Late Summer Distribution of Cetaceans near Barrow, Alaska: Results from Aerial Surveys Conducted During the Bowhead Whale Feeding Ecology Study, 2007–11

• Published in: Marine fisheries review Vol. 79; no. 2; pp. 1 - 22
• Main Authors: Shelden, Kim E. W., Mocklin, Julie A., Goetz, Kimberly T., Rugh, David J., Brattström, Linda Vate, Friday, Nancy
• Format: Journal Article
• Language: English
• Published: Washington Superintendent of Documents 2017
• Subjects: Aerial surveying; Aerial surveys; Animal behavior; Aquatic mammals; Area; Balaena mysticetus; Balaenidae; Barrier islands; Bathymeters; Bathymetry; Biological surveys; Cetacea; Commercial fishing; Continental shelves; Delphinapterus leucas; Distance; Ecological distribution; Ecological effects; Ecological monitoring; Ecology; Ellipses; Erignathus barbatus; Eschrichtiidae; Eschrichtius robustus; Feeding; Feeding behavior; Feeding habits; Fishing; Habitat preferences; Habitat selection; Habitat utilization; Habitats; Ice environments; Identification; Isobaths; Juveniles; Marine mammals; Megaptera novaeangliae; Migration; Observers; Odobenus rosmarus; Offshore; Parameters; Phoca hispida; Photogrammetry; Polar bears; Polar environments; Sea ice; Seals; Shipping; Species; Summer; Ursus maritimus; Whales; Whales & whaling; United States > US; Alaska; Beaufort Sea
• ISSN: 0090-1830; 1939-2044
• DOI: 10.7755/MFR.79.2.1

The aerial survey component of the Bowhead Whale Feeding Ecology Study (BOWFEST) was designed to document patterns and variability in the timing and distribution of bowhead whales, Balaena mysticetus, and to provide an estimate of temporal and spatial habitat use near Barrow, Alaska. Aerial surveys were conducted from late August to mid-September during the period 2007–11 for a total of 171.1 hours flown. In addition to the focal species, observed species included gray whales, Eschrichtius robustus; one hump- back whale, Megaptera novaeangliae; beluga whales, Delphinapterus leucas; ringed seals, Phoca hispida; bearded seals, Erignathus barbatus; walrus, Odobenus rosmarus; and polar bears, Ursus maritimus. Small pinnipeds, such as ringed seal and spotted seals, Phoca largha, were often difficult to differentiate and identify to species given the relatively high survey altitude of 310 m (1,000 ft). Habitat partitioning was evident among the cetacean species observed in greatest numbers: bowhead, gray, and beluga whales. Abundance estimates during this time period ranged from 22 (CV 0.80) to 213 (CV 0.30) bowhead whales, 1 (CV 1.01) to 18 (CV 0.28) gray whales, and 0 to 948 (CV 0.66) beluga whales. Standard deviation ellipses showed each species occupied a unique region within the study area with slight overlaps occurring in some years. Bowhead distribution was oriented along the barrier islands and 20 m isobath on the continental shelf and also included parts of the Barrow Canyon and shelf break that were close to shore. Gray whale distribution oriented along the Barrow Canyon shelf break near the 50 m isobath; while beluga distribution ellipses centered over Barrow Canyon and offshore slope waters. A four-parameter presence-absence model (bathymetry, bathymetric slope, distance from shore, and distance from the shelf break) found both distance from shore and shelf break were significant in predicting the presence of bowhead whales. All four parameters were significant in predicting gray whale presence. Only bathymetry was significant in predicting beluga whale presence. During the 5-year study, 664 unique bowhead whales were identified from 1,415 photographic images. Observers noted feeding behavior during 7–50% of sightings and 15–49% of photographed whales exhibited feeding behavior in any given year. Of the individual whales that were visually or photographically identified as feeding, 81–90% were in shelf waters, and the majority of those were clustered around the 20 m isobath. More feeding behavior was observed and photographed during years when most sightings occurred on the shelf (2007, 2009, and 2010) but not necessarily in years when bowheads were most abundant in the study area (e.g., 2008 and 2010). The lowest percent feeding both visually and photographically occurred in 2008, the only year whale swim direction was predominately westerly, and open mouth (skim) feeding behavior was not observed. Although the paucity of individual resightings (based on photographic recaptures) between survey days (3 matches out of 664 identified whales) suggested very low residence times, the photogrammetric sample (654 whales) was largely comprised of juveniles (65%). Young whales typically are unmarked and, therefore, not matched (only 3–6% were highly or moderately marked in at least one zone on the body). All intrayear matched whales moved east of their original sighting location, which was not expected so close to the westbound fall migration. The BOWFEST aerial study provides a 5-year record of late summer presence of cetaceans in the western Beaufort Sea, adding to the growing body of knowledge on these species and their habitat preferences in this region. This information is particularly important since the western Beaufort Sea is undergoing rapid change as the bowhead whale population continues to grow, other species extend their ranges and increase their numbers in the area, and industrial activity, commercial fishing, and shipping operations are expected to increase in the Arctic as sea ice decreases.