Testing early life history using otolith chemistry and particle tracking simulations

Dispersal in many oceanic species occurs during early life through advection by currents. Yet, on settling, young fish are exposed to environments which can subsequently influence measures used for determining population structure. To overcome this, we used otolith chemistry of Scotia Sea icefish (Chaenocephalus aceratus), a species with a long pelagic larval phase found along the Antarctic Circumpolar Current, to test connectivity between the Antarctic Peninsula and South Georgia based on predictions from a circulation model. Material laid down in the otolith nucleus during early life showed strong heterogeneity, and evidence of heterogeneity between sampling areas on the Antarctic Peninsula. However, at South Georgia, the nucleus chemistry was similar between the eastern and northern shelves, indicating a single, self-recruiting population. Simulations of the large-scale circulation predicted that, consistent with the otolith chemistry, particles released deep on the Antarctic Peninsula shelf during late winter, corresponding to hatching of icefish larvae from benthic nests, are transported in the southern ACC, missing South Georgia but following trajectories along the south Scotia Ridge. Used together, the two techniques promise an innovative approach to generate and test predictions, and resolve early dispersal and connectivity related to the physical circulation of oceanic systems.