Studies show dramatic decline of Hawaiian false killer whalesby Rob Parsons
Visitors and residents alike marvel at the sight of Hawaii's cetacean winter residents, the humpback whales. Due to a few decades of protected species status and continuing research, we know that their once-dwindling numbers have steadily rebounded.
But recent studies indicate a lesser-known species, Pseudorca crassidens, or the false killer whale, has the smallest population of the 18 species of toothed whales and dolphins found in Hawaiian waters. Robin Baird of Olympia, Washington-based Cascadia Research—a 30-year-old nonprofit founded by biologists at Evergreen State College—has studied marine mammals in the Hawaiian Islands since 2000. He's taken a keen interest in Pseudorca, and is helping to elucidate the reasons for their steady decline.
"Until recently," says Baird, "false killer whales hadn't received funding. Nobody was researching them." Studies and photographs by Dan McSweeney of the Wild Whale Research Foundation in the 1980s—and aerial surveys by University of Hawaii's Joe Mobley from 1993 through 2003—show a once vibrant population now in steep decline. Randy Reeves did aerial observations in 1989 that showed several large groups of Pseudorca off the Big Island's Kohala Coast, before the population crashed.
In fact, the surveys done by Reeves and Steve Leatherwood showed that the largest group sizes were almost four times larger than the entire current Hawaiian population estimate for false killer whales. It is now believed there are approximately 123 individuals in the insular Pseudorca population, which has been determined to be genetically unique. In other words, these whales are truly kama'aina. And they're in trouble.
"Tissue and DNA sampling by the Southwest Fisheries Science Center in LaJolla reveal that this island group has been isolated and has evolved here over tens of thousands of years," says Baird. "It is likely that as near-surface predators, they found more predictable, reliable feeding close to the islands."
As top-of-the-food chain feeders, Pseudorca subsists on mahimahi, yellowfin tuna, ono, monchong and other upper-trophic level fish. "Basically, they eat all the same kinds of fish that we do," says Baird.
Their feeding habits are a major factor behind their decline. Dwindling fish stocks mean more competition for their target foods, as their prey become more limited in numbers.
False killer whales are also known for taking fish off hooks, a behavior that has resulted in the creatures being killed as bycatch in open ocean longline fisheries. Whales and dolphins that accidentally ingest hooks, leaders and line may also perish from perforated intestines, an equally insidious threat. Observation of dorsal fin disfigurement is a probable indication of interacting with line fisheries. Placement of satellite tracking tags is done in part to determine the extent of this type of interaction.
Biopsies also show the toxic accumulation of substances such as PCBs and DDTs that compromise the animals' immune systems. With these substances stored in their blubber, they metabolize it more readily when their food supply is unstable.
All these threats point to the Hawaiian false killer whale as being the marine mammal species of greatest conservation concern. The Natural Resource Defense Council recently filed a petition with the National Marine Fisheries Service to list the species as threatened or endangered. If NMFS determines within 90 days that the petition has merit they will convene a biological review team to make an evaluation, a process that could take a full year.
"NRDC has been involved here for years," says Baird, "as has Earthjustice" (which sued NMFS over bycatch). "All our work is collaborative."
Baird, raised in British Columbia, worked with Maui as her home base in 2000-2001. The following year he expanded his work to the Big Island and Oahu. In 2003, the year he began working with Cascadia, they added waters surrounding Kauai to their studies. Baird now makes an average of three trips to Hawaii each year, and publishes results and photos of his work on Cascadia's Web site (cascadiaresearch.org/hawaii/falsekillerwhale.htm).
Photo-identification through unique dorsal fin markings show that Pseudorca form lasting bonds. They have long life spans (into their 60s), and are slow to reproduce, bearing one calf every six or seven years. Thus, their population is likely to be slow to recover from the numerous threats that have seen it rapidly dwindle over the past two decades.
Cascadia's Web site notes one unusual behavioral trait: "[Pseudorca] share their prey, not only with their companions, but also with humans. A Pseudorca that was alone in British Columbia and Washington from the late 1980s until a few years ago, far from their normal range off Mexico, repeatedly caught large salmon and would offer them to boaters. In Hawaiian waters, Pseudorca have offered fish to human snorklers and divers."
The Web link also features an animation display of the movement of five individuals with satellite tags over a ten-day period. They range from waters off South Point, to Kohala, nearly to Hilo and back again. Baird says that earlier this week, two whales were spotted off Oahu's North Shore, another at Penguin Banks and a fourth off the north tip of the Big Island.
Tagging follows the same protocol used over the past 20 years for whales and dolphins, with a small titanium dart attached to the dorsal fin. "Usually the tags stay on about a month," says Baird, "but they have lasted as long as 76 days."
Clearly, greater attention is needed to assure the long-term survival of Pseudorca, and to help them rebound to numbers seen as recently as two decades ago. Given the existing threats and plummeting numbers, the scientific studies Baird is doing with his colleagues and collaborators may be essential to pulling the species back from the brink of extinction.