Researchers study false killer whale found on Maui
Animal’s last meal offers insight into endangered species
Octopus remains were found in the belly of a rare false killer whale on Maui, a dietary discovery that researchers say could help the endangered species.
After a insular false killer whale was found dead on Maui in February, the University of Hawaii Marine Mammal Health and Stranding Lab examined the whale and identified 25 individual pelagic octopuses in its stomach, a previously unknown food item for the creature.
“We did not expect these big pelagic octopuses to be found in its stomach, that’s for sure,” said Kristi West, lab director and an associate researcher at University of Hawaii at Manoa’s Hawaii Institute of Marine Biology. “It points to just how every animal can tell us something about their life out there, in that we thought we had a pretty good idea about what false killer whales eat from prior strandings.”
False killer whales are the least abundant of all the large-toothed whales and live in the tropical and subtropical open ocean. In Hawaii, West said that there are three separate populations: an offshore population, a Northwestern Hawaii population and the insular population, which have been longtime residents of the main Hawaiian islands.
The typical meal plan for insular false killer whales includes diamondback squid, mahi mahi, ahi, ono and other fish that humans eat, but “we’ve never before seen prey items” on the menu.
“It’s really important to understand what these animals eat. They are endangered, of course, and we want to understand any pre-limitations that they may face and how they may act with fisheries,” West said. “It’s really important to understand what’s in their diet, but yeah, we were definitely surprised with this new, unexpected item.”
The question still remains as to whether this whale had been eating octopus throughout its whole life or just before its death.
Although the lab doesn’t have all the answers yet, West said in a news release that future research on the whale will include stable isotope analysis, contaminant analysis and body condition assessment at the time of stranding through blubber examination, which will provide more insight to diet, threats and behavior.
The whale has been monitored here for the past 20 years by the Cascadia Research Collective, West said, with its first sighting in 2000. It was last seen alive off Lanai in December.
By looking at the false killer whale’s teeth, West said that it was about 30 years old before it was found stranded last month. The species usually has a life span of up to 63 years for females and up to 58 years for males, according to NOAA.
“It was pretty decomposed when it was discovered, so I don’t know if our follow-up testing will be able to point to the cause of death, but we always try our best and we have a lot of analysis planned for the future to try and get the best picture possible,” she said.
The Hawaii Institute of Marine Biology noted that an insular false killer whale is the most critically at-risk species of dolphins and whales in Hawaiian waters.
It’s estimated that there are about 170 of them left among the main Hawaiian islands, West said, and are all identified in the Cascadia Research Collective catalog.
Although sad, West said that the stranding incident last month is a rare opportunity for the UH lab to examine an insular false killer whale — the last stranding in Hawaii occurred in 2016.
Aerial survey sightings since the 1980s suggest that the insular false killer whale population declined on average 9 percent per year through at least the early 2000s in Hawaii, according to NOAA.
The reason for the species’ decline is not entirely known, though West said that researchers have a few ideas.
One of the identified threats is false killer whales’ interaction with fisheries when they are searching for food, which can lead to unintentional entanglements, injury or death.
“We’ve had some stranded false killer whales in the past with hooks in their stomach that had been ingested during their attempts to interact with fisheries and gain food through the process,” she said. “Certainly understanding what all that they eat is important in looking at that problem.”
A lot of marine mammals also struggle with “nutritional stress” if they are not getting enough to eat or if food sources contain high levels of pollutants, which can lead to disease.
“Really the foundation to being able to assess that is knowing all the different things that this species likes to eat and is likely to eat so that we can keep an eye on prey limitations that could make an impact on the species,” she said.
UH partners with Cascadia Research Collective, the state Department of Land and Natural Resources and NOAA Fisheries to learn about false killer whales and the threats that they face.
West added that NOAA also creates Take Reduction Teams, which involves a group of experts that make a more immediate plan of action to protect an endangered species.
According to the organization, the goal of such plans is to reduce “the incidental mortality or serious injury of marine mammals from commercial fishing to less than the (potential biological removal) level” within six months of implementation.
Take Reduction Teams could also implement a five-year goal to save a species’ existence, taking into consideration the “economics of the fishery, the availability of existing technology and existing state or regional fishery management plans.”
For more information, visit www.fisheries.noaa.gov.
Researchers rely on the public for reporting any cases of distressed or dead dolphins and whales. To report strandings, call the NOAA Fisheries hotline at (888) 256-9840.
* Dakota Grossman can be reached at firstname.lastname@example.org.