On the Growth of some Lamellibranchs in Relation to the Food-supply of Fishes.

Abstract

During a study of the fauna of the level sea-bottom off Plymouth on which a report has already appeared in this Journal (Ford, 1923), the samples taken in the Petersen bottom-sampler and in the conical dredge were preserved in alcohol and retained. A subsequent re-examination of the accumulated material has provided information on the growth of a number of lamellibranchs, which forms the subject matter of the present paper. As the samples were collected according to a programme arranged expressly to determine the animal communities represented, it was not to be expected that they would yield complete data on the growth of a particular species, but the results are interesting and useful when considered in their relation to the food supply of our food-fishes. I must again acknowledge my indebtedness to Mr. R. Winckworth of Brighton for his continued assistance in identification and measurement of specimens. Such expert confirmation of identification was naturally desirable’ in dealing with the growth of species from the earliest stages. Throughout the paper the term “length” is adopted, meaning the greatest antero-posterior dimension of the shell. This term was used by Weymouth (1923) who gave a figure on page 20 which shows clearly the measurement to which the term is applied. I have also used “length” as a measure of growth-rings on the surface of shells. In Fig. 7 on Plate III, I2 is the length of the second ring on a shell of Spisula solida. Thirty-three genera of lamellibranchs are represented in the material of which all but nine appear among the records compiled by Todd (1907) and Blegvad (1917) of the contents of the stomachs of fishes which include dab, flounder, long-rough dab, plaice, sole, cod, haddock, whiting, cat-fish, viviparous blenny, fresh-water eel, herring and mackerel.