The Spawning Areas of Sand-Eels in the North Sea. 5 
up to the largest in which the larval stages may be looked upon as 
closed. 
The “ Goldseeker ” collections also confirm the remarkable fact, 
which has been commented upon by M‘Intosh and Prince, that on 
the first appearance of the larvie in the plankton very few are found 
with the remnants of the yolk sac attached. The young forms Just 
after the absorption of the yolk appear in sudden profusion. 
Hitherto the larva still retained sufficient yolk of high specific 
gravity to keep it for a time in or on the sand, or at least in its 
immediate vicinity. Larve in this situation are not readily 
captured, for there are obvious practical difficulties in catching such 
delicate organisms in a tow-net working in close proximity to the 
bottom. As the larvze grow they are able to seek the upper layers 
of water, and may afterwards be found at different depths in all 
stages of development. As there are considerable vertical 
movements of both larvze and adults, the numbers captured in one 
locality at different depths vary greatly. This variability is further 
accentuated in the sand-eel because of its well-known burrowing 
propensity. The fact already mentioned concerning the non- 
appearance of the larger but not fully-grown forms in the collections 
from the Northern North Sea in the first quarter of the year, is not 
to be accounted for by these vertical movements. The observations 
have been carried out at all depths under very various physical 
conditions both during the day and at night. 
According to Ehrenbaum (1909) the lesser sand-eel is the earlier 
spawner. In the southern part of the North Sea some of its larvee 
may first appear in the plankton in the autumn months, although 
it is known that the period of maximum hatching lies between 
January and March. ‘The larve of the greater sand-eel do not 
appear in the plankton until very much later, rarely indeed before 
the beginning of May, whilst its maximum hatching period is July 
and August. In the Northern North Sea, on the other hand, as 
has already been stated, few or no larval sand-eels appear in the 
plankton before the month of March. Thus, the hatching period of 
the sand-eel in the Northern North Sea is considerably later than in 
the southern portion. According to M‘Intosh and Masterman 
(1897) there are considerable divergences of opinion in regard to 
the time of spawning of the two species. M‘Intosh states, however, 
that the eggs of A. lanceolatus are probably deposited in June and 
July, and that at St. Andrews the end of December and January 
appear to be the chief months for oviposition of <A. tobianus, 
although ripe adults may be found in later months. (In the 
Baltic the larvee of A. tobianus have been found in the plankton in 
November; and Ehrenbaum has succeeded in artificially fertilising 
the ripe eggs of the same species ‘at Heligoland as early as September.) 
From the known facts concerning the relative abundance and the 
time of spawning of the two species on the East Coast of Scotland, it 
may be asserted with confidence that all the larve captured in 
northern waters during the first quarter of the year belong to 
A. tobiamus. An examination of the records for the earlier months 
of the year is therefore of prime importance. Those records are in 
themselves sufficient to enable us to map out with precision the real 
spawning areas of A. tobianus, for all uncertainty as to the identit 
of the two species has been eliminated, and many additional complex 
problems of distribution have incidentally been greatly simplified. 
