2015 View Assessment of the Demersal Shelf Rockfish Stock Complex in the Southeast Outside District of the Gulf of Alaska
February 21, 2015
Rockfish of the genus Sebastes are found in temperate waters of the continental shelf off North America. At least thirty-two species of Sebastes occur in the Gulf of Alaska. The DSR assemblage is comprised of the seven species of nearshore, bottom-dwelling rockfish (Table 1). These fish are located on the continental shelf, reside on or near the bottom, and are generally associated with rugged, rocky habitat. For purposes of this report, emphasis is placed on yelloweye rockfish, as it is the dominant species in the DSR fishery (O’Connell and Brylinsky 2003).
All DSR are considered highly K-selective, exhibiting slow growth and extreme longevity (Adams 1980, Gunderson 1980, Archibald et al. 1981). Estimates of natural mortality are very low. These types of fish are very susceptible to over-exploitation and are slow to recover once driven below the level of sustainable yield (Leaman and Beamish 1984, Francis 1985). An acceptable exploitation rate is assumed to be very low (Dorn 2000).
Rockfish are considered viviparous although different species have a different maternal contribution (Boehlert and Yoklavich 1984, Boehlert et al. 1986, Love et al. 2002). Rockfish have internal fertilization with several months separating copulation, fertilization, and parturition. Within the DSR species complex, parturition occurs from February through September with the majority of species
extruding larvae in spring. Yelloweye rockfish extrude larvae over an extended time period, with the peak period of parturition occurring from April through June, peaking in May in Southeast Alaska (O’Connell 1987). Although some species of Sebastes have been reported to spawn more than once per year in other areas (Love et al. 1990), no incidence of multiple brooding has been noted in Southeast Alaska (O’Connell 1987).
Rockfish have a closed swim bladder that makes them susceptible to embolism mortality when brought to the surface from depth. Full retention regulations for the commercial fleet have been in place since 2005. Full retention of DSR had been required for the recreational fleet, but beginning in the 2013 season, all charter operators in Southeast Alaska were required to possess and utilize deep-water release devices for releasing non-pelagic (i.e. DSR) rockfish. Historically, release mortality biomass has been estimated using the assumption that released rockfish experience 100% mortality (Green et al. 2013).