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) TRIBUTIONS OF THE
OY, L bale MUSEUM OF ZOOLOGY

a i No. +30: EUROPEAN STUDIES OF THE POPULATIONS
: ee Ber, OF MARINE FISHES

- BY J. R. Dymonp

Reprinted from Bulletin of the Bingham Oceanographic Collection,
Vol. XI, Art. 4, May 1948.

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Reprint from But. Bing. Ocean. Cou., Vol. XI, Art. 4, May, 1948

8. EUROPEAN STUDIES OF THE POPULATIONS
OF MARINE FISHES

By JoHun R. DymMonp

Royal Ontario Museum of Zoology

TABLE OF CONTENTS

Page

emery clevev/at rae itn) oil hi etd ead oils Aouad ies sretld Lethal gibi le wa hidln' aM laid «babe Beara 55
MMII ALTER hoor, GETS Sistah erat ee MO eee euler state amutiss anton Seelard GOS ane, ae ne aii 56
International Council for the Exploration of the Sea................6-. 57
IIS ISIE AR OR Si! 2 ro) ria ats ead tind Wis. tej ane Mane sim euase kata 58
es Or rinetua tions in ADUMAg DCR o 9. cio 6) div x oe aiare.acel a eseieia wilew eiebn ep 59
Fluctuations Due to Hydrographic Conditions.....................005: 60
Fluctuations in the Fauna of the Sea Bottom....................0000- 62
nT Baad ete Mil ek Ai Ne as Ds ete se ed oa AP i Re 63
eames ereemmierirn E ee errs) 2 518 Pee lacs ee WD On ee Oa as VEN 64
NMI CU MINE NESEIES): (721520, chs Some rs eared) avers ght ede Sag 66
0 gl TARE SAAR ie a, AEE Ae a Mies aie a Dales Ea eal aaa MU a FE 70
SC eRMNRIISS STON ee Moe grein, Sueeehe. reat, Set eden aban, ASS Se POSE 70
EME tee ee Eee I Sane ae che eat ae ee Ped Nee. ee os es 71
I ee re ee, ee ETS PI NM) AE TEP OER aa 72
ETT Tyabb a8 Bi ulead RS a RUN i tt se 2 73

ABSTRACT

The study of the fish populations of European waters developed chiefly in the
Scandinavian countries and in Great Britain largely as a result of the economic
importance of the fisheries to these countries.

Outstanding discoveries include the facts that some year-classes are fifty or sixty
times as abundant as others, that such wide fluctuations characterize most of the
important commercial species, that even when fish are abundant there are wide
fluctuations in availability due to hydrographic conditions, and that great fluctua-
tions in abundance also characterize the fauna of the sea bottom.

Demonstration of considerably increased mortality due to fishing has led to action
designed to prevent overfishing. The International Council for the Exploration of
the Sea has contributed materially towards the study of these problems and in
initiating international action to meet situations uncovered.

An important feature of the study of populations has been the recognition and
description of local races—more or less discrete populations having separate spawn-

55

56 Bulletin of the Bingham Oceanographic Collection [XI: 4

ing areas and characterized by average differences in certain morphological characters
such as numbers of vertebrae, of scales and of fin-rays.

The discovery that the age of fish and certain characteristics of their life histories
could be read from the scales has been basic to many phases of population work.
The organization of statistics, especially those on an international scale, has also
been an indispensable tool in population studies.

The understanding of populations and of the factors affecting them has reached
the stage where in some species fishing probabilities have been attempted with
considerable success.

DISCUSSION

Sixty-five years ago Huxley (1881) made some estimates of the
population of herrings in the North Atlantic, based on his work as a
member of two successive Royal Commissions investigating fisheries.
He estimated that there must have been scattered through the North
Sea and the Atlantic at one and the same time scores of shoals of
herrings, any one of which would go a long way towards supplying
the whole of man’s consumption of herrings. He did not believe that
all of the herring fleets together destroyed five per cent of the total
number of herring in the sea in any year. He concluded that:

the best thing for Governments to do in relation to the herring fisheries, is to let
them alone, except in so far as the police of the sea is concerned. With this proviso,
let people fish how they like, as they like, and when they like. . . there is not a
particle of evidence that anything man does has an appreciable influence on the stock
of herrings. It will be time to meddle, when any satisfactory evidence that mischief
is being done is produced.

It should be remembered in connection with this conclusion that it
was reached in relation to the herring and at a time when trawling by
steam-driven vessels had scarcely commenced.

The modern concern of European investigators, such as E. §S.
Russell (1942) and Graham (1943), with what they call the over-
fishing problem is chiefly about demersal species taken by trawling.

Fisheries research in Europe gradually developed during the last
half of the nineteenth century, chiefly in the Scandinavian countries,
in Great Britain and in Germany. The urge to study the fisheries
arose largely from economic necessity. As EK. 8. Russell (1932) pomts
out, in certain communities, notably in northern Norway where the
population is mainly dependent upon fishing for a livelihood, the suc-
cess or failure of the fishing is almost a matter of life or death.

1948} Dymond: European Studies of Populations 57

International Council for the Exploration of the Sea. The Council
has played an important part in stimulating and co-ordinating research
on population problems in European waters. It was formed in 1902
as a result of preliminary international conferences held in 1899 at
Stockholm and in 1901 at Christiana.

The most pressing fishery problem at that time was the supposed
depletion of the plaice in the North Sea through excessive fishing, and
the chief work of the Council until the outbreak of the first great war
was the investigation of the plaice fisheries. However, it had con-
cerned itself also with herring, cod, mackerel, salmon and other food
fishes as well as with hydrological and plankton investigations. At
its last meeting before the war of 1914-1918 the Council decided on a
program for extending its investigations to the North Atlantic gener-
ally, because it was recognized that conditions in the Atlantic had an
important bearing upon conditions in the North Sea and that the
development of steam power in fishing must inevitably extend the
horizon of European fishing interests and consequently of fishing
investigation.

The Council carries out no investigations of its own, although it has
a small staff for recording and co-ordinating data collected by the
participating countries. Each of the participating powers undertakes
a share in agreed programmes of investigations, to be carried out at its
own cost and by the means at its disposal. The co-operative studies
undertaken under the auspices of the Council have usually been con-
cerned with such subjects as, factors affecting abundance of fish in
different areas, effect of destruction of undersized fish, effect of insti-
tution of size-limits of fish that are allowed to be landed, effect of
installation of minimum mesh sizes of nets, closed seasons, nursery
grounds, and whaling.

The countries supporting the work of the Council have varied from
time to time. At present they include Great Britain, France, Spain,
Belgium, Denmark, Eire, Holland, Iceland, Norway, Poland, Sweden
and Finland.

The publications of the Council include:

Rapports et Procés-Verbaux, Publications de Circonstance, Journal
du Conseil, Bulletin Statistique, Bulletin Hydrographique, Bulletin
Planctonique, Bulletin Trimestriel, Faune Ichthyologique de ]’Atlan-
tique Nord, Annales Biologiques, Current Bibliography, and Special
Publications.

58 Bulletin of the Bingham Oceanographic Collection [XI: 4

Fluctuations in Abundance. Wide fluctuations in abundance are a
characteristic feature of animal life in the sea (Kemp, 1938). Because
of the effect of such fluctuations on the economic life of Norway, a
study of fluctuations was undertaken in that country in 1901 by Dr.
Johan Hjort, then Director of Fisheries, aided by Einar Lea and
Oscar Sund. A study of the age composition of the herring stocks of
successive years soon led to the discovery that different year-classes
varied markedly in their contributions to the stock of fish supporting
the fishery (Hjort, 1914, 1926) and that wide differences in the success
of various year-classes was one of the chief causes of fluctuations in
the fishery. This principle was strikingly illustrated by the occurrence
of the rich year-class of 1904, which dominated the Norwegian herring
fishery for a long period of years. Other good year-classes were those
of 1913 and 1918, while those of intervening years were poor.

In the case of the Norwegian cod, specially prolific brood-years were
those of 1904 and 1912. Thompson’s (1930) work on the haddock
showed that in 1920, 1923, 1926 and 1928 the brood was much above
the average, while in the intervening years the supply was moderate
or poor. A specially good brood-year was found sometimes to con-
tribute to the stock up to 25 times as many young haddock as a poor
year. Other workers have found in the case of other species that it is
not uncommon to find fish belonging to one year-class fifty or sixty
times as numerous as those of another.

The fact that year-classes differ widely in their numerical strength
has been demonstrated in the case of most of the important food fishes.
This was emphasized in the reports of a meeting of the International
Council for the Exploration of the Sea held in London in 1929, at
which the problem of fluctuations was given special consideration
(Rapp. Cons. Explor. Mer, 65, 68). Papers were given (1930) by
Hjort, Sund, Thompson, Lea, Hodgson and others on fluctuations in
cod, haddock, hake, plaice, herring, pilchard, sprat and lake herring.

The subject of fluctuations was also considered at a special biological
meeting of the International Council held in 1936 (Comparative studies
of the fluctuations in the stocks of fish in the seas of North and West
Europe, Rapp. Cons. Explor. Mer,.10/ [See, e. g., Sund, 1936)).

In commenting on the problem of fluctuations due to the success or
failure of brood-years, Hjort (1930) stated that there was ‘‘no agree-
ment between the various species of fish in this respect in the same
year. Only in particular cases (herring in the coastal waters of Nor-

1948} Dymond: European Studies of Populations 59

way and the sea around Newfoundland, and cod in the coastal waters
of Norway and Davis Strait) has it been observed that the same year-
classes were unusually abundant, on both occasions in waters situated
widely apart.”

Years when plentiful year-classes of cod were produced more or less
over the whole range of the cod’s distribution in the North Atlantic
are given as 1924 and possibly 1912, 1917 and 1927. It is also be-
lieved that there are probably years of production of poor classes more
or less general over wide areas. It is known for certain, however,
that there are years in which good year-classes are produced in some
regions and moderate or poor year-classes in others. It is assumed,
therefore, that the causes of annual fluctuations are usually restricted
both in space and time.

Causes of Fluctuations in Abundance. Search for an explanation of
the causes of the wide differences in the size of different year-classes
has brought out the fact that there is no necessary connection between
the number of eggs produced in a particular spawning season and the
number of fry which survive. Poor spawning years have often been
good brood-years. It is usually assumed that the critical period of
great mortality falls in the first few days or weeks after the eggs hatch.
Factors suggested as influencing the hatching and survival of young
include the following.

1. The origin of a rich year-class would require the contemporary hatching of the
eggs and the development of the special sort of plants or nauplii which the newly
hatched larva needed for its nourishment (Hjort, 1926).

2. The young larvae might be carried far away out over the great depths of the
Norwegian Sea, where they would not be able to return and reach the bottom on the
Continental shelf before the plankton in the waters died out during the autumn
months of the first year of their life (Hjort, 1926).

Heavy gales may so disturb the sea bottom as to produce conditions
unfavorable for the eggs or larvae.

Sund (1924) found a direct correlation between the rich year-classes
of Norwegian cod and the years of smallest snowfall.

Long term studies such as those of F. S. Russell (1930-1940) are
necessary for the elucidation of factors affecting the success of year-
classes. These studies at the Plymouth Station were aimed at de-
termining the extent to which a planktonic population of young fishes,
comprising some fifty or more species, ranges in its proportional com-

60 Bulletin of the Bingham Oceanographic Collection [XI: 4

position from year to year, and determining also whether or not a good
or bad year for one species held good also for certain other species.
It was hoped that, if a number of species were affected in the same way
in one year, indications of some of the causes of such fluctuations
might be obtained.

During the course of Russell’s studies it was found that a serious
decline in the numbers of young fish was correlated with a marked
change in the amount of phosphate in the waters. Renewal of the
phosphate in the channel appeared to be largely dependent on the
inflow of mixed Atlantic water which is rich in phosphate because it
contains water that has upwelled at the edge of the continental shelf.
It seemed probable that the normal water movements off the mouth of
the channel had undergone changes, and that these changes were in-
directly responsible for the decline in the production of young fish.
A by-product of the study was the discovery that certain planktonic
animals are indicators of water-masses and are thus useful in tracing
water movements.

The variation of such important constituents of sea waters as
phosphate, silicate, nitrite and nitrate, seasonally and with depth, their
replenishment and the part they play as factors of plant growth, have
been studied by Atkins (1926) and Harvey (1928). Phosphate ap-
pears to be a limiting factor, at least at certain times.

The successful rearing of the fry of marine fish by Rollefsen (1939)
is throwing light on the subject of the need of recently hatched fry on
food of a certain size and kind. Plaice larvae have been successfully
reared by feeding with nauplia of Artemia. Cod fry have also been
fed on nauplia of Artemia, but success is not claimed in rearing this
species.

Soleim (1942) has investigated the relation between high mortality
of herring fry and poor plankton.

Fluctuations Due to Hydrographic Conditions. In contrast to the
fluctuations in the fishery due to differences in the size of year-classes,
which tend in most cases to be of short duration, there are fluctuations
due to hydrographic conditions, which tend to be of long-term dura-
tion. Fluctuations due to differences in the success of brood-years
are usually restricted to a certain species in a particular area, while
fluctuations due to hydrographic conditions often extend over a period
of years and involve much larger areas and large numbers of species.

1948} Dymond: European Studies of Populations 61

Fluctuations in migrations of herring to the coast do not necessarily
reflect fluctuations in the stock; they produce changes in availability
rather than changes in abundance. According to Runnstrgm (1937),
in certain years Norwegian herring spawn mainly in deeper water and
on more offshore grounds than in other years, and then the fishery
bears on only a part of the spawning stock. The most extreme
shifting of spawning places seaward seems to have taken place in the
’seventies of the last century when the spring-herring fishery on the
southwest coast was a total failure for a series of years. Herring
shoals were observed at sea, however, and herring roe was found in
deep water. The abundance of herring fry in coastal waters indicated
also that there had not been any considerable decrease in the spawning
stock.

Through the use of the echo sounder the movements of spawning
herring are now followed throughout the season. By this means it
has been shown that the fishery has fallen mainly on shoals spawning
close to the coast while great herring shoals have remained for weeks
unexploited on more offshore grounds.

This type of fluctuation is also illustrated by the Bear Island cod
fishery. In 1925, and for several years following, the Norwegians
found great numbers of cod on the banks surrounding Bear Island.
There had been a former occasion between 1874 and 1882 when cod
were plentiful in this area. Between 1883 and 1925 the grounds were
examined on a number of occasions but very few cod were found.
Another instance is afforded by the cod fishery in West Greenland.
At certain times large concentrations of cod appear on this coast and
spread as far north as Disko Bay, but after a term of years their num-
bers suddenly decline and a protracted period of scarcity follows.
Both these occurrences apparently were due to the fact that for a
period of years in the 1930’s the entire area from Greenland to Bear
Island had become appreciably warmer. Increased sea temperatures
probably of the order of 1.0° to 2.0° C. had allowed various species of
fish to extend beyond the usual limits of their distribution. Hydro-
graphic conditions in this case determined the size of that part of the
stock that was at the disposal of the fishery in a certain area. The
effect of hydrographic conditions may, therefore, mask the effects of
fluctuations due to varying year-class sizes and may at times render
fishery prediction unreliable.

The study of hydrography, and particularly of the currents, is

62 Bulletin of the Bingham Oceanographic Collection (XI: 4

fundamental for an understanding of the life and movements of the
fish. The work of Graham (1924) and Graham and Carruthers (1925)
on the relation of currents and other hydrological conditions to the
life history and distribution of the cod afford examples of the correla-
tion which can be established between hydrographical and biological
conditions. In the study of such relationships the International
Council plays a most important role in organizing systematic sampling
through such agencies as steamships, lightships and research vessels.
The tabulated results, mainly for temperature and salinity, are pub-
lished annually in the Council’s Bulletin Hydrographique.

Fluctuations in the Fauna of the Sea Bottom. Fluctuations also occur
in the fauna of the sea bottom. Davis (1923, 1925), in the course of
extended investigations on the Dogger Bank, found that certain small
bivalves sometimes occurred over enormous areas, thus providing rich
feeding for haddock and plaice. Some of these beds covered areas up
to six or seven hundred square miles. One bed, whose population was
estimated at 4,500,000,000,000 was composed largely of shellfish of a
single year-group. These investigations which continued for several
years showed that great changes took place from year to year in both
extent and location of the beds.

Davis considered that the most probable cause of these fluctuations
was changes in the course of the currents by which the larvae are
passively transported. Species which are restricted to a particular
type of bottom, if they do not happen to be deposited by the currents
on suitable ground, produce scant crops. Subsequent investigations
have shown that fluctuations in the fauna of the sea bottom, as in
the case of the fishes, are the rule rather than the exception and that
this holds good also in the littoral region.

Blegvad (1914) has investigated the food-chains of fish and fish
larvae down to their ultimate elements.

Petersen and Boysen-Jensen (1911) and Petersen (1914, 1918, 1922,
1924) were the first to apply quantitative methods to the study of
bottom fauna of the sea. For use in his studies, Petersen invented a
bottom sampler, since known as the Petersen grab, by means of which
he was able to bring up the soil and animals contained in it from a
definite area of bottom. As a result of his studies of the fauna of sea
bottom, Petersen developed the idea of communities, natural groups
of species inhabiting more or less well defined areas which could be

1948] Dymond: European Studies of Populations 63

mapped. He recognized and mapped the location of eight types of
communities in Danish waters. These were defined with reference to
“characteristic species.’”” One of his communities, for instance, he
called the Macoma community from the prominence of the small
bivalve Macoma baltica in it. Each community had fairly definite
relations to depth of water, character of bottom, and probably also to
such factors as temperature and salinity. Although Petersen recog-
nized the importance of soil texture in determining the distribution
and abundance of bottom organisms, this character has been still
further emphasized by Davis (1925) who is inclined to substitute for
the Petersen community the principle of soil associations.

Fishing Mortality. In regulating fishing in an effort to maintain the
maximum continuous yield it is necessary to have information on rates
of mortality due to fishing and to natural causes. Attempts to esti-
mate reductions in populations arising from each of these causes have
been based on the results of age analysis of fish stocks and of tagging
experiments.

At a meeting of the International Council held in Berlin in 1939
the results of such studies were discussed by E. 8S. Russell, Graham,
Thursby-Pelham, Raitt, Jensen and others (Rapp. Cons. Explor. Mer,
1939, 110). Since the results have also been summarized by E. 8.
Russell (1942) it is perhaps sufficient for the present purpose to quote
one or two examples of the sort of results obtained.

For the haddock of the North Sea, Raitt (1939) concluded:

Of the second-year frequency of the brood of 1923, for instance, 15% was removed
in the third year, a further 50 in the fourth, and 20 in the fifth. Of the second-year
frequency of the brood of 1933, 65% was removed in the third, a further 25 in the
fourth, and nine in the fifth, leaving only one per cent. as against 15 in the case of
the brood of 1923. By the end of its third year the ranks of the 1933 brood were
reduced by two-thirds of their second-year strength, which was as much as the 1923
brood suffered in its third and fourth years together. The average age to which the
1923 brood survived was four, and that of the 1933 brood less than three.

These results give a measure of the increase in the rate of mortality
between 1923 and 1933.

In extensive plaice-tagging experiments carried out from 1929 to
1932 (Hickling, 1938) on the continental side of the southern North
Sea, during which nearly 20,000 fish were marked, it was found that,
excluding the smaller fish which are not returned in their true propor-
tions, the percentage recaptured in the first year after tagging varied

64 Bulletin of the Bingham Oceanographic Collection (XI: 4

from 40 to 55 depending on locality. Judging from the numbers
recaptured, it was concluded that there was a general rate of decrease
in the stock of the order of 70 per cent per annum, a rate which would
leave only two fish per thousand marked still surviving at the end of
the fifth year of life.

The Overfishing Problem. A great deal of attention has been given
in Europe to what is called the Overfishing Problem. Overfishing is
defined as that condition in which the more you fish the less you catch.
One statement of the situation is as follows:—If we start with an un-
fished or virgin stock and gradually increase the amount of fishing, we
get for some time a continuously increasing yield accompanied shortly
by a decreasing catch-per-unit-of-fishing-effort. But the yield does
not go up in direct proportion to the amount of fishing; the ascending
curve of yield begins to flatten out, and there comes a time when a
maximum yield is obtained. Thereafter, if fishing is still further in-
creased, the total yield falls off. That is what is meant by over-
fishing—the state in which the more you fish the less you catch.

If we wish to obtain the maximum steady yield from a stock, we
must fish neither too much nor too little but at an intermediate rate,
such that the number caught multiplied by their average weight is,
and remains at, a maximum. If we fish too little, we do not catch a
sufficient number to give the maximum steady yield in weight. If we
fish too much, the average weight of the fish caught is too low to give
the maximum yield. There must be, it has been concluded, for every
stock of fish an optimum rate of fishing which will give the maximum
steady yield (subject, of course, to variations due to natural fluctua-
tions, which, however, cancel out over a period of years, and to varia-
tions in growth-rate).

A year-class of fish, after it has survived the heavy mortality inci-
dental to its early life, will, if protected from fishing, increase in total
weight for some years, the loss due to natural mortality being well
over-compensated by the growth of the survivors. The only com-
parison I have been able to find between a virgin or unfished stock of
fish is that quoted by E. S. Russell (1942). The population of plaice
on newly discovered grounds in the Barents Sea was found by Atkinson
(1908) to consist almost entirely of large fish, mostly over 40 cm. and
mostly mature. In contrast to this the population of plaice in the
North Sea, which had been fished commercially, consisted of fish

1948] Dymond: European Studies of Populations 65

mostly under 40 cm. in length, and the proportion of mature fish was
much less than in the Barents Sea. The average size at first maturity
is approximately the same in both areas, namely 39-40 cm.

Ever since Petersen’s (1894) work on plaice in Danish waters there
has been general agreement that it must pay the industry to allow fish
to grow to a medium size. H.s studies emphasized the fundamental
importance of rate of growth a..d of food supply. The limited amount
of food restricts the productioa of fish. ‘“‘A stock of plaice with a low
growth-rate will not yield the same annual production as a stock with
rapid growth; a very dense, slowly growing stock will give but a very
poor yield, as almost all the food will go simply to the maintenance of
life and next to nothing can be used for growing purposes.” Rapid
production and early cropping were, in Petersen’s view, the things to
aim at in the regulation of fisheries.

E. S. Russell (1942) points out that in the early days of fishery
science most workers thought that the main thing to aim at was to
keep up the supply of mature fish so that an abundant supply of eggs
and larvae and young fish might be assured. It was thought impor-
tant, therefore, to prevent the capture or destruction of sexually im-
mature fish, and very high size limits were advocated. Petersen
pointed out that such measures might easily defeat their own ends if
they resulted in producing overcrowded stocks of young fish, which
grew slowly and consumed a great amount of food to little purpose.
He advocated size limits of a moderate kind.

Some writers have exaggerated Petersen’s view and oppose all meas-
ures for the protection of undersized fish. Up to a certain point
fishing is good for a stock, since it clears out the accumulated stock of
old slow-growing fish. It thus enables the remainder to grow more
quickly and makes room for the oncoming brood. The thinning of
younger fish should result in increased growth-rate and, therefore, of
productiveness. Up to a point, yield can be increased by increasing
fishing, but after this maximum is reached, increased fishing produces
a less weight of fish (see also Graham, 1943).

There seems to be general agreement on the part of European fishery
biologists that there is too much fishing for demersal fish and that the
fish are being taken too young. Through the machinery provided by
the International Convention on Mesh and Size Limits, undersized fish
are protected from capture.

66 Bulletin of the Bingham Oceanographic Collection [XI: 4

Racial Investigations. One of the aspects of fish populations to
which a great deal of research has been devoted in Europe is the exist-
ence of so-called local races. Within the total area of distribution of
most of the species of fish that have been investigated, local popula-
tions have been found which can be distinguished by morphological
and other characteristics. Thus the cod of the North Sea, of the
Norwegian coast, and of Iceland, are separate stocks, each with its own
spawning grounds and areas of distribution, and each distinguished
from the others by the possession of morphological characteristics
peculiar to it.

One of the first workers who made a careful study of the differences
between local populations was Heincke. Matthews (1886), in an ac-
count of his studies on differences among Scottish herrings, refers to
Heincke’s ‘‘elaborate investigations into the varieties of the herring of
the Baltic, including a few from the North Sea (Peterhead and Norway)
and whose results appear in an excellent report published by the Ger-
man Fishery Commission (Jahrsbericht der Comm. Z. Wissensch.
Untersuch der deutschen Meer, 1878. 1882).”” Matthews (1886, 1887)
used 14 body proportions, as well as counts of fin-rays and keeled
scales in his study of differences among the summer and winter herrings
of the Scottish coasts. He emphasizes the necessity of examining
large numbers of specimens, mentioning the “‘amount of almost
‘drudgery’ entailed in an investigation of this nature . . . In my own
case, the mechanical work entailed amounted to the taking of about
16,000 measurements on the herrings, with over 20,000 subsequent
calculations.”’

Heincke (1898), who is usually given credit for demonstrating the
existence of “‘races’’ among herring, showed that fish from different
areas have characteristics peculiar to themselves. Local populations,
he believed, could be identified by their body proportions and by the
number of certain structures. The body proportions he used included
length of head and the distance from the head to other parts of the
body. Other characters used included number of vertebrae, number
of rays in certain fins and number of scales along the underside of the
fish.

Williamson (1900) followed with work on the mackerel using 27
characters. Later workers have limited their observations to fewer
characters such as vertebral and fin-ray counts, which has enabled
them to make their studies on very much larger numbers of individuals.

1948} Dymond: European Studies of Populations 67

Thus in Schmidt’s (1930) racial investigations on the cod, only two
characters were always examined, namely the number of vertebrae
and the number of rays in the second dorsal fin. Only occasionally
were the number of pectoral and branchiostegal rays examined. His
studies involved the examination of about 20,000 specimens from 114
stations distributed over the greater part of the range of the species in
the Atlantic.

These investigations showed that the cod of the North Atlantic con-
sist of a number of more or less distinct populations, differing from one
another in a number of morphological characters. In vertebrae and
fin-rays of the second dorsal it was found that the number increased
from south to north in the open waters. Thus, in European waters the
lowest values were found west of the British Isles and the highest in
northern Norway. Similarly in American waters, the lowest were
found off the coast of the United States and the highest off northern
Newfoundland and Labrador. There was also a difference in the
average values on the two sides of the Atlantic such that the number
of vertebrae increased from east to west. From west of Scotland,
where the lowest number of vertebrae (51.47) was found, the number
progressively increased around the Faroes, Iceland, East Greenland
and West Greenland to Labrador and northern Newfoundland, where
the highest value (55.46) was found. Paralleling these differences in
the number of vertebrae, the average values for the second dorsal fin
showed an increase from south to north on both sides of the ocean and
an increase from west of the British Isles over the Faroes, Iceland and
Greenland to Newfoundland. In European waters, the number of
second dorsal fin-rays practically never reached 20, whereas average
values above 20 were the rule in American waters.

Typical values were as follows:

Area Vertebrae Second dorsal fin-rays
Nantucket shoals 52.90 19.74
St. John’s, Newfoundland. 54.91 20.48
Belle Isle Strait 55.46 20. 86
West Greenland 53.60 20.32
East Greenland 53.14 20.04
Iceland 52.29-53 . 26 19, 23-19. 94
Northern Norway 53.82 19.84
Southern Norway 52.44 19.55
English Channel 51.75 18.75

Rockall Bank, west of British Isles 51.47 19.46

68 Bulletin of the Bingham Oceanographic Collection (XI: 4

Marked differences were found between vertebral numbers and num-
ber of rays in the second dorsal] fin between inshore (or shallower) and
offshore (or deeper) water, the former having the lower values. Ex-
amples were as follows:

Area Vertebrae Second dorsal fin-rays
Innermost part of Trondhjem Fjord, Norway 52.35 19.24
Outside the fjord 53.76 20.13
In Gulf of St. Lawrence 53. 58-53. 86 19.96-19.71
Outside the Gulf of St. Lawrence 54.16-54.29 20.00-19.87

Schmidt (1917 to 1930; see also Smith, 1921, 1922), in addition to
his racial studies of cod, made a series of very important contributions
to the racial investigations of other species. One of the species on
which much work was done was Zoarces viviparus. This viviparous
fish, he pointed out, was exceptionally well suited for such studies.
Thus one could compare mother and offspring in respect of a whole
series of characters, which were already fully developed in the yet
unborn progeny. Moreover, local populations of Zoarces differed un-
usually widely in a number of characters from those of neighbouring
populations. Thus populations inside the Danish fjords sometimes
had as many as nine fewer vertebrae on the average than those living
outside. The middle parts of the fjords occupied an intermediate
position in such respects. ‘‘. . . no closely investigated fish species,”
he said, ‘‘shows such great differences from population to population.”

Analyses of ten successive year-classes from the same locality showed
only very small variations, or less than one in the average number of
vertebrae. ‘Transplantation of samples of the same population to a
new environment produced a significant change in the number of
vertebrae, or more than one on the average. He also carried out ex-
periments on hatching three different lots of trout (Salmo trutta) eggs
from the same parent at different temperatures. A slight variation
was observed in the number of vertebrae of fishes from the different
lots.

Runnstrgm (1937), in his review of Norwegian herring investiga-
tions, points out that there exist different spawning communities in
Norwegian waters which do not mix to any great degree. Some of
these communities spawn on the coastal grounds while others spawn.
on more offshore grounds, visiting the coastal waters in the large
herring stage only.

1948] Dymond: European Studies of Populations 69

The investigation of these localized breeding populations was facili-
tated by the fact that fish appear on somewhat small sharply defined
banks and in shoals consisting only, or for practical purposes only, of
one biological group of a species. Therefore, the investigation of local
populations was much easier in such waters as those of Norway and
Iceland and of the Faroes than in more extended waters like the North
Sea where the topographical features of the depths of the bottom are
not so distinctly marked.

As to the causes of the morphological differences which characterize
races, Hjort (1930), referring to the proceedings of a special meeting of
the International Council for the Exploration of the Sea held in 1928
(Rapp. Cons. Explor. Mer, 1929, 54) reported that there was then a
“somewhat sharp division of opinion between those, who regard the
formation of races as the result of fortuitous hereditary combinations
of characteristics, and those who regard it as due to an interplay of the
power of adaptation shown by the animals concerned and the physico-
chemical conditions predominating in particular areas of the sea.’’

One of the reasons for the belief that environmental conditions can
and do alter the characters by which races are distinguished is that
such characters are not fixed but may vary from year to year in the
one localized population. On the basis of such evidence, Jensen
(1939b) concluded that ‘‘as regards both plaice and the dab the number
of anal fin rays seems to be positively correlated with the temperature
of the water during the time at which the larvae are quite small.
1 degree C. corresponds to about 0.4 anal fin rays.”

Schmidt (1930) gave it as his opinion that ‘‘Fishery biologists are
evidently unanimous that external factors are capable of altering the
average characters by which races in the fishes are determined. This
has been proved directly by experiment in the common trout (Salmo
truita L.) and in the million fish (Lebistes reticulatus [Peters] Regan) by
varying the temperature during which the development in the ‘critical
period’ took, place .

“Tt would, however, be quite wrong to ignore the fact that the dif-
ferences in the average characters by which the races are determined
may also be of a hereditary, genotypical nature . . .”

At a meeting of herring experts, held under the auspices of the
International Council at the Fisheries Laboratory, Lowestoft, Eng-
land, in 1935, several papers dealing with the herring stocks of various
areas were presented; some of these dealt with “races” in this species

70 Bulletin of the Bingham Oceanographic Collection [XI: 4

(see Andersson, Davis, LeGall, Hodgson, Poulsen, Runnstrgm,
Schnakenbeck, Taning and Wood, 1936).

Statistics. Since many phases of fishery research are based on fishery
statistics, systems for the collection of these statistics have been or-
ganized in most European countries and the International Council
early gave attention to the compiling of international statistics of
catch. A summary of the statistics for northwestern Europe is pub-
lished annually by the International Council as the ‘‘Bulletin Statis-
tique.”’

In Great Britain fishing vessels provide information as to the quan-
tities and kinds of fish landed, classified at least roughly as to size,
where they were taken, what gear was used, the length of the voyage,
and the number of hours actually spent in fishing. This information
is collected daily at all the main fishing ports in Great Britain. An
account of the methods used in collecting statistics is given by E. 8S.
Russell and Edser (1925) and Edser (1925).

Supplementing the general information obtained from the com-
mercial statistics, more specialized data as to size-composition of the
catches are collected by a special staff working partly on fishing vessels
at sea and partly at coastal markets. In 1929, 914,000 fish were
measured at sea and 69,500 in the markets. In addition the age- .
compositiion of the stocks are determined especially for plaice, cod,
herring and haddock. 20,000 plaice otoliths were examined by the
English staffs in 1929.

Scale Studies. The development of techniques for determining the
age and other facts of the life history of fishes from examination of
their scales has contributed greatly to the study of fish populations.

Much of the early work on age determination and the correlation
between the growth of the body and of the scales was carried out in
connection with the Norwegian herring investigations by Dahl, Lea
and others. They, of course, based their investigations on earlier
work by such men as Hintze (1888) and Hoffbauer (1899), who had
interpreted the rings on the scales of carp of known ages. The history
of the advancements and refinements in scale-reading techniques have
been traced by Lee (1920) and Graham (1929).

The study of scales has been found useful not only in determining
the year-class to which fish belong but also in identifying fish of dif-
ferent types of life history. Local populations often differ in spawning

1948] Dymond: European Studies of Populations 71

times and rates of growth. For instance one type of Norwegian her-
ring was found to have an abnormally small increment of growth in
its third year. Such characters as this, which can be read from the
scales, have been useful in recognizing populations and in studying the
composition and recruitment of fish stocks.

Migrations. One of the first questions investigated under the
auspices of the International Council was the extent to which fluctua-
tions in the fisheries might be due to mass movements of fish coming
onto grounds where they were taken by fishermen in some years and
not in others. As already explained, it has been found that, while some
fluctuations in the fishery are caused by variations in the movements
of fish, there are enormous actual differences in abundance from time
to time. The movements of fish have been traced in part by tagging
and in part by the recognition of discrete populations through racial
studies.

Several species of fish, including the cod and herring, have been
shown during their life-time to carry out a migratory movement be-
tween a breeding place and a feeding place often separated by many
hundreds of miles. For instance, one large cod population spawns
about the latitude of the Lofoten Islands. From here the young are
believed to be carried mainly north and east to the Barents Sea by the
current which flows up the coast of Norway. On reaching maturity
these fish are said to return to the spawning grounds off the west
coast of Norway.

E. 8. Russell (1932) says that in general ‘‘the life-history and migra-
tions of a fish-group . . . take place within a closed circle; as a rule
the fish move up-stream to spawn and their eggs and larvae are distrib-
uted downstream by the currents; spawning areas and feeding areas
are often distinct and may be widely separated, and migrations are
mainly for the two purposes of feeding and spawning.”’ Reference in
support of this statement is made to the papers of Damas (1909) and
Schmidt (1909). Hjort’s (1914) paper contains a chapter on the
spawning and migrations of the cod.

Hodgson (1934) describes a similar movement for the herring.

. . we find the spawning migration is against the stream, or contra-natant as it
- been called. Thus the herring, in common with many other fish, carries out the
obvious movement in going up stream to spawn, so that under normal conditions its
young will be brought back to the same area whence the parents came.

72 Bulletin of the Bingham Oceanographic Collection [XI: 4

Also, in the case of the plaice, Buchanan-Wollaston (1923-1926) found
that the great majority of this species in the North Sea collect for
spawning in a particular area off the estuary of the Thames in winter,
where a tongue of warmish water extends up from the Channel and
that their eggs and larvae are carried north and east by the prevailing
current to the shallow continental flats, where they find suitable condi-
tions for their further development.

Prediction. Knowledge of the populations of several species and of
the factors affecting them has reached the stage where forecasts of
probable abundance are possible. This is due in large part to the
ability to recognize year-classes and to compare their relative abun-
dance as they first enter the commercial fishery (Hodgson, 1932).
Such forecasts have been issued for haddock, cod, herring and mackerel
and in the main they have turned out to be remarkably accurate.

it must be remembered that estimates of the relative strength of
year-classes based on observations of young fish as they enter the
fishery are estimates of abundance and not necessarily of availability.
Fish may actually be abundant and not available to the fishermen be-
cause they do not appear at times or at places where fisherman have
been in the habit of finding them. Runnstrgm (1937), as already
mentioned, points out that certain fluctuations in the spring herring
fishery are due to variations in the migrations of the herring to the
spawning grounds. In certain years the herring spawn mainly in deep
water and on more offshore grounds than in other years, and then the
fishery bears only on a part of the spawning stock. The use of the
echo sounder in recent years has overcome variations to some extent
in the fishery due to hydrographical conditions, although this is still
one of the least understood factors responsible for fluctuations in the
fisheries.

Jensen (1939a) discusses the role of hydrographical factors in deter-
mining the yield of mackerel in Danish waters. Their immigration
from the North Sea seemed to be determined by the inflow of water.
Pelagic fish, having no sense of the direction of water movement,
follow the current passively. Predictions based on observations of
water movements failed in three years and came true in eleven.

1948] Dymond: European Studies of Populations 73

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BuiEeGvaD, HARALD
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1 The following references are not intended to be by any means exhaustive. It is
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74 Bulletin of the Bingham Oceanographic Collection [XI: 4

GraHaM, MICHAEL AND J. N. CARRUTHERS
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1948] Dymond: European Studies of Populations 75

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DISCUSSION

Van Oosten: This paper is now open for discussion.

Huntsman: You apparently consider, Professor Dymond, that the theory of over-
fishing is based on the conclusion that it pays to let the fish get bigger. Do you
think that European investigators have excluded the fishing up of the accumulated
stock as well as the purely economic factor to which you have referred, and that
they have really shown that it does pay to let these particular fish get bigger?

Dymond: I don’t think I can answer the question. The term “overfishing”? means
exactly what they say: The more you fish the less you catch. That is apparently a
fact there.

Burkenroad: The North Sea is supposed to have tremendously more fishing than
any of our North American waters. ‘Therefore, we shouldn’t necessarily think it is
essential to follow European conclusions on this side of the Atlantic. We haven’t
the same intensity of fishing here.

Herrington: Georges Bank produces much more for its area than the North Sea.
The: Bank is just a small fraction of the size of the North Sea.

Burkenroad: Is that so? Of all species or just a few?
Herrington: All species.

Needler: I don’t think there is much doubt of the greater fishing intensity in the
North Sea. The North Sea fishery has succeeded in reducing the size of the com-
mercial species much more than in any of our areas in the west.

Kolbe: Isn’t the size of the carnivorous fish important? I like to maintain that the
larger a carnivorous fish is, feeding largely on other fish, the less fish flesh it gives rise
to in terms of the potentialities of the basic plankton; this is because it is eating a lot
of fish that have taken years to grow. Therefore, if your fish become smaller due to
fishing in the North Sea, you can maintain a bigger population than you could on
your Georges Bank.

Herrington: On Georges Bank the haddock, which is a bottom feeder, doesn’t feed
on other fishes.

Burkenroad: The productivity relationships are terribly complicated. You have
a dynamic situation, not static. When a fish eats food it releases nutrients. A
fisherman is interested in standing crops; that is, he cannot fish at a level of popula-
tion that will not permit him to draw his net through the water and bring in a quantity
of material greater than a certain minimum. But you can have a large production
of fish with a small standing crop, at a high rate of turnover.

1948] Dymond: European Studies of Populations 79

Herrington: Mr. Kolbe, I think your statement is still correct, that the higher you
go in the feeding cycle the smaller will be the population. The corn-hog ratio and
the corn-beef ratio are examples of that. It takes so many pounds of feed to produce
one pound of meat.

Burkenroad: Dr. Taylor has calculated the ratio between phosphate and nitrate in
what we take out of the sea in our annual catch in the United States and the amount
in the area of the fishery. The fraction we take out is insignificant.

Needler: The overfishing conception in the North Sea is not based on the total
production at all. Specific reference is made to certain species of fish. One cannot
criticize the conception on the basis of the total productivity and plankton produ?-
tivity andsoon. They still say that, in spite of certain species being overfished, the
total production is not yet overfished. There are still very large quantities of herring
and other species which are not overfished. Overfishing to the stage that Prof.
Dymond says, where the more you fish the less you get, is limited to certain species
on certain grounds and not to the entire productivity of any area or to any one
species over the entire area. So that it boils down to what I think Mr. Herrington
said earlier, that they are concerned not with reducing the total production but
with maintaining the proportion of that production which lies in certain species.
If certain species are more desirable than others, as they evidently are, it may be an
undesirable thing to reduce these species as far as the others. That, I think, is the
claim for overfishing.

Huntsman: The herring constitute the great bulk of the catch of the North Sea

Needler: So that the total take has not been affected—not to the extent of fishing.
more and getting less. In fact, already, right now with food scarce, the English are
using the machinery only to about 50 per cent because they can’t get rid of the catch.

Huntsman: The rule that the more you fish the less you catch may be true for the
haddock and halibut. However, it isn’t a general rule for the bottom fishes.

Dymond: The trouble there is that when you haul your net over a certain bank you
get everything there. It is a matter of compromise.

Huntsman: The best case for study seems to be the halibut in the North Sea. I
would like to see the results critically studied. I would like to see whether it pays to
let them get bigger.

Dymond: The halibut is one of the fish on which they are trying to make a quanti-
tative study. It is a much more difficult situation than off the west coast where
there are only two countries to deal with. In the North Sea they have half a dozen
countries, and it is very difficult to get them to agree on even a method of research.

Herrington: Why don’t we adopt a halibut program on the Atlantic as well as the
Pacific? Are we willing to trade 10 for one—that is, 10 pounds of cod or other species
for one pound of halibut?

Needler: I think it goes even further than that. You can’t build up the production
of halibut—at least you can’t reduce the catch of small halibut and let them grow
bigger—without reducing the catch of other fish that have several times the value.

80 Bulletin of the Bingham Oceanographic Cotlection [XI: 4

Burkenroad: I think the point about desirability is a fundamental one. How is
one fish determined by long-term policy-makers to be more desirable than another?
A fish that is more in demand one year may lose its lead in value the next year be-
cause consumers’ tastes change. There are no satisfactory studies defining the
extent to which the availability of the fish affects the demand for it. Desirability is
neither constant nor objectively determinable, and I doubt that we can safely limit
our science to attempts to prevent one equally nutritious and harvestable fish from
replacing another. Local and temporary changes are important, but they ought not
to obscure our thinking about basic principles.

Herrington: Professor Dymond mentioned the belief in a critical point in the
survival of the young, which might be one or two days in the early stages of develop-
ment. With poor conditions during that critical period you’d have a poor year-class.
A short time ago Sette published a paper on mackerel which I think for the first time
provided some information on the mortality rate of the young from the egg stage to
the time they reach several inches. It was based upon a repeated series of hauls
taken over the nursery grounds for mackerel, using plankton nets with current
meters to measure the volume of water strengths. In that way it was possible to
reduce the catch to terms per cubic meter or some such constant. ‘The whole area
was covered. As I recall, it was found that there was a relatively constant mortality
rate through the egg and larval period with no exceptionally critical point. If you
increased the over-all rate only slightly over the entire period of time, that slight
increase would cause a big decrease in the number of survivals. The mortality rate
over the whole period of the larval life appeared to be the determining factor rather
than extremely high mortality at a particular stage.

Dymond: This theory of the Europeans, and your statement about the mackerel,
seem to assume that the critical factor is not whether the fish hatch but whether they
survive after they are hatched. Do we all assume, and if we do are we correct in
assuming it, that the conditions for hatching are not so critical as the conditions for
survival after hatching?

Needler: I think there is some evidence that survival is usually more important
than the variation in number of eggs and that hatching is less important. It is the
conditions in the first year of life or the first few months—not a particular day or
week—which, of course, are basic in predictions.

Van Oosten: If there is no further discussion we shall now call for the next paper.

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