Allometric Relationships and Sexual Dimorphism in Captive Killer Whales (Orcinus orca)

Abstract

Morphometric data were collected on 30 captive killer whales ( Orcinus orca , 10 males, 20 females) from 1984 to 1996 at SeaWorld parks to document allometric relationships and sexual dimorphism. All nine characters examined exhibited negative allometric linear relationships with total length. Proportional sexual dimorphism was apparent only in length of flipper and height of dorsal fin among larger males. Absolute sexual dimorphism was detected in all categories. Anterior and posterior length of flippers for males were best approximated by a piecewise linear-regression model that suggested a greater rate of growth in larger males. That may have been the result of onset of an adolescent growth spurt for males and perhaps is necessary to maintain hydrodynamic stability. Girth measurements (girth at anterior origin of dorsal fin, girth at axilla, girth at genital slit) regressed on total length were linear for males and smaller females ( 500 cm apparently was due to pregnancies. A piecewise linear-regression described growth of dorsal fins of males. The growth coefficient was greater in larger males. Additionally, adult males had greater dorsal fin ratios (heightibase length) than females. The relationship of distance from blowhole to tip of dorsal fin regressed on total length was significant. This morphometric has applications for estimating length of killer whales during photogrammetric studies of wild animals.