Seasonal Depth Distribution of the Red King Crab (Paralithodes camtschaticus) in Varangerfjorden, Northern Norway

Seasonal Depth Distribution of the Red King Crab (Paralithodes camtschaticus) in Varangerfjorden, Northern Norway

J.H. Sundet and A.M. Hjelset

Seasonal Depth Distribution of the Red King Crab (Paralithodes camtschaticus) in Varangerfjorden, Northern NorwayThis is part of Biology and Management of Exploited Crab Populations under Climate Change
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Description

The red king crab was introduced to the Murman Fjord on the Kola Peninsula in the 1960s, and has since spread to most areas in the southern Barents Sea. Studies in its native areas in the North Pacific Ocean showed that red king crabs undergo seasonal migrations between shallow and deep waters. The degree to which the crab has adapted to its new environment is unknown, but knowledge of its seasonal behavior is essential to the design of stock assessment surveys and for evaluating the impact of the crab on the native fauna in the Barents Sea. Monthly samples of red king crabs taken at the same positions and at five depths in Varangerfjorden, northern Norway, indicated a different seasonal depth pattern among mature crabs of both sexes and a more patchy distribution among mature females than mature males. Mature males seem to enter shallow water in large numbers as early as November, while ovigerous females appear in shallow areas in December. Mature males are observed almost exclusively in deeper areas from June through September, while females are mainly caught in deep waters from June through November. There was no clear pattern in the catches of immature crabs. However, juveniles may not have been adequately sampled, because they are likely to be distributed in habitats shallower than 50 m. Based on this understanding of the seasonal depth distribution of red king crabs in Varangerfjorden, stock assessment surveys of mature crabs should be conducted in deep waters sometime between July and October. Seasonal movements in Varangerfjorden indicate that the crabs may impact benthic communities at all depths, but based on depth-specific residence time, deep-water fauna are most likely to be most affected.

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