2018 Assessment of the Arrowtooth Flounder Stock in the Eastern Bering Sea and Aleutian Islands
Arrowtooth flounder (Atheresthes stomias) are relatively large flatfish that range from central California to the eastern Bering Sea (EBS), and as far west as the Kuril Islands (Orlov 2004). Arrowtooth flounder occur in waters from about 20m to 800m, although catch per unit effort (CPUE) from survey data is highest between 100m and 300m. Spawning occurs in deep water (>400 meters) in the Gulf of Alaska and along the shelf break in the eastern Bering Sea (Doyle et al. 2018). Migration patterns are not well known for arrowtooth flounder; however, there is some indication that arrowtooth flounder move into deeper water as they grow, similar to other flatfish, such as Alaska plaice and Greenland turbot (Barbeaux and Hollowed 2018). This is particularly relevant in the Bering Sea, where there is a separate research survey conducted on the EBS shelf and slope (<200m depth). Fisheries data off Washington suggest that larger fish may migrate to deeper water in winter and shallower water in summer (Rickey 1995).
The survey abundance of arrowtooth flounder is approximately eight times higher in the eastern Bering Sea than in the Aleutian Islands region (Figure 6.2, Table 6.1). The distribution of ages appears to vary b y region and sex; male arrowtooth as old as 37 years have been observed in the Aleutian Islands are not commonly observed older than age 10 on the Bering Sea shelf, while the female length and weight relationships do not vary significantly between the two regions. Arrowtooth flounder begin to recruit to the eastern Bering Sea slope at about age 4. Recruitment to the slope gradually increases at older ages and reaches a maximum at age 9, based on age data from the 1982 U.S.-Japan cooperative survey. However, greater than 50% of age groups 9 and older continue to occupy continental shelf waters. The low proportion of the overall biomass on the slope during the 1988, 1991, and 2016 surveys, relative to that of earlier surveys, indicates that the proportion of the population occupying slope waters may vary considerably from year to year depending on the age structure of the population.
Arrowtooth flounder are batch spawners, spawning from fall to winter off Washington State at depths greater than 366m (Rickey 1995). Spawning females have been found at 400m and males at ≥450m in the Gulf of Alaska, and larvae have been found at depths greater than 200 m (Blood et al. 2007; De Forest et al. 2014). The age composition of the species shows fewer males relative to females as fish increase in age, which suggests higher natural mortality (M) for males (Wilderbuer and Turnock 2009). To account for this process, natural mortality w as fixed at 0.2 for females and 0.35 for males in the model.
The arrowtooth flounder resource in the EBS and the Aleutians is managed as a single stock although little is known about stock structure. There has been no research on this topic for this species.