2016 Assessment of the Sculpin Stock Complex in the Bering Sea and Aleutian Islands
Sculpins are found in both freshwater and marine habitats; they are distributed throughout the BSAI and occupy all benthic habitats and depths. Forty-seven species of sculpins have been identified in the Bering Sea Aleutian Islands (BSAI) region (Families Cottidae, Hemitripteridae, Psychrolutidae, and Rhamphocottidae; Table 1). However, these species are managed as a complex, and the complex natural mortality (M) estimate is based on the biomass of 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). The species composition of the sculpin complex as estimated by bottom trawl surveys of the EBS shelf, EBS slope, and AI demonstrates the diversity of this complex and the regional differences in its composition. The larger species dominate the EBS shelf, with great and plain sculpins being the most common, followed by bigmouth sculpins and yellow Irish lords (Figure 1) and most of the sculpin biomass is found on the EBS shelf, followed by the AI and EBS slope (Figure 2).
Sculpins belong to the superfamily Cottoidea in the order Scorpaeniformes. They are relatively small, benthic-dwelling teleost fish with modified pectoral fins that allow them to grip the substrate, and they lack swim bladders. Most sculpins lay adhesive eggs in nests, and many exhibit parental care for eggs (Eschemeyer 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. These types of reproductive strategies 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 2004-2010 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.
Little is known about stock structure of BSAI sculpin species, and little research on stock structure has been done for sculpins in general. The diversity of sculpin species in the BSAI suggests that different components of the sculpin complex would 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). In the BSAI, yellow Irish lord has been found to exhibit spatial differences in fecundity between the eastern Bering Sea and Aleutian Islands (TenBrink and Buckley 2013). Futhermore, 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 that diet composition differed among and within species. Therefore, the sculpin complex might be managed most efficiently within a spatial context rather than with a global annual aggregate BSAI total allowable catch (TAC).