Feeding ecology of silver hake larvae on the Western Bank, Scotian Shelf, and comparison with Atlantic Cod

Abstract

The feeding ecology of the larvae of silver hake Merluccius bilinearis was examined during two time periods (October 1998 and December 1992) on the Western Bank, Scotian Shelf, north‐west Atlantic, and compared with the feeding ecology of Atlantic cod Gadus morhua larvae collected in the same samples in December 1992. During both time periods silver hake exhibited strong selection for late stage copepodids and adult copepods at a small size (>3·5 mm total length, LT). The niche width measured as the diet breadth index (IDB) of silver hake declined rapidly as they increased in size and remained relatively constant from 3 to 11 mm LT, during each time period. Atlantic cod larvae exhibited a broader niche width that was curvilinear over the same LT. Atlantic cod were also less selective than silver hake, incorporating both naupliar and early stage copepodids in their diets throughout the length classes examined. Simple isometric relationships did not explain the differences in diet, as Atlantic cod larvae continued to feed on early stages of copepods at large size, while silver hake larvae quickly switched to large prey items. The strong selection and narrow IDB observed for silver hake probably reflects adaptation to spawning during the periods between major secondary production peaks in temperate waters.