Temperature variation associated with interannual variability in abundance of juvenile Patagonian toothfish (Dissostichus eleginoides) at South Georgia

A detailed understanding of the life cycles of fished species in relation to their environment is important for assessing the impacts of environmental change and informing fisheries management. Here, we examined the abundance of early life stages of Patagonian toothfish (Dissostichus eleginoides) in relation to temperature in the waters around South Georgia, located in the rapidly changing southwest Atlantic sector of the Southern Ocean, where a commercial fishery for this species operates. Using scientific demersal trawl survey data spanning almost four decades (1986–2023), we modelled interannual variability in the abundance of juvenile Patagonian toothfish (<26 cm and 26–37 cm size-classes) in relation to temperature conditions during spawning, egg-dispersal, larval-dispersal, and post-settlement development stages. Stage-specific temperatures were derived from depth layers reflecting known vertical distributions of Patagonian toothfish during those stages of development. Long-term trends in temperature were evaluated to identify stages that have potentially experienced the largest changes in thermal conditions over time. Juvenile abundance exhibited marked interannual variability, alongside an apparent long-term decline from 1987 to 2023. Interannual variability was strongly correlated with sub-surface temperatures during spawning and egg dispersal, with cooler temperatures corresponding to lower abundance. While the underlying mechanisms require further investigation, we discuss several hypotheses for these temperature relationships, including the possibility that temperature acts directly or as a proxy for other factors, such as oceanographic processes affecting the transport and retention of early life stages. Our findings provide insight into drivers potentially influencing Patagonian toothfish recruitment and population dynamics, highlighting the importance of considering environmental conditions throughout the water column and across key developmental stages in fisheries management, and identifying priorities for future research.