In the late 1980s, the longline fishing industry in Hawaiian waters exploded. And at practically the same time, the population of false killer whales (Pseudorca crassidens) that reside around the Main Hawaiian Islands began a spectacular decline.
The answer to that question lies outside the scope of the investigations undertaken by scientists with the National Marine Fisheries Service to determine the level of extinction risk facing this population of false killer whales – the insular population, as it is called, to distinguish it from the open-ocean, or pelagic, false killer whales that have little interaction with them.
According to the status assessment of the insular stock of the false killer whales prepared by the Pacific Islands Fisheries Science Center in response to a petition to add them to the federal endangered species list, the threat from interactions with gear from Hawai`i’s commercial fleet is by no means the only factor putting their survival in jeopardy.
There is more, including:
- A decline in the amount and size of the prey fish consumed by false killer whales;
- Competition with commercial fishers for prey;
- Environmental contaminants, including persistent organic pollutants such as dieldrin, DDT, and PCBs, which accumulate in the fatty tissue of large ocean predators; and
- The possibility that changes in ocean chemistry associated with increased levels of atmospheric carbon will have a negative effect on the availability of prey.
The good news is that the level of threats posed to the insular population of false killer whales by certain activities prevalent two decades ago has been reduced. These include the live capture of the animals, which ended in the early 1990s, and the establishment in 1992 of a longline exclusion zone, varying seasonally from 25 to 75 miles, around the Main Hawaiian Islands.
The most obvious impact that fishing has on false killer whales consists of the injuries that occur when the animals have run-ins with the lines, hooks, or other gear used by fishers. The hooks, ingested when the false killer whales take bait or fish from lines set by fishing vessels, can cause serious injury or even death, depending on where the hook is lodged. Strong monofilament line can also injure the whales, resulting in disfigurement or loss of flippers or fins.
Since the imposition of the exclusion zones, however, longline gear is not so much a problem as possible interactions with fisheries that operate closer to shore, including the shortline or kaka-line fisheries, and troll and handline fisheries (including bottomfishing). Assessing this risk is difficult, however, given the fact that they are not subject to strict regulation or the requirement to carry observers. Consequently, while the scientists placed the current overall threat from interactions with longline fisheries at 1 (on a scale of 3, with 3 being the highest), the threat from interactions with the troll, handline, shortline, and kaka-line fisheries was placed at 3.
Competition for Prey
While the likelihood of entanglement with longline gear has been reduced, the longline fishery continues to pose a threat to survival of the insular population of false killer whales by reducing the availability of prey. Scientists on the status review team judged this to have been a more serious risk (level 3) in the past than at present (level 2). Competition for prey from the smaller commercial fleets, including troll, shortline, kaka-line, and handline vessels, was also given a 2.
The scientists attempted to quantify this threat by evaluating the total energy demands of the insular population and comparing that to what is taken by the commercial fisheries that target the same fish. “Based on a diet composed entirely of one of the most commonly observed prey (mahimahi), the energy needs of the insular population were estimated as the number of fish potentially consumed on an annual basis,” the report states. “By dividing the total annual caloric needs of the whale population by the caloric value of an average-sized (8 kg) manimahi… approximately 2.9 to 3.9 million pounds of fish would be consumed annually. For comparison, this quantity of fish is similar to the current annual retained catch in the commercial troll fishery and 3 to 4 times greater than the annual catch in the Main Hawaiian Islands handline fishery.”
To investigate further the possibility that the whales face competition for prey from the fishing industry, the scientists then looked at catch rates from the longline fishery. These rates are stated as catch-per-unit-effort (CPUE), expressed as pounds of fish caught per 1,000 hooks set. From a high of nearly 4,000 pounds per 1,000 hooks set in 1953, the longline CPUE has declined to 500 pounds per 1,000 hooks set in 2008. Even as the CPUE rate dropped, the volume of fish retained has soared: from just under 5 million pounds in 1953, to four times that in 2008. Using the CPUE rates as a proxy for the abundance of fish, the scientists concluded that overall abundance of prey available to the false killer whales has been diminished by Hawai`i fisheries.
“A primary assumption in most ecosystem approaches to understanding multispecies population dynamics is that prey biomass fluctuations have a strong influence on predator populations,” the scientists wrote. “If they do, then fishery removals of potential prey in the immediate vicinity of false killer whales (competition), as well as long-term declines in prey biomass over the range of the fish stocks (declining CPUE and biomass) both represent potential threats to Hawaiian insular false killer whales.”
Decreasing Fish Size
The size of prey animals is another factor considered by the scientists on the panel that prepared the status review. “Concern over fish size is based on the hypothesis of increased foraging success with greater energetic reward per successful predation event,” according to the report. In other words, assuming that the amount of energy spent chasing a small fish is the same as that spent chasing a large fish, there’s a “greater energetic reward” when larger fish are caught. If average fish size is diminishing over time, that means that more energy will have to be spent in the effort to obtain prey. In light of the fact that average sizes of tuna and marlin caught commercially have been reduced over the last half century, the scientists assigned an overall level of 2 to this particular threat.
The accumulation of persistent organic pollutants in fatty tissue is something that affects not just false killer whales, but all top oceanic predators. Samples of blubber taken from the insular population showed high levels of PCBs and DDTs, the status review noted. While the levels continue to grow in males throughout their lives, adult females have relatively low levels, having passed these chemicals on to their offspring. This helps explain the fact that subadult whales were found to have higher levels of many such compounds – including dieldrin, polybrominated diphenyl ethers, and hexachlorobenzene – in their blubber than adults. “These young, developing whales may be at higher risk of exposure to these toxic compounds than adults,” the review states. “First-born may be particularly at risk as they receive the highest doses of POPs from their mother compared to subsequent offspring.”
Concentrations of POPs found in three of the nine tissue samples taken from insular false killer whales were greater than the levels associated with a number of biological effects (17,000 nanograms per gram of lipid weight). And, while production and use of some of the chemicals has ceased in Hawai`i, the scientists noted that many of the chemicals continue to be added to nearshore waters. “Activities related to tourism, agriculture, defense, the principal economic contributors in the Main Hawaiian Islands, as well as ongoing coastal development processes … can be potential sources of POPs to nearshore coastal waters in this region,” they wrote.
Overall, they assigned a threat level of 2 to environmental contaminants.
The lack of regulatory mechanisms was assigned a medium (level 2) risk by the review’s authors. While vessels in the longline fishery have carried observers since 1994, the false killer whales with which they interact are thought to belong to the pelagic stock, not the insular population. The fisheries whose grounds overlay the region inhabited by the insular population are regulated, if at all, only lightly.
According to the status review, interactions between these fisheries and the insular false killer whales are most likely to occur in the kaka line and shortline sectors. Although catches by these two fisheries accounted for less than 2 percent of catches by troll and handline fisheries operating in the range of the insular false killer whales, “based on the similarity of [kaka and shortline fisheries] to longline fisheries with respect to gear type and target species,” the scientists write, “it is likely that false killer whales are involved.” An increase in the catch in 2008 “suggests that the shortline fishery could expand rapidly.” What’s more, the fact that the kaka and shortline fisheries involve a series of stationary hooks “with multiple catch online at once” could make it “more attractive and rewarding to a false killer whale group than a few handlines or moving troll lines,” the authors wrote.
Small Population Effects
When populations fall below a certain level, the risk of extinction grows, and not just as a result of inbreeding. “As the number of individuals decreases,” the status report authors wrote, “there are costs,” which include the group’s diminished ability to defend itself, a possible breakdown of cooperative feeding, decreased birth rates as a result of a scarcity of potential mates, genetic issues, and combinations of these factors. With a population estimated at roughly 120 (about 50 more if the population of false killer whales around Kaua`i is included), and a breeding population of less than half that, the risk of reduced genetic diversity to the insular stock was set at level 2. Inbreeding depression and other factors associated with small population size were also assigned a score of 2. Taken together, the risk of extinction posed by the small population was deemed to be high.
High Extinction Risk
In their conclusion the authors wrote, “The small population size and evidence of a decline in Hawaiian insular false killer whales, combined with several factors that are likely to continue to have, or have the potential to adversely impact the population in the near future, describe a population that is at high risk of extinction.”
Mitigation Measures for All False Killer Whales
In July, the False Killer Whale Take Reduction Team issued its preliminary report on ways the fishing industry could lower the number of animals injured in interactions with gear. NMFS set up the17-member team early this year, after it was sued over its failure to do so, in violation of the Marine Mammal Protection Act. (The litigation is now before the 9th U.S. Circuit Court of Appeals. A denial of the claims of the plaintiffs in U.S. District Court in Honolulu led to the appeal to the 9th Circuit. When NMFS then created the Take Reduction Team, the plaintiffs sought to have the case before the 9th Circuit declared moot. NMFS agreed, as did intervenor Hawai`i Longline Association. The motion to dismiss is pending.)
The TRT was concerned with reducing the harm to all false killer whales in the area fished by all sectors in Hawai`i’s commercial fleet. Under the MMPA, the take reduction plan developed by the team has to be aggressive enough so that, within six months of its implementation, the number of animals harmed by commercial fishing is less than the maximum number of animals that can be removed each year from its population (not counting natural mortalities), while still allowing the population to reach or maintain its optimal level. (This level is called the potential biological removal, or PBR.) Within five years of the plan’s implementation, levels of bycatch should approach zero (or, in any event, no more than 10 percent of the population’s PBR).
Recommendations included in the draft take reduction plan included “soft” ones (beefed-up training of owners and captains; increased reporting requirements; translation of educational materials into Vietnamese and Korean as well as “pictorial depictions” to reach illiterate crew members) and “hard” ones, involving changes in gear and fishing practices. Two of the most promising involve the use of circle hooks (which may reduce injury to animals that ingest them) and weak hooks (hooks that straighten out when a false killer whale tries to take a fish that’s already hooked).
If bycatch is not reduced, the TRT has proposed closing waters to tuna-targeting longliners south of the Main Hawaiian Islands. The so-called Southern Exclusion Zone would extend out to the southern EEZ around the islands, from 154.5 degrees W (in the east) to 165 degrees W. The closure would remain in effect from the time a second serious longline interaction with a false killer whale is observed until the end of the calendar year.
According to Nancy Young of the Honolulu NMFS office, no timeline has been set for implementing the take reduction plan. However, the longline fishery has an incentive to reduce the number of animals it takes. First, there’s the threat of increased restrictions if the take level is not reduced. Then, too, any measure that discourages false killer whales from taking fish off their lines means money in the hold.
The NMFS Status Review of Hawaiian Insular False Killer Whales (Pseudorca Crassidens) under the Endangered Species Act is available online:
The Draft False Killer Whale Take Reduction Plan prepared by the Take Reduction Team is also online:
For more information and photos on false killer whales in Hawai`i, visit the website of Cascadia Research Collective:http://www.cascadiaresearch.org/hawaii/falsekillerwhale.htm
We gratefully acknowledge the permission of Cascadia Research Collective members Dan Webster and Robin Baird for the use of photos in this article. Photos were taken under NMFS scientific research permit 731-1774.