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Use of Elemental Analysis in Stock Discrimination of Bristol Bay Sockeye Salmon
Recent precipitous declines in the returns of sockeye salmon (Oncorhynchus
nerka) to Bristol Bay, Alaska, has prompted state and Federal agencies
to declare the region an economic disaster area. Hypotheses related to
the rapid decline of the returns include interception of Bristol Bay sockeye
salmon by illegal high-seas gillnet fishing and changes in the marine ecosystem
that could impact their survival. Specific mechanisms are unknown because
of a lack of stock-specific information on early marine residence and ecology
of immature and maturing sockeye during their rearing in the waters of
the Bering Sea and the North Pacific Ocean. One problem is the difficulty
researchers have in identifying specific stocks or continent of origin
of salmon in mixed-stock catches in various fisheries of Pacific Rim countries.
Several methods have been used to identify Bristol Bay sockeye salmon
stocks from other Pacific stocks including genetics, scale characteristics,
and parasites, all having differing success rates. However, resolution
of stock identification to specific river systems within Bristol Bay is
needed.
The Marine Salmon Interactions and Ocean Carrying Capacity Programs at
ABL in conjunction with the UAF, the U.S Geological Survey, and ADF&G
have initiated a pilot study using the elemental analysis of otoliths as
a tool for separating sockeye salmon smolts from the Kvichak, Egegik, and
Ugashik Rivers in eastern Bristol Bay. We used a chemical microprobe operated
and maintained by the advanced instrumentation laboratory of the UAF to
determine the concentrations of nine common elements found in the freshwater
zone of the sagital otoliths of sockeye salmon smolts. Linear discriminate
analysis provided information on how well the elemental data could be used
to separate the fish by river system. Overall, the proportion of fish
correctly identified by river system was about 72%. Ideally the presence
of a stable marker element unique to a particular system year after year
would increase the accuracy of our ability to separate stocks. In addition,
a baseline elemental analysis should be done on all stocks in the area
each year to preclude uncharacterized stocks from being categorized in
a known group. We believe with fine tuning, the use of probe-based technology
for the discrimination of mixed salmon stocks would be useful to managers
and researchers. Combined with genetic and other analyses, the tools to
accurately identify specific stocks of salmon from mixed stock catches
are becoming available.
By Don Mortensen and Ed Farley.
2002 Sablefish Longline Survey
The AFSC has conducted an annual longline survey of sablefish and other
groundfish in the Gulf of Alaska since 1987. The survey is a joint effort
involving ABL and the Resource Assessment and Conservation Engineering
(RACE) Division. Beginning in 1996, biennial sampling of the Aleutian
Islands region and eastern Bering Sea was added.
The 2002 survey began on 1 June and ends on 5 September. The survey
vessel is the chartered fishing vessel Alaskan Leader. As of 15 July,
the survey had sampled the Aleutian Islands region, the western Gulf of
Alaska, and three seamounts. Killer whales (Orcinus orca) took fish from
the longline at three stations in the western Gulf resulting in lower overall
catches in this area. Catches in the Aleutian Islands region were similar
to catches in 2000, the last time the area was sampled.
Two special projects are being conducted during the 2002 longline survey.
Coral caught on longline is being collected for identification and 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 are being collected throughout the Gulf of
Alaska and will be analyzed for contaminants by ADEC.
By Chris Lunsford.
Sablefish Sampling on Gulf of Alaska Seamounts in 2002
A study to determine the extent, if any, of seamount-to-slope and seamount-to-
seamount sablefish migration has been conducted annually since 1999. As
in previous years, three seamounts were sampled in 2002 during Leg 2 of
the annual sablefish longline survey. Sampling was conducted aboard the
chartered survey vessel Alaskan Leader as it transited the Gulf of Alaska
from Sand Point to Ketchikan. This year, Patton and Murray Seamounts in
the Patton Seamount group and Durgin Seamount in the Gulf of Alaska Seamount
group were sampled for the first time.
About 600 sablefish were tagged and released on the three seamounts, bringing
the total number of tagged fish released on seamounts since 1999 to just
under 3,300. Eleven sablefish tagged on seamounts have been recovered
in the commercial fishery on the slope since the study began, proving that
seamount-to-slope migration does occur.
As with all the seamounts sampled to date, males outnumbered females by
a wide margin, and most of the fish were in spawning or recently spent
condition.
By Nancy Maloney.
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Quarterly April-June 2002 sidebar
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April - June 2002
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