2015 Assessment of the Skate Stock Complex in the Gulf of Alaska
Skates (family Rajidae) are cartilaginous fishes related to sharks. At least 15 species of skates in four genera (Raja, Beringraja, Bathyraja, and Amblyraja) are found in Alaskan waters and are common from shallow inshore waters to very deep benthic habitats (Eschmeyer et al 1983; Stevenson et al 2007). In general, Raja species are most common and diverse in lower latitudes and shallower waters from the Gulf of Alaska to the Baja peninsula, while Bathyraja species are most common and diverse in the higher latitude habitats of the Bering Sea and Aleutian Islands, as well as in the deeper waters off the U.S. west coast. Table 1 lists the species found in Alaska, with their depth distributions and selected life history characteristics, which are outlined in more detail below
In the Gulf of Alaska (GOA), the most common skate species are a Raja species, the longnose skate R. rhina; a Beringraja species, the big skate B. binoculata; and three Bathyraja species, the Aleutian skate B. aleutica, the Bering skate B. interrupta, and the Alaska skate B. parmifera (Tables 2 & 3, Figure 1). Big skates were previously in the genus Raja. The general range of the big skate extends from the Bering Sea to southern Baja California in depths ranging from 2 to 800 m. The longnose skate has a similar range,
from the southeastern Bering Sea to Baja California in 9 to 1,069 m depths (Love et al 2005). While these two species have wide depth ranges, they are generally found in shallow waters in the GOA. One deepdwelling Amblyraja species, the roughshoulder skate A. badia, ranges throughout the north Pacific from Japan to Central America at depths between 846 and 2,322 m; the four other species in the genus Raja are not found in Alaskan waters (Love et al 2005; Stevenson et al 2007). Within the genus Bathyraja, only
two of the 13+ north Pacific species are not found in Alaska. Of the remaining 11+ species, only three are commonly found in the Gulf of Alaska. The Aleutian skate ranges throughout the north Pacific from northern Japan to northern California, and has been found in waters 16 to 1,602 m deep. The Alaska skate is restricted to higher latitudes from the Sea of Okhotsk to the eastern Gulf of Alaska in depths from 17- 392 m (Stevenson et al 2007). The range of the Bering skate is difficult to determine at this time as it may
actually be a complex of species, with each individual species occupying a different part of its general range from the western Bering Sea to southern California (Love et al 2005; Stevenson et al 2007).
The species within this assemblage occupy different habitats and regions within the GOA groundfish Fishery Management Plan (FMP). In this assessment, we distinguish habitat primarily by depth for GOA skates. The highest biomass of skates is found in the shallowest continental shelf waters of less than 100 m depth, and is dominated by the big skate (Figure 2). In continental shelf waters from 100-200 m depth, longnose skates dominate skate biomass, and Bathyraja skate species are dominant in the deeper waters extending from 200 to 1000 m or more in depth (Figure 2). These depth distributions are reflected in the spatial distribution of GOA skates. Big skates are located inshore and are most abundant in the central and western GOA (Figures 3 & 4). Longnose skates (Figures 4 & 5) are located further offshore and appear to be more widespread than big skates.