Estimating mortality for the assessment of a small-scale fishery: Lane snapper (Lutjanus synagris) in Honduras

Abstract

Gillnets are very common in small-scale fisheries. However, data obtained using gillnets are biased because of their size selectivity, making accurate estimation of mortality difficult. This study applied various methods to estimate total, natural, and fishing mortality, using data for Lane Snapper (Lutjanus synagris) collected in Tela, Honduras. Total mortality was estimated using a catch-curve analysis with and without accounting for size-selectivity using fitted selectivity curves, the Chapman and Robson method, and Heincke’s method. Gillnet selectivity of Lane Snapper was best characterized by a skewed normal selectivity curve. The catch-curve method in the absence of correction for gear selectivity produced greater total mortality estimates than the Chapman and Robson and Heincke’s methods, with substantial variation among the three methods. Natural mortality estimates were consistent among five methods: Lorenzen, Peterson and Wroblewski, Sekharan, “FishLife” R package and Pauly’s method. Consequently, variation among fishing mortality estimates was primarily the result of variation in estimates of total mortality. Our results suggest that accounting for gear selectivity is critically important when assessing and managing small-scale fisheries.