Researchers have identified a disturbing crash in the population of false killer whales around the Hawaiian Islands.
Recent aerial surveys, compared with surveys in 1989, suggest a significant decline in numbers of overall whales as well as in the sizes of their pods.
(Image: NOAA photo of false killer whales off Hawaii by Robin Baird.)
The most recent reports were published in the journal Pacific Science by Randall Reeves, Stephen Leatherwood and Robin Baired, under the title, “Evidence of a Possible Decline since 1989 in False Killer Whales (Pseudorca crassidens) around the Main Hawaiian Islands.”
The animals are large members of the dolphin family, and evidence suggests there is a permanent population in the waters around Hawai'i that is genetically distinct from other false killer whale populations.
The 1989 survey found massive pods—some of which had far more whales in it than the entire statewide known population today.
“Groups of more than 300 individuals were seen on three different days, with minimum counts of 380, 460, and 470 individuals in these groups.
“The encounter rate, relative species ranking, and average group size from the 1989 survey were all substantially greater than those from more recent aerial and ship-based surveys.
“The largest group observed in 1989 (470) contained almost four times as many whales as estimated for the entire main Hawaiian Islands from recent aerial surveys,” says the paper abstract.
Current population surveys suggest it's not that all whale species have declined, but that this species has suffered particularly.
“In the 1989 general surveys off the island of Hawai‘i, the false killer whale was the third most frequently sighted species of the nine documented, representing 17% of all sightings.
“In 369 days of boat-based surveys around all the main Hawaiian Islands from 2000 through 2006, undertaken throughout the year, false killer whales accounted for only 1.5% of odontocete groups sighted, and the false killer whale was the 11th most frequently encountered species of odontocete,” the paper says.
What isn't clear is why the decline has taken place—are they short of food because of increased human fishing pressure, or is it something else? That's not yet clear, the researchers say.
For more information on false killer whales, see the NOAA website, http://www.nmfs.noaa.gov/pr/species/mammals/cetaceans/falsekillerwhale.htm, or visit http://www.cascadiaresearch.org/robin/falsekillerwhale.htm.
© Jan TenBruggencate 2009
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