Genetic variation and evidence for population structure in eastern North Pacific false killer whales (Pseudorca crassidens)

Abstract

False killer whales ( Pseudorca crassidens (Owen, 1846)) are incidentally taken in the North Pacific pelagic long-line fishery, but little is known about their population structure to assess the impact of these takes. Using mitochondrial DNA (mtDNA) control region sequence data, we quantified genetic variation for the species and tested for genetic differentiation among geographic strata. Our data set of 124 samples included 115 skin-biopsy samples collected from false killer whales inhabiting the eastern North Pacific Ocean (ENP), and nine samples collected from animals sampled at sea or on the beach in the western North Pacific, Indian, and Atlantic oceans. Twenty-four (24) haplotypes were identified, and nucleotide diversity was low (π = 0.37%) but comparable with that of closely related species. Phylogeographic concordance in the distribution of haplotypes was revealed and a demographically isolated population of false killer whales associated with the main Hawaiian islands was identified (ΦST = 0.47, p < 0.0001). This result supports recognition of the existing management unit, which has geo-political boundaries corresponding to the USA’s exclusive economic zone (EEZ) of Hawai‘i. However, a small number of animals sampled within the EEZ but away from the near-shore island area, which is defined as <25 nautical miles (1 nautical mile = 1.852 km) from shore, had haplotypes that were the same or closely related to those found elsewhere in the ENP, which suggests that there may be a second management unit within the Hawaiian EEZ. Biologically meaningful boundaries for the population(s) cannot be identified until we better understand the distribution and ecology of false killer whales.

Mortality rate acceleration and post-reproductive lifespan in matrilineal whale species

“…A post-reproductive lifespan may also occur in other whale species with stable matrilineal social groups such as false killer whale (Pseudorca crassidens) or sperm whale (Physeter macrocephalus; Marsh & Kasuya 1986;McAuliffe & Whitehead 2005). This life history trait has so far not been found in odontocete species that live in fluid social groups that offer less opportunity for multi-generational transfers (Marsh & Kasuya 1986;Chivers & Danil 2007).…”

“…Classical life history theories predict that the agedependent selection gradient for somatic repair and against the accumulation of deleterious mutations and antagonistic pleiotropy will depend upon the rate of acceleration of extrinsic mortality (Hamilton 1966;Kirkwood 1977;Charlesworth 1994). Empirical support for these hypotheses comes from studies showing guppies suffering lower predation rates to be exhibiting delayed somatic senescence and having an increased lifespan ( Reznick et al 1997( Reznick et al , 2006.…”

Evidence of a Possible Decline since 1989 in False Killer Whales (Pseudorca crassidens) around the Main Hawaiian Islands

“…Recent genetic and photo-identification evidence indicates the existence of a demographically isolated, island-associated population of false killer whales, Pseudorca crassidens (Owen), around the main Hawaiian Islands (Chivers et al 2007, Baird et al 2008. False killer whales around the main Hawaiian Islands are genetically differentiated from those in the outer part of the Hawaiian Exclusive Economic Zone and the surrounding waters of the central tropical Pacific (Chivers et al 2007), although it is unknown how much the ranges of the two groups overlap.…”

“…False killer whales around the main Hawaiian Islands are genetically differentiated from those in the outer part of the Hawaiian Exclusive Economic Zone and the surrounding waters of the central tropical Pacific (Chivers et al 2007), although it is unknown how much the ranges of the two groups overlap. Estimates of the island-associated population are available from two sources: aerial surveys in 1993, 1995, and 1998(Mobley et al 2000 and mark-recapture analysis of photo-identification data collected from 2000 through 2004 .…”

First record of common bottlenose dolphin (Tursiops truncatus) in Canadian Pacific waters

“…False killer whales are a warm-temperate to tropical species that occurs mostly in deep, offshore waters. In the eastern North Pacific, false killer whales typically do not range north of 35°N (Chivers et al 2007). The species was not recorded during a series of extensive cetacean surveys undertaken off the United States mainland west coast from California to Washington State during 1996-2014 (Barlow 2016;Barlow and Forney 2007).…”