(2001 Stock Asessment Summary: part 7)
BSAI Squid and Other Species Complex
The squid assessment updated last year’s
assessment by incorporating new catch information.
The squid stock is managed under Tier 6, OFL
is set equal to the average catch from 1978 through
1995, and ABC is constrained to be no greater than
75% of OFL. The average catch from 1978
through 1995 was 2,624 t. The maximum
permissible value of ABC for 2001 therefore is 1,970
t, which is the Plan Team’s recommended value.
The “other species” assessment is an
update of last year’s assessment, incorporating
new catch and survey biomass information. For
the 2002 fishing year, the author’s recommended
ABC for the other species complex was calculated as
0.75 times the average catch 1978-95, or 19,320 t.
The author recommended OFL for the other
species complex in the year 2002 be calculated as
the average catch from 1978 to 1995, or 25,760
t. The NPFMC SSC recommended that this
strategy be reviewed.
A Generalized Linear Model (GLM) analysis of
historical trawl survey data (1961-82) produced
indices of pollock abundance prior to the start of
the NMFS triennial survey in 1984.
Incorporation of these indices and the
information from a comparative trawling experiment
between an ADF&G 400-mesh eastern trawl and a
NMFS Poly-Nor’eastern trawl made it possible to
extend the time series of pollock biomass and
recruitment back to 1961. Model results
suggest that population biomass in 1961, prior to
large-scale commercial exploitation of the stock,
may have been the lowest observed. Major
increases in pollock abundance occurred prior to the
1977 regime shift, suggesting forcing by some other
aspect of the environment or ecosystem.
The occurrence of large fluctuations in
pollock abundance without large changes in direct
fishing impacts suggests a need for conservative
management. If pollock abundance is controlled
primarily by the environment, or through indirect
ecosystem effects, it may be difficult to reverse
population declines, or to achieve rebuilding
targets should the stock become depleted.
Estimated spawning biomass in 2002 is 158,300 t, a
decrease of 22% from last year’s estimate for
2001, and a decrease of 8% from last year’s
projection for 2002. Lower model estimates of
biomass in 2002 are primarily due to lower than
expected biomass from the 2001 NMFS trawl survey
(65% decrease from the 1999 survey) and low
abundance of spawning adults in the 2001 Shelikof
Strait EIT survey (49% decrease from the 2000
survey). Spawning biomass in 2002 is estimated
to be 26% of unfished. Under the new
Reasonable and Prudent Alternatives (RPA) control
rule approved by the Council, pollock fishing in the
Gulf of Alaska would have to be stopped if biomass
declines to 20% of unfished biomass. Spawning
biomass is projected to be below the B40%
value of 245,000 t. This places Gulf pollock
in Tier 3b. The ABC for 2002 was 53,490 t for the
Western, Central, and West Yakutat areas.
For pollock in Southeast Alaska (East Yakutat and
Southeastern areas), the ABC recommendation is
unchanged at 6,460 t. Pollock in the Southeast
Outside and East Yakutat areas fall into Tier 5.
Under the Tier 5 approach, 2002 ABC is 6,460
t, based on exploitable biomass of 28,710 t as
derived from CPUE data during the 1999 Gulf trawl
survey and a natural mortality estimate of 0.30.
The OFL is 8,610 t. The pollock catch in
the pooled Southeast Outside and East Yakutat areas
never exceeded 100 t during 1991-2000.
GOA Pacific Cod
The 2001 Pacific cod assessment incorporated
several new types of data including: size
composition from 2000 and January-August 2001
commercial fisheries, size composition from the 2001
GOA bottom trawl survey, and biomass estimates from
the 2001 GOA bottom trawl survey. The 2001 GOA
bottom trawl survey biomass estimate was 256,025 t
for the Western and Central areas which was down 10%
from the 1999 estimate for the same areas.
The Bayesian meta-analysis which formed the
basis for risk-adverse ABC recommendations in the
1996-99 assessments was not performed for the 2001
assessment. Similar to procedures used in
2000, the ratio between the recommended FABC
estimate given in the 1999 assessment (0.87) was
assumed to be an appropriate factor by which to
multiply the 2001 maximum permissible FABC
to obtain a recommended 2001 FABC.
The estimated 2002 spawning biomass for the GOA
stock was 82,000 t, down 13% from last year’s
estimate for 2001. The recommended 2002 ABC
for the GOA stock was 57,600 t, down 15% from last
year’s recommendation for 2001. The OFL for
the GOA Pacific cod stock was 77,100 t.
quarterly Oct-Dec 2001 sidebar
Auke Bay Lab