Applications of the longline simulator (LLSIM) using US pelagic longline logbook data and Atlantic blue marlin

Abstract

Abstract Spatiotemporal variability in fishing patterns and species distributions from ocean climatology confound analysis of pelagic longline CPUE. A generalized computer program, LLSIM, was developed to simulate such data to test methods used to quantify abundance trends. The method employs a Monte-Carlo algorithm with a probability of capture computed for each hook on each set based on overlaps of the species- and hook-depth distributions. The method was tested using characteristics of the longline gears and fishing locations of the US pelagic longline fleet and blue marlin latitude-longitude-depth distributions predicted using a species distribution model fitted to 1986–2012 monthly oceanographic data. Catch data were simulated for two hypothetical trends in total abundance. The simulator was capable of performing complex but controlled simulation experiments. Analyses demonstrated the advantage of comparing estimates from alternative standardizations to known true values that are not possible with real data.