ACS Research Committee Report

DIVE BEHAVIOR IN RESIDENT KILLER WHALES
Source: Baird, R. W., M. B. Hanson, E. E. Ashe, M. R. Heithaus and G. J. Marshall. 2003. Studies of foraging in "southern resident" killer whales during July 2002: dive depths, bursts in speed, and the use of a "Crittercam" Number AB 133F-02-SE-1744 for the National Marine Fisheries Service, National Marine Mammal Laboratory, 7600 Sand Point Way N. E., Building 4, Seattle, WA, 98250 USA.

The feeding ecology of southern resident killer whales, which inhabit the waters between southern Vancouver Island and Washington, was investigated using time-depth recorder (TDR) and underwater camera ("Crittercam") tags. The TDRs recorded where in the water column the whales were feeding and the Crittercam was used to try to identify what species of fish they were feeding on. During July, 2002, eight killer whales were tagged, yielding a total of 79 hours of TDR data and one hour of crittercam footage. The maximum dive depth exceeded 228m (the limit of the tag), but the average maximum depth was 141m. In spite of these deep dives, only 2.4% of all dives were below 30m. The TDRs also documented increases in swimming speed and longer dive times, most likely due to feeding activity, during deep dives. The Crittercam footage recorded only surface travel and social behavior, so it could not verify a prey species during deep feeding activity. However, its successful attachment to a killer whale and recording of behavior makes it possible to use this methodology in the future to determine prey species.    

WHISTLES IN HAWAIIAN SPINNER DOLPHINS
Source: Lammers, Marc O. and Whitlow W. L. Au. 2003. Directionality in the whistles of Hawaiian spinner dolphins (Stenella longirostris): a signal feature to cue direction of movement? Mar. Mamm. Sci. 19(2): 249-264.

Dolphins produce frequency modulated whistles, which may promote synchrony and coordination of movement within groups. This study was conducted to determine if whistles have directionality, so that they can convey orientation of the whistling dolphin to other group members. In order to test this hypothesis, a towed 3-hydrophone array was used to record whistles of Hawaiian spinner dolphins. Whistles from dolphins that were moving toward the hydrophone array had higher amplitude and harmonic content than those swimming away. This indicated that the whistle had a directional "beam," which is intuitive because the bones of the dolphin's head would interfere with sound transmission in certain directions. There were different source levels recorded between hydrophones when an animal was nearby; through theoretical modeling, this difference was consistent with a model of a 10kHz whistle beam. Lower frequencies were less directional than higher frequencies and harmonics. Therefore, animals nearby to the whistler would hear the signal differently depending the whistler's orientation. The conclusion here is that whistles may facilitate group cohesion by informing dolphins of the orientation of other group members.    

ACOUSTIC DETERRENT DEVICES REDUCE MARINE MAMMAL BY-CATCH IN FISHERY
Source: Barlow, Jay and Grant A. Cameron. 2003. Field experiments show that acoustic pingers reduce marine mammal by-catch in the California drift gill net fishery. Mar. Mamm. Sci. 19(2): 265-283.

In order to reduce marine mammal by-catch, acoustic deterrent devices (pingers) were attached to nets in the California drift gill net fishery for swordfish and sharks. The by-catch rate was significantly lower for all cetacean species and for all pinniped species, when grouped together when pingers were used. However, when each species was analyzed separately, only short-beaked common dolphins and California sea lions by-catch was significantly less in nets with pingers. Other cetacean and pinniped species were not found to be significant, but the sample sizes were much lower. During the experiment, 74 marine mammals, over half of these common dolphins, were entangled in 609 sets. In both cetaceans and pinnipeds, the entanglement rate in nets with pingers was only one third of what it was in nets without these devices. The pingers did not seem to adversely affect the swordfish or shark catch. Due to the results in this study, new regulations were enacted to make pingers mandatory in the California drift gill net fishery.    

AGE-CLASS SEGREGATION OF BOWHEAD WHALES IN NORTHERN FOXE BASIN
Source: Cosens, Susan E. and Andries Blouw. 2003. Size- and age-class segregation of bowhead whales summering in Northern Foxe Basin: A photogrammetric analysis. Mar. Mamm. Sci. 19(2): 284-296.

There are two stocks of bowheads in the eastern Canadian arctic: one is distributed from Hudson Bay to Foxe Basin and the other from Baffin Bay to Davis Strait. Bowhead whales were aerially photographed in Foxe Basin from 1996 through 1998 to determine if they segregate by age. Female bowheads reach become sexually mature when they are approximately 13.5m in length. The number of whales that were less than 13.5m, or presumed to be juveniles, were 89.3%, 96.6%, and 79.3% in the three years of the study, respectively. The number of whales that were over 13.5m was directly proportional to the number of calves seen, indicating that all of these adults were most likely mothers. Adult males and resting (non-lactating) females were absent from the study area and perhaps were in other areas of this bowhead stock's range, such as northwest Hudson Bay. Foxe Basin seems to be an important area for juveniles and mothers with young-of-the-year calves.    

CALLS OF BRYDE'S WHALES
Source: Oleson, Erin M., Jay Barlow, Jonathan Gordon, Shannon Rankin and John A. Hildebrand. 2003. Low frequency calls of Bryde's whales. Mar. Mamm. Sci. 19(2): 406-419.

Call frequencies were typically less than 60 Hz from all areas. Bryde's whales have a tropical and subtropical distribution and do not migrate long distances, but rather shift toward and away from the equator in the winter and summer, respectively. Calls of Bryde's whales were recorded opportunistically in three geographic areas: eastern tropical Pacific (ETP), southern Caribbean, and northwest Pacific (near Japan). Bryde's whales were the most common species in all three of the study areas. In the ETP, sonobuoys were used to record whale sounds. A total of 104 calls were recorded and six call types were identified. The most common was a two-part, frequency-modulated call with an upper frequency of 37 Hz. In the Caribbean, sonobuoys recorded 31 calls and only one call type. The call identified in this region had a frequency of 44 Hz. and 2-3 harmonics. In the northwest Pacific, hydrophones recorded 22 calls and two call types. The first call had a short duration, a frequency of 46 Hz. and several harmonics; the second call was a pulsed moan with a frequency of 45 Hz. and harmonics that ranged up to 418 Hz. Future work may use these geographically distinctive calls to study the population structure of Bryde's whales.