Predation and food limitation as causes of mortality in larval herring at a spawning ground in British Columbia

Abstract

We quantified both in situ predation on Pac~fic h e r r ~n g (Clupea harenguspallasi) larvae by soft-bodied zooplankton, and microzooplankton prey of herrlng larvae in Kulleet Bay, Vancouver Island, British Columb~a. Samples were collected at 0 to 5 m depth daily at peak larval hatchlng from 14 to 21 Apnl 1985. The hydromedusa Aequorea victoria was the only soft-bod~ed zooplankter that ate hernng larvae. Densities of A. v~ctoria reached as much as 17 m-3, and averaged 1 to 5 m-3. Predation on the herring larvae was severe, averaging 57 I 29 % d-' of the larvae during each sampling penod. Microzooplankton prey of post-yolksac herring larvae were mainly copepod nauplii and eggs, shelled protozoans, and bivalve veligers, and averaged 40.8 + 21.5 1-' in the environment. Thirty-five percent of the larvae contained between 1 and 30 prey items. Feeding by soft-boded zooplankton equalled only 0.2 % of the standlng stock of microzooplankton and could not reduce their populations. We conclude that predation was a major source of mortality of herring larvae In Kulleet Bay In 1985, and that food limitation was not important.