Comparisons of life-history parameters between free-ranging and captive killer whale (Orcinus orca) populations for application toward species management

Abstract

Data collected on life-history parameters of known-age animals from the northern (NR) and southern resident (SR) killer whales (Orcinus orca) of the eastern North Pacific were compared with life-history traits of killer whales located at SeaWorld (SEA) facilities. For captive-born SEA animals, mean age and body length at 1st estrus was 7.5 years and 483.7cm, respectively. Estimated mean age at 1st conception was different (P < 0.001) for the combined data from both northern and southern resident (NSR) free-ranging populations (12.1 years) compared to SEA (9.8 years), as was the estimated mean age at 1st observed calf (SEA: 11.1 years, NSR: 14.2 years, P < 0.001). Average calf survival rate to 2 years of age for SEA animals (0.966) was significantly greater (P = 0.04) than that for SR (0.799). Annual survival rate (ASR) for SEA increased over approximately 15-year increments with rates in the most recent period (2000–2015 ASR: 0.976) improved (P < 0.05) over the first 2 periods of captivity (1965–1985: 0.906; 1985–2000: 0.941). The SR (0.966) and NR ASR (0.977) were higher (P ≤ 0.05) than that of SEA until 2000, after which there were no inter-population differences. Based on ASR, median and average life expectancy were 28.8 and 41.6 years (SEA: 2000–2015), 20.1 and 29.0 years (SR), and 29.3 and 42.3 years (NR), respectively. The ASR for animals born at SEA (0.979) was higher (P = 0.02) than that of wild-caught SEA animals (0.944) with a median and average life expectancy of 33.1 and 47.7 years, respectively. These data present evidence for similar life-history parameters of free-ranging and captive killer whale populations and the reproductive potential and survivorship patterns established herein have application for use in future research concerning the overall health of both populations.

Scientific Correspondence

“…For instance, even if we take a much more conservative approach that only includes captive born animals that have lived beyond 30 d of age (while still recognizing that a bias against captive born animal survival rates will result), a Kaplan‐Meier analysis (Stata Statistical Software: Release 13; StataCorp, College Station, TX) reveals the median life expectancy (MLE) changes from the 14.1 yr value reported by Jett and Ventre () for captive born killer whales to 21 yr. A MLE of 21 yr is not significantly different than the MLE of 20.1 yr found for the southern resident killer whale populations of the Pacific Northwest (Robeck et al . ).…”

“…, Robeck et al . ) are illustrated in Table . It should be noted that for statistical comparison it is necessary to meet the assumption that all individuals have the same survival probability.…”

Scientists clash over lifespan of captive killer whales

“…In the other 2015 study 1 , researchers led by SeaWorld veterinary surgeon Todd Robeck came to a very different conclusion: that animals now in captivity at SeaWorld's US parks live just as long as wild populations. The researchers looked only at animals held at those parks after 2000, and produced a survival rate that is higher than a rate that they calculated for southern…”

Environmental enrichment for Killer whales Orcinus orca at zoological institutions: untried and untested

“…More recent research, comparing the mortality rates of captive and wild Killer whales, indicated that they have similar life expectancies (Robeck et al ., ), although Jett & Ventre () reanalysed the data in this study and showed that although survival has improved it is still below that found in the wild. However, longevity is a crude and not very meaningful measure of success, especially if the Killer whales in zoological institutions have a poor quality of life.…”