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2002 Sablefish Longline Survey Completed

The AFSC has conducted an annual longline survey of sablefish (Anoplopoma fimbria) and other groundfish in Alaska from 1987 to 2002.  The survey is a joint effort involving the ABL and the AFSC Resource Assessment and Conservation Engineering (RACE) Division.  The survey replicates as closely as is practical the Japan-U.S. cooperative longline survey conducted from 1978 to 1994 and also samples gully stations not sampled during the cooperative longline survey.  In 2002, the twenty-fourth annual longline survey of the upper continental slope of the Gulf of Alaska and eastern Aleutian Islands was conducted.  One hundred forty-eight longline hauls (sets) were completed between 4 June 2002 and 3 September 2002 by the chartered fishing vessel Alaskan Leader.  Sixteen km of groundline were set each day, containing 7,200 hooks baited with squid.  When weather permitted a short experimental gillnet was fished during darkness at each station to assess the abundance of 0-age sablefish in near surface waters.

Sablefish was the most frequently caught species on the longline, followed by giant grenadiers (Albatrossia pectoralis), Pacific cod (Gadus macrocephalus), and shortspine thornyhead (Sebastolobus alascanus).  A total of 87,141 sablefish were caught during the survey.  A total of 4,423 sablefish, 588 shortspine thornyhead, and 26 Greenland turbot (Reinhardtius hippoglossoides) were tagged and released during the survey.  Electronic temperature-depth tags were surgically implanted in 135 sablefish.  Length-weight data and otoliths were collected from approximately 2,400 sablefish.  Killer whales (Orcinus orca) took fish from the longline at five stations in the Aleutian Islands region and western gulf as in previous years.  Sperm whales (Physeter macrocephalus) were common near the vessel in the eastern gulf and west Yakutat region and were observed taking fish from the line at several stations.

 In contrast to previous years, no age-0 juvenile sablefish were captured in gill-net sets. The significance of this to the abundance of the 2002 year class is unknown, but it may be indicative of poor survival for this year class.

Two special projects were conducted during the 2002 longline survey.  Coral caught on the longline were collected for identification and sample preservation.  Many specimens including rare and uncommon species were collected in the Aleutian Islands region.  In addition, the Alaska Department of Environmental Conservation (ADEC) is conducting a monitoring project for environmental contaminants in Alaskan fish.   Several species of groundfish commonly caught on the longline survey were collected throughout the Gulf of Alaska and sent to ADEC for contaminants analysis.

By Chris Lunsford.

Juvenile Sablefish Tagging Studies in St.  John Baptist Bay

Ten sonic tags were surgically implanted into juvenile, age-1+ sablefish captured in St. John Baptist Bay, in coastal southeastern Alaska, during 1-6 June 2002.  The tags were programmed to acoustically transmit a record of temperature and depth experienced by the tagged fish.  Mobile acoustic receivers located onboard the NOAA ship John N. Cobb were used to monitor the fish’s movements and habitat utilization in rearing locations in the bay.

Short-term objectives are to use the sonic tags to provide information on juvenile sablefish behavior and habitat use in nearshore rearing areas and timing and duration of the emigration from nearshore rearing habitat. Fixed acoustic receivers located along corridors leading from the rearing locations to the open ocean will be used to monitor the timing of juvenile emigration from their nearshore rearing habitat to the more open waters of the Gulf of Alaska.

Long-term objectives of the study are to utilize archival electronic tags in addition to sonic tags to provide information on juvenile sablefish movement and habitat use during their transition from nearshore rearing areas to offshore areas where they are intercepted by the fishery.  Archival tags will be used to record the temperature and depth experienced by juvenile sablefish from the time they leave the nearshore rearing areas at age 1+ or greater until the time they recruit to the fishery at age 2+ or greater.

By Tom Rutecki.

Sablefish Tag Program Summarized

The AFSC Processed Report 2002-01 "Report to Industry on the Alaska Sablefish Tag Program, 1972-2001" was completed in August 2002, and copies were sent to members of the fishing community who have participated in the tagging program over the years.

The report summarizes the history of the Sablefish Tag Program since its inception in 1972 and lists some of the ways tagging data have contributed to our current knowledge and understanding of sablefish life history.  For example, tagging data, consisting of release and recovery sizes and the length of time fish were at liberty, provide an independent estimate of growth rates.  They also provide a means to validate otolith ages which are difficult to obtain with complete accuracy past 6 or 7 years of age.  Tagging of juvenile sablefish, referred to as "known-age" fish, has provided information on the age at which fish first become available to the fishery.

Analysis of tag data has been and remains the primary method used to study sablefish movements.  Several tagging studies have shown sablefish to be highly migratory for at least part of their life cycle, with the pattern of movement related to fish size.  In general, small fish in the eastern areas of the Gulf of Alaska travel north and westward from their release sites, and large fish tagged in western areas move eastward.  Large fish tagged in the eastern areas have a tendency to remain there.  The stages of sablefish migration coincide with the stages of maturity:  small fish moving west are young and immature and large fish returning eastward are older and mature.  During the migration younger fish, which have come from shallow inshore waters, move farther out on the continental shelf where they mature. As adults they move to deeper waters of the continental slope, where spawning takes place. This migration pattern seems to hold true for all areas except the inside waters of the eastern Gulf of Alaska.  Fish from Chatham and Clarence Straits have a higher proportion of resident or nonmigrating fish than the other areas, and fish which do migrate are more likely to move south into Canadian waters.

Sablefish abundance in Alaska has varied two-fold since the early 1980s, with abundance changes related to the presence or absence of exceptionally strong year classes.  Persistance of the basic migration pattern through wide fluctuations in abundance indicates that the pattern is unaffected by density.

 Recruitment, movement rates, and movement by size and age are discussed in the report, and some predictions are made about the relative strength of recent year classes by area over the next few years.  The report summarizes related studies, such as tag-reporting rates, archival tags, and seamount tagging and addresses unknown factors behind variability in migration rates between years and between individuals.

By Nancy Maloney.


Aleutian Coral Explorations

In July 2002, ABL scientists used the manned submersible Delta and scuba equipment to explore coral habitat in the Aleutian Islands region near the Andreanof Islands and on Petrel Bank (Fig. 1).  Dive observations confirmed that coral was widely distributed in that region; corals and sponges were found at 30 of 31 submersible dive sites.  Disturbance to epifauna, likely from fishing activities was observed at most dive sites and appeared to be more evident in heavily fished areas.  Coral coverage on the substrate ranged from approximately 5% on low-relief pebble substrate to 100% coverage on high-relief bedrock outcrops.  Unique coral habitat consisting of high density gardens of corals, sponges, and other sessile invertebrates was found at five sites between 150 and 350 m depth.  These gardens were similar in structural complexity to tropical coral reefs and shared several important characteristics with tropical reefs, including complex vertical relief and high taxonomic diversity.

By Robert Stone.


Mapping of Habitat of Major Fishing Grounds

Little of the continental shelf and slope of the Alaska Exclusive Economic Zone (EEZ) has been adequately described using geophysical and biological data.   The objective of our study is to map limited areas of the Alaska EEZ for geologic characterization using state-of-the-art technology.  During July 2002 approximately 500 km2 of  seafloor in the vicinity of the commercial fishing grounds of Pamplona Spur near Yakutat were mapped using a high-resolution multibeam echosounder that included coregistered backscatter data.  Survey depths ranged from about 100 m to 750 m.   The area mapped is characterized as a formerly glaciated area of  irregular seabed with mixed sediments (mostly sand, mud, and gravel) and high-relief areas consisting mostly of boulders.  Combined with submersible observations and fishing effort data, the mapping will allow habitat and geological characterization of the areas in relation to fishing intensity.  This  mapping effort is complementary to similar mapping that was done last year in the vicinity of Cape Ommaney in Southeast Alaska and on Portlock Bank northeast of Kodiak.

By Jon Heifetz.

Southeast Alaska Steller Sea Lion Prey Study

Cruises five and six of the 2002 Southeast Alaska Steller sea lion (Eumetopias jubatus) prey study were conducted in Lynn Canal on 6-7 September and in Frederick Sound on 8-16 September aboard the chartered fishing vessel Viking Storm.  Well into the second year of the study, these cruises mark the second opportunity for interannual comparison.   The purpose of the study is to test the hypothesis that juvenile Steller sea lion prey diversity and seasonality are related to Steller sea lion population trends.  It is a comparison study to a research program concurrently conducted near Kodiak Island by the University of Alaska.

Data on abundance of biota, sea lion diet, and biochemical content of fish were collected. During the cruises, prey abundance and biomass were measured using echo-integration and midwater trawl.  Sea lion scat was collected during the Frederick Sound leg of the cruise at haulouts on Sail Island and Southwest Brothers Island  to infer sea lion diet.  Fish also were collected for proximate and fatty acid analysis.  Abundance data indicates that fish species caught in both Lynn Canal and Frederick Sound were very similar between the September 2001 and 2002 surveys, with the exception of little to no juvenile salmon caught during 2002.  In addition, initial observations indicate frequency of juvenile walleye pollock in the catches was greater than last year.  Also notable is the large and frequent catches of jellyfish that were characteristic of Frederick Sound in September for both years.  Abundances and vertical distribution of young- of-the-year walleye pollock, mature pollock and Pacific whiting appeared relatively similar in both areas between years, as did the small quantities of Pacific herring and eulachon in Frederick Sound that were restricted to bays.  In Lynn Canal, a large biomass of pelagic herring schools was observed along the Breadline, the nearshore area of Lynn Canal just north of Juneau.

Distribution of marine mammals appeared related to forage fish abundance. Steller sea lion abundances and distributions from aerial surveys conducted by Jamie Womble (University of Alaska Fairbanks) were very similar between years for the two study locations.  Several humpback whales were observed in Lynn Canal, and many were seen in Frederick Sound, including several mother-calf pairs.  The sea lions and the whales were most often feeding in areas coincident with juvenile and young-of-the-year walleye pollock catches.  In addition, nearly 100 harbor seals were seen hauled out on a rocky island south of Price Island in Gambier Bay near dense schools of juvenile pollock and herring schools.  Future 2002 cruises are scheduled for early December 2002.

By Johanna Vollenweider.

Southeast Alaska Coastal Monitoring

Surveys were continued for the sixth consecutive year in support of the Southeast Alaska Coastal Monitoring (SECM) project in 2002.  This project was initiated in 1997 to study the habitat use and early marine ecology of juvenile (age -.0) Pacific salmon.  The SECM research addresses components identified in the NMFS Strategic Plan and the NPAFC 2001-2005 Science Plan.  The goal of the SECM research is to build a time series of data to examine how biophysical parameters affect regional stocks of salmon with respect to habitat use, marine growth, and hatchery-wild stock interactions, and to understand these relationships in conjunction with environmental change, year-class strength of salmon, and coastal marine carrying capacity of salmon.

In the 2002 season, SECM research was conducted during 30 cruise days using the NOAA ship John N. Cobb over four time periods from May to August.  Thirteen core stations were repetitively sampled each time period, and a total of 5,262 juvenile salmon and 3,329 nonsalmonids were captured in 79 surface trawl hauls.  Associated oceanographic sampling at each station included vertical profiling of the water column to 200 m, surface water sampling for chlorophyll and nutrients, and zooplankton sampling with three types of nets.

In September 2002, annual summary data for SECM research conducted in 2001 were submitted to the NPAFC as Documents 630 and 631.  These summary data include information on process studies (diel feeding periodicity and prey fields of salmon, and gastric evacuation rates). The studies were  initiated to provide more accurate input parameters for bioenergetics models, which will in turn, be used to evaluate salmon habitat quality (growth potential) and coastal marine carrying capacity.

By Joe Orsi.


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