where they 
appear as little cyst-like bodies attached to the peritoneum. In 
teleosts the development of a Plerocercoid larva ends the life- 
history of the Tetrarhynchus, which then dies and degenerates ; 
but in rays and dogfishes the larva completes its metamorphosis, 
gets into the intestine and becomes a sexually mature Cestode. 
Here, then, we doubtless have some Cestode (but evidently 
not a Tetrarhynchus) which has so entered a cul-de-sac in its 
life-history, has died, become invested in a cyst wall which 
shields the host from its further reaction, and so gives rise to 
these peculiar bodies. 


Tue “ Oyster Parasite,” Gasterostomum gracilescens. 


This is the well-known Bucephalus haimeanus, Lacaze- 
Duthiers.* We have found it already in this district, but 
never in such a heavy infection as in this case. It occurred in 
cockles that were being dissected in a vacation Biology course, 
held at the Piel Laboratory in August, 1921. The infected 
molluscs were bright yellow in the upper part of the visceral 
mass, and out of 55 specimens examined 3 were infected. The 


* See Miss Lebour, ‘A Review of the British Marine Cercarie,”’ 
Parasitology, Vol, IV, No. 4, 1912, p. 424. 


234 


235 


parasites occur in long, greatly-tangled, tubular and branching 
sporocysts. These are represented in A and F, Fig. 4. They 
are full of larvee in various stages of development, but these 
are rather more numerous than are shown in the figures. The 
fully-developed Cercariz are represented in Fig. 4, B and C, 
and less mature ones are shown by D and KE. The body of the 
worm is covered by very closely set spines, arranged in trans- 
verse rows. The tails are extremely long and highly mobile, 
retaining this mobility for some time even after they have 
been accidentally detached from the body. The living sporo- 
cysts and larvee make most interesting objects, but apart from 
their occurrence there is nothing remarkable to record about 
them. Except for the very long tails their characters are just 
such as have been described by Miss Lebour. 


A MyxXoOSPORIDIAN FROM THE HAKE. 


In February of this year, Dr. Hanna, Port Medical Officer 
for Liverpool, sent me the head of a large hake which exhibited 
several tumours. There were three of the latter: one situated 
just in front of each orbit and the third exactly between the 
other two and on the roof of the skull. Each was about an 
inch in diameter and was raised above the general surface by 
about half to three-quarter inch. As usual the skin was much 
broken over these tumours. Cutting down into them it was 
found that they were cartilaginous and that each was full of 
little opaque specks, about one-half a millimetre in average 
diameter. This, of course, at once suggested the nature of 
the tumours—hypertrophy of the cartilage of the head due to 
an extensive infection by a Myxosporidian parasite. In the 
Twelfth Annual Report of this Laboratory (for 1903, pp. 46-62), 
Dr. H. M. Woodcock described various Myxosporidian parasites 
from local fishes, including one from the cartilage of the auditory 


236 


Capsule of a plaice: this he called Spherospora platesse. In 
a later report (No. 15, for 1906, pp. 207-208) Dr. Woodcock 
describes another Myxosporidian which occurred in the sclerotic 
of the Norway Pout, Gadus esmarkii, and this he called 
Myzxobolus esmarkii. Since then we have found that similar 
Myxosporidia are not at all uncommon in the cartilage of the 
auditory capsule of whiting and cod, and these parasites are 
probably identical with the latter one characterised by Dr. 
Woodcock. 

In the hake described here the sclerotic of one eye is 
heavily infected with the Myxosporidian cysts in a way that is 
quite similar to that seen in the specimen of Gadus esmarkii 
referred to above. Not only so, but almost everywhere in the 
skull; wherever there is cartilage the same condition exists. 
There are blunted projections into the mouth, and on cutting 
into these they are seen to be cartilaginous and to contain 
numerous Myxosporidian cysts. Evidently we have to deal 
with a very heavy infection. 

Rough sections were made of the tumours on the head 
and these were found to consist of a fibrous cartilage. Round 
each cyst there appeared to be a thin limiting membrane, but 
there was no fibrous capsule. However, the fixation had been 
a simple, weak formalin one, and so the preservation was too 
imperfect to admit of close study of the histology. 

Fig. 5 shows two of the spores. A is stained with Mann’s 
methyl-blue-eosin and B with carbol fuchsin. The spores are 
lenticular in shape, but very nearly spherical (10 by 9 ~) when 
seen on the flat. There are two oval polar capsules, each 
measuring about 4 w in longest diameter. There is a large 
iodinophilous vacuole. The fixation was so imperfect that 
none of the stains (Mallory and also hemalum were used) 
were able to demonstrate the nuclei. No polar filaments 
could be seen. 


237 


So it is perhaps risky to attempt to identify the organism, 
but it may be safe to place it in the genus Myzobolus; and it 
resembles the form called M. esmarki, by Woodcock, so closely 
that it is not improbable that such is its species. 


Biq. 6. 


ma) 


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Yot 


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| - Lee 
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- 


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hee Onn | onl fis 
bad b) tee 4 efi Tabet a 


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oS} 


LANCASHIRE AND WESTERN 
Se wblisktiikhis, JOINT COMMITTEE. 


el Oe) 


ON THE 


MUEISoE ES 
IN THE RIBBLE ESTUARY. 


Report on the Mussels from the Ribble 
Training Wall. 


By W. Birtwistle. 


A preliminary topographical survey of these mussel beds 
was made in July 1921 by Mr. Scott, and a provisional report 
was then made tothe Committeet. The location of the mussel 
beds, the positions of the sewer outfalls up to date, and the 
characters of the sewage effluents were observed. Further, 
the directions in which these effluents moved were carefully 
noted, as well as the general appearance of the mussels and 
their surroundings. It was then decided that a bacteriological 
examination should be made of those mussels which, from 
topographical evidence, would be expected to show the 
greatest and least possible pollution respectively. 


The locality chosen as probably showing the greatest 
pollution was the Church Scar Bed, and that showing as little 
as any was at a point on the North Training Wall, 13} miles 
from the dock gates at Preston. The exact position is opposite 
the No. 2 Gas Buoy shown on the chart of the 1920 survey of 
the Ribble and Estuary. 


DESCRIPTION OF THE RESPECTIVE LOCALITIES. 
Church Scar Bed. 


This bed extends from about 500 yards west of Lytham 
Pier, adjacent to the northern bank of the Channel for about 
1,000 yards, ending about the tenth mile. Occupying a some- 
what irregular shape, its greatest breadth from the Channel 
boundary is about 150 yards, opposite St. Cuthbert’s Church, 
from which it takes its name. It bares at low water, when 


+ Printed in Superintendent’s Report for Quarter ending 30th Sept., 1921. 


the mussels are gathered by hand. The mussels are matted 
together and form wave-like undulations on a soft, slimy 
mud—in some places 18 inches deep. When the bed was 
visited in the hot weather of the summer, it had a most 
offensive smell, not unlike that of a cesspit. This was not 
noticed on this second visit in November, and the bed was 
much cleaner, probably as a result of abnormally high spring 
tides and much rainy weather. These physical conditions will 
probably tend to minimise the pollution of the mussels. The 
sreatest contribution to the pollution may be expected from 
the Lytham and Ansdell outfalls, which are situated about a 
mile and a quarter to the N.W. from the centre of the bed. 
There are two outfalls about ten yards apart, and these convey 
practically all the sewage of Ansdell and Lytham. The 
effluent is quite untreated, and contained much paper and 
feeces. The direction of flow at low water is m a south- 
easterly direction towards Church Scar bed. About 300 
vards away, however, it tended to flow south, and was lost 
in the innumerable channels on the sand bank. Thus, the 
effluent does not actually flow over the bed. The ebb stream 
itself, however, ebbs mainly in the direction of and over the 
westerly end of the mussel bed, so that it is reasonable to 
suppose that towards the end of the ebb the bed is extremely 
liable to pollution. Another probable source of temporary 
pollution, although perhaps not great, is a large barge which 
is permanently moored over the bed, and which grounds at 
low water. This barge is fitted to accommodate gangs of 
workmen for varying periods, so that here is a pollution 
actually on the bed. . 


Training Wall. Gas Buoy No. 2. 153 miles from Preston 
Docks. 


This point is on the Northern Wall, about two or three 
feet above the level of dead low water at ordinary spring 


tides. The impression one gets here is that the mussels are 
clean and well scoured. There is neither smell nor mud, and 
they are evenly distributed on the shingle and stones forming 
the top of the wall. The main sources of pollution of these 
mussels would be the effluent from the Preston Sewage Farm 
at Freckleton, between the third and fifth miles on the 
northern side of the Channel. The only treatment this 
sewage gets is coarse screening, sedimentation and irrigation 
on the Sewage Farm; it is simply sewage with the coarser 
matter removed. This effluent is run off into the Channel, 
and has to flow about nine miles before reaching the mussels 
under consideration, and it is probable that the dilution must 
largely reduce the risk of serious pollution. Another probable 
source of pollution was evident in the effluent from the Lytham 
East sewer. This drains down a mud gutter, and empties 
into the channel about 70 yards in front of the Pier at dead 
low water. This is about the ninth mile, or four-and-a-half 
miles away from the mussels under consideration. The 
volume of effiuent is small, and it has four-and-a-half miles 
to travel down channel before it reaches the mussels; the 
risk of pollution is not serious. A very important source of 
pollution is the effluent from the Ansdell and Lytham outfalls 
referred to as probably polluting Church Sear Bed. This 
finds its way into the Channel, and must be included as one 
of the sources of pollution of the latter. It appears to find 
its way into the Channel above the 133 mile point, probably 
somewhere about the 10} mile point, in its most concentrated 
condition at low water. 


MetruHops oF BacTERIOLOGICAL EXAMINATION. 


Two samples were collected in the early morning of 
November 3rd, 1921, from the respective areas, packed in sterile 
air-tight tins, and brought to Liverpool immediately after 
collection. The Church Scar sample was examined the same 


afternoon. The North Wall sample was packed in ice and 
dealt with the following morning, November 4th. The usual 
procedure was followed, viz.: an emulsion of five mussels in 
250 c.c. of sterile water, giving a proportion of one mussel in 
50 ¢.c., or one-fiftieth of a mussel in | c.c. was made. One 
c.c. of this diluted emulsion was plated in MacConkey’s Bile 
Salt Neutral-red Lactose Agar, five plates being made, and 
these were incubated at 37° C. for 24 hours. In addition, four 
tubes of Bile Salt lactose litmus broth were inoculated as 
follows. From the original emulsion of five mussels in 250 c.c. 
of sterile water, 1 ¢.c. was taken and put into 100 ¢.c. of sterile 
water. This was called Dilution I., and each ¢.c. contained the 
equivalent of =jth part of a mussel. 


From Dilution I., | ¢.c. was taken and put into another 

100 c.e. of sterile water. This was called Dilution Il., and 
. 1 

each ¢.c. contained i 0th part of a mussel. 

From Dilution IT, 1 ¢.c. was taken and put into 100 c.c. 
of sterile water and called dilution ITI., and each e.c. contained 

1 « 

soo000000h part of a mussel. 


From Dilution III., 1 ¢.c. was taken and put into 100 c¢.c. 
of sterile water and called Dilution LV., and each ¢.c. contained 
1 
& 000,000,000 part of a mussel. 


Thus, four dilutions were made, each succeeding one 
being 100 times more dilute than its predecessor. From each 
Dilution I[., I1., III. and IV., 10 ¢.c. were taken and put into 
four tubes respectively of Bile Salt, lactose, litmus broth 


and incubated at 37° C. Thus it will be seen that the quantity 
of mussel in each tube was jth in L., sath in LH., synth in 
(NEE, chaal saeeinan LY 


It is not considered necessary to give details of sterilisa- 
tion, except that all the usual precautions were observed. 
After 24 and 48 hours’ incubation at 37° C., the plates were 
counted, with the following results :-— 


Church Sear. 


I.—24 hrs. 7 white, 83 smallred, 0 large red colonies. 
ASh LOO) 130 35 Gyre. 


32 


I1.—24 ,, Tete 90 *; 3 99 29 
48 ,, Si) 260 “ 6 » » 
PET 240 13,) 9 Gar» 100 3 6 35 PA 
£518. EZ i ge S00 sS 16 » » 
PVH 24 2 43 LOO a + e > 
48550 V4 in e230. i 12 H » 
V.—24 ,, 


48 ,, was not counted. General fusion of colonies. 


In the above results the round white colonies varied from 
approximately ;5th” to gth” in diameter, the small red from 
approximately 34nd” to 75th”, and the large red from kth” 
to th’. Some of the large red colonies tended towards a 
paler shade, almost a pink, while the small red were a deep 
red surrounded by a rosy halation. The white colonies 
without exception had a small red centre. After 24 hours’ 
incubation, the plates showed a large number of microscopic 
red points, which resolved themselves into the usual small 
red colonies. The results of incubation of the Bile Salt 
lactose litmus broth were as follows :— 


I.—This tube after 24 hours showed an acid re- 
action and was gassing freely. This contained ~4,th 
part of a mussel. 

II.—This tube after 48 hours showed a slight acid 
reaction, but no further change after prolonged in- 


5 . . 1 
cubation. This tube contained x oth part of a mussel. 


IIT. and IV. showed no reaction, even after pro- 
longed incubation. 


As a result of these tests and the consequent evidence of 
the presence of the Bacillus coli group of organisms, it was 


decided to submit several colonies for detailed examination. 
This was very kindly carried out by Mr. Smith, of the Bacterio- 
logical Department in the School of Pathology, whose report 
is embodied in this one. He examined a plate of each sample, 
on which white colonies were numerous. These were regarded 
as significant of recent pollution, and were subcultured with 
the following results :—Lactose A, Saccherose +, Glucose +, 
Mannite +, Maltose +, Indol —, Motility +; A = Acid, + = 
acid and gas, — = no reaction. The organisms were identified 
as Friedlander’s Pneumobacillus. No organisms of known 
pathogenicity were found. The relative proportions of 
occurrence of the different organisms studied were Pneumo- 
bacillus Friedlander +, B. Coli + + +, Streptococci + +. 


The most significant of these results is the relative abun- 
dance of Streptococci. This organism exists in large numbers 
in human feeces, and its association with other fecal bacilli 
not only indicates serious, but also recent, pollution as it 
is a delicate organism and only survives for a short time when 
isolated. 

North Training Wall. 15} miles from Preston Docks. 


+ 


No. 2 Gas Buoy. 


1.—24 hrs. 0 white, 100 small red, 0 large red colonies. 


[ids a oD if ee co 
fpeton SG? tae BERD ir pe Ps " 
IV.—24 ,, Quits O70) = 16 a a 
V.—24 ,, 5 ,, This plate was sent to Bacteriological 


Department and not counted, but 
contained a large number of small red 
colonies. 


VI.—24 ,; | uae 177 small red, 2 large red colonies. 


After 48 hours a great many more microscopic red colonies 
became visible, in addition to those already counted, so that 


these counts only represent the minimum number of organisms 
present. The small colonies which were counted were those 
easily visible to the unaided eye, and were mostly about 7;th” 
in diameter or less, and were well scattered. 


Result of Incubation in Bile Salt Lactose Litmus Broth :— 


Four tubes were inoculated as before, with the following 
results :— 


Tube I., after 24 hours’ incubation, showed an 
acid reaction but no gas formation, but after 48 hours 
was gassing freely. There was no reaction in Tubes 
II., III. and IV. after 48 hours. 


These four tubes were incubated for a long period, 
but no further reactions were observed. 


The result of the examination of the suspected white 
colonies on Plate V. by Mr. Smith was as follows :—Lactose 
A, Mannite A, Maltose A, Indol +, Motility +. A= acid 
production. An agglutination test against Bacillus typhosus 
and Bacillus dysenterie was carried out with negative results. 
The organism examined was identified as Bacillus pyogenes 
fetidus. Other bacilli present were Bacillus coli and Strepto- 
coccus. No organism of known pathogenicity was found. 
Here again is evidence of fecal pollution, but of a different 
character from the Church Scar sample. The main feature 
is the relative abundance of lactose-fermenters and the absence 
of non-lactose fermenters. 


Comparison of the two Samples. 


In comparing the two samples, the following explanations 
should be carefully noted. The average number of organisms 
per mussel in the Church Scar sample is estimated from four 
plates after 48 hours’ incubation. The fifth plate was dis- 


carded owing to a general fusion of the colonies in the centre, 


10 


thus rendering a count of no value. The count after 24 hours 
is shown. In the North Training Wall the average number 
of organisms per mussel is estimated from five plates after 
24 hours incubation. After 48 hours the increase in the 
number of colonies was very considerable, but these were all 
microscopic ; consequently, it was decided not to count them ; 


so the estimation shows the minimum organisms per mussel. 


Average numbers of organisms of different categories 


found per mussel :— 
N. Training 


Church Sear. Wall. 
24 hrs. 48 hrs. 94 hrs. 

Lactose fermenters— 
Small colonies ... 4,662 ...11,500  ... 16,200 
Large Colonies ... 162... 425 ... 240 
Lactose non-fermenters 275 ... 425 1... 10 


Acid and gas were produced in lactose, bile salt, litmus 
: . . 1 
broth in =3,th part of a mussel, and acid only in jyoth part 
of a mussel in the case of the Church Scar sample. 


Acid and gas were similarly produced in 535th part of a 
. . 1 . 
mussel, but no reaction was observed in sp.th part in the case 
of the Training Wall sample. 


CONCLUSIONS. 
Church Scar.—There is evidence of recent fecal pollution 
borne out by topographical evidence, and particularly by the 


presence of Streptococci in relative abundance. The presence 
. . "WW: . 1 
of acid forming bacilli was detected in sooth part of a mussel. 


North Training Wall.—The pollution here appears to be 
of a more diffuse nature. There are more lactose fermenting 
bacilli and fewer non-lactose fermenting organisms than in 
the Church Scar sample. Topographical evidence would 
suggest that sewage bacilli have to undergo a longer period of 
isolation from their normal habitat than those reaching 
Church Scar. This may have resulted in a natural selection 


11 


in the course of which bacillus coli remains, while the less 
resistant non-lactose fermenters are eliminated. Probably 
at the late ebb and early flood the water is highly infected with 
bacillus coli, so that these mussels may always contain a large 
number of this organism. The presence of streptococci 
suggests a recent fecal pollution. The nearest point of 
infection would be the point referred to at the ten-and-a-halt 
mile mark (three miles away) where the Lytham and Ansdell 
sewers ultimately discharge into the Channel. The presence 
of streptococci seems to indicate, therefore, that the Training 
Wall beds are little better than those at Church Scar. The 
significance of the presence of Friedlander’s Baeillus and 
Bacillus pyogenes fetidus in the Church Sear and Training 
Wall samples respectively is not discussed. Conclusions as to 
the degree of pollution are best based on the occurrence of 


bacillus coli and streptococci. 


Before concluding this report, thanks are expressed to the 
Ribble Navigation Committee and to Mr. Cochrane, the 
Assistant Engineer, for the invaluable assistance given. 
Without his help it would have been a most unsatisfactory 
undertaking, if not impossible. The Engineer's launch, the 
* Aid,’ was placed at our disposal on the two occasions these 
beds were visited, thus enabling a wide area to be examined 
while uncovered by the tide in a minimum of time. 


It is, perhaps, not out of place to report on the value of 
mussels to an undertaking like the Ribble Training Walls. 
The intention is to make Preston a seaport town, and to 
accomplish this it has been necessary to dredge a deep channel 
as far as the deep water, some 14 to 16 miles away. To 
ensure the permanence of this channel, each bank has been 
reinforced with rubble practically all the way from the Docks. 
The constant danger is the washing away of the walls, as they 
are only loose stones and easily dislodged by strong tide. 


12 


The mussels, however, accumulating in large numbers on 
these walls, form a fine natural binding material, and are 
regarded vory favourably by engineers in charge of this 
work. 


OBSERVATIONS ON THE ABOVE REPORT. 
By Professor J. Johnstone, D.Sc. 


It is not any easier to give practical interpretation to the 
above report than to any others made on the local shellfish 
layings. So far as I know, nothing has happened lately that 
tends to cast strong suspicions on the mussels taken from the 
Ribble Training Walls, and in the absence of such strong 
suspicions the bacteriological evidence produced does not 
seem to me to justify any restrictive measures. It must be 
noted that some degree of bacterial pollution must be expected 
in all the mussels taken from such a foreshore as that of 
Lancashire. Considering everything, it may be safely con- 
cluded that some degree of pollution may reasonably be 
neglected. What then are we to understand by ~ some.” 
There has been no official ruling or utterance on this point, 
either by the Public Health or the Fisheries Central Authori- 
ties, and until this has been made it is unsafe to base any 
recommendations as to restrictive action on bacteriological 
evidence alone. 


This caution is all the more necessary since we know that 
mussels may be exposed to notable contamination after they 
have been “* removed from the fishery ” and are being handled 
on their way to the consumer ; evidence that this may be the 
case was produced at a public enquiry into the contamination 
of mussels from the localities mentioned in this report. The 
case for action (if any) ought rather to rest on the topographical 
and epidemiological evidence—that has been the general 
opinion—so far as there has been any general agreement on 
the matter. 


13 


I have seen these localities myself and have made 
analyses (which agree as well as can be expected with those 
made by Mr. Birtwistle). I found in 1913 a mean of 21,000 
organisms per mussel from samples taken from the Training 
Wall. and 19,000 per mussel from a sample taken from Church 
Scar in 1916. The conditions that may be seen in the Channel 
adjacent to the Training Wall do not suggest pollution at 
all; the water, and the banks, &c., exposed on the ebb tide 
look clean and healthy, and this was also the opinion expressed 
by Mr. Scott, who has had very much experience of this kind 
and is a highly competent judge. The Royal Commissioners 
on Sewage Disposal say much the same thing. ~* Our general 
impression,’ they wrote, ~ of the whole Ribble Estuary was 
very favourable. In spite of the extensive and populous 
district draining into it, and the varied industries contributing 
their trade effluents, no marked indications [of sewage] are 
to be found, even a few miles below Preston, while at Lytham 
all signs have disappeared.” (Rept. V., App. VI. ed 4284, 
1908.) 


} 


But the impression that one obtains by personally 
examining Church Scar is different. There is evidence of 
recent and immediate sewage pollution; there are privies 
actually discharging on the Scar itself, and there are two large 
outfalls of crude sewage about a mile and a quarter away from 
the centre of the mussel bed. The latter may smell offensively, 
and in addition to all that, there is the general pollution of 
the Ribble. Whatever value the fishery on Church Scar may 
have cannot be much, but much or little, it seems reasonable 
to urge that mussels taken from this bed should certainly not 
be marketed for human consumption without being relaid, 
or otherwise purified. If that is impossible, then the fishery 
had better be prohibited. 


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