Workshop on the re-evaluation of management plan for the Icelandic cod stock (WKICECOD)

WKICECOD 2021 met online to benchmark the assessment methods and evaluate harvest con-trol rules for Icelandic cod. The assessment model was changed during this benchmark. The previous assessment model was a statistical catch at age model with fishing mortality of each age group modeled as a random walk. The new assessment has similar characteristics but is based on having fixed separable periods. The age range of survey indices used in the assessment and the non-linear assumption between stock-in-numbers and survey indices were both extended to include older age groups than before. The effect of these changes resulted in a downward revi-sion of the reference biomass in the last three years compared to the 2020 assessment. The final model has a reasonable retrospective performance albeit with a slight bias in reference biomass estimates (~2.4%).

A Management Strategy Evaluation (MSE) was conducted using a short cut approach to generate assessment and forecast error. The assessment error was auto-correlated to emulate historically observed sequential periods of over- or under-estimation of stock biomass. A stochastic hockey-stick recruitment model was used, assuming that the reduction in productivity estimated in 1985 continues in the future.The current HCR which uses a harvest rate (HR) of 0.20 of the fishable biomass (age 4+) was found to still be precautionary and to be robust to historical assessment bias. Reference points were re-estimated. The optimum harvest rate in the absence of assessment error is 𝐻𝐻𝑅𝑅𝑚𝑚𝑚𝑚𝑚𝑚=0.24 (0.23 including assessment error).