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Resource Ecology and Ecosystem Modeling Program

Feeding Ecology Among Myoxocephalus Sculpins in the Eastern Bering Sea

Three of the largest species of Myoxocephalus sculpins are widely distributed across the continental shelf of the eastern Bering Sea: plain sculpin (M. jaok), great sculpin (M. polyacanthocephalus), and warty sculpin (M. verrucosus). Consistent distinction among all three of these species has occurred since about 2000, and diet descriptions for each individual species are sparse.

Stomach samples from all three species were collected during AFSC bottom trawl surveys during 2000 and 2006-2008. We divided each species into size categories and calculated the diet overlap among all species-size pairs using both the number and weight composition of the stomach contents (Table 1 below).

The highest diet overlap generally occurred between size categories within each species (in bold face in the table), especially for plain sculpin and great sculpin. The warty sculpin had a high degree of diet overlap with the great sculpin, especially in the 46-55 cm and 36-45 cm size-categories. The plain sculpin had low diet overlap with both warty and great sculpin.

The patterns in diet overlap are generally consistent with the geographic distributions of each species and the prey available to them. The plain sculpin is caught primarily on the inner shelf and has a diet of shrimp, mysids, and other small crustaceans that decrease in importance with increasing body size while flatfishes and other fishes increase in importance with increasing body size.

Table 1.  Diet overlap indices among size categories (FL in cm) of three species of Myoxocephalus sculpins (great, plain, and warty).  Indices above the diagonal were calculated using the numeric composition of the diet and indices below the diagonal were calculated using the gravimetric composition of the diet.  Bold indices highlight comparisons within a species.
   Species
   FL (cm)
Great
26-35
Great
36-45
Great
46-55
Great
56+
Plain
<26
Plain
26-35
Plain
36-45
Plain
46-55
Plain
56+
Warty
26-35
Warty
36-45
Warty
46-55
Great 26-35   63.91 55.05 49.43 25.77 26.34 35.79 41.56 6.89 47.78 60.05 48.95
Great 36-45 56.33   83.33 75.01 14.49 17.87 24.89 37.54 19.06 30.90 51.59 67.60
Great 46-55 49.51 77.64   83.23 10.57 11.60 17.86 30.52 15.45 23.84 48.42 71.92
Great 56+ 47.72 69.32 74.46   8.91 14.53 21.46 29.14 12.90 15.23 38.61 66.10
Plain <26 21.76 13.43 10.38 26.27   71.69 54.32 29.75 3.29 37.90 37.03 16.44
Plain 26-35 22.72 14.16 10.47 26.31 55.04   80.83 42.69 14.80 40.47 35.24 16.47
Plain 36-45 27.71 25.40 20.24 36.16 41.68 84.95   54.36 21.77 48.85 44.12 21.41
Plain 46-55 25.51 28.17 24.63 33.61 25.93 68.48 72.74   49.25 41.10 47.45 34.32
Plain 56+ 5.05 11.47 4.93 18.75 17.24 58.62 61.63 57.54   12.31 24.17 9.90
Warty 26-35 28.78 24.79 21.30 12.84 21.96 19.29 22.17 21.11 3.50   64.05 33.03
Warty 36-45 47.90 67.22 64.23 53.21 7.43 8.06 12.84 23.30 3.50 51.53   55.12
Warty 46-55 35.60 65.09 60.74 49.75 0.95 1.63 6.00 20.76 2.06 19.77 67.32  

The great sculpin is caught primarily on the middle shelf and consumes Chionoecetes crabs at all sizes examined, while eelpouts and smaller fishes decrease in importance with increasing body size and gadids, flatfishes, and scavenged offal increase in importance with increasing body size.

The warty sculpin also inhabits the middle shelf but is most abundant in northern areas frequently influenced by the "cold pool." The warty sculpin diet includes less fish than the other two species, with lyre crabs, other crabs, shrimp, and other small crustaceans decreasing in importance with increasing sculpin body size and Chionoecetes crabs increasing in importance with increasing body size.

figure 1, see caption
Figure 1.  The sizes (carapace width, mm) of C. opilio consumed by sizes (fork length, cm) of great sculpin (circles) and warty sculpin (triangles) in the eastern Bering Sea.  The regressions with 95% confidence intervals for each sculpin species are shown.

Most of the Chionoecetes crabs consumed by warty and great sculpins are snow crabs (C. opilio), and the size of the snow crab consumed generally increases with the size of the sculpin predator, with great sculpin preying on slightly larger snow crabs relative to their body size than the warty sculpin (Fig. 1).

By Todd TenBrink and Troy Buckley
 

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