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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AFSC Quarterly Research Reports April-June 2005
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