PREY FIELD AND DIET OF LARVAL COD ON WESTERN-BANK, SCOTIAN SHELF

In vertically integrated samples (from less than or equal to 75 m) taken around and over Western Bank in November and December 1991, and January 1992, densities of larval cod (Gadus morhua) correlated with those of copepods, notably with relative densities of copepodids plus adults of predominant prey, Pseudocalanus spp. and Paracalanus parvus. Pseudocalanus showed a large increase from time of cod spawning but was concentrated over the bank through gyral circulation rather than enhanced productivity. Numbers of both copepods in stomachs of larvae <10 mm were significantly related to their field densities, when controlled for sample month, larva size, and time of day. Stomach fullness was related to sample month, time of day, size of larva, and density of Pseudocalanus, but not P. parvus. Smaller larvae from four depths at four stations over the bank in late 1992, ate mostly nauplii of Pseudocalanus and Centropages typicus. Numbers eaten were strongly related to their field densities, weakly to sample depth, and not to larva size. Stomach fullness was positively related only to densities of Pseudocalanus nauplii. Larvae >5-6 mm switched to larger prey, mostly Pseudocalanus copepodids. More research is needed on interactions between copepod behaviour and the physical mechanisms that concentrate or disperse them on offshore banks.