SCIENTIST AT WORK: A PATTERN OF DOLPHINS
Scott Baker, associate director of the Marine Mammal Institute at Oregon State University, writes from Samoa, where he studies the formation of local communities among dolphins, and their genetic isolation from one another.
Sunday, August 5
Oceania, stretching across the Pacific from New Guinea in the west to Rapa Nui (Easter Island) in the east, is the largest expanse of island habitat in the world. Viewed from space, this ecozone is truly the “blue planet,” dotted with the emerald green of many thousands of islands, ranging in size from the smallest motu of an atoll in Tuvalu to the continental remnants of New Caledonia and the volcanic “high islands” of Hawaii and Tahiti. Encompassing the human cultural divisions of Melanesia, Micronesia and Polynesia, the more than 20 island nations and territories of this region represent only a small fraction of the earth’s landmass but, under the International Law of the Sea, control a large proportion of the world’s oceans and biodiversity.
An unknown number of islands in Oceania are home to local communities of dolphins. Unlike the large, nomadic herds of dolphins found in the open oceans, these island communities often number less than a few hundred individuals and show a strong attachment to specific islands. We think that in adapting to the local environment around each island, these communities have become genetically isolated from one another, and from the larger “founder” populations in the open ocean. But to survive and to continue to adapt, small populations must maintain genetic diversity through reproductive connectivity. As genetic diversity is lost by chance in one small population, it can be restored by the interchange and mating with individuals from other populations, near or far. In the dolphins, we expect this connectivity and isolation to be influenced by seascape features, like water depth and the distance between islands, but also social forces, like the size of local communities and even cultural specialization.
Our project seeks to describe this “pattern of dolphins” throughout Oceania. By collecting small samples of skin with a biopsy dart, we can access the “molecular archive” found in the DNA of each individual. With this, we can reconstruct the genetic relationships among individuals and communities and relate these to seascape features. Although we will collect samples from any of the species we encounter, our primary focus will be on the dolphins that seem to form local communities around the various islands – these are the spinner dolphins, bottlenose dolphins, rough-toothed dolphins and melon-headed whales (actually a dolphin with the wonderful scientific name Peponocephala electra).
Kahuora/Wikipedia.OrgMap with the cultural divisions of Oceania.
Our goals are twofold: first, to improve our basic understanding of dolphin diversity, and second, to provide guidance on the design of large marine protected areas under consideration for the region. These highly social and long-lived species are top predators and play an important but poorly understood role in the ecosystem of these islands. If large marine protected areas are to be successful in preserving biodiversity and ecological function, their design must provide for the different life history characteristics of top predators, like sharks and dolphins.
Recognizing that Oceania is simply too vast to survey exhaustively, I am working with colleagues from the South Pacific Whale Research Consortium to identify locations that will provide the first broad brush strokes of this seascape. For more than a decade, we have worked together on documenting the recovery of humpback whales on their breeding grounds in the South Pacific, using photo identification of tail flukes and genetic samples to estimate abundance and describe migratory movement. These populations had been devastated by the poorly regulated commercial whaling of the 20th century and, in particular, by the illegal whaling of the Soviet Union after World War II. Although our efforts were directed toward humpback whales, we also collected samples of dolphins whenever possible, contributing some of the first records for species lists in some of the more remote island nations. For our project, we are focusing on more directed surveys of dolphins in representative regions, including the Society Islands and the Marquesas Islands of French Polynesia in the east and the nations of the Solomon Islands and Vanuatu in Melanesia to the west.