Cautious catch limits and strong fishery compliance. Multiple data inputs for stock assessment, including three regular surveys. Fishery has little known impact on PET species; potential for such impacts is limited due to seabird avoidance measures and protective closures for marine mammals.
Persistent weak recruitment has led to a long population decline despite very conservative catch levels. Causes of declining abundance of immature fish are poorly understood. Some research gaps have been identified in assessment.
Support federal budget for surveys and continued research on recruitment and other factors affecting population.
Scientists at the National Marine Fisheries Service’s Alaska Marine Science Center prepare the annual assessment using the Stock Synthesis 2 model. Primary data inputs in the BSAI include a longline survey, trawl surveys of the continental shelf and slope, catch records, and historical observer reports (for length frequency composition) (Source : Ianelli, Wilderbuer, and Nichol, 2007).
The 2007 longline and trawl surveys produced mixed results. The longline survey index increased slightly from 2006 but remained below levels seen in 1996-2005. The shelf trawl survey biomass estimate declined approximately 20% from 2006.
The 2007 assessment authors classify Greenland turbot in the BSAI as a Tier 3a stock under FMP Amendment 56, based on the projected spawning biomass in 2008 of 58,125 tonnes, comfortably above the B35% threshold of 33,382 tonnes. Due to persistent low recruitment, assessment authors recommended an Acceptable Biological Catch of 2,540 tonnes, about 20% of the maximum permissible value under the harvest policy. The harvest policy is designed to leave a buffer between advised maximum removals and the level of removals that would constitute overfishing. Fofl (i.e. overfishing level) is 15,600 tonnes, based on F35% (Ianelli, Wilderbuer, and Nichol, 2007).
Biomass reference points (female spawning biomass):
B35% : 33,382 tonnes, designated as Fofl (i.e. threshold for reduced harvest rate)
B40% : 38,151 tonnes
B100% : 95,377 tonnes
Fishing mortality reference points:
FABC (maximum permissible ABC) = F40% = 0.462
2008 maximum potential removals under FABC : 12,171 tonnes
2008 recommended ABC: 2,540 tonnes
(Source: Ianelli, Wilderbuer and Nichol, 2007)
Low and declining, unlike other BSAI flatfish, but still well above critical levels.
Female spawning biomass in the BSAI is estimated to be 58,125 tonnes for 2008, about 52% above B40% (38,151 tonnes), according to the 2007 draft assessment (Ianelli, Wilderbuer, and Nichol, 2007)
Peak landings of 63,000 to 78,000 tonnes occurred during the 1970s; harvests have declined since early 1980s. TAC has been set low since 1986, (10,000 tonnes or lower), due to concerns about low recruitment, according to the NMFS FishWatch service. Estimated total biomass (age 1+) in the BSAI peaked in 1972 at 759,000 tonnes and has since declined, hitting a low of 101,020 tonnes in 2005, with the current level slightly higher at 104,116 tonnes (from Table 5.8 in draft assessment, Ianelli, Wilderbuer and Nichol, 2007).
Historically Greenland turbot has been fished with bottom trawls and fixed gear. Since 1998 tight harvest limits have been imposed, with the result that much of the TAC is now reserved for incidental catch (though marketable) in fisheries targeting other species (Source: from Catch History and Fishery Data section, 2007 draft assessment, Ianelli, Wilderbuer and Nichol, 2007). However, a small targeted fishery continues to land Greenland turbot, primarily with demersal longline gear.
Greenland turbot in the BSAI are managed under the North Pacific Fishery Management Council’s fishery management plan for groundfish. Historically BSAI Greenland turbot were managed together with arrowtooth flounder until 1985. Diverging abundance trends and market values prompted a move to separate management. Flatfish are lightly harvested. Since 1998, elimination of halibut bycatch allowance for Greenland turbot directed trawling has prevented any targeted trawl fishing in the BSAI.
Total harvests–targeted and incidental—have been kept below the TAC consistently (100% of catches during 1997-2006 were below TAC).
Targeted catches of Greenland turbot in the BSAI have taken only a portion of the TAC during recent years. For example, 1,198 tonnes were landed as target catch in 2006, against a TAC of 2,740 tonnes. The remainder of the TAC was taken by fleets targeting other species.
Area closures to prevent disturbance of endangered Steller sea lions are in effect (see below under Marine Reserves). Estimates of seabird incidental catch by demersal longline vessels in Alaska show a marked decline since the late 1990s, coincident with introduction of seabird avoidance techniques to prevent take of endangered short-tailed albatross (See regulatory timeline and details at (Seabird Bycatch Reduction Program-Regulations).
Sightings of short-tailed albatross are rare, accounting for 11 out of more than 9,000 birds recorded in several recent surveys (Melvin et al.,2004). Total estimated take of all seabird species was 4,095 birds in 2004; gulls (2,606) and fulmars (830) predominate, according to data published by Washington Sea Grant (Melvin et al., 2004). The proportion of seabird incidental catch occurring in fisheries targeting turbot is uncertain but likely to be small.
Greenland turbot and sablefish inhabit similar depth and are frequently taken together, either as target or bycatch species. Some halibut and seabirds are incidentally taken. Among species with sensitive life history characteristics, longline vessels targeting Greenland turbot account for 17% of bycatch of sleeper sharks taken in the BSAI (Source : Boldt et al., seabird Ecosystem Considerations chapter, draft BSAI SAFE report, NMFS, 2007). Greenland turbot are taken as bycatch in other groundfish fisheries, including fleets targeting sablefish, Pacific cod, rockfish, flatfish, and others.
Near ocean floor. Juveniles spend 3 to 4 years on continental shelf, then move to slope. Adults are found at 328 to 3,280 ft depth. This species prefers cold temperatures, muddy substrates. Known prey include crustaceans, squid, and fish (NMFS, FishWatch).
The 2007 assessment authors note that the dramatic decline in abundance of immature Greenland turbot since the late 1970s is not yet understood. Researchers from the NMFS REFM division are modeling multi-species interactions, including possible effects from increased populations of predators, while other research examines migration and climatic influences.
A network of bottom trawl closures exists in the U.S. Bering Sea
(See map of closures through 2006 at figure ES 1 in document posted at (Bering Sea Habitat Conservation).
To protect Steller sea lion feeding grounds near rookeries and haulouts, pot and longline cod vessels are prohibited from fishing in many nearshore areas. Closed areas include parts of the Aleutian Islands, waters around Sea Lion Rock along the northern Alaska Peninsula, the Walrus Islands and Cape Newenham at the northwest edge of Bristol Bay, most of Hall Island and parts of St. Lawrence island, and the Pribilof Islands
(See map at Steller Sea Lion Mitigation Committee Reference Materials). To avoid disturbing Pacific walrus around their haulouts, all groundfish fishing is prohibited within 12 nm of Round Island, the Twins, and Cape Pierce (Witherell and Woodby, 2005).