Long rough dab (Hippoglossoides platessoides) of the Barents Sea and Svalbard area: ecology and resource evaluation
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Based on data from Norwegian and Russian bottom trawl surveys in the years 1988-1993, the paper considers distribution, population structure, growth and reproduction of long rough dab (Hippoglossoides platessoides) of the Barents Sea. Based on effort statistics from the commercial fleet and data from commercial trawlers hired or inspected by Norwegian authorities, the paper also gives a preliminary evaluation of the resource potential. Long rough dab was the most abundant flatfish at moderate depth in the Barents Sea and the abundance increased during the period 1988-1993, particularly in the outer part of the distribution area. This increase in abundance and distribution area was probably largely caused by the very strong 1986 year class. Eastern, northern and shallow areas were dominated by relatively small fish. Spawning occurred over wide areas, but the fishes in the northern part may to some extent have migrated to spawning grounds further south. Males reached 50% maturation at age 5 and females at age 10. The growth rates of males and females were almost linear and not very different for age groups less than 10. Mortality was higher for males and nearly all fish older than 10 years were female. The results indicated that growth rate for the very strong 1986 year class was density dependent. The estimated total biomass of long rough dab in the Barents Sea increased from 70 000 metric tons in 1988 to more than 200 000 tons in 1993. The bycatch of long rough dab in the Norwegian fisheries was estimated to less than 1000 tons. The total catch of long rough dab in the Barents Sea was probably less than 0.2 % of the standing biomass. Although the precision of these estimates are low, there seems to be a considerable potential for biologically safe exploitation of this resource.