A state-space catch-at-length assessment model for redfish on the Eastern Grand Bank of Newfoundland reveals large uncertainties in data and stock dynamics

TL;DR

This study introduces a state-space age-structured catch-at-length model for redfish in Newfoundland, highlighting significant data uncertainties and the need for improved sampling to better understand stock dynamics.

Contribution

The paper develops a novel ACL model that incorporates temporal variations and addresses limitations of previous surplus production models for redfish assessment.

Findings

Large uncertainties in survey and fishery data.

Model required high process errors for good fit.

Recommendations for improved sampling and biological data collection.

Abstract

We developed a state-space age-structured catch-at-length (ACL) assessment model for redfish in NAFO Divisions 3LN. The model was developed to address limitations in the surplus production model that was previously used to assess this stock. The ACL model included temporal variations in recruitment, growth, and mortality rates, which were limitations identified for the surplus production model. Our ACL model revealed some important discrepancies in survey and fishery length compositions. Our model also required large population dynamics process errors to achieve good fits to survey indices and catch estimates, which also demonstrated that additional understanding of these data and other model assumptions is required. As such, we do not propose the ACL model to provide management advice for 3LN redfish, but we do provide research recommendations that should provide a better basis to model the 3LN redfish stock dynamics. Recommendations include implementing sampling programs to determine redfish species/ecotypes in commercial and research survey catches and improving biological sampling for maturity and age.