Early life history connectivity of Antarctic silverfish (Pleuragramma antarctica) in the Ross Sea

Abstract

A recent population hypothesis for Antarctic silverfish (Pleuragramma antarctica), a critical forage species, argued that interactions between life history and circulation associated with glacial trough systems drive circumpolar distributions over the continental shelf. In the Ross Sea, aggregations of eggs and larvae occur under fast ice in Terra Nova Bay, and the hypothesis predicted that dispersing larvae encounter outflow along the western side of Drygalski Trough. The outflow advects larvae towards the shelf‐break, and mixing with 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. We ruled out misidentification using an innovative genetic validation. Silverfish larvae comprised 99.5% of the catch, and the highest population densities were found in Drygalski Trough. The results provided no evidence to reject the population hypothesis. Abundance indices, back‐calculated hatching dates, length distributions and growth were congruent with a unified early life history in the western Ross Sea, constrained by cryopelagic early stages in Terra Nova Bay. By contrast, a sample in the Bay of Whales revealed much smaller larvae, suggesting either a geographically separate population in the eastern Ross Sea, or westward connectivity with larvae spawned nearby by fish sourced from troughs upstream in the Amundsen Sea. These results illustrate how hypotheses that integrate population structure with life history can provide precise spatial predictions for subsequent testing.

Spatial structuring and life history connectivity of Antarctic silverfish along the southern continental shelf of the Weddell Sea

“…In the Weddell Sea, White & Piatkowski (1993) noted that dense larval distributions found over the continental slope east of the Filchner Trough mouth were consistent with an earlier hypothesis of westward dispersal by surface currents (Hubold 1984). Much of the evidence for the role of hydrography in connectivity between silverfish populations has been derived from indirect observation using monodisciplinary approaches (Hubold 1984, Kellermann 1986, 1996, Agostini et al 2015, Brooks et al 2018). Yet multi-disciplinary studies can allow cross-corroboration and comparison between complementary techniques (Begg et al 1999, Sturrock et al 2012, while understanding of the physical context can help to directly address the role of physical-biological interactions in structuring silverfish populations (Ashford et al 2017, Davis et al 2017, Brooks et al 2018).…”

“…They found evidence supporting a unified population spatially constrained by cryopelagic incubation under fast ice at the head of the trough. Thus, after hatching in December-January, larvae were found in large numbers in the trough outflow and inflow during February−March, whereas few were found elsewhere in the western Ross Sea (Brooks et al 2018).…”

“…Fish reaching the continental shelf-break become exposed to currents along the continental slope, which transport them to trough systems downstream (Ashford et al 2017). Brooks et al (2018) examined the cross-shelf component of the hypothesis by comparing samples of larvae caught along the outflow and inflow of the Drygalski Trough in the western Ross Sea. They found evidence supporting a unified population spatially constrained by cryopelagic incubation under fast ice at the head of the trough.…”

“…Several studies have implicated structuring and connectivity between Antarctic silverfish by current and front systems. As well as noting that fish reaching the ASC in the Ross Sea become exposed to along-shelf connectivity, Brooks et al (2018) suggested that larvae found in the Bay of Whales may have been spawned by fish transported along the AACC from the eastern Amundsen Sea. found, in addition to regional connectivity along the ASC, evidence of a recent influx of silverfish in the inflow of Marguerite Trough off the western Antarctic Peninsula.…”

The Weddell Gyre, Southern Ocean: Present Knowledge and Future Challenges

“…The pelagic life history of P. antarcticum takes advantage of shelf circulation to obtain a circumpolar distribution (Brooks, Caccavo, et al, ). Initial studies in the southern Weddell Sea showed that the postlarvae of P. antarcticum concentrate over the continental slope and inner shelf depressions reaching densities as high as 88 individuals per m 2 and representing 85–98% of all planktonic fish larvae (Hubold, ).…”