Title: Modeling Natural Mortality and the Consequences for Biological Reference Points

Authors: Elizabeth N. Brooks¹ and Kate Siegfried²

Abstract: A variety of models exist for deriving natural mortality, from the simplest methods that estimate an age-constant value to methods that calculate age-specific mortality from length or weight relationships (Lorenzen 1996, 2000; Peterson and Wroblewski, 1984; Chen and Watanabe, 1989). We conducted a simulation study where natural mortality was modeled according to several of the different methods available, and then estimated the corresponding biological reference points (MSY, F_MSY, SSB_MSY, SPR_MSY). This analysis explores the sensitivity of BRP estimates to assumptions about natural mortality, and to the uncertainty in biological parameters from which it could be derived. Status determination with respect to overfished and overfishing, and the associated thresholds and control rules, are also affected by the different methods applied.

¹Elizabeth N. Brooks, Northeast Fisheries Science Center, Woods Hole, MA

²Kate I. Siegfried, Southeast Fisheries Science Center, Panama City, FL