DURHAM, N.C. – Historic whaling records and anecdotal sightings have long suggested that many species of whales and dolphins live or breed in the remote waters of American Samoa, the only U.S. territory in the Southern Hemisphere.

Yet conservation of these animals, which for management purposes are considered protected species under the U.S. Marine Mammal Protection Act, has been hindered by a lack of scientific data on their abundance, distribution, composition and stock structure.

Two surveys led by a 91 marine biologist are helping fill in those gaps.

Results of the surveys, published this month in the Journal of Cetacean Research and Management, confirm the presence of at least seven species of whales and dolphins previously believed to live or breed in American Samoa, and provide the first confirmed sightings of four additional species: bottlenose dolphins, false killer whales, rough-toothed dolphins and dwarf sperm whales.

“Our findings give resource managers some of the essential missing information they need to develop long-term conservation strategies for these protected populations,” says David W. Johnston, a research scientist at the 91 Marine Lab in Beaufort, N.C. 

“Data generated from our surveys, and from comparative genetic tests of stock structure we performed, provide baseline information for future efforts to quantify the abundance and structure of management units of odontocete cetaceans in the waters of American Samoa, and assess the sustainability of their populations there,” he says.

American Samoa is located 14 91s south of the equator in the central Pacific Ocean, about halfway between New Zealand and Hawaii. About 64,000 people live on its four main volcanic islands and two coral atolls, which, combined, cover an area only slightly larger than Washington, D.C.

Between 2003 and 2006, Johnston and colleagues from the National Oceanic and Atmospheric Administration (NOAA) and the University of Hawaii conducted a series of small-boat surveys of cetaceans in the coastal waters of American Samoa’s largest island, Tutuila. They conducted four surveys during the austral winter and one in austral summer. In 2006, they conducted surveys from aboard the 68-meter NOAA oceanographic research vessel Oscar Elton Sette in coastal and offshore waters of three smaller islands, Ofu, Olosega and Ta’u, and two outlying coral atolls, Swains Island and Rose Atoll.

“All told, we encountered a total of 58 groups of dolphins or whales, including spinner dolphins, rough-toothed dolphins, sperm whales, false killer whales, bottlenose dolphins, dwarf sperm whales, short-finned pilot whales and three groups of unidentified odontocetes,” Johnston says. Some of these species previously had been reported in the region’s waters, but most of those reports were based on single observations, anecdotal reports and opportunistic sightings, whaling records, or periodic reports of stranded animals.

“Ours were the first scientific surveys dedicated for this purpose,” Johnston explains.

Observers onboard the vessels documented the location of each sighting using geographic positioning systems and estimated the size of the groups that were spotted and the depth of the water at each encounter. Whenever possible, they took high-resolution digital photographs of the animals, which were later used to confirm species identifications and create a reference catalogue of sighted animals.

The scientists collected skin or blubber biopsies from about two-thirds of the encounters. To investigate stock structure, they compared genomic DNA extracted from 16 tissue samples of spinner dolphins from American Samoa to samples collected from spinner dolphins off the Big Island of Hawaii.

Comparative tests of mitochondrial region diversity and allele frequencies between spinner dolphins from these two regions revealed that the dolphins from American Samoa have a higher genetic diversity and were genetically distinct from those from Hawaii, Johnston explains. The tests revealed evidence of some gene flow between the island groups, but it was low enough that spinner dolphins from American Samoa appear to demographically discrete on an ecological timescale, and, thus, could be considered separate management units for conservation purposes.

Unlike many other South Pacific island groups, American Samoa has limited coastal development and ecotourism, suggesting that threats to dolphins and whales from these sources may be minimal. Threats from bycatch mortalities – which can occur when species like dolphins and whales accidentally become ensnared in fishing gear – may pose more of a concern. No mortalities have yet been reported in American Samoa, but Johnston says there is ample evidence of bycatch in nearby Independent Samoa. And the longline commercial fishery in American Samoa, he notes, has only recently begun posting independent by-catch observers on its fishing vessels.

“It’s important that we give resource managers in the region the information they need to devise management plans to deal with these threats if and when they arise,” he says.

Further studies will be needed to assess these potential threats, he says, and to estimate more fully the diversity and abundance of the cetaceans in the region’s waters. Additional genetic and photo-ID studies will help establish the relationships between cetaceans sampled in American Samoa and those found in nearby Pacific Island Region nations. In particular, coordinated surveys with researchers in Independent Samoa would be useful for stock assessments of several of the species, such as spinner dolphins and bottlenose dolphins.

Johnston’s collaborators on the research were Jooke Robbins of the Provincetown Center for Coastal Studies; Marie Chapla Hill of the University of Hawai’i at Manoa’s Joint Institute for Marine and Atmospheric Research and the Pacific Islands Fisheries Science Center; David Mattila of the Hawaiian Islands Humpback Whale National Marine Sanctuary; and Kimberly Andrews of the Hawai’i Institute of Marine Biology.