Studies show dramatic decline of Hawaiian false killer whales
by Rob Parsons
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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.