Age, growth, and sexual dimorphism of the Southern Hemisphere long-finned pilot whale (Globicephala melas edwardii)

Emma L Betty; Karen A Stockin; Bethany Hinton; Barbara A Bollard; Adam N H Smith; Mark B Orams; Sinéad Murphy

doi:10.1093/jmammal/gyab165

Age, growth, and sexual dimorphism of the Southern Hemisphere long-finned pilot whale (Globicephala melas edwardii)

J Mammal. 2022 Feb 3;103(3):560-575. doi: 10.1093/jmammal/gyab165. eCollection 2022 Jun.

Authors

Emma L Betty¹, Karen A Stockin¹, Bethany Hinton¹, Barbara A Bollard², Adam N H Smith³, Mark B Orams⁴, Sinéad Murphy⁵

Affiliations

¹ Cetacean Ecology Research Group, School of Natural Sciences, College of Sciences, Massey University, Auckland, New Zealand.
² School of Engineering, Mathematical and Computational Sciences, Faculty of Design and Creative Technologies, Auckland University of Technology, Auckland, New Zealand.
³ School of Computational Sciences, College of Sciences, Massey University, Auckland, New Zealand.
⁴ Faculty of Health and Environmental Sciences, Auckland University of Technology, Auckland, New Zealand.
⁵ Marine and Freshwater Research Centre, Department of Natural Sciences, School of Science and Computing, Galway-Mayo Institute of Technology, Galway, Ireland.

Abstract

Knowledge of population biological parameters can contribute to assessing the resilience of a population in the face of increasing anthropogenic pressures. Southern Hemisphere long-finned pilot whales (Globicephala melas edwardii) are susceptible to high rates of live stranding-related mortality. However, the biological parameters of this population largely are unknown. In this study, age, growth, allometry, and sexual dimorphism are described using teeth and external body measurements obtained from 515 male, 776 female, and 229 individuals of unknown sex, stranded on the New Zealand coastline between 1948 and 2017. Maximum ages of 31 and 38 years were estimated for males (n = 163) and females (n = 239), respectively. Females ranged in length from 160 to 500 cm (modal size class 400-449 cm) and males from 165 to 622 cm (modal size class 500-549 cm). Length-at-birth for both sexes was estimated at 170 cm using a logistic regression model. Growth models for both sexes indicated a preliminary rapid growth phase followed by a second phase of slower growth. For males, a two-phase growth model also indicated a moderate growth spurt around the average age at attainment of sexual maturity (ca.12-13 years). Asymptotic lengths were estimated at 570 and 438 cm for males and females, respectively. We found strong evidence of sexual size dimorphism, with males significantly larger than females for 13 of 14 external measurements. We also found sexual dimorphism with respect to shape, with males having proportionally longer pectoral fins, wider tail flukes, and taller dorsal fins, than females. Estimates of length-at-birth, maximum ages, and sexual shape dimorphism for G. m. edwardii differed from those previously reported for the North Atlantic subspecies (G. m. melas), which may indicate subspecies or population-level differences in morphology, longevity, and sociality.

Keywords: New Zealand; age estimation; allometry; asymptotic length; biological parameters; cetacean; growth models; life history; mass stranding.