January 1, 2009
Pygmy Killer Whales Stay Close To Hawaiian Islands
A new study of pygmy killer whales shows that those living off Hawaii tend to stay close to the islands and don't swim out to the open ocean, researchers said.
One of the least understood marine mammal species, there are very few of the whales (probably less than 200 individuals) in this distinct pygmy killer whale population off the islands.
The research published Tuesday in the journal Marine Mammal Science suggests the population's limited number makes it more vulnerable than other whale populations to potentially harmful human behavior, including fishing and Navy sonar.
Robin Baird, a marine biologist with the Olympia, Wash.-based Cascadia Research Collective, said it is much more likely that human activities could impact and hurt the population.
The research was based on an ongoing photo identification project launched in the mid-1980s by Daniel McSweeney of the Wild Whale Research Foundation in Holualoa on the Big Island.
The study examined 3,431 photos of pygmy killer whales taken over 22 years. Most of the whales were spotted off the Big Island, though a few were found off Oahu, Lanai and Niihau.
Photos were used to distinguish the whales by their body scars, dorsal fin shapes and other distinctive characteristics. Researchers repeatedly came across the same whales, including one individual who was spotted over a 21-year period.
Pygmy killer whales appear to be social animals, with many staying close to other individuals for at least 15 years, the study found. Their stable, long-term relationships resemble the social behaviors of killer whales and pilot whales.
The elusive pygmy killer whales are found in tropical and subtropical waters around the world, but are among the least understood toothed whales, in part because they generally live in the open ocean and so are harder for scientists to study.
Hawaii's group was the only known case of a pygmy killer whale population that remained isolated in one area and didn't venture out to the open ocean, Baird said.
The pygmy killer whales were spotted, on average, about 3.7 miles from Hawaii shores. The furthest offshore sighting was at 9.3 miles.
"Hawaii's pygmy killer whales, like Cuvier's beaked whales and almost 10 other whale and dolphin species living in island waters, don't venture far because there isn't much food for them just outside Hawaiian waters," said Baird.
The whales tend to stay near the islands, their most reliable source of food.
However, Hawaii's pygmy killer whales are so rare that they accounted for only 11, or 1.2 percent, of 889 whale and dolphin sightings the researchers made off Hawaii between 2000 and 2007.
The small numbers of the pygmy killer whale stand in contrast to the humpback whale. It is an endangered species yet as many as 10,000 individuals migrate to Hawaii's waters from Alaska to breed and calve each winter. But Baird said the small number of pygmy killer whales made it difficult to monitor for harmful effects of human activity.
"They're encountered so infrequently that any particular population of the species could be dramatically declining and we would never know it," Baird said. "That's one of the problems with very rare species."
According to the study, there has been no documented case of a pygmy killer whale being hurt by sonar, however, there's low probability anyone would be able to document such harm given the whales are so rare and because they generally spend their time miles offshore.
But environmentalists maintain that the Navy's mid-frequency active sonar can disrupt whale feeding patterns, and in the most extreme cases can kill whales by causing them to beach themselves.
While the Navy has acknowledged that its sonar"”used to hunt enemy submarines"”may harm some marine mammals, it says it takes steps to protect whales, including having ships power down their sonar when whales are nearby and posting marine mammal lookouts on deck.
Another potential human source of harm to pygmy killer whales includes offshore fishing, but the study said there has been no report of a pygmy killer whale dying as a result of Hawaii's long-line tuna and swordfish fishery.
However, the mouth of a pygmy killer whale that stranded on Oahu in 2006 had hook and line marks, indicating fishing lines affect the animals.
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