Temporal stability of the maturation schedule of capelin (Mallotus villosus Mueller) in the Barents Sea

Capelin in the Barents Sea are primarily harvested in a terminal fishery that targets maturing indiviuals. Theory predicts that, in a semelparous population (i.e., one in which reproduction is seasonal, synchronous, and followed by parental mortality), an unselective, terinal fishery (i.e., one in which most of the fish that are not caught will not have a new spawning opportunity) does not generate strong selection for changed age and size at mturation. The probabilistic maturation reaction norm (PMRN) method was applied to test this prediction and to detect possible temporal changes in length at maturation o Barents Sea capelin between 1978 and 2008. Maturation reaction norms suggest that maturation is age-independent in capelin, but that males require a larger size to attainthe same maturation probability as females. No temporal trends in length at maturation could be detected, thus confirming the theoretical prediction. Furthermore, none of thecandidate environmental variables tested to explain the temporal variability in length at maturation (water temperature and capelin biomass) consistently shoed a significant correlation with the PMRN midpoints

Larval fish distribution and retention in the Canary Current system during the weak upwelling season

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Heavy metals in zooplankton and decapod crustaceans from the Barents Sea.

Trace metals (Cd, Cu, Pb and Zn) were analysed in zooplankton samples and decapod crustaceans collected on cruises of "RV Walther Herwig III" to the Barents Sea (Summer 1991, 1994 and 2000). We found a substantial spatial heterogeneity in the decapod crustacean Pandalus borealis, with increasing Cd concentrations from the south (North Cape Bank; 0.7 mg kg super(- 1) DW) to the north (north of Svalbard; 4.7 mg kg super(- 1)), supporting the hypothesis that the frequently reported Cd-anomaly in polar crustaceans might be extended to the Barents Sea. Regarding various crustaceans and zooplankton collectives (2000) a distinct interspecific heterogeneity of metals was obvious, with lowest Cd concentrations in euphausiids and chaetognaths and highest ones in decapods and hyperiid amphipods; lowest Cu concentrations in chaetognaths and copepods and highest ones in euphausiids and decapods; and lowest Zn concentrations in euphausiids and decapods and highest ones in some copepods. For Pb many values were below or close to the limit of detection, suggesting that Pb concentrations about 0.4 mg kg super(- 1) might serve as a regional background value. Results for Cd, Cu and Zn in copepods of this study are largely within the reported range, but high Cd concentrations in copepods from summer in contrast to reported lower ones during winter/spring may be related either to changing accumulation strategies of the copepod species involved or to seasonally changing Cd absorption in copepods from food

Harp seal body condition and trophic interactions with prey in Norwegian high Arctic waters in early autumn

In September 2016, a marine ecosystem survey covered all trophic levels from phytoplankton to seals in the Arctic Ocean to the west and north of Svalbard. At the ice edge, 26 harp seals were sampled to assess whether recent environmental changes had affected their diets and body condition by comparing our current results with previous investigations conducted 2-3 decades ago in the northern Barents Sea, when the ice edge was located much further south. Our results suggest that the body condition was slightly but significantly lower for one year and older seals in 2016 compared with seals sampled in the early 1990s. Furthermore, we confirmed previous findings that polar cod (Boreogadus saida) and the pelagic hyperiid amphipod Themisto libellula still dominate the seal diet. One consequence of current ice edge localisation north of Svalbard is that the water depth underneath is now 500 m and deeper, which probably explains the absence of bottom associated species, and the presence of species such as Atlantic cod (Gadus morhua) and blue whiting (Micromesistius poutassou) as alternative species in addition to polar cod and T. libellula in the seal diets. Stable isotope data also suggest possible long-term importance in the seal diet of T. libellula and of low trophic level benthopelagic prey such as the squid Gonatus fabricii over mid-trophic level pelagic fishes, but with a strong component of small, benthopelagic fish such as blue whiting. The long-term importance of pelagic crustaceans was also suggested from the fatty acid analyses. Assessment of the abundance of prey showed that T. libellula was by far the most abundant prey species in the upper water layers, followed by krill (mainly Thysanoessa inermis), Atlantic cod and polar cod. Prey-preference analyses indicated that polar cod was the most preferred prey species for the seals