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Evidence of a Possible Decline since 1989 in False Killer Whales (Pseudorca crassidens) around the Main Hawaiian Islands1 Randall R. Reeves,2 Stephen Leatherwood,3 and Robin W. Baird4,5 Abstract: Recent evidence indicates that there is a small, demographically iso- lated, island-associated population of false killer whales (Pseudorca crassidens) around the main Hawaiian Islands. Although it is known that false killer whales in Hawai‘i are sometimes killed or seriously injured in the Hawai‘i-based long- line fishery, it is not known whether such interactions have resulted in a reduc- tion in population size or whether other factors have been negatively influencing population size. We report the results of an aerial survey in June and July 1989, the purpose of which was to obtain a minimum count of the number of false killer whales around the main Hawaiian Islands. The false killer whale was the third most commonly seen species of odontocete off the island of Hawai‘i dur- ing the survey, representing 17% of sightings. Groups of more than 300 indi- viduals were seen on three different days, with minimum counts of 380, 460, and 470 individuals in these groups. The encounter rate, relative species rank- ing, and average group size from the 1989 survey were all substantially greater than those from more recent aerial and ship-based surveys. The largest group observed in 1989 (470) contained almost four times as many whales as estimated for the entire main Hawaiian Islands from recent aerial surveys (121 individuals, CV ¼ 0.47) or mark-recapture analyses (123 individuals, CV ¼ 0.72). There- fore, the population of false killer whales around the main Hawaiian Islands may have declined substantially since 1989. The cause or causes of such a de- cline are uncertain. Recent genetic and photo-identification of the central tropical Pacific (Chivers et al. evidence indicates the existence of a demo- 2007), although it is unknown how much graphically isolated, island-associated popula- the ranges of the two groups overlap. Esti- tion of false killer whales, Pseudorca crassidens mates of the island-associated population are (Owen), around the main Hawaiian Islands available from two sources: aerial surveys in (Chivers et al. 2007, Baird et al. 2008). False 1993, 1995, and 1998 (Mobley et al. 2000) killer whales around the main Hawaiian Is- and mark-recapture analysis of photo-iden- lands are genetically differentiated from those tification data collected from 2000 through in the outer part of the Hawaiian Exclusive 2004 (Baird et al. 2005). The estimate from Economic Zone and the surrounding waters aerial surveys was 121 (CV ¼ 0.47), and the estimate from mark-recapture was 123 (CV ¼ 0.72). Evidence from dorsal fin disfigure- 1 Manuscript accepted 5 June 2008. ments suggests that the island-associated pop- 2 Okapi Wildlife Associates, 27 Chandler Lane, Hud- ulation is involved in fishery interactions of son, Quebec J0P 1H0, Canada. some kind (Baird and Gorgone 2005). False 3 Deceased. 4 Author for correspondence. killer whales are killed and seriously injured 5 1 Cascadia Research Collective, 2182 West 4th Ave- in the Hawai‘i-based long-line fishery (For- nue, Olympia, Washington 98501 (e-mail: rwbaird@ ney and Kobayashi 2007). The rate of mor- cascadiaresearch.org). tality and serious injury in this fishery is greater than the total population within the Pacific Science (2009), vol. 63, no. 2:253–261 Hawaiian Exclusive Economic Zone, both : 2009 by University of Hawai‘i Press the island-associated whales and those in the All rights reserved outer Exclusive Economic Zone, is thought 253 254 PACIFIC SCIENCE . April 2009 to be able to sustain (Carretta et al. 2007). (other species). To obtain minimum counts, Whether the bycatch in the long-line fishery each observer logged his counts indepen- has resulted in a population decline is un- dently on each orbit until he considered that known. The two available population esti- the number detected had peaked and stabi- mates, one from the mid- to late 1990s and lized. The observers then discussed the fig- one from the early to mid-2000s, are too im- ures and agreed on a minimum count to be precise for a meaningful trend analysis, and logged for that sighting. Locations of sight- there is no information on how the bycatch ings were determined using loran and noted should be apportioned between the island- on a nautical chart. Distances of sightings associated and the outer Exclusive Economic from shore were determined by reference to Zone populations. Here we report on an ae- plotted chart locations and are thus likely rial survey in 1989 that provided a minimum only accurate to G1 km. Photographs were count of false killer whales around the main taken to document species and indicate rela- Hawaiian Islands. We also consider the impli- tive sizes of groups encountered. In most cations of this minimum count in relation to sightings of false killer whales, and in all of the question of the island-associated popula- them involving more than approximately 30 tion’s current status. individuals, it was clear that animals at the surface were being replaced frequently by an- materials and methods imals coming to the surface from some depth. Therefore, each photograph provided only In June and July 1989 an aerial survey was a static view of the groups at the surface at flown along various portions of the lee a given instant, and the counts from photo- (western and southwestern) shores of the is- graphs alone were considered negatively lands of Hawai‘i, La¯na‘i, and O‘ahu. The biased. purpose of the survey was to obtain a mini- mum count of false killer whales around the results main Hawaiian Islands that could be used in an application for a live-capture permit. The Thirty survey hours were flown on eight days survey was made from a fixed-wing, two- from 23 June 1989 through 2 July 1989, with engine aircraft (Partenavia P68C) flying at 20 hr off the island of Hawai‘i, 5 hr off the approximately 229 m (750 ft) above sea level island of La¯na‘i, and 4.5 hr off the island of and a speed of approximately 167 km/hr (90 O‘ahu (Table 1). The flights off La¯na‘i and knots), although the speed and altitude were O‘ahu were general surveys, as were 2 days varied when necessary to improve naviga- of flights (totaling 13.5 hr) off Hawai‘i. Dur- tional fixes and confirm species identifica- ing general surveys (total 23 hr) conditions tions. The two principal observers (R.R.R., were considered excellent for all but 2 hr of S.L.) were both experienced in identifying a effort off O‘ahu. The general surveys off the diversity of cetaceans from aerial platforms. island of Hawai‘i produced 30 sightings of On the first day of surveys the plane followed odontocetes from nine different species, in- a zigzag pattern from the coast of the island cluding five sightings of groups of false killer of Hawai‘i out to about 55 km from shore whales (Table 2). Focused surveys off the is- (Figure 1). Two types of surveys were under- land of Hawai‘i resulted in an additional nine taken: general surveys, with broad geographic sightings of false killer whales, with at least coverage and where all species observed were one sighting during each day with survey cov- recorded, and directed surveys targeting areas erage. No sightings of false killer whales were where false killer whales had been sighted on made off other islands, although six other previous days. Once located, a group of ceta- species of odontocetes were sighted. ceans was orbited until the species was identi- The number of orbits of groups to deter- fied and the two principal observers were mine minimum numbers ranged from 1 to 16 satisfied that they had a minimum count (false (median ¼ 3). Minimum group sizes of false killer whales) and/or an acceptable estimate killer whales ranged from 2 to 470 individuals Figure 1. Map showing approximate boundary of general survey area (heavy dashed line) off the island of Hawai‘i and locations of false killer whale sightings (squares) in 1989. The 100 m (dotted line near shore), 1,000 m, and 2,000 m isobaths are shown. The largest groups observed (>300 individuals) were all in the cluster of sightings in the northern part of the survey area. These surveys were undertaken before availability of GPS mapping capability and therefore the exact survey lines flown were not recorded. 256 PACIFIC SCIENCE . April 2009 TABLE 1 discussion Summary of Aerial Survey Effort in June–July 1989 Sighting locations of island-associated false killer whales in directed surveys around No. of Days (hr) No. of Days (hr) the main Hawaiian Islands since 2000 have Island General Surveys Directed Surveys ranged from 1.6 to 31.9 km from shore Hawai‘i 2 (13.5) 4 (7) (median ¼ 8 km [R.W.B., unpubl. data]), La¯na‘i 2 (5.0) — whereas the nearest sighting of a group of O‘ahu 2 (4.5) — putatively offshore individuals was some 42 km from shore (Baird et al. 2008). Given the repeated sightings in 1989 of large groups over a number of days at distances of approx- (median ¼ 35.5). Sizes of groups orbited imately 4.5 to 11 km from the island of three or more times ranged from 11 to 470 Hawai‘i, it is likely that those groups be- (median ¼ 195 individuals). Groups of more longed to the island-associated population than 300 individuals were seen on three sepa- rather than an offshore population.

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