(2001 Stock Asessment Summary: part 5) BSAI Flathead Sole
The 2001 assessment was implemented using AD
Model Builder as a modeling platform and
incorporated new catch and survey information. The
2001 EBS bottom trawl survey biomass estimate was
514,023 t, a 29% increase relative to last year’s
estimate. The 2000 Aleutian Island trawl
survey biomass estimate was 8,970 t.
Reliable estimates of B_{40%},
F_{40%}, and F_{35%}
exist for this stock and, therefore, it 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 141,903 t, 0.30, and
0.38, respectively. Given that the projected 2002
spawning biomass of 262,402 t exceeds B_{40%},
the ABC and OFL recommendations for 2002 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 2002 ABC of 82,572 t.
The OFL was determined from the Tier 3a formula,
where an F_{35%}
value of 0.38 gives a 2002 OFL of 100,770 t.
Model projections indicate that this stock is
neither overfished nor approaching an overfished
condition.
BSAI Other Flatfish Complex
The 2001 assessment was implemented using AD
Model Builder as a modeling platform for Alaska
plaice only. The 2001 assessment incorporated
new catch and survey information. The 2001
biomass estimates from the EBS bottom trawl survey
were 538,319 t for Alaska plaice and 78,293 t for
the remaining species in the “other flatfish”
complex. The biomass estimate for Alaska
plaice was 23% higher than the 2000 estimate.
In 2001, excluding Alaska plaice, the species
composition of the other flatfish are Dover sole
(<1%), rex sole (28%), longhead dab (16%),
Sakhalin sole (<1%), starry flounder (55%), and
butter sole (1%). Relative to 2000, Alaska
plaice and other flatfish increased.
Projections of Alaska plaice abundance show
that the population will gradually decline due to
low recruitment.
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 132,856 t
(Alaska plaice only), 0.279, and 0.344,
respectively. Given that the projected 2002
spawning biomass (Alaska plaice only) of 264,838 t
exceeds B_{40%},
the Plan Team’s ABC and OFL recommendations for
2002 were calculated under subtier “a” of Tier
3. Because 87% of the “other flatfish”
category is Alaska plaice and the assessment author
calculates plaice separately, the author recommended
setting the ABC and OFL for Alaska plaice separately
from the other species. 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 2002 ABC of 142,764 t for Alaska
plaice. For the remaining species in the
flatfish complex, the author recommended F_{ABC}
at the F_{40%}
level (=0.30), which is the maximum allowable under
Tier 3a. Projected harvesting at the F_{40%}
level gives a 2002 ABC of 18,065 t for “other”
nonplaice flatfish.
As with the ABC, the Plan Team recommended
separating Alaska plaice from “other” flatfish
for OFL. The Plan Team’s OFL was determined from
the Tier 3a formula, where for Alaska plaice an F_{35%}
value (=0.35) gives a 2002 OFL of 171,736 t.
For the “other flatfish” species, the
author recommended an F_{35%}
value (=0.38) giving a 2002 OFL of 21,832 t.
Model projections indicate that this stock
complex is neither overfished nor approaching an
overfished condition.
BSAI Pacific Ocean Perch
A review of the available data for BSAI Pacific
ocean perch (POP) and a series of potential
population models were presented to the Plan Team
and discussed at the September 2001 meeting.
The Plan Team recommended that a single BSAI
model was appropriate for assessment of POP.
Motivations for this change include the paucity of
data in the EBS upon which to base an agestructured
assessment, and uncertainty that the EBS POP
represent a discrete stock. In the
combined model, the fishery harvest level and
fishery age and length compositions are computed for
the entire BSAI area, and the Aleutian Islands
survey is used as an index of abundance. The
historical EBS slope surveys are not utilized.
Reliable estimates of B_{40%},
F_{40%}, and F_{35%}
exist for this stock and, therefore, this stock
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 140,660 t, 0.048,
and 0.057, respectively. Projected spawning
biomass for 2002 is 134,694 t, placing POP in the
EBS in subtier “b” of Tier 3. The maximum
F_{ABC} value
allowed under Tier 3b is 0.046. Projected
harvesting at a fishing mortality rate of 0.046
gives a 2002 catch of 14,776 t, which is the
recommended ABC. The OFL fishing mortality
rate is 0.055 under subtier 3b. Projected
harvesting at a fishing mortality rate of 0.055
gives a 2002 catch of 17,510 t, which is the
recommended OFL. Model projections indicate
that this stock is neither overfished nor
approaching an overfished condition.
Cont. >>>


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