During the second quarter of 2011, Resource Ecology
and Ecosystem Modeling (REEM) Program staff began
focusing their efforts on analyzing stomach contents
from the Gulf of Alaska. The contents of 2,706 stomach
samples from 26 species were analyzed from the Gulf
of Alaska, and 925 stomach samples from 3 species
were analyzed from the Bering Sea. Detailed analysis,
with high taxonomic resolution of prey types and enumeration
of all prey items, was performed on walleye
pollock samples collected during a 2010 hydroacoustic
survey for a Bering Sea Integrated Ecosystem Research
Program (BSIERP) project. This quarter, 825 euphausiid
prey from these stomach samples have been measured
and will be used in a future comparison with
net-caught euphausiids. Tissue samples of muscle and
liver from arrowtooth flounder, Pacific cod, and walleye
pollock have been dried, ground, and tinned (160,
276, and 137, respectively) in preparation for stable
isotope analysis. Fishery observers returned stomach
samples from 133 arrowtooth flounder, 97 walleye pollock,
and 15 Pacific cod from Alaskan fishing grounds.
In total, 8,272 records were added to the REEM food
habits database.
Stomachs are being collected this spring and summer
during the AFSC’s hydroacoustic survey of the
Gulf of Alaska, the bottom trawl survey of the Gulf
of Alaska, and the groundfish and crab survey of the
eastern Bering Sea. Shipboard analysis of stomach contents
is also being conducted on board one of the Gulf
of Alaska bottom trawl survey vessels.
By Troy Buckley, Geoff Lang, Mei-Sun Yang,
and Richard Hibpshman
Summer Food Habits of Arctic Cod in the Eastern Bering Sea
The Arctic cod (Boreogadus saida) is an ecologically important inhabitant in Arctic
waters that extends its distribution southward into the eastern Bering Sea during
colder years. The Arctic cod, known to be a predator of a variety of zooplankton
and a prominent prey for many birds, marine mammals, and other fishes, is a nodal
species in the Arctic marine foodweb. Arctic cod are caught during the AFSC
groundfish and crab surveys in the eastern Bering Sea, especially during colder
summers. Stomach samples have been collected from them during previous surveys
on an ad hoc basis over the years but were targeted during the 2010 surveys,
yielding 320 samples.
Figure 1. Summer diet composition of 6- to 26-cm FL Arctic cod in the eastern Bering Sea.
Most of the Arctic cod stomach samples analyzed to date were sampled prior
to 2010. These 253 Arctic cod ranged in length from 6 to 26 cm fork length (FL),
with the large majority of the stomach samples obtained from fish between 10 and
18 cm FL. The diet of these Arctic cod consisted mostly of small crustaceans in
all the size categories examined, but some differences in diet with predator length
were seen (Fig. 1). Chaetognaths tended to decrease in importance with increasing
size of Arctic cod. Fishes (Teleostei) and slightly larger crustaceans (Decapoda;
shrimp and crabs) were consumed primarily by Arctic cod over 15 cm. A consistent,
more general trend with increasing size was the gradual decrease in pelagic prey
(chaetognaths, copepods, euphausiids, and hyperiid amphipods) and the gradual
increase in more benthically oriented prey (gammarid amphipods, mysids,
cumaceans, and decapod crustaceans). When analyzed, the stomach samples collected
in 2010 may provide some geographically interesting results, as the majority
of them were collected in the northern Bering Sea between Saint Matthew Island
and the Bering Strait.
By Troy Buckley, Caroline Robinson, and Kimberly Sawyer.
