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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.

Conservation of these animals, which 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 Duke University marine biologist are helping fill in those gaps.

Results of the surveys, published last 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. They also 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 Duke University 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 (toothed whales) in the waters of American Samoa, and assess the sustainability of their populations there,” he says.

Slideshow: Toothed Whales in American Samoa
Mid-Pacific Islands shelter at least a dozen species of Odontocete (view slideshow)

Observers documented the location of each sighting using geographic positioning systems. They 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 identifications of the species and to create a reference catalogue of the sighted animals.

“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 had been reported previously 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.

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

These comparisons revealed evidence of some gene flow between the island groups. However, the flow was low enough that spinner dolphins from American Samoa appear to be demographically discrete on an ecological timescale, and, thus, could be considered separate management units for conservation purposes.

Tourism and fishing are minimal threats to the dolphins and whales for now, but “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,” Johnston 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 assessing the stocks of several 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.

Robyn P. Walker is a first-year Master of Environmental Management student at Duke’s Nicholas School of the Environment.

Blog: Daily Mail Online