Model for Examining Early Ocean Limitation of Pacific Salmon Production

A computer simulation model was used to examine growth and survival of all major British Columbia salmon stocks during their first 6 mo of ocean life. Factors included in the calculations were the space–time distribution of zooplankton production, timing of salmon ocean arrival and migration especially as regards overlaps between stocks, feeding and growth in relation to food availability, and mortality rates in relation to body size. It is concluded that ocean limitation of production is unlikely unless only a small fraction of total zooplankton production is available to the salmon. The model emphasizes several critical uncertainties about the marine biology of salmon: rates of replenishment of near surface zooplankton stocks (where most salmon feeding occurs) from deeper water have not been adequately measured, and the functional response of salmon to prey density is not understood. There is inadequate data on the relationship between body size and mortality rate, and migration patterns of juvenile fis...