Based on re-analyses of whaling records and surveys, important areas appeared to be (1) the Southeastern Bering Sea slope and shelf, (2) eastern Aleutian Islands, and (3) Gulf of Alaska slope and abyssal plain. Since 1980, the only area where right whales have been seen consistently is on the middle-shelf of the Southeastern Bering Sea. However, acoustic detections and single sightings have been reported in most other regions. In fact, the results of this study refute conclusions in another study that a "habitat shift" occurred when right whales moved from deep continental slope waters in the SEBS during the 1940s to 1960s to now occupy "a different habitat" on the middle-shelf of the SEBS. Given that right whales have been seen in middle-shelf waters from the 19th century to the present, it appears that the SEBS middle shelf was and continues to be important habitat for this species. Although there has been a conspicuous absence of right whale sightings from the outer shelf and slope habitat in recent years, this may be due, at least in part, to a lack of survey effort there. Results of acoustic recorder deployments along the slope are much anticipated.
All sightings since 1979 were in waters less than 200 m deep which may simply reflect the paucity of search effort elsewhere. From the commercial whaling era to the late-1960s, right whales were commonly seen in waters greater than 2000 m deep, indicating that their distribution is not restricted to shallow continental shelves. North Pacific right whale sightings through the centuries have been associated with a wide variety of oceanic features, and there is little in common in the bathymetry of these regions. These whales appear to have a greater pelagic distribution than that observed in the North Atlantic - perhaps because of the wider availability of larger copepods in Alaskan waters.
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