In Search of Optimal Harvest Rates for West Coast Groundfish

Abstract

In this paper, I explore how patterns of compensatory mortality, as assessed through stock–recruitment relationships, may influence optimal harvest rates and relative yields for several West Coast groundfish stocks. To do this, I revisited Clark's (1991) groundfish life history model and maximin (i.e., maximize the minimum) yield approach to evaluate target harvest rates for five stocks (Dover sole Microstomus pacificus, lingcod Ophiodon elongatus, sablefish Anoplopoma fimbria, Pacific hake Merluccius productus, and widow rockfish Sebastes entomelas) using recent estimates of fishery and life history parameters and stock–recruitment data. I found that a spawning-stock-per-recruit target of roughly 35% of its unfished amount would be reasonable for these stocks if Clark's assumed stock–recruitment parameters are representative and the policy goal is a maximin yield. In contrast, use of estimated stock–recruitment parameters suggested more conservative percentages of the unfished spawning stock per recruit and more conservative harvest rate targets for most stocks. A key implication of this work is that Clark's groundfish life history model is sensitive to the stock–recruitment shape parameters. As a result, these parameters should be estimated where possible or imputed using results from meta-analyses. Overall, a conservation target of roughly 35% of the unfished spawning stock per recruit is very likely too low for lingcod, sablefish, and widow rockfish stocks under current environmental conditions, but it may be adequate for Dover sole and Pacific hake stocks.