Older is always better – making age structure a focal point for sustainable fisheries management

Big, old, fat, fecund females play a critical role in marine fish populations.

Older and larger fish contribute disproportionately to spawning success, are more resilient to stressors, and play important roles in collective space use.

Despite this, global fisheries management is currently stuck in a paradigm of maximised yield (characterised by Maximum Sustainable Yield, MSY) where total allowable catches are set without consideration of whether a population has the size or age structure needed to support sustainability.

Part of the problem is a lack of tools (indicators and reference points) capable of translating the importance of size and age from scientific paper to policy. In this project, we will address this issue directly.

Specifically, we will take a new age-based indicator (ABI), ABIMSY, and develop it into an operational tool for fisheries management.

In doing so our aim is fourfold: (1) to increase biological realism via the introduction of stochastic processes; (2) to increase utility via the estimation of probabilities allowing decision makers to use age structure as a focal point for management; (3) to increase generality via tailored indicator thresholds (with different target fishing mortalities) that allow ABIMSY to not only inform stock assessment but also management directives on ecosystem health and Good Environmental Status (GES); (4) to increase usability via the development of an open source R package that will facilitate the global use of ABIMSY.