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Resource Ecology & Fisheries Management  (cont.)

(2001 Stock Asessment Summary: part 8)
GOA Flatfish

Recommended ABC (t) for 2002
for GOA Flatfish Group
  Western Central WYAK EYAK/SEO Total
Deep-water 184 2,221 1,326 1,146 4,877
Rex sole 1,277 5,537 1,599 1,053 9,466
Shallow water 23,548 23,079 1,181 1,738 49,546
Flathead sole 8,997 11,409 1,591 687 22,684
Total 34,006 42,246 5,697 4,624 86,573

The flatfish group is subdivided into deep-water flatfish, rex sole, shallow-water flatfish, and flathead sole.  The 2002 exploitable biomass for each category is based on a delay difference model that includes estimates of growth, natural mortality, and recruitment, as well as biomass estimates from the 1996 and 2001 bottom trawl surveys.  ABC and OFL were calculated by species, with individual species identified as Tier 4, 5, or 6 depending upon the available data.  The 2001 GOA bottom trawl survey biomass was used as the current biomass for calculation of ABC.

The overfishing levels for the flatfish groups are determined by the fishing mortality rates determined from the tier structure and the exploitable biomass estimates of the individual species.  The catch levels associated with those fishing mortality rates are:

Species complex Yield (t)
Deep-water flatfish 6,426
shallow-water flatfish 61,807
Flathead sole 29,532
Rex sole 12,324
Total 110,089

GOA Arrowtooth Flounder

The 2002 estimated female spawning biomass of arrowtooth flounder was 1,098,130 t.  This estimate was based on abundance estimates derived from an age-structured model developed with AD Model Builder software.  Similar to the previous assessment, the model accommodated a higher proportion of females in the larger size intervals of both survey and fishery data by giving males a higher mortality rate than females.  Exploitable biomass in 2002 is estimated to be greater than B40%, and ABC was determined to be 146,264 t based on Tier 3a calculations (F40% = 0.134).  Using Tier 3a criteria, the overfishing level based on F35% = 0.159 is estimated at 171,057 t.

GOA Atka Mackerel

Prior to 1997, exploitable biomass and ABC for Atka mackerel were based on triennial bottom trawl survey estimates.  However, schooling behavior, patchy distribution, and habitat preference make this species difficult to sample with standard trawl survey gear.  Atka mackerel are also poor targets for hydroacoustic surveys because they lack swim bladders.  Re-evaluation of historical survey data indicated abundance estimates prior to 1997 were also compromised by high variability.  Thus, existing GOA bottom trawl survey data has limited utility for either absolute abundance estimates or indices for Atka mackerel.

The Plan Team continues to support a bycatch only fishery as a conservative harvest policy for Atka mackerel because:  1) there is no reliable biomass estimate; 2) localized depletion may occur; and 3) this species has previously exhibited a particular vulnerability to fishing pressure in the GOA.  The Team recommends an ABC of 600 t in 2002 to satisfy bycatch needs in other fisheries.

GOA Thornyheads

In 2001, the thornyhead assessment was updated with several new types of data including: 1999 - 2000 harvest levels by gear, biomass estimates from the 2001 GOA bottom trawl survey, and relative population numbers from the 2001 sablefish longline survey.  Alternate models examined assumptions regarding natural mortality and length at age.  The recommended ABC and spawning stock biomass levels were 2,494 t and 23,235 t, respectively.

By Anne Hollowed.

Bering Sea Walleye Pollock
BSAI Pacific Cod
BSAI Yellowfin Sole
BSAI Greenland Turbot
BSAI Arrowtooth Flounder
BSAI Rock Sole

BSAI Flathead Sole
BSAI Other Flatfish Complex
BSAI Pacific Ocean Perch
BSAI Other Red Rockfish
Other Rockfish
AI Atka Mackerel

GOA Pollock
GOA Pacific Cod
GOA Flatfish
GOA Arrowtooth Flounder
GOA Atka Mackerel
GOA Thornyheads

BSAI Squid and Other Species Complex

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