Use of a dynamic population model to estimate mortality and recruitment trends for Bonefish in Florida bay

Abstract

Bonefish (Albula vulpes) are popular fish for sports anglers in South Florida. Despite the implementation of catch and release policies, there is concern that numbers are declining. Previous work found a significant downward trend for Bonefish CPUE from 1980 to 2014, and a structural breakpoint in the year 2000. Our objective was to develop and use an age-structured model to explore the relative role of recruitment and changes to adult mortality to explain the decline. Parameters for Bonefish growth, mortality, fecundity and recruitment were compiled from previous research and literature. The CPUE time series from 1980 to 2014 was used to fit the model. Recruit survivorship was responsible for explaining most of the variation in the CPUE time series, while adult survivorship had a significant downward trend. There was no statistically significant structural breakpoint in the survivorship time series, but there was a shift in the mean values in 1998 for adult survivorship and 2008 for recruit survivorship. The shift in adult survivorship is close to the CPUE breakpoint and thus interpreted as driving that change. The fact that there is also a shift in recruit survivorship is cause for concern and warrants continued monitoring of Bonefish populations and research into spawning and recruitment. There is a need to identify biophysical, climatological and habitat variables that are responsible for recruitment and mortality anomalies, and the time series estimates generated in this study will be useful for the analysis of management and conservation decisions in relation to these variables.