Principles of assessing exploited fish populations and an introduction to the CMSY methodology

CMSY methodology

In July 2022, the Sea Around Us team released a suite of free video tutorials regarding the CMSY stock assessment method, a product of collaboration with the University of British Columbia and MAVA Foundation

The data-poor CMSY method was developed by Froese et al. (2017) as an improvement over the ‘Catch-MSY’ method initially published by Martel and Froese (2013). Later on, CMSY itself was further refined to overcome several of its deficiencies, thus leading to the latest version of the package named CMSY++.

This latest version of the CMSY package is an advanced state-space Bayesian method for stock assessment that estimates fisheries reference points (Maximum Sustainable Yield MSYFmsyBmsy) as well as status or relative stock size (B/Bmsy) and fishing pressure or exploitation (F/Fmsy) from catch and (optionally) abundance data, a prior for resilience or productivity (r), and broad priors for the ratio of biomass to unfished biomass (B/k) at the beginning, an intermediate year, and the end of the time series. The method includes a part that deals with catch-only data and another that requires additional abundance data (Bayesian Schaefer Model). Both methods are based on a modified Schaefer surplus production model. The main advantage of BSM, compared to other implementations of surplus production models, is the focus on informative priors and the acceptance of short and incomplete (i.e., fragmented, with missing years) abundance data.

As an addition to the written step-by-step user guide of the method, the Sea Around Us team created four, 6-minute easy-to-grasp animated tutorials that can be freely accessed by scientists, students, decision-makers, and other stakeholders who are keen to understand the implementation of this powerful stock assessment tool whose results may inform fisheries management globally. Personally, I was fortunate to be able to contribute to this effort by translating the scripts of the video tutorials in Greek, one of the nine languages available.

Enjoy watching!

CMSY tutorial trailer
Principles of CMSY – Part 1
Principles of CMSY – Part 2
Principles of CMSY – Part 3
Principles of CMSY – Part 4