Saturday, June 12, 2010

"Our" false killer whales

A new study of false killer whales in the Pacific indicates that, well, the ones around Hawai'i are homebodies.

That is, they not only tend to hang around the Islands, but they also seem to limit their breeding to the community of false killer whales around Hawaii.

(Image: A leaping false killer whale. Credit: Robin W. Baird, Cascadia Research Collective.)

A new paper by marine researchers and geneticists looks into genetic tests taken of whales around the world, but primarily in the Pacific and Indian Oceans. It found there's a group of whales, related to each other, that seem to be regularly found around Hawai'i.

Oddly, false killer whales found in Hawai'i waters can include representatives of both this local population of whales, and the larger population of Pacific and Indian Ocean whales.

For humans, the local and wide-area whales can be told apart, so far, only by genetics.

But they clearly can tell each other apart.

“Hawai‘i insular false killer whales have both a low estimated current abundance and strong social structure , though details of the mating system remain unknown,” says the paper, which was published in May 2010.

This research builds on previous work, but is hardly the end of the story.

“Given that false killer whales are a naturally uncommon species, many decades will likely be needed to collect samples that adequately represent their distribution,” the paper says.

Once concern is that a population of only a few dozen whales may be genetically at risk. It is not clear whether the group occasionally allows a non-local whale to join the gene pool.

“We estimate that the effective population size of Hawai‘i insular false killer whales is less than 50 animals. This population is probably naturally small with a strong social structure that limits genetic diversity,” the paper says.

“Although no data are available for calculating trends in abundance for Hawai‘i insular false killer whales, observational data suggest abundance may have declined precipitously over the last two decades,” it says.

Among the things unclear in false killer whale research is whether other island or coastal areas have similar distinct populations of the animals. It does happen regularly with other marine mammals.

“There are several other examples of cetaceans that have morphologically and genetically differentiated units occupying adjacent coastal or island habitats and pelagic habitats. These include coastal or island populations of pantropical spotted dolphin, common and Indo-Pacific bottlenose dolphins, spinner dolphin, and short-finned pilot whale. Knowledge about false killer whales occupying other island and coastal habitats around the world would be valuable to interpreting the results presented here,” the paper says.

The study is entitled “Evidence of Genetic Differentiation for Hawai'i Insular False Killer Whales (Pseudorca crassidens).”

Authors are Susan J. Chivers, Robin W. Baird, Karen M. Martien, Barbara L. Taylor, Eric Archer, Antoinette M. Gorgone, Brittany L. Hancock, Nicole M. Hedrick, David Matilla, Daniel J. McSweeney, Erin M. Oleson, Carol L. Palmer, Victoria Pease, Kelly M. Robertson, Jooke Robbins, Juan Carlos Salinas, Gregory S. Schorr, Mark Schultz, Janet L. Thieleking and Daniel L. Webster. They include representatives of government and private institutions from Hawai'i, the Mainland, Australia and Mexico.

Also see some of our previous posts on this topic here and here and here.

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© Jan TenBruggencate 2010

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