Body size, sex ratio and diet composition of Arctogadus glacialis (Peters, 1874) (Pisces: Gadidae) in the Northeast Water Polynya (Greenland)

Abstract

Little is known about the biology and feeding ecology of Arctogadus glacialis (Peters, 1874), an endemic gadid fish species occurring circumpolarly in both ice-free and ice-covered Arctic seas. In this study we analysed specimens sampled from bottom trawl and Agassiz trawl catches conducted at eight stations in water depths from 115 to 490 m in the Northeast Water Polynya off Greenland in August 1990. Size composition and sex ratios were assessed for 585 fish with standard lengths ranging from 7.8 to 34.5 cm. Median fish sizes at the stations ranged between 8.6 and 18.8 cm. Quantitative stomach content analyses of a subsample of 175 specimens revealed that in the Northeast Water A. glacialis fed almost exclusively on pelagic prey. Truly benthic organisms were not found in the stomachs, and sympagic species were rarely recorded. Overall, calanoid copepods were the major prey in terms of numbers. However, stomach contents varied considerably between fish size groups. In terms of prey biomass, copepods dominated the diet of small fish (< 12 cm), primarily occurring at shallow stations (115-250 m), whereas amphipods and mysids were relatively more important for larger fish (> 16 cm), which dominated the catches at deep stations (360-480 m). The broad variety of diet composition indicated an opportunistic pelagic feeding pattern.