Acoustic deployments reveal Antarctic silverfish under ice in the Ross Sea

Abstract

Antarctic silverfish (Pleuragramma antarctica Boulenger) are a keystone species in the Ross Sea. Silverfish eggs and larvae are abundant during spring amongst the sub-surface platelet ice in Terra Nova Bay. It is not known whether the eggs are spawned elsewhere and accumulate under the ice or whether there is mass migration of silverfish to coastal spawning sites in winter. To test the latter hypothesis, an upward-looking 67 kHz echo sounder was moored in Terra Nova Bay to observe potential silverfish migration. The echo sounder was deployed at 380 m in a seabed depth of 550 m and ran for 210 days from 15 May until 11 December 2015. Acoustic reflections consistent with silverfish were observed at depths of 230–380 m during 9–22 September. This timing is consistent with the presence of eggs typically observed in October. Adult silverfish were also detected with an echo sounder and camera deployed through the ice in McMurdo Sound on 10 November 2015. Juvenile silverfish, but not adults, were observed through the ice in Terra Nova Bay during 11–16 November 2017. This paper provides a proof of concept, showing that innovative use of acoustics may help fill important observation gaps in the life history of silverfish.

Gone fishing: Adélie penguin site-specific foraging tactics and breeding performance

“…The fact that more fish were caught off InIs may also be due to favourable conditions for rapid growth of P. antarctica larvae near polynya, in line with autumnal phytoplankton blooms (Vacchi et al 2012). Indeed, Terra Nova Bay seems to be particularly rich in silverfish at various growth stages (Davis et al 2017, O'Driscoll et al 2018. Concerning the slight difference in breeding chronology between the two colonies, the colder weather and blizzard we recorded at InIs during early incubation could have delayed hatching.…”

“…The fact that more fish were caught off InIs may also be due to favourable conditions for rapid growth of P. antarctica larvae near polynya, in line with autumnal phytoplankton blooms (Vacchi et al 2012). Indeed, Terra Nova Bay seems to be particularly rich in silverfish at various growth stages (Davis et al 2017, O‘Driscoll et al 2018).…”

Productivity and Change in Fish and Squid in the Southern Ocean

“…The silverfish life-history hypothesis incorporates these physical-biological interactions, predicting that crossshelf circulation mediates retention within populations and exposure to along-shelf transport pathways (Agostini et al, 2015;Ashford et al, 2017b;Brooks et al, 2018b;Caccavo et al, 2018Caccavo et al, , 2019. Schools of adult silverfish have been observed moving inshore along the Antarctic Peninsula (Daniels and Lipps, 1982), and aggregations attributed to adult silverfish have been detected using bio-acoustic tools in the Ross Sea, supporting the hypothesis that silverfish are moving into Terra Nova Bay during winter to spawn (O'Driscoll et al, 2018b). Large amounts of eggs develop within the platelet ice layer under the fast ice in the western Ross Sea (Vacchi et al, 2012).…”

“…Moorings, normally deployed for the study of currents and environmental conditions, might represent suitable platforms for acoustic instrumentation, allowing observations also in periods of the year when vessels cannot operate due to the sea-ice cover. At Terra Nova Bay, echosounder deployment on moorings allowed the observation of reflections consistent with adult silverfish in September, providing complementary information in support of the hypothesis of coastal migration of fish for spawning during that period (O'Driscoll et al, 2018b).…”

Midtrophic fish feeding modes at the poles: an ecomorphological comparison of polar cod (Boreogadus saida) and Antarctic silverfish (Pleuragramma antarctica)

“…The polar cod can reach up to 460 mm in total length (TL) (Mecklenburg et al 2018), but TL is generally < 250 mm (Cohen et al 1990). With an average 7-8 years life span, it becomes sexually mature between the age of 2-3 years (Hop and Gjøsaeter 2013;Mueter et al 2016;Nahrgang et al 2016) and is the Mecklenburg et al 2018) Life mode Pelagic Pelagic Migration, movements Diel vertical migrations with fish moving shallower depths at night and deeper during the day (Plötz et al 2001;Fuiman et al 2002;Robison 2003;Lancraft et al 2004) Spawning migrations are believed to take place from open waters to the coastal ice shelves (Koubbi et al 2011;Ghigliotti et al 2017;O'Driscoll et al 2018) Adults perform diel vertical migrations under the ice. Seasonal vertical migrations toward the bottom prior to winter are observed in juveniles and adults (Benoit et al 2010;Geoffroy et al 2016) The species may undertake extensive migrations (Ponomarenko 1968;Hop and Gjøsaeter 2013;Kessel et al 2017) Adult size (average) 15 cm (Fischer and Hureau 1985) 25 cm (Cohen et al 1990) Maximum age 14 years (Hubold and Tomo 1989;Sutton andHorn 2011) 8 years (Gillespie et al 1997) Trophic level 3.6-4 (Pinkerton 2017) 3.3-3.5 (Christiansen et al 2012) Diet Generalist (Pinkerton 2017;Tavernier and Giraldo, 2017) Opportunistic feeding habit (Pinkerton 2017;Carlig et al 2019) Ontogenic shifts in prey consumption (Kellermann 1987;Giraldo et al 2011;Tavernier and Giraldo 2017) The diet in adults is dominated by euphasiids and copepods; a number of other invertebrates are taken by adults; piscivory is uncommon but can be relevant at the local level…”