Hawaiian False killer whale numbers in steep decline

False Killer whale leaping from the sea. c) Robin W. Baird/www.cascadiaresearch.org

February 2010. Pseudorca, or false killer whales, are a large toothed whale that lives in the tropical and sub-tropical open ocean. In Hawaiian waters there is a small population associated with the main Hawaiian Islands that are long-term residents.

Pseudorca are uncommon everywhere; they are at the top of the food web, and like other top predators are naturally rare. A National Marine Fisheries Service (NMFS) study of all of Hawaiian waters out to the international boundary found that false killer whales were the least abundant of the 18 species of toothed whales and dolphins found in Hawaiian waters.

Dramatic decline in numbers and group size
Recent evidence indicates that the insular population of Pseudorca in Hawai‘i has declined dramatically over the last 20 years. Five years of aerial surveys undertaken from 1993 through 2003 by Joe Mobley of the University of Hawai‘i West O‘ahu have shown a steep decline in sighting rates. Group sizes of the largest groups documented in surveys undertaken in 1989 were almost four times larger than the entire current population estimate.

False killer whales are very slow breeding, which means that they are very vulnerable. c) Robin W. Baird/www.cascadiaresearch.org

Photographic ID
In Hawaiian waters Pseudorca regularly use near-shore areas. The island-associated population is genetically differentiated from Pseudorca in offshore Hawaiian waters. Photographs obtained by researcher Dan McSweeney (of the Wild Whale Research Foundation, based in Holualoa) from the mid-1980s and 1990s have been used to demonstrate that this population has long shown fidelity to the area.

Very slow population recovery rates
The most recent population estimate for the insular population is just 123 individuals. Like the killer whale (not particularly closely related but with a very similar skull), Pseudorca are long-lived (into their 60s), slow to reproduce, having one calf only every 6 or 7 years, and do not start reproducing until their teens. Like humans, females go through menopause, and have a long post-reproductive period. Thus Pseudorca populations would be very slow to recover from any impacts from human activities. Also like killer whales, because they are long-lived predators, they accumulate high levels of toxins and may be impacted by competition with human fisheries.

False killer whales are known to offer fish to each other, and occasionally to humans.  c) Dan J. McSweeney/Wild Whale Research Foundation

Offering prey to humans
Photo-identification work has demonstrated that Pseudorca have long-term bonds. They 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 snorkelers and divers.