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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