2016 Assessment of the Thornyhead Stock Complex in the Gulf of Alaska
Shortspine thornyhead (Sebastolobus alascanus; SST) are a long lived, deep dwelling species that inhabit the northeastern Pacific Ocean from Baja Mexico to the Gulf of Alaska (GOA), westward to the Aleutian Islands (AI), eastern Bering Sea (BS), and into the Seas of Okhotsk and Japan (Echave et al. 2015). Adult SST are generally found along the continental slope at depths of 150 – 450 m. Thornyheads (Sebastolobus species) are groundfish belonging to the family Scorpanenidae, which contains the rockfishes. While thornyheads are considered rockfish, they are distinguished from the “true” rockfish in the genus Sebastes primarily by reproductive biology. Thornyheads are also differentiated from Sebastesin that they lack a swim bladder, making them ideal tagging specimens.
The National Marine Fisheries Service (NMFS) Auke Bay Laboratory (ABL) has released 13,897 tagged SST in Alaska waters since 1992, and over 220 of those fish have been recovered. Data from the releases and recoveries are maintained in the ABL Groundfish Tag Database. Since 1997, tagging in offshore waters has occurred aboard chartered commercial vessels during the NMFS annual Domestic Longline Survey. Approximately 5% of the longline survey catch of SST are tagged and released each year, which generally equals about 500 – 1,000 fish per year. Offshore tagging has included conventional anchor tags and internally implanted electronic archival tags. Analysis of tag data is the primary method used to examine SST movement patterns and can assist with questions regarding stock structure and growth. The purpose of this document is to present a brief summary of release and recovery data of SSTs.