ZOOPLANKTON PREY SELECTION BY JUVENILE FISH IN NOVA SCOTIAN SHELF BASINS

The stomach contents of fish <100 mm standard length (SL) and fish >10 0 mm SL, collected during June and October in two deep basins on the S cotian Shelf, showed that juvenile cod and silver hake fed primarily o n the two most abundant species of zooplankton in the basins: Calanus finmarchicus and Meganyctiphanes norvegica. These zooplankton were abu ndant in the basins during the 2 months, forming high concentrations a t depths below 200 m during the day. In June, fish (<100 mm SL) concen trated in the upper 50 m during both day and night. Cod and wolffish c ollected between 195 and 240 m had a large percentage of C. finmarchic us in their stomachs, suggesting that these fish exploited the high co ncentrations of C. finmarchicus below 200 m depth. There was no eviden ce that Calanus hyperboreus was eaten by any juvenile fish species. Ca lanus finmarchicus was the most common prey of cod feeding in the top 50 m, but the percentages of C. finmarchicus stages IV and V were lowe r in the stomachs than in the water column. Cod showed a strong prefer ence for M. norvegica, with this prey species having a modified Ivlev' s index of 1, indicating that cod were highly selective for this speci es. There was no evidence that C. hyperboreus stage IV was eaten by an y of the species of fish. Silver hake and dogfish (>100 mm SL) both fe ed on M. norvegica and C. finmarchicus in the deep regions of the basi ns. In October, silver hake was the most common juvenile fish in the b asins, feeding primarily on small stages of M. norvegica. The populati ons of fish (>100 mm SL) in the basins were mainly species known to fe ed heavily on euphausiids. The two basins are unique regions of the sh elf because of the large populations of Calanus copepods and M. norveg ica they contain all the year around, thereby providing an attractive feeding ground for many species of fish, particularly silver hake.