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Status of Stocks & Multispecies Assessment Program

Groundfish Stock Assessments for 2005 Fishery Quota Recommendations (part 2)

Gulf of Alaska

The sum of the recommended ABCs for 2005 is 539,263 t, a 6% increase from the 2004 total. In the GOA, full assessments were presented for walleye pollock, Pacific cod, rex sole, shortraker/rougheye rockfish, Dusky rockfish, and sablefish whereas other stocks were based on modified projections from last year’s assessments (i.e., under the new biennial cycle).

The largest percentage increase was from pollock (+27%), followed by deep water flatfish (+12%), arrowtooth flounder (+11%), Pacific ocean perch (+2%), pelagic shelf rockfish (+2%) and northern rockfish (+5%).

The species with ABCs that declined relative to 2004 are Pacific cod (-6%), sablefish (-4%), flathead sole (-13%), and demersal shelf rockfish (-9%).

Full assessments for all GOA stocks will be prepared next year since data from the 2005 summer bottom trawl survey are anticipated.

Data limitations pose assessment difficulties for less abundant (minor) rockfish species. Together with other nontarget species, such as sharks, skates, sculpins, and octopus, accurately assessing the vulnerability of these species represents a major challenge for the agency. Effort to monitor the status of nontarget species has improved, and steps have been taken to ensure that adequate data collection programs are in place in advance of directed fishery development.

In 2004, the Plan Teams and Council reviewed an update on the status report for GOA skates and made further conservation moves by separating “big” and “longnose” skate species from the aggregate complex known as “skates.” GOA-wide OFLs and area-specific ABCs and TACs were thus established for “big” and “longnose” skates separately. For the “other” skates (combined Bathyraja spp.) complex, OFL, ABC, and TAC remain GOA-wide.

Similarly, AFSC scientists developed a new assessment of shortraker and rougheye rockfish. This resulted in specific conservation recommendations to limit fishing mortality for each species. The Council recommended breaking out shortraker rockfish and rougheye rockfish from the combined management category. Consequently, OFLs, ABCs and TACs are specified for these rockfish species separately.

AFSC scientists expanded their efforts to incorporate issues identified in the ecosystem considerations chapter into their assessments. Simple food webs that focused on a particular assessed species were prepared for several species. The GOA walleye pollock assessment provided a preliminary assessment of the key predators of pollock in the GOA. Arrowtooth flounder, Pacific halibut, Pacific cod, and Steller sea lions were key predators of pollock. Detailed analyses of time trends in predator size-at-age revealed that pollock may be a limiting resource for species dependent on older age groups of pollock, while no evidence of prey limitation was evident in species that rely on younger age groups of pollock.

Bering Sea/Aleutian Islands

Total BSAI groundfish biomass for 2005 (17.5 million t) is down slightly from last year. Overall, the status of the stocks continues to appear favorable, although some stocks are declining due to poor recruitment in recent years. The sum of the ABCs for 2005, as recommended by the Scientific and Statistical Committee (SSC), is about 3.0 million t, approximately 575,000 t less than the sum of the 2004 ABCs.

The Council recommended a 2005 EBS pollock ABC of 1.96 million t, a value below the maximum permissible level. The Council recommended a TAC for this species of 1,478,500 t. The Council reviewed and accepted a new age-structured analysis of Aleutian Islands pollock. For precautionary reasons, they recommended ABC and TAC levels of 29,400 t and 19,000 t, respectively, which is well below the maximum permissible ABC level of 43,200 t.

The 2004 bottom trawl survey resulted in a BSAI Pacific cod biomass estimate that is down 1% from the 2003 estimate and near the minimum for the time series. Due to a declining trend in abundance, the Council recommended a 2005 ABC of 206,000 t, below the maximum permissible level of 227,000 t. The TAC was recommended to equal the ABC for Pacific cod.

The sablefish survey abundance index decreased 5% from 2003 and follows an 8% decrease between 2002 and 2003. Spawning biomass is projected to decrease slightly (2%) from 2004 to 2005. The Council-recommended ABC and TAC for the Bering Sea was 2,440 t; for the Aleutian Islands the Council recommended an ABC (=TAC) level of 2,620 t.

BSAI yellowfin sole biomass increased 13% from last year, which resulted in an ABC recommendation of 124,000 t and a TAC of 90,686 t.

For Greenland turbot, assessment uncertainties and stock structure issues led to a conservative ABC recommendation of 3,930, well below the maximum permissible value of 15,500 t.

Arrowtooth flounder biomass remains high, and the recommended ABC was 108,000 t while the TAC was only 12,000 t (for bycatch purposes).

This year’s EBS bottom trawl survey resulted in a northern rock sole biomass estimate that was 18% higher than last year. Nevertheless, the stock is expected to decline, as are several other flatfish stocks, due to low recruitment in recent years. The recommended ABC was 132,000 t, and the TAC was 41,500 t.

BSAI Pacific ocean perch biomass estimates suggests a moderately increasing trend, given the new Aleutian Islands survey data. The 2005 ABC recommendation increased to 14,600 t from the 2004 level of 13,300 t.

The 2005 ABC recommendations for northern rockfish also substantively increased to 8,260 t from the 2004 level of 6,880 t.

For the past 2 years, shortraker and rougheye rockfish species have been split to species-specific ABC recommendations. The 2005 ABC recommendations have increased by 14% from last year’s levels, giving 596 t and 223 t for shortraker rockfish and rougheye rockfish, respectively.

The recommended 2005 ABC of 124,000 t for Atka mackerel is up substantially (86%) compared to the 2004 level, due to new survey data and indications of recent strong year classes. The TAC recommendation for Atka mackerel was 63,000 t.

By Jim Ianelli

Atka Mackerel Tag Recovery Cruise 2004 in the Aleutian Islands, Alaska

The first objective of the Center’s Atka mackerel tag release-recovery studies is to determine the efficacy of trawl exclusion zones as a management tool to maintain prey abundance for Steller sea lions at local scales. Trawl exclusion zones were established around sea lion rookeries as a precautionary measure to protect critical sea lion habitat, including local populations of prey such as Atka mackerel. Localized fishing may affect Atka mackerel abundance and distribution near sea lion rookeries. Tagging experiments are being used to estimate abundance and movement between areas open and closed to the Atka mackerel fishery.

During the years 1999-2003, we released roughly 32,000 tags in Seguam Pass: 14,520 near Tanaga Island and 14,700 near Amchitka Island. A recovery charter recovered tagged fish in Seguam Pass and Tanaga Island and Amchitka Island areas.

The 2004 cruise lasted approximately 16 days, starting in Dutch Harbor, Alaska, on 7 October and ending in Adak, Alaska, on 23 October. A total Pass of 66 tows were conducted: 32 tows in Seguam, 20 tows near Amchitka Island, and 14 tows near Tanaga Island. A total of 1,485 t of Atka mackerel were examined for tags. Of these, 836 t were caught in Seguam Pass, 336 t were caught near Amchitka Island, and 313 t were caught near Tanaga Island.

During the cruise, a total of six tagged Atka mackerel were recovered: two in Seguam Pass, three near Amchitka Island, and one near Tanaga Island. Tag recovery rates were estimated by seeding the catch with tagged fish. Recovery rates were high, ranging from 90% to 100% depending on area and stratum. In addition to tag recoveries, catch composition was determined, and sexed length frequencies and biological samples were collected for every haul. Biological samples consisted of gonads, stomachs, and age structures from randomly selected fish. During the course of the cruise, 655 biological samples and 10,283 sexed length data were collected.

The surprisingly low number of tags recovered in all areas may have been due to the large recruitment of age-3 and -4 Atka mackerel into the population during 2003 and 2004. Budget constraints prevented the release of tagged fish during this year, so the tagged population released in the previous years was most likely diluted by incoming year classes of untagged smaller fish. The length frequency data, species composition data, and biological samples collected during this cruise will give us insight into the population structure and will be used for studies on Atka mackerel reproductive ecology and food habits. Some of this information will be incorporated into an integrated tagging model as auxiliary information modeling the Atka mackerel population dynamics.

Bob Lauth from the Center’s RACE Division participated in the recovery cruise and used the fishing vessel Seafisher as a platform for his video drop camera system. The video drop camera was used for locating Atka mackerel nesting sites and documenting the location, depth, and habitat-type at nesting sites. There were 9 camera drops in Seguam Pass, 11 around Amchitka Island, and 3 near Tanaga Island for a total of 23 camera drops.

Real-time video feed and winch control were used to navigate the towed video camera to avoid hanging up while the vessel and camera drifted over the bottom. Video feed was recorded with GPS (global positioning system) overlay and a digital video recording device, and the drop camera was also equipped to record depth and temperature. Camera drops lasted from 10 to 60 minutes and ranged from 70 to 170 m depth.

By Kimberly Rand and Susanne McDermott


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