Introducing selfisher: open source software for statistical analyses of fishing gear selectivity
M. Brooks, Valentina Melli, Esther Savina, Juan Santos, Russell B. Millar, Finbarr G. O’Neill, Tiago Alexandre Matias da Veiga Malta, Ludvig Ahm Krag, Jordan P. Feekings
Abstract
There is a need to improve fishing methods to select for certain sizes and species while excluding others. Experiments are conducted to quantify selectivity of fishing gears and how variables such as gear design (e.g., mesh size, mesh shape), environmental parameters (e.g., light, turbidity, substrate) or biological parameters (e.g., fish condition) alter selectivity; the resulting data need to be analyzed using specialized statistical methods in many cases. Here, we present a new tool for analyzing this type of data: an R package named “selfisher”. It allows estimating multiple fixed effects (e.g., fish length, total catch weight, environmental variables) and random effects (e.g., haul). A bootstrapping procedure is also provided. We demonstrate its use via four case studies, including (A) covered codend analyses of four gears, (B) a paired gear study with numerous covariates, (C) a catch comparison study of unpaired hauls of gillnets and (D) a catch comparison study of paired hauls using polynomials and splines. This software will make it easier to model selectivity, teach statistical methods, and make analyses more repeatable.