2015 Assessment of the Thornyhead Stock Complex in the Gulf of Alaska
February 21, 2015
Thornyheads (Sebastolobus species) are groundfish belonging to the family Scorpanenidae, which contains the rockfishes. The family Scorpanenidae is characterized morphologically within the order by venomous dorsal, anal, and pelvic spines, numerous spines in general, and internal fertilization of eggs. While thornyheads are considered rockfish, they are distinguished from the “true” rockfish in the genus Sebastes primarily by reproductive biology; all Sebastes rockfish are live-bearing (ovoviviparous) fish, while thornyheads are oviparous, releasing fertilized eggs in floating gelatinous masses. Thornyheads are also differentiated from Sebastes in that they lack a swim bladder. There are three species in the genus Sebastolobus, including the shortspine thornyhead Sebastolobus alascanus, the longspine thornyhead Sebastolobus altivelis, and the broadfin thornyhead Sebastolobus macrochir (Eschmeyer et al. 1983, Love et al. 2002).
Thornyheads are distributed in deep water habitats throughout the north Pacific, although juveniles can be found in shallower habitats. The range of the shortspine thornyhead extends from 17 to 1,524 m in depth and along the Pacific Rim from the Seas of Okhotsk and Japan in the western north Pacific, throughout the Aleutian Islands, Bering Sea, Gulf of Alaska, and south to Baja California in the eastern north Pacific (Love et al. 2005). Shortspine thornyheads are considered most abundant from the Northern Kuril Islands to southern California. They are concentrated between 150 and 450 m depth in cooler northern waters, and are generally found in deeper habitats up to 1,000 m in the warmer waters of this range (Love et al. 2002).