Diet and trophic niche of Antarctic silverfish (Pleuragramma antarcticum) in the Ross Sea, Antarctica

The diet of Antarctic silverfish (Pleuragramma antarcticum) was evaluated by examining stomach contents of specimens collected in the Ross Sea (71°–77°S, 165°E–180°) in January–March 2008. Silverfish (50–236 mm standard length, SL) and silverfish prey items were analysed for stable isotopic composition of carbon and nitrogen. According to index of relative importance (IRI), the most important prey items of silverfish were copepods (IRI 81% over all specimens), predominantly Metridia gerlachei and Paraeuchaeta sp., with krill and fish having low IRI (IRI 2.2% and 5.6% overall). However, according to weight of prey in stomachs, fish (silverfish and lanternfish) and krill dominated diet overall (48% and 22% respectively), with copepods being a relatively minor constituent of overall diet by weight (9.9%). Piscivory by silverfish occurred mainly in the extreme south-west of the region and near the continental slope. By weight, krill identified to species level in silverfish stomachs were predominantly Euphausia superba (14.1%) with some E. crystallophorias (4.8%). were identified in silverfish stomachs. Both distLM modelling (PRIMER-permanova+) on stomach contents (by IRI) and stepwise generalised linear modelling on stable isotopes showed that SL and location were significant predictors of silverfish diet. Larval/post-larval silverfish (standard length, SL<90 mm) consumed exclusively copepods. Large adult silverfish (SL>179 mm) consumed predominantly fish by weight, especially in the north (near the Ross Sea slope) and in the SW of the Ross Sea. Juvenile silverfish (SL 96-151 mm) consumed predominantly krill by weight. Amphipods were important prey items for large adult silverfish in the west of the Ross Sea. General concordance between stomach contents and trophic level of silverfish and prey based on δ¹⁵N was demonstrated. Silverfish trophic level was 3.5 (larval/post-larval fish) and 4.0 (fish aged 3+).