Comment: How should fisheries scientists and managers react to uncertainty about stock-recruit relationships?

Abstract

Gilbert (1997) does us a service in reminding us how little we really know about the relationship between spawning stock biomass (SSB) and recruitment (R). In particular, he asks us to question the validity of the common wisdom about this relationship: that R is positively related to SSB, at least at low SSB (this is what he calls the stock recruitment paradigm). I find the analyses he presents thought provoking, and I support his general conclusion that the empirical evidence for this paradigm is, at least for marine spawning bony fish, weak. However, I think he goes too far in the conclusions he draws from these analyses. The particular conclusion I want to address concerns the use of threshold biomasses in fisheries stock assessment and management. Gilbert points out that there is an extensive literature on methods to manage fisheries so as to keep the SSB above some threshold level. The rationale for such methods is that they protect against low recruitment (i.e., they assume the stock recruitment paradigm). Gilbert claims that his results show that such methods are not irelevanti for marine spawning bony fishes. This is because, for these species, iperiods of low recruitment appear to be environmentally induced and unavoidable.i I believe we should not accept this conclusion. To focus the discussion let us consider a fisheries management decision that needs to be made for a particular stock of a marine spawning bony species: whether to accept or reject the stock recruitment paradigm. This means deciding whether