Characterization of male killer whale (Orcinus orca) sexual maturation and reproductive seasonality

Longitudinal serum testosterone concentrations (n = 10 males) and semen production (n = 2 males) in killer whales were evaluated to: (1) characterize fluctuations in serum testosterone concentrations with respect to reproductive maturity and season; (2) compare morphologic changes to estimated age of sexual maturity, based on changes in serum testosterone concentrations; and (3) evaluate seasonal changes in sperm production. Classification of reproductive status and age class was based on differences (P < 0.05) in serum testosterone concentrations according to age; juvenile males ranged from 1 to 7 years (mean ± S.D. testosterone, 0.13 ± 0.20 ng/mL), pubertal males from 8 to 12 years (2.88 ± 3.20 ng/mL), and sexually mature animals were 13 years and older (5.57 ± 2.90 ng/mL). For captive-born males, serum testosterone concentrations, total body length and height to width ratio of the dorsal fin were 0.7 ± 0.7 ng/mL, 495.6 ± 17.5 cm and 1.14 ± 0.13 cm, respectively, at puberty; at sexual maturity, these end points were 6.0 ± 3.3 ng/mL, 548 ± 20 cm and 1.36 ± 0.1 cm. Serum testosterone concentrations were higher (P < 0.05) from March to June than from December to February in pubertal animals (4.2 ± 3.4 ng/mL versus 1.4 ± 2.6 ng/mL) and than from September to December in sexually mature animals (7.2 ± 3.3 ng/mL versus 4.0 ± 2.0 ng/mL). Ejaculates (n = 90) collected from two males had similar (P > 0.05) sperm concentrations across all months. These data represent the first comprehensive study on male testosterone concentrations during and after sexual maturation, and on reproductive seasonality in the killer whale.