2014 Assessment of the Sculpin Stock Complex in the Bering Sea and Aleutian Islands
March 04, 2014
Forty-eight species of sculpins have been identified in the Bering Sea Aleutian Islands (BSAI) region (Families Cottidae, Hemitripteridae, Psychrolutidae, and Rhamphocottidae; Table 1). These species are managed as a complex, and biomass estimates are based on the six most abundant sculpins in the BSAI: bigmouth (Hemitripterus bolini), great (Myoxocephalus polyacanthocephalus), plain (Myoxocephalus jaok), threaded (Gymnocanthus pistilliger), warty (Myoxocephalus verrucosus), and yellow Irish lord (Hemilepidotus jordani). This non-target species complex is assessed biennially, to coincide with the frequency of trawl surveys in the Bering Sea and Aleutian Islands, with full assessments in even years. The 2013 executive summary can be found at http://www.afsc.noaa.gov/REFM/Docs/2013/BSAIsculpin.pdf. BSAI sculpins are managed as a Tier 5 stock, and a weighted average of species-specific natural mortality rates (M) is applied to the aggregate sculpin biomass to estimate standard reference points.
Sculpins belong to the superfamily Cottoidea in the order Scorpaeniformes, and are found in both freshwater and marine habitats. Sculpins are distributed throughout the BSAI and they occupy all benthic habitats and depths. They are relatively small, benthic-dwelling teleost fish with modified pectoral fins that allow them to grip the substrate, and they lack swim bladders. The six most common sculpin species in the BSAI appear to have a range of natural mortality, from 0.14-0.45 (TenBrink and Aydin 2009; Hutchinson and TenBrink 2011).
Little is known about stock structure of BSAI sculpin species, and little research on stock structure has been done for sculpins in general. However, other known aspects of their life history are relevant to this question. Most if not all sculpins lay adhesive eggs in nests, and many exhibit parental care for eggs (Eschmeyer et al. 1983). Markevich (2000) observed the sea raven, Hemitripterus villosus, releasing eggs into crevices of boulders and stones in shallow waters in Peter the Great Bay, Sea of Japan. This type of reproductive strategy may make sculpin populations more sensitive to changes in benthic habitats than other groundfish species such as walleye pollock, which are broadcast spawners with pelagic eggs. In the western Pacific, great sculpins (Myoxocephalus polyacanthocephalus) are reported to have relatively late ages at maturity (5-8 years, Tokranov, 1985) despite being relatively short-lived (13-15 years). This suggests a limited reproductive portion of the lifespan relative to other groundfish species. Fecundity for the great sculpin in East Kamchatka waters ranged from 48,000 to 415,000 eggs (Tokranov 1985). Age and growth information is available for the great sculpin, yellow Irish lord, bigmouth, plain and warty sculpin based on samples collected from the 2005-2008 Eastern Bering Sea (EBS) shelf survey (TenBrink and Aydin 2009). Known life history characteristics for the most abundant sculpin species along the EBS shelf are presented in Table 2. Recent work has also provided information on diet and reproduction in large sculpins in the BSAI.
The diversity of sculpin species in the BSAI suggests that each sculpin population might react differently to natural or anthropogenic environmental changes. Within each sculpin species, observed spatial differences in fecundity, egg size, and other life history characteristics points to local population structure (Tokranov 1985). All of these characteristics indicate that sculpins as a group might be managed most efficiently within a spatial context rather than with a global annual aggregate BSAI total allowable catch (TAC). A recent study by TenBrink and Buckley (2012) found evidence for habitat partitioning among species M. jaok, M. polyacanthocephalus, and M. scorpius. They found that within species, larger individuals tend to be found in deeper water and diet composition differed among and within species.