2016 Assessment of Greenland Turbot (Reinhardtius Hippoglossoides) in the Bering Sea and Aleutian Islands
Greenland turbot have life history characteristics that complicate assessment surveys in the Eastern Bering Sea and Aleutian Islands region. There continues to be issues in rectifying inconsistencies between the NMFS Shelf surveys and NMFS Slope surveys.
Greenland turbot (Reinhardtius hippoglossoides) is a Pleuronectidae (right eyed) flatfish that has a circumpolar distribution inhabiting the North Atlantic, Arctic and North Pacific Oceans. The American Fisheries Society uses “Greenland halibut” as the common name for Reinhardtius hippoglossoides instead of Greenland turbot. To avoid confusion with the Pacific halibut, Hippoglossus stenolepis, the common name Greenland turbot, which is also the “official” market name in the US and Canada (AFS 1991), is retained.
In the Pacific Ocean, Greenland turbot have been found from the Sea of Japan to the waters off Baja California. Specimens have been found across the Arctic in both the Beaufort (Chiperzak et al. 1995) and Chukchi seas (Rand and Logerwell 2011). This species primarily inhabits the deeper slope and shelf waters (between 100 m to 2000 m; Fig. 5.1) in bottom temperatures ranging from -2°C to 5°C. The area of highest density of Greenland turbot in the Pacific Ocean is in the northern Bering Sea. Juveniles are believed to spend the first 3 or 4 years of their lives on the continental shelf and then move to the continental slope (Alton et al. 1988; Sohn 2009; Fig. 5.2). Adult Greenland turbot distribution in the Bering Sea appears to be dependent on size and maturity as larger more mature fish migrate to deeper warmer waters. In the annual summer shelf trawl surveys conducted by the Alaska Fisheries Science Center (AFSC) the distribution by size shows a clear preference by the smaller fish for shallower (< 100 m) and colder shelf waters (< 0°C). The larger specimens were in higher concentrations in deeper (> 100 m), warmer waters (> 0°C) (In Barbeaux et al. (2015): Fig. 5.3, Fig. 5.4 Fig. 5.5, and Fig. 5.6). It appears that for years with above average bottom trawl bottom temperatures the larger turbot ( > 20 cm) are found at shallower depths (In Barbeaux et al. (2015): Fig. 5.7).
Juveniles are generally absent in the Aleutian Islands regions, suggesting that the population in the Aleutians originates from the EBS or elsewhere. In this assessment, Greenland turbot found in the two regions are assumed to represent a single management stock. NMFS initiated a tagging study in 1997 to supplement earlier international programs. Results from conventional and archival tag return data suggest that individuals can range distances of several thousands of kilometers and spend summer periods in deep water in some years and in other years spend time on the shallower EBS shelf region.