Feeding and growth of polar cod in fjords of Svalbard

• Main Author: Johannessen, Leif Sindre
• Other Authors: Stein Kaartvedt
• Format: Master Thesis
• Language: English
• Published: 2007
• Subjects: polar torsk Boreogadus saidaarktis calanus fødeøkologi Svalbard Kongsfjorden Billefjorden polartorsk; VDP::480; Arctic; Billefjorden; Svalbard; atlantic cod; Boreogadus saida; Kongsfjord*; Kongsfjorden; polar cod; Polartorsk; Themisto; Copepods
• Online Access: http://hdl.handle.net/10852/11660; http://urn.nb.no/URN:NBN:no-17838

Polar cod (Boreogadus saida) were collected in two different fjords around Svalbard in 2006 to address their feeding ecology and growth. Kongsfjorden was sampled in spring and in autumn to investigate seasonal patterns. Billefjorden, which is characterized by more Arctic water masses, was included in the autumn sampling to address impacts by spatial differences in environmental factors as temperature and prey community. The copepods Calanus spp were the most numerous prey item at any season and locality. The krill Thysanoessa spp contributed for about 30 % of the diet in spring and were at that time the second most dominating prey species in terms of numbers, and likely the most prominent prey in terms of biomass. In autumn the second most dominating prey species had been replaced with the amphipods Themisto spp. No clear diet shift was detected, but larger species, as Themisto spp and Thysanoessa spp, became gradually more important with size. Four age classes were found with age class 1 and 2 being most abundant. Billefjorden was characterized by having almost exclusively young polar cod. In my studies there were also some indications that temperature enhances growth in polar cod. The youngest cohort in Kongsfjorden in spring coincided with the youngest cohort in Billefjorden in autumn, suggesting a lower growth rate for polar cods living in Billefjorden. Temperature also seems to have an effect on abundance. Polar cod were absent in waters over 3¢ª C and in autumn it had been replaced by Atlantic cod at localities where it was found in spring.