Aerial Surveys to Study Bowhead Whale Feeding Ecology
The Bowhead Whale Feeding Ecology Study (BOWFEST) was initiated in May 2007 through an interagency agreement (IA) between the Minerals Management Service (MMS) and the National Marine Mammal Laboratory (NMML). The $5 million IA covered a 5-year period of study, which included field seasons in 2007, 2008, and 2009. Currently, the MMS is granting NMML an additional $3 million to continue the study for two more field seasons, with the whole program to be completed in 2012.
The study has been conducted by NMML scientists and (through grants and contracts from NMML) by scientists at the Woods Hole Oceanographic Institution, University of Rhode Island, University of Alaska Fairbanks, University of Washington, Oregon State University, and North Slope Borough Department of Wildlife Management (NSB DWM). Fieldwork has been coordinated with the NSB, MMS, Alaska Eskimo Whaling Commission, Barrow Whaling Captains' Association, and Alaska Department of Fish and Game.
BOWFEST focuses on late summer oceanography and prey densities relative to bowhead whale (Balaena mysticetus) distribution north and east of Point Barrow, between the Alaska coast and latitude 72°N and between longitudes 152°W and 157°W. Aerial surveys, boat-based surveys, and acoustic monitoring provide information on the spatial and temporal distribution of bowhead whales in the study area.
Figure 2. Sightings of bowhead whales near Barrow, Alaska, in 2007, 2008, and 2009 (top to bottom) during aerial surveys to study the whales' feeding ecology. The inner (more intensely covered) survey area is indicated with cross-hatchings; the outer (less surveyed) area is indicated by diagonal lines.
The aerial survey component of BOWFEST is designed to document patterns and variability in the timing and locations of bowhead whales. In addition, aerial photography provides information on residence times (through reidentification of individual animals) and sizes of whales (through photogrammetry).
With the consideration of acoustic mooring locations, preset oceanographic transects, bathymetric gradients, and distance from the base of operations (Barrow), a two-part study area and aerial-trackline sampling scheme was devised with an intensely surveyed inner area and reduced coverage in the outer area (Fig. 2).
Using a NOAA Twin Otter, NMML scientists conducted aerial surveys on 6 days (30.6 flight hours) between 23 August and 11 September 2007, 8 days (42.7 hours) between 27 August and 16 September 2008, and 5 days (18.0 hours) between 29 August and 18 September 2009. Options for flying were greatly limited by fog, low cloud ceilings, and high winds.
During these surveys, there were 10 sightings of bowheads (approximately 40 whales) in 2007, 56 sightings (approximately 163 whales) in 2008, and 25 sightings (approximately 52 whales) in 2009. In 2007, nearly all the bowheads appeared to be feeding as indicated by mud plumes and multiple swim directions; however, aerial observers could recognize feeding activity in only 4 of the 56 bowhead sightings in 2008 and 5 of the 25 sightings in 2009.
Examination of the photographs will provide more precise records of how many whales were feeding as evidenced by mud on the body, open mouths, and the presence of feces. "Traveling" was the most commonly recorded behavior, indicating that bowheads were most likely migrating through the study area. Most of the bowhead sightings were along a coastal tangent marked by the 20-m isobath (an estimated 85% (77 of 91) of the sightings were in water between 10 and 35 m deep or along a projection of this line to the west).
Results of this research program show that in late summer (mid-August to mid-September), bowheads are generally on a westward feeding migration through the study area, predominately along the 20-m isobath, and that most of the whales near Barrow are feeding on krill.
Prey densities increase on the shelf after upwelling, favorable east winds are followed by weak or southerly winds. This "krill trap" likely contributes to the high proportion of feeding whales seen in this area.
A good understanding of bowhead behavior and distribution, as exemplified by this study, is needed to minimize potential impacts from petroleum development activities, possible commercial fishing in the future, and the anticipated increase in vessel traffic associated with diminishing arctic sea ice.
