Estimating delayed density-dependent mortality in sockeye salmon (<i>Oncorhynchus nerka</i>): a meta-analytic approach

Abstract

Delayed density-dependent mortality can be a cause of the cyclic patterns in abundance observed in many populations of sockeye salmon (Oncorhynchus nerka). We used a meta-analytical approach to test for delayed density dependence using 34 time series of sockeye data. We found no consistent evidence for delayed density-dependent mortality using spawner - spring fry or spawner-recruit data. We did find evidence for delayed density-dependent mortality at a 1 year lag for the spawner - fall fry and the spawner-smolt data; however, effects at lags greater than 1 year were weak and not statistically significant. Between-cohort interactions at a 1-year lag are not sufficient to cause the observed cycles in adult abundance, although they will tend to reinforce patterns established by other mechanisms. Our results imply that reductions in fishing mortality in off-peak years should result in an increase in abundance.