Abstract
Growth modelling is a fundamental component of fisheries assessments but is often hindered by poor quality data from biased sampling. Several methods have attempted to account for sample bias in growth analyses. However, in many cases this bias is not overcome, especially when large individuals are under-sampled. In growth models, two key parameters have a direct biological interpretation: L0, which should correspond to length-at-birth and L∞, which should approximate the average length of full-grown individuals. Here, we present an approach of fitting Bayesian growth models using Markov Chain Monte Carlo (MCMC), with informative priors on these parameters to improve the biological plausibility of growth estimates. A generalised framework is provided in an R package ‘BayesGrowth’, which removes the hurdle of programming an MCMC model for new users. Four case studies representing different sampling scenarios as well as three simulations with different selectivity functions were used to compare this Bayesian framework to standard frequentist growth models. The Bayesian models either outperformed or matched the results of frequentist growth models in all examples, demonstrating the broad benefits offered by this approach. This study highlights the impact that Bayesian models could provide in age and growth studies if applied more routinely rather than being limited to only complex or sophisticated applications.
Highlights
Understanding the growth of aquatic taxa such as fish, sharks, molluscs and crustaceans is imperative for effective fisheries assessments
The Bayesian model for silvertip sharks produced similar length-at-age results to the frequentist model between ages 3 and 14, after which the Bayesian model asymptoted sooner (Fig 1). This provided a more appropriate L1 that corresponded to the species biology the L0 was estimated lower for the Bayesian model which more closely matches the known length-at-birth
The generalised framework presented here demonstrates the impact that Bayesian methods could make for standard length-at-age studies
Summary
Understanding the growth of aquatic taxa such as fish, sharks, molluscs and crustaceans is imperative for effective fisheries assessments. Biased sampling often hinders growth estimation when not all length or age classes can be effectively sampled [4]. In this situation, additional methods are often applied to account for imperfect data such as constraining model fits or interpolating data through methods such as back-calculation [5, 6]. Additional methods are often applied to account for imperfect data such as constraining model fits or interpolating data through methods such as back-calculation [5, 6] While these can be effective, in many instances biologically implausible growth estimates can still occur to varying degrees [4]
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