False killer whales (Pseudorca crassidens) from Japan and South Africa: Differences in growth and reproduction

Abstract

Age and reproductive information for 65 false killer whales stranded in South Africa in 1981 are compared with similar material from 156 animals examined from drive fisheries in Japan in 1979 and 1980. Sizes at birth, sexual maturation, and physical maturity all indicated that both sexes were 10%-20% larger in Japan than South Africa. Females reached sexual maturation at similar ages (8-10.5 yr) in both populations, and although sample sizes were too small to establish male ages at puberty precisely the ranges in Japan (10.5-18.5 yr) and South Africa (5.25-17.5 yr) were not inconsistent. The initial ovulation rate for females from South Africa was 65% lower (and the apparent pregnancy rate 82% lower) than those from Japan and there were fewer animals 2 yr old within the school, but the magnitude of these differences suggests that the stranded school's reproductive performance was probably impaired. Collectively these comparisons and the literature indicate substantive size differences between false killer whales in different populations, although the patterns of growth appear similar. Firm conclusions about any geographical differences in reproduction require additional data.

False killer whales and fisheries interactions in Hawaiian waters: Evidence for sex bias and variation among populations and social groups

“…Conversely, it is possible that male false killer whale interactions with fisheries are more likely to be lethal. Males are, on average, larger and heavier than females (Ferreira et al 2014), and thus might have a greater likelihood of breaking lines when hooked, and trailing gear may impede feeding or locomotion. However, if females are interacting with fisheries at a higher rate, then fisheries-related mortality may have a disproportionate influence on population dynamics, influencing the rate of growth, and thus potential recovery, of the population to a greater extent than if fisheries-related mortality rates were equal for both sexes or were biased towards males.…”

Evidence for a postreproductive phase in female false killer whales Pseudorca crassidens

“…Both stranded and shore-drive samples are characterised by few large juvenile and sub-adults [23, 25, 28]. In contrast to short-finned pilot whales [16], aggregations of maturing males have not been observed.…”

“…False killer whale teeth were sectioned longitudinally through the center of the pulp cavity to a thickness of 40-50 μ m [25]. Sections were then decalcified and stained with haematoxylin before mounting in Canada Balsam.…”

Biological matrices for sampling free‐ranging cetaceans and the implications of their use for reproductive endocrine monitoring

“…Most of the existing information on marine mammal reproductive physiology is based on the observation of captive individuals (Robeck et al 2001) or on histological examination of gonads and reproductive tracts from by-caught, harvested, or stranded animals (Neuenhagen et al 2007). Though very valuable, these sample sets are frequently biased, because certain demographic groups are either over-represented or under-represented (Thayer et al 2003, Ferreira et al 2014.…”