Fishing and environmental variability: Hjort’s third idea, the one that got away
Friday seminar by Louis W. Botsford from University of California
A number of recent findings regarding the effects of fishing and environmental variability on age-structured fish populations are changing our understanding of that important interaction, even 100 years after Hjort’s seminal paper. Cohort resonance (Bjornstad, et al. 2004) was a key result, as was the realization that fishing intensified its effects (Worden, et al. 2010), a result that followed from Sissenwine and Shepherd’s (1987) graphical interpretation of the equilibrium condition for age structured models. Cohort resonance refers to the fact that age structured populations with density-dependent recruitment are more sensitive to environmental variability on time scales near one generation time, and very long time scales. This effect is greater in shorter-lived species, and it becomes stronger as fishing increases, leading to increasing overall variability. Cohort resonance is a plausible explanation for the observed increases in variability with fishing. I will illustrate these ideas with a number of examples from our laboratory and others.
Louis W. Botsford
Wildlife, Fish, and Conservation Biology
University of California
Davis CA 95616