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Resource Ecology & Ecosystem Modeling Program

Fish Stomach Collection and Lab Analysis

Laboratory analysis was performed on 3,032 groundfish stomachs from the eastern Bering Sea and 684 stomachs from the Aleutian Islands region and Gulf of Alaska. During this quarter, 158 stomachs were returned by fishery observers. In total, 16,720 records were added to the groundfish food habits database.

By Troy Buckley, Geoff Lang, and Mei-Sun Yang

Predator/Prey Interactions

The Resource Ecology and Ecosystem Modeling (REEM) Program estimated total biomass of snow crabs consumed by groundfish predators in the Bering Sea between 1997 and 2001 (Lang et al. 2005; analysis has allowed us to update long-term estimates of crab consumption in the region (Fig. 1 below). The main predator of snow crabs was Pacific cod, consuming at least 75% of the total biomass removals of snow crabs by predators between 1997 and 2001.

Figure 1, see caption
Figure 1.  Estimated number at-age of snow crabs (C. opilio) consumed by groundfish during May-September from 1984 to 2001 in the eastern Bering Sea.

The remaining predators were flathead sole, walleye pollock, Pacific halibut, northern rock sole, skates, Alaska plaice, and yellowfin sole. Biomass of snow crabs consumed by Pacific cod was highest in 2001 (160,353 metric tons (t)) and lowest in 1999 (62,848 t). Most of the snow crab consumed in 1997 through 2000 were less than 25-mm carapace width or approximately age 0 to age 1.

Similar to the 1993-96 period, consumption of snow crab by groundfish predators other than Pacific cod did not occur every year, particularly in 1998 and 2001, and was least prevalent in small-mouthed flatfish. This could indicate the availability of fewer small snow crab in the 1993-2001 period compared to the 1990-92 period where consumption was more widespread across all predators. Declines in predation consistent with population declines indicate that monitoring the amount of predation on small crabs by these predators may provide early indications of the presence of abundant year classes of crabs.

By Katie Dodd, Geoff Lang, and Kerim Aydin


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