FISHERY BOARD FOR SCOTLAND.
SCIENTIFIC INTVESTICATIONS,
1912.
No. I.
ON THE EGGS OF CERTAIN SKATES {RAIAy
(with 5 Plates).
BY
Dr. H. C. WILLIAMSON, M.A., D.Sc, F.R.8.E.,
Marine Laboratory. Aberdeen.
This paper may he referred to as :
''Fisheries, Scotland, Sci. Invest., 1912, I." (July, 1913).
LONDON:
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1913.
Price Sixpence.
FISHERY BOARD FOR SCOTLAND.
ON THE EdGS OF CERTAIN SKATES (RAIA).
BY
H. CHAS. WILLIAMSON, M.A., D.Sc, F.R.S.E.,
Makine Laboratory, Aberdeen.
(Plates I.-V.J
The egg-cases or purses of the different species of Skates differ
markedly from one another. They have tests of a somewhat horny
nature, and enclose the yellow yolk (ovum) surrounded by the
translucent albumen (white yolk).
Beard* described the purses of five species, viz., JRaia batis, clavata,
maculata, circularis, radiata. No figures of the purses accompanied
his paper. I have prepared drawings of the egg-cases of seven
species of skates. Most of the specimens Avere obtained at Aberdeen
Fishmarket by Mr. P. Jamieson, formerly attendant at the Laboratory.
The purse of a skate is somewhat rectangular in shape. It has its
four angles produced into curved horns, which vary much in length
in the different species. The lateral borders are usually flattened
into a more or less broad margin. In circularis it is rounded. In
macrorhynchus it is moulded.
Baia macrorhynchus, Raf. {Raia nidrosiensis, Collett). Jumbo
Skate (Aberdeen). — This species has the largest purse of the
collection. A drawing made from a dried example is shown in
natural size in fig. 7. It was not unlike a huge purse of Baia hatis,
but it had no side tendrils. Mr. Eunson presented two purses
which were taken out of a skate at Aberdeen in April. They were
about 10| to 11 inches (26-5-28 cm.) in total length. Measured
along the middle line they were 9y^ inches (24-3 cm.) long. In
extreme breadth they measured at the ends, in one case, 4^ and 5
inches (107 and 12-7 cm.) respectively, while the breadth across the
middle of the length was 5^ inches (14 cm.). In the case of the
second, the extreme breadths were, at the ends, 3|f and 4f inches
(10 and 11-7 cm,), and across the middle 5^ inches (13-9 cm.). The
lateral edge of the purse forms a high Ion efitudinal ridge.
Baia batis, L. — This fish is known as Skate, Grey Skate, and Blue
Skate. Its purse is shown in natural size in fig. 2. It has attached
to either side of one end (the lower end, according to Beard) a long
golden tendril, composed of fine silken hairs entwined in a soft, rope-
like form. The egg-case, when taken from the skate, is of a light
amber colour. Its test is composed of two layers which separate
readily (fig. 1). The outer layer is of light amber colour, and is
* Beard, J.— "On the Development of the Common Skate (fcaia batis)."
Three plate.s. Eighth Annual Report of the Fishery Board for Scotland, Part
III., for 1889. 1890. Pp. 300 et seq.
Wt. 3377/8—500—7/1913.
4 Fishery Board for Scotland.
formed of parallel longitAirlinal fibres. The inner layer is darker in
colour. It is more fragile and brittle than the outer layer ; it cracks
across in any direction. It is thickened at the side seams of the
purse, filling up the angle. In the latter its central region may be
lighter in colour than the rest. The inner \a,jev is, however, also
formed of longitudinal strite.
Beard says that slit-like apertures are to be found on the inner side
of the extremities of the horns. According to this author, the chief
time of reproduction is in March and April, but some eggs are
developed and fertilised in all the other months of the year. He
considered that development requires nine or ten months. The rate
of development in the early summer months was as rapid again as in
winter.
A large purse was sent from one of the Aberdeen fish -yards to the
Laboratory in January. It is shown in natural size in fig. 6. It was
evidently an abnormally big purse of R. batis. It was similar in
colour, and had tendrils of just about the same length as those of a
normal purse. It had been flattened, and the contents were broken
up. It was, however, possible to make out that it had contained only
one egg. The cB.vitj was a single large one. The ovum had been in
the broader half. The yellow yolk was confined to that part, but
some of the white yolk had been forced into the other half. The white
yolk, although it adheres strongly to the test of the purse, is not
organicallj^ connected to it.
Eaia ciavata, L. (The Roker). — The purse of this form is shown in
natural size in fig. 8. When taken from the parent it is of a
larainarian colour. Stringy appendages were attached to the purse
here shown. But some purses of this species have no strings. One
piH'se was of the same length as the one drawn, but much narrower.
Beard received the purses of this form from January to June.
Bugnion states that the average weight of the egg of this species
is 30 grammes.
Haia macitlata, Montagu. — Beard received in April a consignment
of purses taken from Raia maculaia. He could find no difference
between them and the purses of Raia ciavata. Holt & Calderwood,*
however, figure the purse taken from a female of this species
measuring 28 inches (70 cm.) in length (fig. 12). The purse
measured 2|- inches (6-7 cm.) x 1^ inches (4-3 cm.). The external
surface is smooth.
Raia hlanda. Holt and Calderwood. — The purse taken from a female
46 inches (115 cm.) in length, measured, exclusive of the horns, 5^
inches (13'6 cm.) x 3 inches (7'6 cm.)* (fig. 10). The external
surface is smooth. It is readily distinguished from the purse of
macidata by its greater size. There is not much difference in the
relative length of the horns in the two species.
Raia microcellata, Montagu. — The purse taken from a female 34
inches (85 cm.) in total length, measured 3^^ to 4 inches (9 to 10
cm.) X 2\ inches (57 cm.)* (fig. 11).
Raia circularis, Couch. (The Cuckoo). — The purse is seen in natural
size in fig. 4. Its horns are very long. When found in the sea the
purse is often black. Beard received the purses of this species from
Februaiy to June.
*HoLT, E. W. L., and Calderwood, W. L. " Survey of Fishing Grrounds,
West Coast of Ireland, 1890 1891. Report on the Rarer Fishes." Five plates.
Trans. Boy. Dublin Society, N.S. Vol. V. Part IX. 1893-1896.
On the Eggs of certain Skates {Rata). "5
Rata fullonica, L. (Shagreen Ray). — The purse of this fish resembles
that of circularis, but it is of larger dimensions (fig. 3).
Raia lintea, Fr. — Two purses were obtained by Mr. Erlendsson in a
female taken in 70-80 fms., 16 miles S.W. of Snaefellojoteul, Iceland,
in June. The purse resembles that of Raia fullonica (fig. 3), but it
is larger. One example had a body 11 cm. long by 8 cm. wide. The
longer horns were 10 to 11 cm. in length. The little horns were
shorter than the little horns in Raia fullonica.
Raia radiata, Donovan. — This purse is the smallest of those
described in this paper. The test is felty on the outside. Some
silky hairs hung loosely from the purse. Beard says that it is always
quite flat on one side and strongly convex on the other. The embryo
is usually found under the flattened side of the purse. He further
states that the purses of this species were plentiful at Aberdeen in
February and March, and continued to be got until June at least. I
received from Mr. Eunson two purses taken from the skate in
October.
Raia oxyrhynchus, L. — This purse (fig. 9) was found in the cloaca
of the fish. It has a felty external surface. It contained no ovum.
The sides of the end of the purse marked x. in the figure were adhering
together, but they were readily separated. The remains of j^ellow
yolk were found inside the purse. The egg had been expelled b}^
violence before the mouth of the purse had been properly sealed.
Along the lateral edge of the purse there was a border of woolly stuff
which resembled the material of which the tendrils of batis Avere
composed, but here it was attached along the whole edge.
Raia alba, Lacep : Raia marginata, Lacep. — The Bottle-nose Ray.
A purse taken from the bottle-nose ray is described by Holt.* It
does not appear to difier greatly, in so far as concerns the shape of
its body, from that of R. batis. Its greatest length in the middle line
was 6-^ inches (17"4 cm.), and its greatest breadth was 5y^ inches
(13'8 cm.). The posterior horns, about 3y^^ inches (87 cm.) in length,
are stout, flattened, and tapering. They are strongly bent in a
ventral direction, and incline semewhat towards each other. The
anterior horns are long and ribbon- like. They are 9f inches
(24-5 cm.) in length, and they taper from a width of -| inch (2-2 cm.)
to one of about ^ inch ("6 cm.) at the extremity. They are ver}^
thin, and are supported by a thickened longitudinal ridge. Each
horn is inwardly curved so as to meet and cross its fellow. The axis
of the ribbon is gradually rotated. The fine longitudinal ridges on
the surface of the purse are most distinctly beaded. Each is, in fact,
beset by minute transverse crests. This beaded appearance seems to
be quite characteristic. Coiich f and Day $ describe a purse which
they believed to belong to Myliohatis aqiiila. It is the purse of the
Bottle-nose Ra3^
According to Bugnion,§ the average weight of the egg of R. alba
is 90 grammes.
* Holt, E. W. L. — "The Bottle-nose Ray (? Raia alba, Lacep), and its Egg-
purse." Journal of the Marine Biological Association. Vol. V. (N.S.). 1897-99.
Pp. 181-183.
t Fishes of Great Britain.
I British Fishes, i.
§ Bugnion, E. — Le Developpement des Selaciens (Acanthias vulgaris, et
Scyllium canicula) et des Raies {Raia alha, R. clavata). Proces-Verbaux.
Pp. xxxi-xxxiv. Bulletin de la Societe Vaudoise des Sciences Naturelles. 3e S.
Vol. XXX. No. 115. Lausanne, 1894.
6 Fishery Board for Scotland.
Day states that he had received a pnrse of Raia alha. The purse
measured 16 inches x 64- inches. It is possible that the parent of
this purse was macrorhyncMis.
The following paragraph is extracted from Beard's paper : — "The
author inclines to the view that the purse of a skate is partly formed
in the oviduct before the egg leaves the ovary. Fertilization must be
effected in the upper limit of the oviduct. For some weeks at least
the egg undergoes development within the maternal oviduct, and there
it normally lies till the first traces of the embryo appear. It is then
laid by the mother skate, and undergoes its subsequent long develop-
ment at the bottom of the sea. i^ever more than two eggs, one in
each oviduct, are found in a single skate."
Bugnion says that the test of the egg of the skate is formed in a
glandular thickening of the oviduct {glande nidamenteuse). At this
part, the cavity of the organ is dilated, flattened, and exhibits four
horns or prolongations in which the four points of the egg are
moulded. There is only one egg in the oviduct in the process of
development. Impregnation of the egg is effected in the superior
part of this organ before the test is formed. The freshly laid egg does
not enclose an embryo, but only a little scar similar to that of the egg
of the domestic fowl before inciibation. In fifteen days after the
extension of the egg, the embryo measured 7 mm. in length.
While there seems to be no doubt that the egg is usually extruded
while the embryo is in a very early stage of development, it has been
asserted b}^ fishermen that little skate have been found inside purses
taken out of the mother.
Eggs of skate have, Mr. Thomson informs me, been taken in
considerable numbers on ground 16 miles south-south-east of
Aberdeen by the trawl towing off the shoal water on Aberdeen Bank.
EXPLANATION OF PLATES.
Plates L, II., III., IV., V.
Fig. 1 . Transverse section of purse of Raia batis ; approximately natural size.
yy, yellow yolk (ovum) ; try, white yolk.
,, 2. Purse of Raia batis, natural size.
,,3. ,, Rata fullonica, ,,
,,4. ,, Raia circularis, ,,
,, 5. ,, Raia radiata, ,,
,, 6. Abnormal purse of Raia batis, natural size.
,, 7. Purse of Raia macrorhynchus (dried specimen), natural size.
,,8. ,, Raia clavata, natural size.
,,9. ,, Rfiia oxyrhynchiis, ,,
,,10. ,, Raia blanda, reduced. (After Holt and Calderwood).
,, 11. ,, Raia mierocellata, ,, ,, ,,
,, 12. ,, Raia maculata, ,, ,, ' ,,
) «7ys »0. .,/,2
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PLATE IV.
f464F). ZiTj/e. 500. Il/l2. BANKS & CO LTD.
Plate V.
10.
11.
12.
Afttr Holt & Calderwood.
Purses of Skates.
Wt 3.377-8 500 5/13 MF&E.
FISHERY BOARD FOR SCOTLAND.
SCIENTIFIC INVESTIGATIONS.
19 12.
No. II.
THE DISTRIBUTION OF THE LARV^ OF
THE EEL IN SCOTTISH WATERS
(with 1 Chart).
BY
ALEXANDER BOWMAN, D.Sc.
This Paper may be referred to as :
Fisheries, Scotland, Sei. Invest., 1912, II." (Dec. 1913).
G L A S G O W :
PRINTED UNDER THE AUTHORITY OF HIS MAJESTY'S
STATIONERY OFFICE
By JAMES HEDDERWICK & SONS LIMITED.
To be purchased, either directly or through any Bookseller, from
H.M. STATIONERY OFFICE (Scottish Branch), 23 Forth Street, Edinburgh ; or
WYMAN AND SONS, Limited, 29 Breams Buildings, Fetter Lane, E.G.,
and 54 St. Mary Street, Cardiff ; or
E. PONSONBY, Limited, 116 Grafton Street, Dublin ;
or from the Agencies in the British Colonies and Dependencies,
the United States of America, the Continent of Europe and Abroad of
T. FISHER UNWIN, London, W.C.
19 13.
Price Fourpence.
FISHERY BOARD FOR SCOTLAND.
THE DISTRIBUTION OF THE hiWfE OF THE EEL
IN SCOTTISH WATERS
{With One Chart).
By ALEXANDER BOWMAN, D.Sc.
There is no more fascinating chapter in the history of marine
investigation than that which tells of the elucidation of the life stoiy
of our common fresh-water eels. Those two dominant instincts in
the life of a fish, viz., the instinct to feed and the instinct to breed,
compel our European eels to seek at one period of their
existence the fresh waters of our rivers and streams, in which they
feed and grow, and at another period for the purpose of breeding,
such utterly different physical conditions as the warm deep waters
of the Atlantic. One can understand now how a profound mysterv
surrounded the propagation of this species for so long a time, and
how such a mystery could not be cleared away save only by costly
oceanic exploration, and by the development of modern engines and
methods of research.
Only within the last few years have the main facts of this story
been made clear, chiefly through the brilliant researches of the
Danish and Norwegian investigators. Dr. Johann Schmidt and Dr.
Johann Hjort, which researches followed and in a large measure
extended the discoveries of Professor Grassi in regard to the eels of
the Mediterranean,
We now know that the fresh-water eels which inhabit the rivers of
Western Europe were born in mid- Atlantic over great depths, and
that they themselves, as they grow up, must seek again the deep,
warm, salt water before they can reach maturity and reproduce
their kind. The young larvae are found far out in the Atlantic,
and as they grow up into quaint, transparent, leaf -like forms
(Leptocephali) , are carried by the prevailing currents towards the
edge of the Continental plateau. There, outside the 1000-med:re
line, they are found as fully-grown Leptocephali during the summer
months, over the long stretch from the westward of the Faeroe
Islands to northward of the Coast of Spain.
Towards the end of summer (August-September), these fully-
grown, leaf -like larval eels begin a retrogressive change, and, aided
again by the prevailing curi'ents, make their way towards the coast,
gradually assuming the fonn and appearance of an elver, or young
eel.
It is clear, therefore, that the stock of eels in the rivers which flow
into the Baltic and North Sea must be derived from the Atlantic
(2887) Wt. 1853/3—500—12/1913.
4 . Fishery Board for Scotland.
either by way of tlie English Channel or round the Xorth of vScot-
land.
The records from Scottish waters are of value, therefore, not only
in extending our knowledge of the northerly limits of distribution
of the Leptocephali, but also in defining more precisely the time
•and intensity of the migration of the young " glass eels " round the
North of Scotland.
The Larvm of the Common Fresli^^cater Eel.
Of the Leptocephalis larvae of the Common Eel only 13 specimens
have been obtained in the course of our work ; and that the
Scottish records of Leptocephali are not more numerous is simply
to be accounted for by the infrequency of our visits to the deep
Atlantic waters of the west coast. Dr. Schmidt has shown that
the Leptocephali are found outside the 1000-metre line, but in
decreasing abundance towards the north. One of onr thirteen
specimens was got within this 1000-metre area at 58° 43' N. 9° 45'
W. on August 23rd, 1910. It was at stage three of the retrogressive
metamorphosis, and is thus only an additional record to the normal
distribution found by Schmidt. Most of our Scottish stations have
been to the north of this 1000-metre line, and the other twelve
specimens captured are of interest as being apparently sporadic
examples which liaA^e been driven early from the main stock of
Leptocephali by the strong current iiinning towards the north-east.
Perhaps the most interesting of these records is an example which
had been earned away to the N.E. over the Wyville-Thomson ridge,
into the Faeroe- Shetland Channel, and which even in the month of
August had reached a higher latitude than the north point of Shet-
land; it was found in 61° 17' N. 1° 22' W. This specimen,
75 mm. in length, was not very far advanced in its metamorjihosis,
and had onlv reached stage two on the 11th of August. A specimen
which was caught on July 6, 1904, at 59° 61' N. 6° 00' W., and
which still retained its lai'val teeth, not having begun the retrogi'ade
metamoi-phosis, shows us how in some years the ]ire vailing drift
may drive the larvae inwards very early. The records of the other
two stations also help to show this, and indicate that even in August
many of the lai-vae are far advanced in their retrograde meta-
moqihosis. At 59° 15' N. 7° 10' W. one had proceeded so far as
stage four, one had reached stage three, another between stages two
and three, whilst the other six specimens taken on the same station
at the same time were at stage two.
In spite of the fact that our observations are comparatively few,
and that our work in the deep waters has been practically confined to
the months of July and August, these records of the Leptocephali
help us considerably towards an understanding of the route taken
round the North of Scotland by the immigrating lai-vae. Had our
work in the Atlantic, and that around the North of Scotlana,
extended through the months of September, October, and Novem-
ber, then we should have doubtless been able to trace in a more
thorough way the migration of the Leptocephali, and of the glass-eel
into which they presently turn. Our more continuous work in the
North Sea itself throws a good deal of light upon the distribution of
these glass-eels.
Report on the Distribution of the Larva- of the Eel. 5
The Distribution of the Young Glass Eels.
Our obsei-vations in the North Sea extend over a period of nine
years, from April, 1904, to March, 1913.
From the table supplied, it is seen that all the records of glass-eels
occur within the period of the year extending from November to
May, and although more numerous observations have been made in
the other half of the year, from April to November, no records have
been made of these transparent glass-eels in the northern Noi-th Sea.
Thus the Scottish records confirm the statements made by Schmidt
that the migration of the glass-eels is limited to the winter and
spring months, and that these glass-eels are derived from the meta-
morphosing stages of the previous summer found out in the Atlantic.
The records of the Leptocephali on the west, and the time of
occuiTence of the larvae, in the North Sea show us that an annual
stock is passing inwards round the North of Scotland in the months
of September to January or February. Our records of the Lepto-
cephali indicate that the migration in the North of Scotland is aided
greatly by the strong north-easterly current, and the occun-ence of
glass-eels in the Noiih Sea as early as November points to the fact
that the young eels reach the North Sea via the North of Scotland at
least as readily as by the apparently much shorter route through
the English Channel.
Schmidt has shown that this strong easterly current which aids
the eels in their migration also carries enormous quantities of
Atlantic pelagic organisms into the North Sea. Thus he shows
that such passive organisms as Salps (Salpa fusiformisj, which were
limited in the North Atlantic in May to the west of the Hebrides,
and were absent from the Norwegian and North Seas, were found
in these latter areas towards the end of July and August, having
pushed themselves to the north, and also into the North Sea, in large
numbers.
Now the larval eels were also found at these localities to the West
of Scotland from. May to September, yet from our records the glass-
eels do not arrive in the North Sea much before November, that is to
say, some months after the advent of the Salps ; although the larval
eels are by no means such passive organisms as vSalps. The records
of capture help us considerably, for it may be said almost as an
invariable rule that the glass-eels are only caught at the surface at
night. There are no surface records for mid-day hauls, and, indeed,
the greatest number obtained in one haul of quarter-hour duration
was 18, got at St. 42 (56° 28' N. 0° 53' W.) on February 11,
1911, about 3 a.m. This peculiarity has been well brought
out by Johansen for the North Sea, Skagerak, and Cattegat; and
Schmidt has also shown that the Leptocephali behave in a similar
manner, approaching the surface waters during the darkness.
These diurnal vertical movements must play no inconsiderable part
in modifying the influences of the surface currents on the horizontal
distribution of the eel-larvae, and it is therefore more easy to under-
stand why the glass-eels should be later in arriving in the Nor'th Sea
through the influence of the currents than some other pelagic but
more passive Atlantic organisms.
The first records of the arrival of the new stock of eels in Scottish
waters were made in November. Two of the specimens were pro-
6 Fishery Board for Scotland.
cured on the 6th November, 1907, at Station 3 (Lat 59° 10' N.
Long. 1° 27' W.), and they seem to suggest that the glass-eels gain
access to the North Sea through the passage between Orkney and
Shetland. The two specimens captured on 21st November, 1912,
at Lat. 58° 30' N. 2° 30' W., right at the Pentland Firth, on the
other hand, suggest the view that part of the stock may come
through the Pentland Firth into the North Sea.
The most interesting record is probably one made in December,
1902. A specimen was taken by H.M. " Jackal " on the 8th of this
month, at Lat. 61°12'N. 10°52'E. Here is an individual which
has been carried very far to the north-east, even as early as Decem-
ber ; but this record is the more easily explicable when taken in
together with the record of the Leptocephalus caught to the north
of Shetland in the month of August. There is no doubt that a great
part of the supply of eels to the northern shores of Norway is derived
from the Atlantic by way of the Faeroe-Shetland Channel, across
which the larvae are carried! early by the rapidly-moving Gulf-
stream cun-ent. Part of the stock of eels to the west of the Hebrides
must be carried towards the North of Scotland, and split fan-like by
the intervening Orkney and Shetland Islands before entering the
North Sea.
The other records for December are also interesting, although only
single specimens have been found at each observation station. In
December, 1908, as early as the 3rd of the month, glass-eels had
penetrated into the North Sea as far south as a line east from the
Firth of Forth. This is the most southerly limit of our observation
stations, so that in reality the stock of glass-eels may have extendted
much further south. There is no doubt but that these specimens
had come from the north, and it should also be noted that they were
captured at localities at some considerable distance fi^om the coast.
The probability is that these would have been earned still further
south later in the year. The stations which have been examined in
January are, unfortunately, very few, but our Februaiy observa-
tions are numerous and the records of glass-eels are as frequent as are
those of December. This is undoubted proof, therefore, that the
glass-eels are fairly general in their distribution over the northern
North Sea in the winter months, from December to February, and
that they are found even far from the coast. On the other hand, the
March observations, which have extended over as wide an area and
are more numerous than the February ones, give much fewer records,
and the glass-eels captured have been found comparatively near to
the coast. Apparently the great annual wave of immigrating glass-
eels has pa-ssed over this area between the months of December and
February. That this is probably the case is further corroborated by
the fact that the glass-eels have completely disappeared from our
area in the month of April. Our area of investigation is necessarily
limited in extent, and there is no reason for supposing that there are
no glass-eels beyond the area investigated.
The line of stations running east from the Firth of Forth has
proved very rich in glass-eels during the first months of the year,
numerous records being obtained from the same stations in different
years. It is obvious that the glass-eels not only spread over the
northern North Sea, but that many are carried coastwise down into
the southern portion ; and we are justified in saying that the
B&port on the. Distribution of the Larvcc of the Heel. 7
southern half receives a poi-tion of its stock, at any rate, from
the North of Scotland. The absence of records of glass-eels in the
southern North Sea fi-om November to February may be due to the
lack of observations during these months. For, as stated by
Schmidt, Gilson obtained large numbers off Oape Griz Nez in the
beginning of Febiniary. We cannot judlge too accurately the time
of arrival of the glass-eel off the coast from the time of the ascent of
the elvers of the neighbouring streams ; for, as we see from the
Scottivsh records, the glass-eels may be off the coast as early as
December, although the ascent of the rivers is not apparently under-
taken much before the month of May. The records for the winter
months in the southern North Sea are very incomplete. There are
Danish records, however, for the months of March and April, and
from these it is obvious that part of the stock is at least derived
from the north. Johansen has given February as the date of the
earliest record for the " Sound," whilst the pelagic glass-eels occur
in quantities in the Salter paris of the Danish waters in the months
of March and April. Thus these records are in good agreement
with the times of arrival of the glass-eels off the Scottish coast, and
confirm the view that the Baltic derives part of its stock of eels by
way of Scottish waters. The Norwegian record of a glass-eel taken
in April in the northern part ol the North Sea might possibly be
that of an individual which had entered the North Sea early by waj^
of the North of Scotland, and had been carried by the anti-cyclonic
current round the North Sea.
Our records for »Scotland are too few, and belong to too many
different year groups, to make any comparison as to the relative sizes
of the Leptocephali and glass-eels with those from other localities ;
but the reduction in size during the metamorphosis is brought out
in the table.
The annexed chart illustrates, in a summary way, the points
already set forth. We see the Leptocephali distributed in the
month of August from westward of the Hebrides to the north of
Shetland, in the line of the Gulf-stream current. Obsei^ation in
the same region being lacking for the months of September and
October, we lose track of the migration during that period. But we
next pick up the young- glass-eels in the month of November, just
within the North Sea, to the eastward of the Pentland Firth and the
Fair Isle Channel. In the middle of the North Sea, all the records
relate to the months from December to February. On the other
hand, the whole of the observations in the eastern part of the North
Sea, eastward of 2° E., including all those in the region of the
Skagerak and on the Norwegian coast, are for the months of March
and April. The same is true of the observations within the Firth of
Forth, and much the same is indicated also by those in the Moray
Firth. The net result, accordingly, is that the Leptocephali, in
their pa.ssage round the North of Scotland, are metamorphosing into
glass-eels in the autumn months ; that a great stream of them is
passing through the northern North Sea about December and there-
•after till February ; while from this central stream the glass-eels
spread coastwards, on either side of the North Sea, reaching the
coast about March and April. They then ascend the rivers as
" elvers," in May or during the latter part of April, especially during
the first half of May.
Fishery Board for Scotland.
Lejptocephali of the Conger Eel.
We have only one record of the Leptocephalus of the Conger
caught dui'ing these nine years' investigations, and it was taken on
the 27th August, 1911, at 50° 58' N. 2° 27' W. Dr. Fulton has,
however, given two records for the Moray Firth and a record of two
specimens captured in Aberdeen Bay, whilst M'lntosh and Master-
man also record two which had been captured on the west coast of
Scotland.
The combined records for the easi coast give us some idea of the
time of arrival of the young Conger in the northern North Sea. The
stage in the retrograde metamorphosis of oui' specimen apparently
lies between those of Fulton's two specimens. The lai-va is
128 mm. long, 11 mm. broad, and has lost its larval teeth.
According to Schmidt, the Conger propagates both in the Mediter-
ranean and in the eastern part of the Atlantic between 30° and 40°
N. Lat., but not ofE the shores of the British Islands or France, nor
further to the north and east. On account of the long pelagic life
of the larvse they become distributed over very wide areas.
Schmidt has also shown that the Conger spawns in spring and
summer in the warm salt water of the south, and by the end of the
first winter the Leptocephali have reached a size of about 5 cms.
Our Scottish specimens are, therefore, of considerably greater age,
and are perhaps about two j^ears old, having been carried very far
from their original home.
The records, although so few, are wonderfully consistent with
those of the fresh- water eel, and when the specimen caught by
Collett on Januaiy 12th, 1898, is taken into consideration there is
no doubt but that the larvse of the fresh-water eel and the Conger
gain access to the shores of northern Europe by the aid of the same
prevailing physical conditions. One would naturally expect a more
extended area for the Conger, since the duration of its larval life is
much o^reater than that of the fresh- water eel.
Wt 1853-3 .501) 9, 13 M'F &.
Report on the Distribution of the Larvce of the Eel.
TABLE I.
Records of Leptocephali of Anguilla vulgaris.
Month.
Year.
Date
of
Month
Station.
Apparatus.
Depth
of Ap-
paratus.
Size.
July {
1906
6
59''41'N.
6°00'W.
Young Fish
Trawl.
230m.
*hr.
1
75 mm.
r
1
Aug. .
1910
23
58'>43'N.
9°45'W.
Do.
600m.
Do.
3
79 mm.
1911
11
61<>17'N.
lo22'W.
Do.
250m.
Do.
2
75 mm.
23
59^15'N.
^°10'W.
Do.
600m.
Do.
2
68-68-68
71-72 mm.
2-3
66 mm.
3
70 mm.
4
62 mm.
60m,
Do.
2
82 mm.
59*50'N.
6*16'W.
Small
Trawl.
478m.
Ihr.
2
77 mm.
TABIiE II.
Leptocephali of Conger vulgaris.
Aug.
1911
17
59'^58'N.
2°27'W.
Small
Trawl.
102m.
|hr.
—
128 mm.
Dec. j
1903?
27
Smith Bank
(MorayFirth)
Small mesh
Cod-end
Otter trawl
28 fms.
—
—
145 mm.
Feb. j
1903?
12
Moray Firth
South of
Smith Bank.
Do.
24 fms.
—
—
123 mm.
May -
1904
4
Aberdeen
Bay.
Do.
4-5 fms.
—
— 1 —
10
Fishery Board for Scotland,
TABLE III.
Record of Glass Eels.
I
Monti
1 Year.
Station.
Lat. Long.
j^
Apparatus.
"Si
6
Time.
Duration
of Haul.
OJ
Size in
mm.
Aver-
age
Size.
71ram.
(67-74)
s .
>
1907
3
metres
113
1 metre
Cheese Cloth
113
16
Mid-
night.
15 rain.
2
73-74
1912
58"30'N.
2°30'W.
70
Do.
35
70
21
21
Do.
Do.
67
70
i-
1902
61°12'N.
r52'E.
—
Do.
8
5 p.m.
Do.
75
70-5
(64-75)
1906
44
57
Do.
20
6 p.m.
Do.
64
1908
41a
95
Petersen Young
Fish Trawl
95
3
7 p.m.
30 min.
71
416
92
1 metre
Cheese Clotli
92
3
10.30
p.m.
15 min.
72
March. February.
1906
42
71
Do.
17
8.30p.m.
30 min.
67-74
681
(59-74)
{37}
Do.
10
17
17
Do.
Do.
Do.
69
Do.
35
Do.
69
Petersen
Young Fish
Trawl
17
Do.
Do.
1
70
35
17
Do.
Do.
2
67-70
41c
78
1 metre
Cheese Cloth
18
1 a.m.
Do.
2
65-73
416
86
Do.
18
5. 30p.m.
Do.
2
63-68
Do.
5
18
Do.
Do.
1
71
30
60
12" fine Silk
V
19
8 p.m.
-
1
67
Petersen Young
Fish Trawl
30
19
9 p.m.
30 min.
2
65-66
1907
41c
80
Do.
80
5
11 p.m.
Do.
1
68
38
110
1 m. Cheese CI.
7
1.30a.m.
15 min.
2
67-74
1908
Cruden
26
Do.
26
3
6 p.m.
15 min.
1
71
38
144
Do.
20
9 p.m.
15 min.
1
69
1909
41c
70
Do.
13
3 a.m.
Do.
1
73
1911
42
74
Do.
11
3 a.m.
Do.
18
-so irV A -Sb
(f 5 -fr Th ^'V
1 I 1 1
TU TT TIT 1^
1906
Sinclair
Bay
VI.
F. of Forth
47
12" fine Silk
V
21
Do.
1
65
65-46
(63-69)
{.3}
28
Do.
V
29
—
Do.
1
67
1911
III.
F. of Forth
19
1. m. Ch. CI. at-
tached to Trawl
18
23
—
Do.
1
63
IV.
F. of Forth
13
Do.
13
25
11.30
a.m.
1 hour
10
■et 7T rfV
T7 ITS eiT
Report on the Bistrihutiooi of the Larva' of the Eel.
11
TABLE Ilia.
Further Records of Glass Eels in Scotland ; from Williamson, '-On the
Eeproduction of the Eel," S.F.B. XIII.
Date.
No. of
Specimen.
Size in
mm.
Locality.
January 12-14, 1891
1
66
f Bottom Tow Net,
\ offSarclet, Caithnes.s.
January 28-30, 1891 ... 2
65
r Bottom Tow Net,
[ E. of May Island.
March 1, 1895
70
/ M'Intosh Net, Inver-
\ keithing Bay, F. of Forth.
March 21, 1891
65-7
r M'Intosh Net,
\ off Anstruther, F. of Forth.
March 28, 1889
65
/ Midwater Net,
\ St. Andrews Bay.
April, 1885
66
/ Dug up on Sands,
\ St. Andrews.
April 12, 1892
71-5
/ M'Intosh Net,
\ Cuh-oss, F. of Forth.
May 8, 1895
67-5
\ Saltwater Pool,
/ St. Andrews.
REFERENCES.
Schmidt, Johs. — "Contributions to the Life History of the Eel"
(AnguiUa vulgaris, Fiem.)
Rapports et Proces-Verbaux du Conceil intern', pour I'explor
de la nier ... ... ... ... ... ... 1906
" On the Distribution of the Fresh-Water Eels throughout
the World."
Med. fra Komm. for Had. Sea Fisheri Bd. III., No. 7 ... 1909
' ' Remarks on the Metamorphosis and Distribution of the
Larvpe of the Eel."
Ibid., No. 3 ... ... ... ... 1909
Biology of the Eel-Fishes, especially of the Conger.
"Nature" ... ... ... ... ... ... 1911
— — Contributions to the Biology of some North Atlantic Species
of Eels.
Videnekat. Med. fra den Nat., Vol. xliv. ... ... ... 1912
' ' Danish Researches in the Atlantic and Mediterranean on
the Life-Histoi-y of the Fresh-Water Eel."
Rev. internal Hydrobiologie und Hydrographie ... ... 1912
Petersen, C. G. Joh. — "Larval Eels of the Atlantic Coasts of Europe."
Med fra Komm. for Havandersok. Bd. I., No. 5 ... ... 1905
Johansen, A. C. — Remarks on the Life History of the Young Post-
Larval Eel.
76irf., Bd. I., No. 6 ... ... ... ... ... 1905
Schmidt, Johs. — On the Occurrence of Leptocephali (larval muraenoids)
in the Atlantic, West of Europe.
Med. fra. Komm. for Havand. Bd. III., No. 6 ..-. ... 1909
Hjort, Johs. — Eel-Larvae (Lepto brevirostris) from the Central Atlantic.
"Nature," Vol. Ixxxv. ... ... ... ... ... 1910
Murray, Sir John, and Hjort, Dr. Johan. — "The Depths of the Ocean." 1912
Fulton, Dr. T. Wemyss. — " The Young of the Conger."
S.F.B. Report XXIL, XXIIL ... ... ... 1904,1905
Williamson, Dr. C. H. — "On the Reproduction of the Eel."
S.F.B. Report, XIII 1894
1/
Ill !!
o vvnbc u'4
387
