Joint ICES-PICES Working Group on Impacts of Warming on Growth Rates and Fisheries Yields (WGGRAFY; outputs from 2023 meeting)

The Joint ICES-PICES Working Group on Impacts of Warming on Growth Rates and Fisheries Yields (WGGRAFY) aims at assessing the global impact of warming sea temperatures on fish growth, and its implications for commercial fisheries yield. WGGRAFY has four objectives: (i) assess and compare growth models, (ii) investigate changes in fish growth across multiple marine ecosystems, (iii) assess fish growth changes impacts on fisheries yield, and (iv) collate global length-at-age data into a database. For the first objective, the capacity of modelling growth changes across species was compared for two candidate models: a state-space growth model and a dynamic factor analysis. The former managed to distinguish between cohort and annual effects on growth changes but failed to detect a similar growth response across species, while the latter did identify a common directional trend in body size across a majority of species but failed to attribute this trend to temperature changes. For the second objective, two data analyses and two model-based studies are presented. The first data analysis on Eurasian perch showed the importance of considering mortality rates alongside growth rate to understand the implications of warming for fish populations size structure. The second data analysis on Korea chub mackerel showed that warming resulted in larger sizes of young fish, faster maturation, and higher yield-per-recruit. The model-based studies showed the importance of including reproduction processes and stressors other than temperature into growth models. For the third objective, analyses of warming-induced growth changes implications on fisheries yield were performed in two ecosystems: Chinese waters and the southeast Bering Sea. Both analyses used Bayesian modelling. Results indicate a warming-induced loss of fisheries yield in Chinese waters, although with some discrepancies among regions and species. In the Bering Sea, warming resulted in larger young age classes and smaller old age classes, which is consistent with TSR and suggests that fisheries productivity might be altered. For the fourth objective, ongoing efforts to build a global length-at-age dataset are described. For its next term WGGRAFY plans to keep on pursuing its four objectives, but with the addition of the impact of growth changes on size-structures ecosystem by using size spectrum modelling.