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Trophic Relationships of Commercial Fishes in the Pacific Waters off Southeastern Kamchatka and the Northern Kuril Islands

Trophic Relationships of Commercial Fishes in the Pacific Waters off Southeastern Kamchatka and the Northern Kuril Islands

Alexei M. Orlov

Trophic Relationships of Commercial Fishes in the Pacific Waters off Southeastern Kamchatka and the Northern Kuril IslandsThis is part of Ecosystem Approaches for Fisheries Management
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Description

Of the fish species in Pacific waters off the northern Kuril Islands and southeastern Kamchatka, 19 are commercially important and most abundant. Among them are three groups with different feeding habits: (1) planktophages (walleye pollock, Theragra chalcogramma; Atka mackerel, Pleurogrammus monopterygius; Pacific ocean perch, Sebastes alutus); (2) benthophages (rock greenling, Hexagrammos lagocephalus; rock sole, Pleuronectes bilineatus; Bering skate, Bathyraja interrupta; Okhotsk skate Bathyraja violacea); and(3) predators (sablefish, Anoplopoma fimbria; Pacific cod, Gadus macrocephalus; Greenland turbot, Reinhardtius hippoglossoides Kamchatka flounder, Atheresthes evermanni; Pacific halibut, Hippoglossus stenolepis; Alaska skate, Bathyraja parmifera; shortraker rockfish, Sebastes borealis; broadbanded thornyhead, Sebastolobus macrochir; shortspine thornyhead, Sebastolobus alascanus; Aleutian skate, Bathyraja aleutica; whiteblotched skate, Bathyraja maculata; and Matsubara skate, Bathyraja matsubarai). The biology of the 19 species in these waters has not been studied in detail and little investigation has been done on their trophic relationships.

Based on shipboard scans of stomach contents in 1992-1996(15,763 stomachs were analyzed, of which 9,429 contained food), dietary composition was investigated and some aspects of trophic relationships were analyzed. For all species of each group, Schoener's indices of dietary overlap were calculated. Level of feeding competition was determined based on intra-annual dynamics of feeding intensity and features of spatial (vertical and horizontal) distribution of fish concentrations.

Among planktophages the maximum index value (60.0%) was characteristic of diets of Pacific ocean perch and pollock. The maximum feeding intensity for both species appeared during similar periods (May-July). At the same time, the characteristics of spatial distribution of concentrations of pollock and Pacific ocean perch differed widely indicating a low level of feeding competition between them.

Among benthophages the greatest dietary overlap was noted for rock sole and Bering skate (73.3%) and Bering and Okhotsk skates (65.5%). The dissimilarity of characteristics of feeding intensity dynamics and spatial distribution showed a low level of feeding competition between these species. Among predatory fishes the maximum index values of dietary overlap were characteristic of shortraker rockfish and broadbanded thornyhead(82.7%), whiteblotched skate and sablefish (62.2%), shortraker rockfish and shortspine thornyhead (61.4%), Greenland turbot and Kamchatka flounder (60.1%), and whiteblotched and Aleutian skates (60.0%). For all of those pairs (except for sablefish and whiteblotched skate) the high similarity of intra annual dynamics of feeding intensity was noted. However, similar characteristics of spatial distribution of fish assemblages were noted only for shortraker rockfish and broadbanded thornyhead, which indicates a high level of feeding competition between these species.

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