Brooks CM, Caccavo, JA, Ashford J, Dunbar R, Goetz K, La Mesa M and Zane L. (2018) Early life history connectivity of Antarctic silverfish (Pleuragramma antarctica) in the Ross Sea. Fisheries Oceanography, 00, 1-14.
A recent population hypothesis for Antarctic silverfish (Pleuragramma antarctica), a critical forage species, argued that circumpolar distributions documented over the continental shelf are maintained by interactions between life history processes and the circulation associated with glacial trough systems. In the Ross Sea, aggregations of cryopelagic eggs and larvae are found under fast ice in Terra Nova Bay, and dispersing larvae are predicted to encounter the shelf outflow along the western side of the Drygalski Trough. The outflow advects the larvae towards the shelf-break, where mixing with the trough inflow facilitates return toward the inner shelf. To examine the hypothesis, we compared samples of P. antarctica collected near Coulman Island in the outflow, along Crary Bank in the inflow, and a third set taken over the rest of the Ross Sea. Any misidentification was ruled out using an innovative genetic validation. Silverfish larvae comprised more than 99% of the overall catch from all combined tows, and the highest population densities were found in the Drygalski Trough. The results provided no evidence to reject the population hypothesis. Instead, abundance indices, back-calculated hatching dates, length distributions and growth were congruent with a unified early life history for larval silverfish in the western Ross Sea, constrained by cryopelagic early stages in Terra Nova Bay. By contrast, a single tow in the Bay of Whales revealed much smaller larvae, suggesting either a geographically separate population with a coherent early life history in the eastern Ross Sea; or westward connectivity with spawning fish sourced from troughs located upstream in the Amundsen and Bellingshausen Seas. These results illustrate how hypotheses that integrate population structure with life history processes can provide precise spatial predictions across geographically separated systems, to facilitate highly targeted sampling designs in subsequent testing.