NATIONAL MARINE MAMMAL LABORATORY (NMML) (cont.)

Cetacean Assessment and Ecology Program

Cetacean Survey Aboard the Miller Freeman

Three marine mammal observers participated on a cetacean survey from 5 June to 3 July 2004 aboard the NOAA ship Miller Freeman as a piggyback project during an acoustic-trawl survey for walleye pollock conducted by the AFSC’s Resource Assessment and Conservation Engineering (RACE) Division. The primary objective was to document cetacean (whales and dolphins) distribution in waters of the southeast Bering Sea shelf and to collect line-transect data for abundance estimation. A secondary objective was to collect photo-identification and biopsy samples from selected species, including humpback and killer whales.

The pollock acoustic study surveys tracklines from near shore to the shelf break, providing an ideal format for a line-transect cetacean survey. Surveys to determine distribution and abundance of cetaceans are costly and, therefore, are often confined to coastal waters where the logistics are most practical, or to areas of the ocean where marine mammal mortality associated with commercial fishing is particularly high. The shelf waters of the Bering Sea have not met either criteria and so are comparatively under-sampled for cetaceans. The opportunity to use the Miller Freeman as a survey platform is, therefore, very beneficial to our studies. Multiple years of data are providing a clearer picture of cetacean distribution and abundance in the eastern Bering Sea.

Figure 2.  Completed track line and small cetacean sightings.

The cetacean survey was conducted from the flying bridge of the 215-ft long Miller Freeman. Two observers searched through 25x150 power binoculars at starboard and port stations. Observers were at an eye height of approximately 12 m, with ship speed roughly 11 kts during surveys. A data recorder searched the trackline with naked eye, using Fujinon 7x50 hand-held binoculars to confirm sightings. The observers rotated positions every half hour during a 2-hour shift, followed by a half hour break. The survey was suspended for meals, fishing operations, inclement weather, and when light levels were too low for efficient observations. If time permitted, the survey was suspended when humpback whales or killer whales were sighted to conduct sampling for photo-identification and biopsy collection.

Figure 3.  Completed trackline and whale sightings.

The survey included the shelf waters of the eastern Bering Sea (Fig. 2 above). Analyses of data from 6 to 30 June yielded a total of 2,032 km of trackline surveyed with 93 cetacean sightings (896 individuals). An additional eight cetacean sightings were made (32 individuals) during off effort periods. Species included harbor porpoise, Dall’s porpoise, Pacific white-sided dolphins, killer whales, minke whales, fin whales, and humpback whales (Table 1, Figs. 2 and 3). Pacific white-sided dolphins were seen only once in a very large school on the north side of the Alaska Peninsula, near an area where they have been seen on past surveys. Harbor porpoise were seen only four times, in a small area in the southern middle shelf area, while Dall’s porpoise distribution was more widespread across the more southern half of the survey area. Killer whales were seen predominantly around the Pribilof Islands, or near Unimak Pass. The six minke whale sightings were spread out across the western half of the survey area near the 100 m depth contour. Fin whales were seen only near the eastern edge of the survey, with none seen along the shelf break where the species has been common during past surveys. Humpback whale sightings were spread out, with most seen near shore from Akutan Island and west along the Alaska Peninsula. The most northerly sighting was a humpback whale approximately 300 km north of the Pribilof Islands.

The ship was stopped 11 times to collect photographs and biopsy samples; seven times for killer whales and four times for humpback whales. Photographs from these encounters will be analyzed to identify individuals and then matched to existing catalogues to look at movements and to be included in ongoing mark/recapture studies. Biopsy samples will be used for stock determination.

By Janice Waite

>>>continued

AFSC Quarterly Research Reports Apr-June 2004