Title: A comparison of stock assessment models of lemon sole (Microstomus kitt) in Icelandic waters

Abstract

Zhongxin Wu´s final project will be published in due time. Until then we share the abstract and a link to a poster.

This study compares three stock assessment approaches to evaluate the population dynamics of lemon sole (Microstomus kitt) in Icelandic waters: (1) the Stochastic Surplus Production Model in Continuous Time (SPiCT), (2) the ICES category 3 data-limited method using the rfb rule, and (3) two statistical catch-at-age models (a4a, using FLa4a and SAM, using FLfse). The rfb rule recommended a catch of 1,184 tonnes for the two fishing years following 2025, representing a 4.1% increase from the previous advice, driven by rising biomass and declining fishing pressure indicators. SPiCT assessments indicated a healthy stock, with biomass approaching B_MSY and fishing mortality declining substantially since a peak of approximately 2.2 F_MSY in 1999, now remaining at or below F_MSY. Both catch-at-age models showed a long-term decline in fishing mortality following historical peaks, although they differed in the magnitude of estimates. Spawning stock biomass was historically high but has declined in recent years. Diverging recruitment trends between a4a and SAM reflect data limitations, highlighting differences in how model uncertainty is treated in the models. Despite methodological differences, all models consistently indicate reduced fishing pressure and a recovering stock. This tiered modelling strategy–integrating both data-limited and data-rich approaches–offers a flexible and adaptive framework for stock assessment under varying data availability, aligning with the evolving needs of fisheries management in some developing countries.