Acoustic Methods of Monitoring Antarctic Silverfish Distribution and Abundance
Acoustic methods have the ability to detect and quantify distribution and abundance of Antarctic silverfish (Pleuragramma antarctica) across a range of spatial and temporal scales. The main advantage of acoustic surveys over traditional net-based sampling methods for silverfish is that the larger adult fish are unlikely to avoid the echosounder. Acoustic surveys also allow relatively wide coverage over the whole water column in a short time period because data are collected while the vessel is steaming at 8–10 knots. The key uncertainties, as with most acoustic surveys, are target identification and target strength. These uncertainties are compounded because silverfish do not have a gas-filled swim-bladder and so are a relatively weak acoustic target. Use of multi-frequency acoustic data helps discriminate silverfish from krill and other associated species, and broadband acoustics has considerable potential in this regard. Acoustic target strength has been derived from scattering models and in situ and ex situ measurements. Adult silverfish exhibit different scattering properties to post-larvae and juveniles. In the Ross Sea, adult silverfish are distributed widely over the shelf and tend to form layers at 100–400 m depth. Juvenile silverfish of 50–80 mm standard length occur shallower and were observed as a weak layer centred at about 80 m depth.
KeywordsAcoustics Target strength Geographical distribution Forage fish Ross Sea Antarctica
NZ IPY-CAML research was funded by the New Zealand Government under the New Zealand International Polar Year-Census of Antarctic Marine Life Project (Phase 1: So001IPY; Phase 2: IPY2007-01). We gratefully acknowledge project governance by the Ministry of Fisheries Science Team and the Ocean Survey 20/20 CAML Advisory Group (Land Information New Zealand, Ministry of Fisheries, Antarctica New Zealand, Ministry of Foreign Affairs and Trade, and National Institute of Water and Atmosphere Ltd). The authors also acknowledge the Italian National Programme for Research in Antarctica (PNRA) and ENEA for supporting the acoustic survey in the Ross Sea during several expeditions to Antarctica by R/V Italica.
- Ackley SF, Bengtson JL, Boveng P et al (2003) A top-down, multidisciplinary study of the structure and function of the pack-ice ecosystem in the eastern Ross Sea, Antarctica. Polar Rec 39:219–230Google Scholar
- Azzali M, Leonori I, Biagiotti I et al (2010) Target strength studies on Antarctic silverfish (Pleuragramma antarcticum) in the Ross Sea. CCAMLR Sci 17:75–104Google Scholar
- Demer DA (ed) (2015) Calibrations of acoustic instruments. ICES Cooperative Res Report 326Google Scholar
- Pinkerton MH, Bradford-Grieve JM, Hanchet SM (2010) A balanced model of the food web of the Ross Sea, Antarctica. CCAMLR Sci 17:1–31Google Scholar