iio The Field Naturalist 's Quarterly May 



in evidence on our shores during the summer months ; 

 whilst those — like the flaky cod — which would keep better 

 under a trying condition of temperature, are present on our 

 coasts in winter only. It is therefore necessary that the 

 student of first causes should seek some explanation of the 

 coming of fish to our shores other than the resulting benefit 

 to the blest subjects of King Edward. 



Temperature is probably the indirect, and the conse- 

 quent increase of food the direct, cause of this phenom- 

 enon in the fish world. The waters of only a few 

 fathoms deep, within, say, the three-mile zone, do not 

 get warmed up to a certain degree of temperature until 

 some time in April or May or even June, according to 

 the seasonal conditions of each individual year. When 

 that temperature is reached, the waters become the scene 

 of reawakening life, and the creatures of infinitesimal size 

 — the larval or adult crustaceans, molluscs, or medusae, 

 which are the components of "plankton" — once more 

 thicken the bays and estuaries with their nutritious abund- 

 ance, and attract the shoals of hungry fish from the 

 deeper water. It may be also that the increasing tem- 

 perature makes their enemies, the sharks and others, 

 more active in pursuit of their prey, and from these, too, 

 the inshoring shoals find respite in the shallows. 



In conclusion, it must be insisted that any comparison 

 of the migratory instinct in the two realms, the air and 

 the water, especially as regards punctuality year after 

 year, should always take account of the distinction in- 

 dicated at the beginning of this article — the greater 

 obscurity of life in the seas, and, more particularly, the 

 slighter attention that has been paid to the study of the 

 life-history of fishes. For every student of fishes, particu- 

 larly in the natural state, there are a thousand students 

 of birds. Every country ramble reveals to the watchful 

 observer some new trait of bird life, whereas to a merely 

 nodding acquaintance with the habits of sea-fish, even 

 more than of those which dwell in rivers or ponds, go 

 years and years of inquiry and patient study. Thus it 

 is that in this matter of migration, arrival and departure 

 alike, the movements of the more familiar bird visitors 



