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Auke Bay Laboratory (ABL)

Groundfish Assessment Program

Survey Strategies for Assessment of Bering Sea Forage Species

Numerous ecologically important fish species are commonly found in nearshore environments in the Bering Sea, where they feed or spawn. Nearshore areas also provide crucial nursery habitat for the juvenile life stages of many fish species. The continental shelf region is used as a feeding area and migratory corridor for many of these same species. Lack of information on forage species composition, distribution, and movements limits our understanding of the ecological role of forage species in the Bering Sea, and hinders efforts to conserve forage species and to enhance the recovery of declining marine mammal populations such as Steller sea lions.

Researchers from the AFSC, the NOAA Environmental Technology Laboratory, and from several universities designed a study to test a suite of methods for estimating forage species abundance in the Bering Sea, from nearshore to continental slope habitats. Sample results will be used to identify strengths and constraints of single and integrated approaches in an effort to optimize habitat-specific surveys. This information is needed because many forage species are not targeted in standard AFSC research surveys.

In June 2005, two research cruises for forage species were conducted in the southeastern Bering Sea, with one group of scientists onboard the chartered fishing vessel Great Pacific targeting offshore waters of the continental slope and continental shelf, and a second group of scientists onboard the chartered fishing vessel Kema Sue targeting nearshore waters. A third group of scientists employed Light Detection and Ranging (LIDAR) and visual surveys from a chartered airplane.

The aerial surveys covered 23,125 km. Acoustic surveys by the offshore vessel covered 540 km. Twenty-four offshore stations were completed; these stations included 22 MultiNet (multi-opening zooplankton net) deployments, 18 conductivity-temperature-depth (CTD) casts, 2 ZOOVIS-SC (zooplankton camera) deployments, and 21 midwater trawl deployments. Not all sampling gears were deployed at all stations because of species targeting, replicate deployments, and equipment problems. Eighteen stations were completed by the nearshore vessel and included 70 beach seine deployments and 11 jigging locations. A remotely operated underwater vehicle (ROV), which was to be used in the nearshore environment, was not deployed because of weather and time constraints.

More than 35 species of fishes were captured by midwater trawl on the offshore cruise. The dominant forage species catch was northern smoothtongue (Leuroglossus schmidti). Common forage species were the myctophids northern lampfish (Stenobrachius leucopsarus) and California headlightfish (Diaphus theta), squid (Gonotopsis borealis), and Pacific herring (Clupea pallasi). The number of species captured varied widely with location. Shallower stations closer to land were dominated by walleye pollock (Theragra chalcogramma) and Pacific herring. Deeper offshore stations (>200 m at night in >400 m water depth) were dominated by L. schmidti and the myctophid species S. leucopsarus, S. nannochir, Lampanyctus jordani, and D. theta.

This midwater sampling broadened our understating of the North Pacific ichthyofauna. Several specimens that were captured added to a very limited number of records or were first records for the northeast Pacific Ocean, Alaskan waters, or the Bering Sea. Eight species caught were previously known from less than 12 specimens in Alaskan waters. Two of these are the first records for the Bering Sea and one is the first record for Alaskan waters.

On the nearshore cruise, more than 25 species of fishes were captured by beach seining. Catches varied widely from no fish to more than 15,000 fish per seine haul with the highest catches coming from sandy nonvegetated habitats. The dominant forage species captured was Pacific sand lance (Ammodytes hexapterus); approximately 35,000 sand lance were captured, and they occurred in 60% of the seine hauls. Other commonly captured forage fish were Pacific sandfish (Trichodon trichodon) and young-of-the-year gadids.

At 22 stations on the offshore cruise, a total of 99 zooplankton samples were collected for zooplankton identification. Based on macroscopic scans, calanoid copepods, mysids, euphausiids, chaetognaths, and hyperiid amphipods were the most abundant taxonomic groups in zooplankton samples. A total of 646 fish samples were collected by midwater trawl, and approximately 250 fish samples were collected by beach seine for proximate composition, fatty acid composition, diet and condition, and taxonomic verification.

The aerial surveys offshore found a surface layer from 2 to 5 m in depth that varied in thickness and, based on net sampling, consisted mainly of large copepods. Patchy, larger targets lay from 8 to 30 m in depth and probably extended below attenuation range (30 m). Aerial surveys also located "hot spots" mainly along the continental shelf break. The hot spots consisted of 3 to 40 humpback, fin, and sei whales, thousands of seabirds (mostly shearwaters), concentrated patchy targets characteristic of fish schools, and obvious foraging activity (e.g., bubble feeding by humpback whales, regurgitated euphausiids from shearwaters). These hot spots were observed on multiple days and appeared to move northeast along the shelf break at about 20 km per day. Fewer signal targets, seabirds, and marine mammals were located near shore; however, a few fish schools were visible and may have been sand lance and herring.

This information provides a clearer picture of the full diversity and distribution of fishes in the Bering Sea region. The North Pacific Research Board funded the study.

By Michael Sigler


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