Modelling the distribution of larval fish in a western boundary current using a multi-voyage database

Across the world’s oceans, western boundary currents are strengthening and warming faster than the global average. This is expected to have large impacts on the distribution of pelagic fishes, as their dispersal and physiological range limits shift. Monitoring the distribution of larval fish assemblages, sampled with plankton nets, allows for population and community-level responses to climate-driven changes to be observed without reliance on fisheries data. Here, we characterise patterns in the distribution of larval fish over 15° of latitude with highly variable conditions driven by a western boundary current, the East Australian Current, using a newly available larval fish database supplemented with recently collected samples. Using generalized additive mixed models, we show strong non-linear relationships between larval fish taxonomic richness and abundance with latitude. During autumn, winter and spring, both larval fish abundance and richness are greater in equatorward latitudes (28°S) than in more poleward ones (43°S), with this pattern reversed during the summer. The region where the East Australian Current separates from the coast delineates a zone of marked change in larval fish richness and abundance. Analyses of larval fish assemblages using Gaussian copula graphics models revealed a strong association between assemblage composition and temperature. The direction of temperature effects on individual taxa varied greatly, highlighting the complex nature of possible climate-driven shifts. Our study highlights the utility of compiling multi-voyage databases and their role in monitoring the global oceans.