ACS Research Committee Report

SOCIAL STRUCTURE OF BOTTLENOSE DOLPHINS IN THE BAHAMAS
Source: Rogers, C.A., Brunnick, B. J., Herzing, D.L., and Baldwin, J.D. 2004. The social structure of bottlenose dolphins, Tursiops truncates, in the Bahamas. Mar. Mamm. Sci. 20 (4): 688-708.

The social structure of offshore bottlenose dolphins is not well understood because most studies of this species have been conducted within only a few kilometers of shore. In the Bahamas, there are two communities of dolphins; one is close to shore (Southern dolphins) and one is over 27 kilometers offshore (Northern dolphins). However, both communities of dolphins are from the same population; they all are found in warm, shallow water and are relatively small in size compared to the dolphins found in the southeastern U.S. This study was conducted from May to September 1993 to 2002 on the Northern community of bottlenose dolphins off of Grand Bahama Island. During this study, 170 individual dolphins were identified. Total number of sightings for each individual ranged from two to 78 sightings. The difference in number of resightings indicates that only some of the dolphins were residents of the area, while some may be from other communities. Some individuals showed a site fidelity for up to 17 years. Group size ranged from one to 25, with a mean size of 4.58 individuals. Groups containing only one or two individuals made up 41% of the total groups. Mean group size was significantly higher in groups that contained a calf. Feeding and socializing groups were significantly larger than traveling groups. Associations were non-random, indicating that individuals seem to prefer to associate or avoid certain other individuals. Over half of the associations observed were between members of the same sex. These results indicate that these offshore dolphins have similar social structures to the better-studied coastal populations.    

EFFECT OF WATERCRAFT NOISE ON BOTTLENOSE DOLPHIN ACOUSTIC BEHAVIOR IN SARASOTA BAY, FLORIDA
Source: Buckstaff, K.C. 2004. Effects of watercraft noise on the acoustic behavior of bottlenose dolphins, Tursiops truncates, in Sarasota Bay, Florida. Mar. Mamm. Sci. 20 (4): 709-725.

Bottlenose dolphins in coastal areas must deal with a great deal of anthropogenic (human-produced) noise, but the greatest source may be watercraft. A resident community of 140 bottlenose dolphins in Sarasota Bay, Florida, are exposed to vessels passing within 100 meters about every six minutes in the daytime. This study looked for short-term changes in dolphin whistle frequency range, duration, and rate of production when these vessels were in close proximity. The duration and frequency range of dolphin signature whistles did not change significantly depending on vessel proximity. However, dolphins did whistle significantly more often when a vessel was approaching than when it was in close proximity, after it departed, or when no vessels were present. The increase in whistle production may indicate an increased arousal, an effort for the dolphins to communicate with and perhaps approach one another. The increase in whistle rate may also be a way for the dolphins to compensate for the noisier environment and ensure that information is being conveyed.    

MODELS INDICATE AN INCREASE IN THE ANTARCTIC BLUE WHALE POPULATION
Source: Branch, T.A., Matsuoka, K., and Miyashita, T. 2004. Evidence for increases in Antarctic blue whales based on Bayesian modeling. Mar. Mamm. Sci. 20 (4): 726-754.

Antarctic blue whales were heavily exploited in whaling efforts during the 20th century. Their estimated population size prior to the onset of whaling efforts was 239,000 whales. Whaling already had depleted the population to about 35% by the 1930s, but that number was halved again by the 1940s. The International Whaling Commission gave the Antarctic blue whales complete protection in 1964, but illegal Soviet whaling killed another 850 individuals between 1964 and 1973. In 1973, when observers became mandatory on all whaling vessels, the Antarctic blue whale hunt was over, but it left only about 360 individuals. In this study, Bayesian models were fitted to sighting records from 1968 to 2001 in order to determine the rate of increase of this endangered population. The models indicate that Antarctic blue whales are increasing at a mean rate of 7.3% annually. This rate of increase is fairly high compared to other blue whale populations in the world, but it is equivalent to some other baleen whale species. The estimated population size of Antarctic blue whales in 1996 was still only 1,700, which was only 0.7% of their pre-whaling numbers.   

ABUNDANCE AND POPULATION TREND OF WESTERN ARCTIC BOWHEAD WHALES
Source: George, J.C., Zeh, J., Suydam, R., and Clark, C. 2004. Abundance and population trend (1978-2001) of western Arctic bowhead whales surveyed near Barrow, Alaska. Mar. Mamm. Sci. 20 (4): 755-773.

A survey for western Arctic (Bering, Chukchi, and Beaufort Seas) bowhead whales was conducted from April to June, 2001, near Barrow, Alaska. Visual observers recorded 3,295 new bowhead whales, including 121 new calves. In addition, autonomous acoustic recorders ("pop-ups") were also used from April through May to locate bowhead whales. The pop-ups recorded 27,023 locations of vocalizing bowhead whales. From these data, the estimated number of bowhead whales in this area was 9,025. The two methods were combined to create a population estimate of 8,100 to 13,500 bowhead whales in this area. The estimated annual increase rate of the population from 1978 to 2001 was 3.4%. The rate of increase, as well as the high number of calves in 2001 indicate that this population is steadily recovering. This recovery is probably caused by a low rate of anthropogenic (human-caused) mortality, a healthy habitat, and a well-managed subsistence hunt. However, new anthropogenic impacts, such as offshore oil drilling and increased ship traffic, as well as sea ice retreat and ecosystem changes could have an impact and should be monitored.   

HISTORICAL OBSERVATIONS OF HUMPBACK AND BLUE WHALES IN THE NORTH ATLANTIC
Source: Reeves, R.R., Smith, T.D., Josephson, E.A., Clapham, P.J., and Woolmer, G. 2004. Historical observations of humpback and blue whales in the North Atlantic Ocean: Clues to migratory routes and possibly additional feeding grounds. Mar. Mamm. Sci. 20 (4): 774-786.

Humpback whales have been studied extensively in coastal feeding and breeding areas, but their migratory pathways are largely unknown. Blue whales have been studied in the Gulf of St. Lawrence, but their occurrence in other North Atlantic locations is also unknown. This study looks at the historical distributions of these two whale species using sighting and catch data from American 18th and 19th century whaling logbooks. These data suggest that the humpback whale migration route from the feeding grounds to the tropical breeding grounds was often offshore, rather than along coastal routes. In addition, there were humpback whales that fed along the Mid-Atlantic Ridge, which is well south of their modern feeding grounds, during the summer. It is unknown whether this offshore feeding area is still used by modern humpback whales. Blue whales occurred in the southern half of the North Atlantic during the fall and winter, but farther north during the spring and summer. Few data are available to suggest a migratory route for this species.    

UPDATE ON THE POPULATION STATUS OF NORTH ATLANTIC RIGHT WHALES
Source: Hall, L. 2004. North Atlantic right whale consortium meeting.

As of 2003, the catalog of North Atlantic right whales, held by the New England Aquarium, contains 342 right whales that are thought to be alive. There are an additional 100 animals that are presumed dead and 17 are known dead. There were at least 16 calves born in 2004. There were two known mortalities in 2004; they were a mother and a full-term fetus that died after a ship strike.    

A CASE OF ADOPTION IN A NORTH ATLANTIC RIGHT WHALE
Frasier, T.R., Hamilton, P.K., Brown, M.W., Kraus, S.D., and White, B.N. 2004. North Atlantic right whale consortium meeting.

Comparisons of North Atlantic right whale genetic and photographic databases found two mother-calf pairs in 1987 that were not genetically consistent with a mother and a calf. Further analyses indicate that the two calves were switched between the mothers. Both the genetic and photographic databases were rechecked for errors and both had multiple sightings/samples of the pairs during that year. Therefore, human error does not seem to have played a role in the inconsistency. The most likely explanation is that the two mother/calf pairs gave birth in close proximity and at approximately the same time, and then the calves switched mothers before the mother/calf recognition system had developed. The two calves remained with their "adopted" mothers throughout the lactation period.