Japanese and Taiwanese pelagic longline fleet dynamics and the impacts of climate change in the southern Indian Ocean

Climate change is projected to continue shifting the distribution of marine species, leading to changes in local assemblages and different interactions with human activities. With regard to fisheries, understanding the relationship between fishing fleets, target species catch per unit effort(CPUE), and the environment enhances our ability to anticipate fisher response and is an essential step towards proactive management. Here, we explore the potential impact of climate change in the southern Indian Ocean by modelling Japanese and Taiwanese pelagic longline fleet dynamics. We quantify the mean and variability of target species CPUE and the relative valueand cost of fishing in different areas. Using linear mixed models, we identify fleet-specific effortallocation strategies most related to observed effortand predict the future distribution of effortand tuna catch under climate change for 2063–2068. The Japanese fleet's strategy targets high-value species and minimizes the variability in CPUE of the primary target species. Conversely, the Taiwanese strategy indicated flexible targeting of a broad range of species, fishing in areas of high and low variability in catch, and minimizing costs. The projected future mean and variability in CPUE across species suggest a slight increase in CPUE in currently high CPUE areas for most species. The corresponding effortprojections suggest a slight increase in Japanese effortin the western and eastern study area, and Taiwanese effortincreasing east of Madagascar. This approach provides a useful method for managers to explore the impacts of different fishing and fleet managementstrategies for the future.