PLANKTON OP THE GULF OF MAINE 
105 
refused them when offered in the aquarium is interesting as suggesting that the mack- 
erel is rather an exception in feeding on this pteropod. Naked pteropods are never 
plentiful enough in the Gulf of Maine to be of any importance as food for larger 
animals. 
Probably all the fishes that eat plankton consume buoyant fish eggs to some 
extent, the amount taken depending chiefly on the local supply conveniently available. 
Thus Brook and Calderwood (1886) found fish ova more or less prominent in the diet 
of Scottish herring, according to the varying abundance of the eggs in the plankton, 
and although fish eggs have not actually been recorded from the stomachs of Gulf of 
Maine herring there is no reason to doubt that the latter consume them whenever 
they offer, as is also the case in the English Channel, according to Lebour’s (1924a) 
recent studies. 
Mackerel also are known to take eggs of their own as well as of other species. 
Fish eggs have been found in small mackerel from the Woods Hole region, to quote a 
local instance, and in European seas medium-sized specimens of the American 
pollock ( Pollachius virens ) eat considerable amounts of fish eggs among other 
plankton. 
The only groups of planktonic animals sufficiently plentiful in the Gulf of Maine 
to be of any importance in its natural economy, but which are not regularly con- 
sumed by its fishes in as large quantities as the supply allows, are the medusae, 
siphonophorae, and ctenophores. E. J. Allen (1908) and Goode (1884 and 1884a) 
record medusae and siphonophores from mackerel stomachs; but this is exceptional, 
and although they may bite out pieces of large medusae this is probably for the sake 
of the amphipods (Hyperia) living within the cavities of the latter (Nilsson, 1914). 
It would not be surprising to find mackerel gorging on Pleurobrachia in the Gulf of 
Maine at the places and times when this ctenopliore swarms, for Andrew Scott 
(1924) reports mackerel in the Irish Sea full of them during one of their incursions. 
The spiny dogfish ( Sqtialus acanthias) feeds to some extent on ctenophores 
(Pleurobrachia) in spring, the fish often containing them when they first appear at 
Woods Hole in May; and in north European waters this troublesome little shark 
sometimes devours ctenophores in such quantity that their stomachs are full of 
them (Mortensen, 1912, p. 72 , fide Dr. C. G. J. Petersen). The lumpfish likewise 
feeds regularly on medusae and ctenophores in European waters, hence probably 
in the Gulf of Maine, and the sunfish (Mold mold), which is only an accidental 
visitor to the gulf, subsists chiefly on these watery organisms (Bigelow and Welsh, 
1925, p. 303) ; but so far as is known neither the herring tribe nor any of the gadoids 
ever eat them— in fact, no Gulf of Maine fishes other than those just mentioned. 
With the young fry of the whole fish population of northern seas dependent 
for their existence on the supply of plankton, it is but natural that many attempts 
should have been made to correlate the movements and migrations of the more 
important food fishes with local and temporal fiuctations in the supply, either of 
the plankton as a whole or of such members of it as serve as the chief diet of the 
particular species in question, as well as with the far-reaching physical phenomena 
that may be looked on as the ultimate causes of such fluctuations. Thus, to mention 
only a couple of examples, Bullen (1908) has established at least a plausible causal 
