(Quarterly Report for Jul-Aug-Sep 1999)
Identification and Characterization of Atka Mackerel Reproductive Habitat
In August 1999, RACE and REFM fishery scientists collaborated for a second consecutive year to find areas in the Aleutian Islands where Atka mackerel (Pleurogrammus monopterygius) spawn. No nesting sites were found the previous summer after searching 10 days in the eastern end of the Aleutian chain near Unalaska. This years efforts focused in the central Aleutian Islands region around Seguam Island and near the northeast corner of Amlia Island.
The basic biology of Atka mackerel is sparsely studied despite its commercial value and importance as a key forage species for the endangered Steller sea lion and other marine piscivores. A peculiar aspect of Atka mackerel life history is that the adults switch from a predominantly pelagic to mostly demersal existence during the spawning season. In the summer and early fall, adults migrate to shallower water where females deposit their eggs onto rocky substrate. Males fertilize the demersal egg clusters and remain behind to guard a territory containing batches of embryos, nests. Such nesting sites have been documented in Russian waters but have never been verified in U.S. waters until now.
The commercial fishing vessel Vesteraalen was chartered and used as the primary support vessel. A 6-m, rigid-hulled inflatable was deployed from the support vessel and used for exploring nearshore areas. Underwater video and SCUBA diving were the primary research tools to locate and study Atka mackerel nesting areas. The towed video camera we used did not have adequate resolution to detect the embryo clusters as it was dragged through the water. Direct observations by divers were necessary to verify the presence of nests. During 5 days of field work, scientists made a total of 18 dives, filmed more than 8 hours of underwater video footage, collected numerous biological specimens with hook-and-line (jigging) and spearfishing, and measured depth and temperature at nesting sites. The principal nesting site chosen for most of this work was on the northeast side of Seguam Island south of Finch Cove. The depth of the dive site was between 15 and 30 m, and the bottom consisted of rock outcrops interspersed with moderate-sized boulders less than 0.5 m in diameter. Fist-sized clumps of embryos were deposited in the interstices of boulders, and their color blended with the encrusting algae and other marine life. Nest sizes were difficult to discern because males were guarding nondiscrete batches of embryos spread over areas more than 1 m in diameter. Behaviors of aggregated adults and guardian males at nesting sites were observed in situ using an autonomous underwater video recorder. Strip transects were also used to estimate the density of nests. Stomachs of red Irish lord (Hemilepidotus jordani), yellow Irish lord (H. hemilepidotus), Pacific cod (Gadus macrocephalus), and male Atka mackerel that we captured in the nesting area all contained Atka mackerel embryo masses, indicating predation and cannibalism of Atka mackerel nests were common.
RACE and REFM scientists plan to continue exploring the temporal and spatial distribution of Atka mackerel nesting areas in the central and western Aleutian Islands and learn more about this peculiar fishs nesting habitat and behavior. Such information may ultimately be useful for developing an index of population abundance for this important commercial and forage species.
By Bob Lauth.
The Effect of Speed on Bottom Tending of a Research Trawl
In late September scientists from the Groundfish Assessment Program conducted a bottom trawling experiment off the Washington coast using the chartered commercial fishing trawler Sea Storm in late September. Trawling operations occurred in depths ranging between 55 and 183 m. The objective of the experiment was to determine the range of trawling speeds which produces optimal bottom tending performance for our standard Noreastern survey trawl and to learn how the trawls performance deteriorates at speeds outside this range.
Specific objectives included:
Monitoring and measuring the extent of footrope contact with the seafloor at varying vessel speeds ranging from 2.0 to 4.5 knots.
Determining the speed and direction of ocean bottom currents interacting with the trawl to estimate the speed of the trawl moving through the water.
Determining the speed at which footrope contact with the bottom becomes unstable.
Determining if there is a relationship between speed and footrope height off bottom.
Measuring the time required for the footrope to settle back to the bottom at varying speeds.
The standard RACE Noreastern
bottom trawl was towed at varying speeds. The codend was left open to avoid capture of any
fish. The trawl speed over the ground and through the water was measured using
differential GPS, a trawl-mounted current meter, and a moored current meter in the
vicinity of our trawling activities. The footrope contact of the trawl was observed at
fishing speeds between 2.0 and 4.5 knots. Bottom contact, including footrope height
off bottom during periods of no contact, was measured using a tilt meter mounted on the
footrope. A self-contained underwater video camera system was used to verify the
tilt meters performance.
Trawling operations first targeted an area of smooth sand bottom. Paired tows were made in opposing directions to enable us to measure effects due to prevailing current conditions. A second deeper site consisting of a level mud substrate was also explored.
By Ken Weinberg.
West Coast Sediment Map and Relationship to Groundfish Distribution
The Groundfish Assessment Program is participating in a collaborative, multi-agency effort involving NOAA, the U.S. Geological Survey (USGS), the Geological Survey of Canada, and the Ocean Sciences Institute (OSI), University of Sydney, Australia, to make a surficial sediment map of the U.S. west coast continental shelf and relate the distribution of fish and invertebrate species caught in RACE triennial bottom trawl surveys to bottom type.
The project uses a fuzzy logic database, developed by a senior research fellow at OSI, which can use both qualitative as well as quantitative data. The system enables the user to create numerical values for qualitative data points or retrieve specific data types based on queries. So far the scientists have collected and entered about 10,000 data points with good coverage for large portions of the triennial survey area. They will continue to add more data sets as they become available and attempt to fill holes in the sediment map. Mark Zimmermann of the Groundfish Program delivered portions of three seminars describing new interpretations of RACEBASE data to familiarize USGS with the fisheries data:
Possible importance of rocky untrawlable areas in biomass estimation of some species
Significance of unusually small catches in the early years of the survey
The need for a proper species assemblage analysis for relating fish to habitat type. If the group can demonstrate relationships between fish and some measure of sediment type, then they may be able to test the validity of stratum boundaries currently used in the triennial survey, which are based on latitude and depth, and suggest new boundaries based on other biologically significant factors.
By Mark Zimmermann.
MIDWATER ASSESSMENT AND CONSERVATION ENGINEERING
Pollock Survey of Eastern Bering Sea Shelf
Scientists in the Midwater Assessment and Conservation Engineering (MACE) Program conducted an acoustic-trawl survey of walleye pollock on the eastern Bering Sea shelf between 12 June and 29 July aboard the NOAA ship Miller Freeman. The survey design consisted of north-south transects spaced 20 nmi apart (except in the horseshoe area where the spacing was 10 nmi) and proceeded from east to west starting at long. 160°20W and ending at long. 178°55W. Acoustic data were collected continuously along transects between sunrise and sunset; night operations were devoted mainly to target strength experiments and net sampling for young-of-the-year pollock and zooplankton. Biological samples of echosign across the Bering Sea shelf comprised 98 midwater, 14 bottom, 4 Marinovich, and 48 Methot trawls. We obtained water temperature profiles at each haul location and other select locations, as well as continuous surface thermosalinograph data. Preliminary results show pollock acoustic backscatter (from 14 m below the surface to within 0.5 m of the bottom) absent or very low in the east, but then increasing around 165°W northwest of Unimak Island (Figure 1, .pdf file). Pollock backscatter was lower between 166°-167°W and then increased again, remaining relatively continuous from about 168°W westward to the U.S./Russia border. The highest pollock concentrations were between 173°W and 177°W. In contrast to geographic distributions from previous surveys (1994, 1996, and 1997), the 1999 pollock distribution was centered farther offshore. Vertical distribution of echosign was about 50% off bottom (10 m off to the surface) and 50% near bottom (10 m off to the bottom), except for the horseshoe area and the western-most transect, where greater than 60% and less than 10% was off bottom, respectively. West of the Pribilof Islands, pollock were rarely found in waters with bottom depths shallower than 100 m. Water temperatures were lower than in recent years. Pollock captured in midwater/bottom trawls ranged from 9-79 cm in length. Adult pollock ($30 cm in length) were found throughout the shelf; smaller fish (<30 cm) were encountered north of the Pribilof Islands and again west of 172°W and south of about 61°30N. Pollock smaller than 20 cm (age-1 pollock) were captured only occasionally. East of the Pribilofs, pollock modal lengths were 36, 47, and 25 cm; west of the Pribilofs modal lengths were smaller: 30, 45, and 22 cm, respectively. Preliminary analysis indicates that 8.4% of total pollock acoustic backscatter was located in the Steller sea lion Critical Habitat (CH) area, 17.5% was east of 170°W outside of the CH, and 74.1% was west of 170°W, which was similar to earlier years. Acoustic backscatter will be scaled with biological data from the trawl catches to provide estimates of abundance-at-length and age. Preliminary analyses indicate the biomass has increased from 1998 and the dominant year class is 1996.
By Steve deBlois.
Tests of Flexible Halibut Excluders for Sole Fisheries
From 21 to 30 August 1999, RACE scientists tested the effectiveness of devices to exclude halibut from the catches of commercial sole fisheries. The chartered fishing vessel Golden Fleece, a 110-ft factory trawler, towed a commercial bottom trawl with excluders installed in the intermediate section, just ahead of the trawls codend. Trawl sites in the Gulf of Alaska were selected for high abundance of rex, Dover, and flathead soles. The excluders were based on designs developed by groundfish harvesters, similar to one tested last year in an experimental fishery sponsored by the Groundfish Forum. These consisted of a sloped panel with large square holes, crossing the interior of the intermediate, leading to a flat, horizontal tunnel along the top of the net through which large halibut can escape. The smaller target species pass through the holes in the panel and the floor of the tunnel, leading them back to the codend.
The devices tested in August were flexible enough to be wrapped over a net reel, making them more usable aboard smaller trawlers (The device tested in 1998 used a rigid panel of welded aluminum.) Other changes from previous designs included 2 - 3 rods secured across the selection panels to keep them fully spread and an auxiliary panel that herded fish downward and then forced them against the selection panel along half of the sloped section and all of the tunnel. Three selection panels were compared, including mesh panels with 6 X 6-inch and 7 X 7-inch holes and a flexible grate, constructed of fiberglass rods and hose, with 7 X 7-inch holes. An auxiliary net and codend were used to recapture fish coming out of the escape tunnel for comparison with the catch in the main codend.
Preliminary analyses show that the excluders were quite effective at retaining target species while excluding halibut. The 6-inch mesh and the 7-inch flexible grate let more than 90% of the halibut that entered the trawl escape, while retaining approximately 80% of the target species. The 7-inch mesh excluded only about half of the halibut, but retained more than 95% of the soles. Further analyses will explore whether the excluders released the larger soles at a rate different from the rate for the smaller fish.
By Craig Rose.
Symposium Marks Polish Centers 25th Year
Members of the Fisheries Oceanography Coordinated Investigations (FOCI) program traveled to Gdynia and Szczecin, Poland, during 5-9 July to participate in a symposium marking the 25th anniversary of the Polish Plankton Sorting Center and to attend the annual meeting of the advisory committee for the Sorting Center. The Polish Plankton Sorting Center processes approximately 7,000 plankton samples per year that are collected by various NMFS Fisheries Science Centers. The staff in Poland are highly skilled and experienced in such a demanding activity and provide NMFS with an important function in a remarkably short turn-around time.
The symposium in Gdynia entitled International Symposium on Fisheries Ecosystem Research and Assessments consisted of 18 presentations, many of which highlighted the contributions of the Sorting Center to fisheries ecosystem studies. Ann Matarese presented a paper coauthored by her and Deborah Blood, Advances in the Knowledge of the Distribution and Abundance Patterns of the Early Life History Stages of Northeast Pacific and Bering Sea Fishes: Ichthyoplankton Research Conducted by the Alaska Fisheries Science Center (1971-1996), and a paper by Morgan Busby, herself, Blood, and Ma»gorzata Konieczna (of the Sorting Center), Advancements in Ichthyoplankton Taxonomy in the Northeastern Pacific Ocean and Bering Sea: Research Conducted by the Alaska Fisheries Science Center 1965-1999." Art Kendall presented Status of Recruitment Studies of Northeast Pacific Fishes and a paper by Jeff Napp and Debbie Siefert entitled Contributions by Zaklad Sortowania I Oznaczania Planktonu (Morski Instytut Rybacki) to Fisheries Oceanography in the Northeast Pacific Ocean and Bering Sea. During the symposium Ken Sherman of the Northeast Fisheries Science Center, Don Hoss, of the Southeast Fisheries Science Center, and Art Kendall (AFSC) received medals awarded by President of Poland Aleksander KwaŃniewski for their contributions to this cooperative effort between the United States and Poland.
At the advisory committee meeting, in Szczecin, operations and achievements of the Sorting Center for the previous year were reviewed, and plans for the coming year were developed. During the meeting, each staff member of the Sorting Center received certificates from both the Polish government and NMFS for their outstanding work.
FOCI scientists attended the ICES Symposium TransAtlantic Study of Calanus, from 24 to 27 August in Tromso, Norway. They presented one paper (Baier and Napp, Population dynamics of Calanus marshallae in the southeastern Bering Sea: the influence of climate) and one poster (Napp and Baier, Calanus marshallae (Frost) Gonad Maturation and Egg Production in the Southeastern Bering Sea).
Studies in Russia
Morgan Busby of Recruitment Processes traveled as an invited visiting scientist to St. Petersburg, Russia, during 10-23 July to conduct research at the Laboratory of Ichthyology of the Zoological Institute, Russian Academy of Sciences. During his visit he examined type and nontype specimens of snailfishes (family Liparidae) described from the Sea of Okhotsk and other localities of the Russian Far East. He also discussed taxonomic problems and zoogeography of snailfishes in the Bering Sea with ichthyologists of the Zoological Institute and snailfish expert Dr. David Stein from the United States who was also visiting the laboratory. In addition, Morgan verified identifications of specimens of Allocareproctus jordani and Liparis marmoratus collected in the Bering Sea. These snailfishes were previously known only from the Sea of Okhotsk and Kuril Island archipelago. He also provided a summary report of some preliminary results of his research to the Zoological Institute.
By Art Kendall.
A member of the Recruitment Processes Program participated in an ABL Ocean Carrying Capacity cruise to the southeastern Bering Sea from 12 to 26 July aboard the chartered vessel Great Pacific. The purpose of the cruise was to determine the abundance and distribution of young outmigrating Bristol Bay sockeye salmon. The Recruitment Processes Programs participation involved the collection of samples to determine the abundance and distribution of salmon prey and the distribution and abundance of age-0 pollock.
Members of the Recruitment Processes Program participated in a cruise to the Bering Sea, 20 July-1 August, aboard the Japanese research vessel Oshoro Maru to monitor the abundance of young-of-the-year walleye pollock. This was the fifth consecutive year that this survey has been made in cooperation with Hokkaido University.
Scientists also participated in a Southeast Bering Sea Carrying Capacity (SEBSCC) cruise during 2 - 19 September in the southeastern Bering Sea aboard the NOAA ship Miller Freeman. Sampling was conducted for three separate projects within the SEBSCC program. Principal Investigators included G. Swartzman from the University of Washington and K. Coyle from the University of Alaska Fairbanks. The objectives of the cruise were:
To continue studying the effect of hydrographic fronts on the marine ecology of the Pribilof Islands vicinity.
To continue the acquisition of long-term monitoring of biological and physical conditions in the southeast Bering Sea.
Scientists from a variety of
institutions participated in the cruise due to the multidisciplinary objectives. Further
details are available in the FOCI Cruise Report.
The hydrographic-front study, which began in 1994, emphasizes the trophic importance of young-of-the-year (age-0) walleye pollock in the marine ecology around the Pribilof Islands. As in previous years, CTD (conductivity-temperature-depth) casts were used to locate the front along two transects that radiate out from each of the two main islands, St. George and St. Paul. The front is a region of partially stratified (thermally) water that surrounds each island. Biological samples, including plankton, micronekton, and nekton samples were collected along each transect inshore of the front (well mixed), at the front, and offshore (stratified). As in previous years, almost all fish collected in midwater tows were age-0 pollock, and jellyfish (Chrysaora melanaster) were a major component of the plankton. Marine bird observations and multifrequency acoustic data were also collected along each transect.
The biophysical monitoring of the southeast Bering Sea involved CTD casts and collecting plankton, and microplankton along two transects. Transect location was chosen to monitor conditions across the shelf, along the 70-m isobath, and to coincide with mooring location. Additional sampling was conducted near each mooring to verify the accuracy of data collected by the moored instruments.
By Art Kendall.