Aleutian Islands Region
By Skip Zenger.
2002 Bering Sea Shelf Crab-Groundfish Bottom Trawl Survey
Temperatures were warmer than the long-term mean from 1982. Mean bottom temperature was 3.27EC, compared to the long-term value of 2.44EC. Surface temperature values were closer, with this years mean of 6.88EC and the long-term mean of 6.58EC.
A total of 393 stations were sampled, including 18 special stations from inner Bristol Bay, to continue our evaluation of yellowfin sole spawning populations during the sampling period. Abundance estimates for the major species showed few unexpected changes from 2001.
Walleye pollock, as expected from the indication of incoming recruits during 2001, was up slightly in 2002 to 4.8 million metric tons (t). Pacific cod was one of the few surprises, with a decrease from 830,000 t in 2001 down to 616,000 t this year. Cod had been decreasing steadily over a several year period until an upturn in 2001.
Among the flatfish species, yellowfin sole and flathead sole were slightly higher in abundance in 2002. Northern rock sole, Alaska plaice, arrowtooth flounder, and Greenland turbot were all down, but none significantly.
After the survey, two important experiments were completed. The first step in a year-long series of survey experiments between the AFSCs Kodiak Laboratory and the ADF&G was completed to examine life history characteristics of snow crab (Chionoecetes opilio). These collections were made near St. Matthew Island and near the Pribilof Islands and included the collection of live animals for transfer to the Kodiak Laboratory.
The second experiment took place in Bristol Bay and examined the escapement of red king crab (Paralithodes camschaticus) under the footrope of the 83-112 trawl used in the annual Bering Sea surveys. The study is extremely important in the development of abundance estimates. Results will be reported at a later time.
By Gary Walters.
2002 Eastern Bering Sea
Upper Continental Slope
Biennial Groundfish Survey
Out of 156 tows attempted, 141 tows were completed successfully and used for biological assessments. Approximately 147 fish species and 240 invertebrate species were identified over the course of the survey. The most abundant fish species sampled along the EBSUCS were giant grenadier (81,535 kg), Pacific ocean perch (12,964 kg) and popeye grenadier (9,208 kg), accounting for 66% of the total fish biomass caught. Crabs (Tanner, king, and lyre; 2,797 kg), sea stars (1,441 kg) and sponges (1,239 kg), accounted for 60% of the total invertebrate biomass caught. Results of the survey are being analyzed and will be provided to scientific teams assessing eastern Bering Sea stocks.
By Lyle Britt.
Defining Habitat of Juvenile Pacific Cod
The objective of our 1-year study was to identify juvenile Pacific cod habitat in Chiniak Bay, Alaska. A variety of nearshore habitats were sampled during 10-22 August 2002. Stations were sampled along depth transects such that each transect had one station at depths of < 5, 10, 15, 20, 25, and 30 m. At each of the 68 stations sampled, the relative abundance of juvenile cod and groundfish was measured along with habitat characteristics. Habitat complexity (sediment type, vertical relief, percentage of algae cover, associated invertebrates) was recorded at each station with an underwater video camera with real-time video. Vertical profiles of water temperature and salinity were measured at each station and a sediment sample was archived for grain size analysis, which will be used to verify the sediment type observed in the video.
A total of 6,077 fishes were captured, and juvenile Pacific cod ranked sixth in abundance among groundfish species. A total of 333 juvenile Pacific cod were captured, with lengths ranging from 40 to 113 mm. Our study verified the presence of juvenile Pacific cod in nearshore areas of Chiniak Bay. Once the distribution of juvenile Pacific cod is related to habitat complexity and physical properties (such as sediment grain size, depth, temperature, and salinity) then the habitat characteristics of their nursery areas can be defined.
By Alisa Abookire.
Effects of Seafloor Sediment Composition, Depth, and Food Availability
on Groundfish Distribution
Sampling in each area consisted of three distinct sampling phases: 1) the initial acoustic survey of the area, 2) sediment and benthic infaunal sampling, and 3) trawl sampling. Acoustic information from the ships echosounder was collected continuously during the entire cruise. The goal of the initial phase of acoustic sampling in each area was to identify areas of trawlable bottom with acoustically distinct sediment types. The results of this initial survey determined areas for further investigation. Sediment grabs were attempted at least four times along each identified tow path to allow ground-truthing of the acoustic sediment data and characterization of the macrofaunal assemblage at each site. The grab samples will undergo grain size analysis by standard sieve fractionation. The remainder of each sample will be sieved through a 0.5-mm mesh and the macrofauna (preserved in formalin) will be identified to the lowest taxon possible. A video transect of the bottom along the path of each sampled site was conducted as time allowed.
Gear, as well as biological and effort data collection methods used during the trawl sampling phase, were similar to those used on the Gulf of Alaska and Aleutian Islands biennial bottom trawl surveys. An aluminum plankton net frame was attached to the headrope of the trawl. The frame opening was 40 x 50 cm and the net mesh size was 505 micron. The goal of the zooplankton sampling was to characterize the distribution and abundance of zooplankton available to fish in the area sampled. Stomachs were also collected from a variety of commercially and ecologically important fish species to allow the description of the diets of the fish inhabiting the study area and allow comparison of their actual diets to the availability of potential prey items estimated from the grab and plankton sampling.
By Michael Martin.
Auke Bay Lab