Friday, October 31, 2008

Orcas, bottlenoses and other cetacean stuff

Hawai'i is known for its humpback whales. You can see them breaching from shore. You can take whale watch tours to get closer. And if you're a regular ocean user like a canoe paddler, sometimes you have to brake for whales.

Few folks know much about Hawai'i's other whales—many don't even know they're there.

(Image: A bottlenose dolphin leaping. Normally it's spinner dolphins that do the acrobatics in Hawaiian waters. Credit: Robin W. Baird/Cascadia Research.)

But they are. They show up occasionally in distress, like the dramatic black-and-white orca that washed ashore at Brennecke's Beach on Kaua'i last week—emaciated and near death, as its pod reportedly patrolled offshore.

In the San Juan Islands between Seattle and Vancouver, orcas are the whale of choice for whale-watching expeditions, just as humpbacks are in Hawai'i.

Orcas or killer whales are rare in Hawai'i, but not unheard of, said Robin Baird, of Cascadia Research. Baird is one of a premier researcher on whales in Hawaiian waters. Among local cetaceans, only false killer whales have a smaller population around Hawai'i, he said.

“They (orcas) are extremely uncommon around the Main Hawaiian Islands,” he said. Because they are so infrequently seen, little or nothing is known about their movement.

These days, in Hawai'i, monk seals are becoming more familiar to beachgoers, as the numbers in the Main Hawaiian Islands continue to grow. For folks who swim in the bays and nearshore waters, spinner dolphins are not uncommon.

Among dolphins, another species is also fairly readily seen, Baird said. That's the bottlenose dolphin. In a new paper published last week in Marine Mammal Science, Baird and co-authors say that an extensive review of photographic evidence indicates that bottlenose populations are homebodies.

Many marine mammals can be identified photographically by distinctive features like color and scar patterns.

They found that there are distinctive populations around each of the main Hawaiian Islands, including Ni'ihau, Kaua'i, O'ahu, Moloka'i, Maui, Lāna'i, Kaho'olawe and Hawai'i. There's considerable evidence that the same individuals show up in their home waters, and that they very infrequently move from one island to another.

“Dispersal among the different areas was estimated at less than 1% per year,” the authors said in a press release.

What this means for conservation is that they may need island-by-island protection.

“The evidence of multiple independent populations within the main Hawaiian Islands has a number of implications for conservation and management,” the authors said. “The fact that there are multiple isolated populations means that populations around any particular island (or group of islands) is smaller and more vulnerable to human impacts.”

Once again, the more you learn, the more you realize that on a species-by-species basis, there's no one-size-fits-all solution to managing natural resources.

Citation: Baird, R.W., A.M. Gorgone, D.J. McSweeney, A.D. Ligon, M.H. Deakos, D.L. Webster, G.S. Schorr, K.K. Martien, D.R. Salden, and S.D. Mahaffy. In press. Population structure of island- associated dolphins: evidence from photo-identification of common bottlenose dolphins (Tursiops truncatus) in the main Hawaiian Islands. Marine Mammal Science. DOI: 10.1111/j.1748-7692.2008.00257.x

URL to see a copy:

©2008 Jan W. TenBruggencate

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