Juvenile walleye pollock aggregation structure in the Gulf of Alaska

Juvenile walleye pollock aggregation structure in the Gulf of Alaska

S.C. Stienessen and C.D. Wilson

Juvenile walleye pollock aggregation structure in the Gulf of AlaskaThis is part of Resiliency of Gadid Stocks to Fishing and Climate Change
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Description

Size and shape patterns of juvenile walleye pollock (Theragra chalcogramma) aggregations in the Gulf of Alaska are described in relation to biophysical factors such as depth of the aggregation in the water column, water temperature, and age and body condition of the aggregation members. Aggregation characteristics were measured with acoustic data collected with a vertically oriented echosounder, and biophysical data were collected with a large midwater trawl and temperature-depth sensors from two areas near Kodiak Island, Alaska, during 1995-1997 and 2000-2002. Juvenile walleye pollock spatial patterns were expressed using fish aggregation length, height, fractal dimension, and density.
Redundancy analysis (RDA) was used to examine the associations of the biophysical factors with the size and shape descriptors of juvenile walleye pollock aggregations. Fish aggregation height increased as a function of fish age, and there was a negative association between depth of the aggregation in the water column and density of fish in the aggregation. There was also a negative association between body condition of the fish and the fractal dimension of the aggregation. These results demonstrate that relatively easily measurable environmental and biological factors can be useful in describing and potentially predicting spatial patterns of fish aggregations. Associations in the fish
aggregation structure and biophysical measurements were consistent with expectations based on predation and foraging theory.

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