The Natural Resources Defense Council has filed a lawsuit in federal court in Washington, D.C., to force the National Marine Fisheries Service to make a final listing decision on a dolphin species whose population numbers less than 200 individuals (NRDC v. Bryson, 12-826, D.D.C.).
“[W]e have determined that the Hawaiian insular false killer whale is a distinct population segment (DPS) that qualifies as a species under the ESA,” NMFS said in the proposal. “Moreover, after evaluating threats facing the species, and considering efforts being made to protect the Hawaiian insular DPS, we have determined that the DPS is declining and is in danger of extinction throughout its range.”
In addition, NMFS said:
Reduced genetic diversity, inbreeding depression, and other Allee effects associated with small population size represent a high risk to current and future Hawaiian insular false killer whales. The current estimated number of breeding adults (46 individuals) is so small that inbreeding depression could have increasingly negative effects on population growth rate and other traits, including social factors (such as reduced efficiency in group foraging and potential loss of knowledge needed to deal with unusual environmental events), may further compromise the ability of Hawaiian insular false killer whales to recover to healthy levels.
NMFS described the “Allee effect”:
The decrease in per capita population growth as population size declines is often referred to as the ‘‘Allee effect’’ or ‘‘depensation’’ (see references in Oleson et al., 2010) . In essence, as the number of individuals decreases there are costs from a lack of predator saturation, impaired anti-predator vigilance or defence [sic], a breakdown of cooperative feeding, an increased possibility of inbreeding depression or other genetic issues, decreased birth rates as a result of not finding mates, or a combination of these effects. The Allee effect increases risk to small populations directly by contributing to the risk of extinction, and indirectly by decreasing the rate of recovery of exploited populations and, therefore, maintaining populations at a smaller size where extinction risk is higher for a variety of reasons (Dennis, 1989; Stephens and Sutherland, 1999). In addition, social odontocetes (such as false killer whales) may be particularly vulnerable over and beyond the numerical loss of individuals to the population (Wade and Reeves, 2010).
In its complaint, NRDC said, “Since the mid-1980′s the Hawaiian insular false killer whale population has undergone a substantial and pronounced decline. NMFS estimates that the historic abundance of this population was around 769 whales, with a lower limit of 470 whales. Currently, the best estimates of the population size are around 150 whales. This represents a dramatic departure from historic abundance. Evidence suggests that much of this decline has occurred over the past 10-20 years, and while some threats to the species are apparent, the reason for the decline is not known.”
Honolulu Advertiser (5/23/12) (“The National Marine Fisheries Service recommended 18 months ago that the population be listed. Under federal law, the agency had one year to decide whether to do so.”)