FEEDING ECOLOGY AND CONDITION OF LARVAL AND PELAGIC JUVENILE REDFISH SEBASTES SPP

Eggs and nauplii of Calanus finmarchicus were the preferred prey types of redfish larvae whereas Oithona spp. copepodites were not, even though they were within the preferred size range. Significant seasonal and annual differences in larval diet of redfish resulted from differences in the availability of preferred prey. Seasonally, feeding was related to the succession of the spring dominance of C. finmarchicus to summer dominance of Oithona spp. Interannually, feeding was related to differences in the timing of spring spawning and temperature-dependent development of C. finmarchicus. Earlier spawning and faster development of C. finmarchicus, dependent on warmer water temperatures, resulted in poorer feeding conditions for redfish larvae. Under these conditions redfish larvae: (1) ate predominantly nauplii and copepodites of Oithona spp.; (2) ate less food by weight; (3) had lower relative body condition; and (4) there was a delayed size at metamorphosis from larvae to pelagic juveniles. Total prey concentrations between years did not determine better feeding and condition of redfish larvae, whereas the availability of preferred prey types did. Specifically, a lower abundance of C. finmarchicus nauplii resulted in better feeding conditions than a higher abundance of Oithona spp. copepodites. These results emphasize that measuring total prey biomass within preferred prey sizes is not sufficient when evaluating larval redfish feeding conditions. There was a switch in diet for pelagic juveniles to include Oithona spp, copepodites as preferred prey, in addition to copepod eggs and nauplii. This switch in diet coincided with changing prey availability due to the seasonal succession of zooplankton on Flemish Cap, Canada. Metamorphosis from larvae to juveniles at smaller sizes and younger ages is hypothesized to be advantageous to annual survival of redfish due to an increased foraging ability.