Characterizing aspects of rockfish (Sebastes spp.) assemblages in the Aleutian Islands, Alaska

Characterizing aspects of rockfish (Sebastes spp.) assemblages in the Aleutian Islands, Alaska

R.F. Reuter, and P.D. Spencer

Characterizing aspects of rockfish (Sebastes spp.) assemblages in the Aleutian Islands, AlaskaThis is part of Biology, Assessment, and Management of North Pacific Rockfishes
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Description

Understanding the spatial and temporal persistence of rockfish (Sebastes spp.) communities in the Aleutian Islands would help define their essential habitat as well as aid in the management of their fisheries. It is known that some Sebastes spp. can be distributed non-uniformly or uniformly within discrete depth zones throughout the North Pacific, but it is not known whether these patterns are consistent within assemblages of Sebastes species. In this study, five years of data from surveys conducted between 1991 and 2002 were used to analyze rockfish species associations in the Aleutian Islands. Agglomerative hierarchical cluster methods were used to create small-scale haul-groups (groups defined by hauls with similar species composition) and large-scale species-groups (defined for the entire Aleutian Islands area) using rockfish species and three primarily benthic species that make up the main fisheries in the Aleutian Islands (Atka mackerel [Pleurogrammus monopterygius], Pacific cod [Gadus macrocephalus], and sablefish [Anoplopoma fimbria]). Six haul groups were found, three of which were persistent throughout the five-year study period. The dominant species within these groups were Pacific cod, Pacific ocean perch (Sebastes alutus), and a group with a combination of rougheye rockfish (Sebastes aleutianus), shortraker rockfish (S. borealis), and shortspine thornyhead (Sebastolobus alascanus). Depth and longitude were found to be important environmental parameters in describing a haul group. For example the rougheye rockfish, shortraker rockfish, and shortspine thornyhead group was a deepwater slope haul group, whereas the Pacific ocean perch group occurred mainly in the lower shelf depth zone. The three main haul groups were located in consistent geographical areas suggesting spatial persistence: locations such as the north side of Amlia Island and near Little Sitkin Island were found to be areas where the rougheye rockfish, shortraker rockfish, and shortspine thornyhead haul group was persistent. The identification of areas where rockfish aggregations consistently occur may assist in defining logical areas for spatial management strategies such as marine protected areas.

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