2018 Assessment of the Skate Stock Complex in the Bering Sea and Aleutian Islands
Because two different assessment methodologies are used for skates, this report deviates somewhat from
the format of other Stock Assessment and Fishery Evaluation (SAFE) documents.
Skates (family Rajidae) are cartilaginous fish related to sharks. At least 15 species of skates in four genera, Raja, Beringraja, Bathyraja, and Amblyraja, are distributed throughout the eastern North Pacific and are common from shallow inshore waters to very deep benthic habitats (Eschmeyer et al. 1983, Stevenson et al. 2006). Table 1 lists the species found in Alaskan waters, with their depth distributions and selected life history characteristics.
The species within the skate assemblage occupy different habitats and regions within the BSAI Fishery Management Plan (FMP) area (Figure 1). In this assessment, we distinguish three habitat areas: the eastern Bering Sea (EBS) shelf (< 200 m depth), the EBS slope (> 200 m depth), and the Aleutian Islands (AI) region. Skate species composition varies widely among the regions, with the highest diversity observed on the EBS slope (Table 2 & Figure 2). The areas also differ in skate abundance with the vast majority (88% in 2016) of skate biomass found on the EBS shelf (Table 2 & Figure 3). In 2016 the slope had 8% of the skate biomass and the AI 4%; before the 2012 survey biomass was higher in the AI than on the slope. Within the BSAI, skate abundance and species composition also vary by depth and species diversity is generally greatest on the upper continental slope at 250 to 500 m depth (Figures 4 & 5; Stevenson et al. 2006). On the EBS slope skate biomass is highest in the 200-400 m depth stratum, and in the AI biomass is greatest between 100 m and 200 m (Figure 5).