Figure 1. The National Marine Mammal Laboratory conducts searches for gray whales using only one observer in a small shed.
Figure 2. The Southwest Fisheries Science Center conducts searches with two observers in a comfortable trailer.
The National Marine Mammal Laboratory (NMML) has been responsible for providing abundance estimates of gray whales (Eschrichtius robustus) most years since the mid-1960s. Counts used in these estimates have come from shore-based counts conducted at Granite Canyon in central California. However, starting in 2008, the gray whale census is being conducted by the Southwest Fisheries Science Center (SWFSC). Now NMML’s role in the gray whale census is to assist in the transfer of information, document procedures, and provide parallel counts to compare the old counting protocol to the new methods used by the SWFSC.
For example, NMML has maintained the basic technique of one observer searching alone for whales and writing the data by hand on a field form (Fig. 1). In contrast, the SWFSC operates with pairs of observers, with one observer dedicated to searching for whales while the other assists with the search and types the data into a computer (Fig. 2). The computer program shows the SWFSC observers where whale groups have been sighted and predicts where they should look for subsequent sightings of the same groups.
Throughout most of January, one to three NMML observers rotated through 3-hour watches, sitting in a small, wooden shed on the edge of a 22-m sea cliff. Meanwhile, from 2 January to 9 February, SWFSC observers rotated through 1.5-hour watches while conducting an independent effort in a nearby trailer.
As in most recent years, observations through a fix-mounted, high-powered (25X) binocular provided an index of the offshore distribution of whales within the observers’ viewing range. The SWFSC will provide an abundance estimate, and both NMML and the SWFSC will conduct an analysis of how well matched the two sighting efforts were.
By David Rugh
Bowhead Whale Feeding Ecology Study
The National Marine Mammal Laboratory (NMML) received funds from the Department of the Interior’s Minerals Management Service (MMS) for a 5-year $5,095,000 study of bowhead whale (Balaena mysticetus) feeding ecology, starting in 2007. This study focuses on late summer oceanography and prey densities relative to whale distribution over continental shelf waters within 100 miles north and east of Point Barrow, Alaska. Participating researchers from NOAA Cooperative Institutes are from the Woods Hole Oceanographic Institution, University of Rhode Island, University of Alaska–Fairbanks, University of Washington, and Oregon State University. Fieldwork is coordinated with the North Slope Borough, Alaska Eskimo Whaling Commission, Barrow Whaling Captains’ Association, Alaska Department of Fish and Game, and MMS.
Aerial surveys and acoustic monitoring provide information on the spatial and temporal distribution of bowhead whales in the study area. Oceanographic sampling helps identify sources of zooplankton prey available to whales on the shelf and the association of this prey with physical characteristics (hydrography, currents) which may affect mechanisms of plankton aggregation. Prey distribution will be better understood by examining temporal and spatial scales of the hydrographic and velocity fields in the study area, particularly relative to frontal features. Results of this research program may help explain increased occurrences of bowheads feeding in the western Beaufort Sea (in U.S. waters), well west of the typical summer feeding aggregations in the Canadian Beaufort Sea. Increased understanding of bowhead behavior and distribution is needed to minimize potential impacts from petroleum development activities.
