Preliminary Results of the 2009 EBS Flatfish Essential Fish Habitat Study
Figure 1. Stegocephalidae amphipod from the eastern Bering Sea. Photo by Caroline Robinson.
A total of 1,147 Alaska plaice (Pleuronectes quadrituberculatus), northern rock sole (Lepidopsetta polyxystra), flathead sole (Hippoglossoides elassodon), yellowfin sole (Pleuronectes asper), and longhead dab (Pleuronectes proboscideus) stomachs were collected from 27 stations in the eastern Bering Sea.
These stomachs were analyzed as part of an EFH project (in collaboration with Cynthia Yeung, RACE Division) that focuses on correlating the diets of some small-mouth flatfish with their specific habitats in the eastern Bering Sea.
Grab samples were collected at each of the 27 stations. The habitat types for the stations were categorized as sandy (% sand > 80), muddy sand (50 < % sand < 80), sandy mud (50 < % mud < 80), and muddy (% mud > 80).
The diets of these small-mouth flatfish included polychaetes, clams, amphipods (Fig. 1), and brittle stars. Diets varied among predator species, among size-groups of the same predator, and among habitat types. An interesting finding was that the diet shifted from habitat to habitat, even for the same predator species. The results indicate that it is important to combine habitat information with food habits information for better understanding of the predator-prey relationships in the marine ecosystem.
By Mei-Sun Yang
Trophic Level Patterns Indicated by Stomach Contents and Stable Istotope Analyses
Dr. Kerim Aydin attended the annual meeting of the North Pacific Marine Science Organization (PICES) held in Portland, Oregon, from 22 to 31 October. He presented a paper entitled "An analysis of 30 years of seasonal and geographic variability in marine food webs through fish food habits and stable isotope analyses."
The paper summarized the final results of a North Pacific Research Board funded project. Of particular interest was an indication that trophic levels as calculated from stomach contents showed higher trophic levels for walleye pollock on the outer shelf of the eastern Bering Sea than the inner shelf, while analysis of stable isotope ratios of nitrogen showed higher trophic levels on the inner shelf, particularly in Bristol Bay.
This difference highlights that stomach contents analysis primarily measures trophic level as a function of zooplanktivory/piscivory within fish, while stable isotope results may be dominated by lower-trophic level (within zooplankton) processes such as uptake water mass and microzooplankton food-chain length.
