Does Accounting for Environmentally Variable Growth in Stock Assessments Improve Estimation? A Case Study of Pacific Hake (Merluccius productus)

Fisheries stock assessments typically assume fish grow according to a theoretical growth curve (e.g. von Bertalanffy, Richards, or Gompertz) that is constant through time to convert ages to weights. It is widely accepted that fish growth varies due to biotic and abiotic factors, but accounting for this variation in assessments complicates estimation greatly. In cases where there is evidence for significant annual variation in somatic growth, such as Pacific hake (Merluccius productus), estimation of growth can be bypassed and instead weight-at-age data from research survey or fishery observations used directly. The advantages and tradeoffs between these two methods are poorly understood, despite the fact that this information provides the scientific foundation for management decisions. We used Monte Carlo simulations to identify conditions under which using empirical weight-at-age data in stock assessments provided more robust estimates of stock status and management reference points than cases when growth is internally estimated with some assumed growth curve. Results of this research will provide guidance to fisheries scientists regarding the circumstances (i.e., fishing pattern, life-history type, and data availability) under which it is most beneficial empirically incorporate growth data rather than estimating growth.