BSAI Yellowfin Sole
The 2002 assessment incorporated new catch and survey information. This
year's EBS bottom trawl survey resulted in a biomass estimate of 2,003,400
t, an increase of 8% from last year's survey. As in previous years, the
catchability of yellowfin sole is modeled as a linear function of water
temperature.
Reliable estimates of B_{40%},
F_{40%}, and
F_{35%} exist for this stock and,
therefore, qualify for management under Tier 3 of the BSAI Groundfish FMP. The updated
point estimates of B_{40%},
F_{40%}, and
F_{35%} from the present
assessment are 385,000 t, 0.115, and 0.138, respectively. Given that the projected 2003
spawning biomass of 452,800 t exceeds B_{40%},
the ABC and OFL recommendations for 2003 were calculated under subtier "a" of Tier 3. The author recommended
setting F_{ABC} at the
F_{40%} (=0.115) level,
which is the maximum permissible level under Tier 3a. Projected harvesting at the
F_{40%} level gives a 2003
ABC of 113,600 t. The OFL was determined from the Tier 3a formula, where an
F_{35%}
value of 0.138 gives a 2003 OFL of 134,800 t. Model projections
indicate that this stock is neither overfished nor approaching an overfished
condition. Stock projections show the yellowfin sole stock will continue
to decline despite low exploitation rates. The decline is due to the low
recruitment in the last decade.
BSAI Greenland Turbot
The current assessment updated last year's assessment, incorporating new
catch and survey information. The 2002 survey biomass estimates for the
EBS shelf and slope were 21,616 t and 27,589 t, respectively. The 2002
survey biomass estimate for the Aleutian Islands was 9,891 t.
In 2002, research on an alternative assessment model was presented. Part
of this research involved incorporation of additional data published in
Russian reports. The SSC has determined that reliable estimates of
B_{40%},
F_{40%}, and
F_{35%}
exist for this stock and that this stock, therefore, qualified
for management under Tier 3 of the BSAI Groundfish FMP. The updated point estimates of
B_{40%},
F_{40%} and
F_{35%}
from the present assessment are approximately
54,000 t, 0.26, and 0.32, respectively. Projected spawning biomass for
2003 was 67,800 t, placing Greenland turbot in subtier "a" of Tier 3.
The estimates of current spawning biomass and
B_{40%} were lower than previous
years because the new Eastern Bering Sea slope survey biomass estimates
were included in the assessment. The maximum permissible value of
F_{ABC} under Tier 3a is 0.26.
Assessment authors recommended that the 2003
F_{ABC}
should be based on the 5year average fishing mortality, resulting in a
2003 ABC of 5,880 t. This value was recommended because of uncertainty
in the survey biomass estimates. The recommended OFL for this stock was
17,800 t.
Model projections indicate that this stock is neither overfished nor approaching
an overfished condition.
BSAI Arrowtooth Flounder
The present assessment updated last year's assessment, with incorporation
of new catch and survey information. The 2002 EBS bottom trawl survey
resulted in a biomass estimate of 355,100 t, a 13% decrease relative to
the 2001 trawl survey. In 2002, RACE conducted an assessment of the EBS
slope. The biomass estimate for arrowtooth flounder derived from this
new survey was 61,200 t. The 2002 biomass estimate for the Aleutian Islands
stock was 88,700 t. However, this biomass estimate was not included in
the model.
The new slope survey biomass estimates were incorporated into the model
by configuring q for the shelf and slope to be equal to 0.87 and 0.13,
respectively. These values reflect the proportion of the EBS stock observed
in the shelf and slope regions.
Model runs were made with sexspecific natural mortality rates. The preferred
model fixed male natural mortality rate at 0.281 and the female natural
mortality rate at 0.2. This model configuration was consistent with the
author's hypothesis that differences in sex ratios in observed catches
is due to differential sexspecific survival rates.
Reliable estimates of B_{40%},
F_{40%}, and
F_{35%} exist for this stock and, therefore,
it qualifies for management under Tier 3 of the BSAI Groundfish FMP. The
updated point estimates of B_{40%},
F_{40%}, and
F_{35%} from the present assessment
are 206,300 t, 0.30 and 0.38, respectively. Given that the projected 2003
female spawning biomass of 436,400 t exceeds B_{40%},
the ABC and OFL recommendations for 2003 were calculated under subtier "a" of Tier 3. The author recommended setting
F_{ABC} at the
F_{40%} (=0.30) level,
which is the maximum permissible level under Tier 3a. Projected harvesting at the
F_{40%}
level gives a 2003 ABC of 112,300 t.
The OFL fishing mortality rate is computed under Tier 3a,
F_{OFL} =
F_{35%} =
0.38, and translates into a 2003 OFL of 139,000 t. Model projections indicate
that this stock is neither overfished nor approaching an overfished condition.
BSAI Rock Sole
The 2002 assessment incorporated new catch and survey information. This
year's EBS bottom trawl survey resulted in a biomass estimate of 1,901,800
t, a 21% decrease relative to the 2001 estimate. An AI trawl survey was
performed in 2002 and resulted in a biomass estimate of 57,700 t, which
represents only 3% of the BSAI rock sole combined biomass estimate from
the trawl surveys.
Survey catchability was incorporated into the 2002 stock assessment to
account for herding and temperature effects on rock sole capture. This
results in a marked reduction in the present and historical biomass estimates
of BSAI rock sole.
Reliable estimates of B_{40%},
F_{40%}, and
F_{35%} exist for this stock, which
therefore qualifies rock sole for management under Tier 3 of the BSAI Groundfish
FMP. The updated point estimates of B_{40%},
F_{40%}, and
F_{35%} from the present
assessment are 158,600 t, 0.176, and 0.213, respectively. Given that the
projected 2003 spawning biomass of 303,100 t exceeds
B_{40%},
the ABC and OFL recommendations for 2003 were calculated under subtier "a" of Tier 3.
The author recommended setting F_{ABC} at the
F_{40%} (=0.176) level, which
is the maximum permissible level under Tier 3a. Projected harvesting at the
F_{40%}
level gives a 2003 ABC of 110,200 t. The OFL was determined from the Tier 3a formula, where an
F_{35%}
value of 0.213 gives a 2003 OFL of 131,700 t. Model projections indicate that this stock
is neither overfished nor approaching an overfished condition. Stock projections for the
rock sole stock continue to show declines, as do several other flatfish stocks, due
to the low recruitment in the last decade.
BSAI Flathead Sole
The 2002 assessment incorporated new catch and survey information. The
2002 EBS bottom trawl survey biomass estimate was 574,946 t, a 12% increase
relative to last year's estimate. The 2002 AI trawl survey biomass estimate
was 9,894 t.
The 2002 assessment was implemented using AD Model Builder as a modeling
platform. The model was configured as a splitsex population. Age compositions
were developed for each sex to account for differential growth across sexes.
Reliable estimates of B_{40%},
F_{40%}, and
F_{35%} exist for this stock, and therefore,
is qualified for management under Tier 3 of the BSAI Groundfish FMP. The updated point estimates of
B_{40%},
F_{40%}, and
F_{35%}
from the present assessment are 124,289 t, 0.286, and 0.355, respectively.
Given that the projected 2003 spawning biomass of 224,526 t exceeds
B_{40%},
the ABC and OFL recommendations for 2003 were calculated under subtier "a" of Tier 3.
The author recommended setting F_{ABC} at the
F_{40%}
(=0.286) level, which is the maximum permissible level under Tier 3a. Projected harvesting at the
F_{40%} level gives a 2003
ABC of 66,410 t. However, it is unlikely that the total ABC will be taken
in 2003 because the total catch of flathead sole has been well below the
ABC for several years.
The OFL was determined from the Tier 3a formula, where an
F_{35%} value of
0.355 gives a 2003 OFL of 80,563 t. Model projections indicate that this
stock is neither overfished nor approaching an overfished condition.
BSAI Alaska Plaice
The 2002 assessment for Alaska plaice incorporated new catch and survey
information. The 2002 biomass estimate from the EBS bottom trawl survey
was 424,971 t for Alaska plaice, a 27% decrease from the 2001 survey biomass
estimate.
Reliable estimates of B_{40%},
F_{40%}, and
F_{35%} exist for this stock complex
and, therefore, it qualifies for management under Tier 3 of the BSAI Groundfish FMP.
The updated point estimates of B_{40%},
F_{40%}, and
F_{35%}
from the present assessment are 130,888 t, 0.279, and 0.344, respectively.
Given that the projected 2003 spawning biomass of Alaska plaice (255,676 t) exceeds
B_{40%},
the Plan Team's ABC and OFL recommendations for 2003 were calculated under subtier "a" of Tier 3.
For Alaska plaice, the author recommended F_{ABC} at the
F_{40%} level (=0.279),
which is the maximum allowable under Tier 3a. Projected harvesting at the
F_{40%} level gives a 2003 ABC of 137,015 t for
Alaska plaice. It is unlikely that the total ABC will be taken in 2003
because the total catch of Alaska plaice has been well below the ABC for
several years. Stock projections of Alaska plaice show that the population
will gradually decline due to low recruitment.
The OFL for Alaska plaice was determined from the Tier 3a formula, where, for
F_{35%} value (=0.344)
gives a 2003 OFL of 164,822 t. Model projections indicate that Alaska plaice is
neither overfished nor approaching an overfished condition.
>>>continued


quarterly OctDec 2002 sidebar
AFSC Quarterly
Research Reports
Oct.Dec. 2002
Contents
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