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Status of Stocks & Multispecies Assessment Program

Groundfish Stock Assessments for 2007:  Gulf of Alaska (GOA)

In the GOA, assessments were presented for 17 stocks and assemblages and an extensive appendix on the status of “Other species groups” was also prepared. This appendix was prepared at the request of the Council for regulatory analyses that are underway so that revised specification processes can be evaluated.

The sum of the recommended ABCs for 2007 is 490,327 t which represents a 2% decrease from the 2006 total. Since new survey data were unavailable for GOA stocks, a number of assessments consisted of projections from the 2005 SAFE reports (with updated catches). However, full assessments were completed for GOA pollock, Pacific cod, sablefish, and northern rockfish. Brief summaries of each GOA species or species group follows.


GOA Pollock:  The 2006 winter Shelikof Strait EIT survey was 13% less than the 2005 estimate. The model estimate of spawning biomass in 2007 is 160,670 t, which is 29% of unfished spawning biomass and below B40% (220,000 t). Projections incorporating uncertainty in the stock assessment indicate that there is very low probability that the pollock stock will drop below critical levels in the near future.

A new analysis conducted with the GOA ecosystem model compared estimates of predation mortality and fishing mortality relative to population production in order to determine whether total mortality exceeded production. The results suggested that high predation mortality plus conservative fishing mortality might exceed GOA pollock production at present, and that this condition may have been in place since the late 1980s or early 1990s. Although this analysis was considered preliminary by the ecosystem assessment authors, it provides additional support for continued precautionary management of GOA pollock. Management Strategy Evaluation (MSE) analyses on GOA pollock continues. Alternative operating model configurations for the MSE are being derived from ecosystem modeling so that the potential for adjustments to ABC recommendations can be evaluated.


GOA Pacific Cod:  The current assessment estimate of spawning biomass for 2007 is 126,903 t, up about 9% from last year’s estimate for 2006 and above the B40% value of 103,000 t. The short-term trend in ABC indicates declines since the 2001-03 year classes are almost certainly below average. To stabilize these somewhat (and to allow for further model developments to occur) the ABC was recommended to be the same as in 2006: 68,859 t. This compares with a maximum permissible value from the model of 81,200 t.
 

  Figure 3, see caption
Figure 3.  Female spawning biomass trends for Alaska-wide sablefish including projections, 1960-2020. Shading represents relative uncertainty levels.



 
Table 1.
Species 2006 ABC 2007 ABC Change
Other slope rockfish 4,152 4,154 0%
Northern rockfish 5,091 4,938 -3%
Pacific ocean perch 14,261 14,636 3%
Shortraker 843 843 0%
Rougheye 983 988 1%
Pelagic shelf rockfish 5,436 5,542 2%
Demersal shelf rockfish 410 410 0%
Thornyhead rockfish 2,209 2,209 0%
Total 33,385 33,720 1%
 

GOA/BSAI Sablefish:  The present assessment departs from previous years’ assessments by using a split-sex age-structured model and incorporating Gulf of Alaska trawl survey lengths and biomass estimates for depths of 500 m or less. The split-sex model approach is appropriate given the differences in growth and maturity between males and females. Data from the trawl survey was included to improve estimates of recruitment, since trawl surveys tend to catch smaller fish than the longline survey. The longline survey abundance index increased 8% from 2005 level but showed a 2.5% decrease from 2004 to 2005, while the fishery abundance index decreased by 4%. Spawning biomass is currently about 38% of the estimated unfished level and is projected to drop slightly in the near term (Fig. 3). The Council-recommended 2007 ABC was 20,100 t, compared to 21,000 t for 2006.


GOA Flatfish:  Arrowtooth flounder 2005 survey biomass estimate (for the western and central GOA) was 1.65 million t compared to 479,000 t for Pacific halibut and 661,000 t for all other flatfish species in this region. The 2007 ABC recommendation for arrowtooth flounder increased 3% from the 2006 value to 184,000 t. As is the case for most flatfish species in the GOA, arrowtooth flounder continue to be lightly exploited with a 2006 catch of 14,400 t. The other flatfish management groups and 2007 ABCs were: deepwater flatfish—8,707 t (compared to 2006 catch of 389 t); shallow-water flatfish—51,450 t (compared to 2006 catch of 7,605 t); flathead sole—39,110 t (compared to 2006 catch level of 2,644 t); and rex sole—9,100 t (compared to 2006 catch level of 3,380 t).


GOA Rockfish:  For Pacific ocean perch, the 2007 ABC increased by 3% to 14,261 t based on projections from the previous year’s model. For northern rockfish, a completely revised assessment was presented and the 2007 ABC dropped from the 2006 value of 5,091 t to 4,938 t. The summary of GOA rockfish ABCs relative to the 2006 levels are given (in t) in Table 1.
 

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