Can Pitch & Roll DST distinguish between pelagic and demersal behaviour of adult Greenland halibut

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Can Pitch & Roll DST distinguish between pelagic and demersal behaviour of adult Greenland halibut

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Pelagic behavior of adult Greenland halibut (Reinhardtius hippoglossoides)

It is evident from several field experiments with vertical longlines and archival tags, as well as concurrent studies of predator-prey relationships, that adult specimens of the deep-water flatfish Greenland halibut (Reinhardtius hippoglossoides) make regular excursions several hundred meters through the water column. The distribution of longline catches within the water column is confined to a well-defined depth layer overlapping with the distribution of blue whiting (Micromesistius poutassou), an important prey species, and depth recordings from archival tags overlap with Atlantic herring (Clupea harengus), the other major fish prey. The degree of pelagic use varies with fish size as well as seasons. Smaller individuals are found further off the bottom, and pelagic activity is greatest during early autumn. Interaction with pelagic prey species can influence results from bottom trawl surveys

Pelagic occurrence of Greenland halibut (Reinhardtius hippoglossoides) studied by means of vertical longlines

In order to calculate reliable survey indices it’s important to know the dynamics of vertical distribution of a fish species. The vertical distribution of Greenland halibut (Reinhardtius hippogolossoides) cannot be studied acoustically due to low acoustic contrast. Therefore a series of experiments were designed to catch the species pelagically in the Barents Sea. Sampling was made by means of vertical longlines during three time periods of the year. The paper presents preliminary results from the experiments. Catch-rates through the water column was analysed and population structure compared between demersal and pelagic samples. Stomachs from bottom trawls were analysed to identify pelagic prey. At 400-700 m bottom depth, individual Greenland halibut were caught up to 420 m off the bottom. Individuals of all sizes were caught pelagically, but catches were dominated by smaller males. Pelagic occurrence varied between sampling periods, being more important in August and December than in March. Still, pelagic prey were found in stomachs from all seasons