2016 Assessment of the Shortraker Rockfish Stock in the Bering Sea and Aleutian Islands
February 13, 2016
Shortraker rockfish (Sebastes borealis) are distributed along the continental slope in the north Pacific from Point Conception in southern California to Japan, and are commonly found between eastern Kamchatka and British Columbia (Love et al. 2002). As adults the species occurs in a narrow range of depths on the continental slope centered at ~350 m (Rooper 2008) often in areas of steep slope (Rooper and Martin 2012). Love et al. (2002) indicates the species is found at shallower depths during early life history. In bottom trawl survey data, the species is most common through the Aleutian Islands (AI) and northern Gulf of Alaska (GOA). In the Bering Sea they are found on the slope survey but not on the shelf survey.
This species is among the longest-lived animal species in the world, reaching ages > 150 years. The species is viviparous with spawning believed to occur throughout the spring and summer (Westerheim 1975, McDermott 2004). Little is known of shortraker rockfish early life history and habitat preferences, as immature fish are rarely observed. Studies of habitat preferences in the GOA indicate shortraker rockfish may be more abundant in boulder patches with associated Primnoa coral (Krieger and Ito 1999, Krieger and Wing 2002). Shortraker rockfish consume large benthic or near-bottom prey, including myctophids, shrimp and squid (Yang et al. 2006).
Several types of research can be used to infer stock structure of shortraker rockfish, including larval distribution patterns and genetic studies. In 2002, an analysis of archived Sebastes larvae was undertaken using data collected in 1990 off southeast Alaska (650 larvae) and the AFSC ichthyoplankton database (16,895 Sebastes larvae, collected on 58 cruises from 1972 to 1999, primarily in the GOA). The southeast Alaska larvae all showed the same morph, and were too small to have characteristics that would allow species identification. A preliminary examination of the AFSC ichthyoplankton database indicated that most larvae were collected in the spring, the larvae were widespread in the areas sampled, and most were small (5-7 mm). The larvae were organized into three size classes for analysis: <7.9 mm, 8.0-13.9 mm, and >14.0 mm. A subset of the abundant small larvae was examined, as were all larvae in the medium and large groups. The larvae were assigned to four morphs identified by Kendall (1991), where each morph was associated with one or more species. Most of the small larvae examined belong to a single morph, which contained the species S. alutus (Pacific ocean perch), S. polyspinus (northern rockfish), and S. ciliatus (dusky rockfish). Some larvae (18) belonged to a second morph which was identified as S. borealis (shortraker rockfish) in the Bering Sea. The locations of these larvae were near Kodiak Island, the Semidi Islands, Chirikof Island, the Shumagin Islands, and near the eastern end of the AI.