Life History and Reproductive Parameters in an Increasingly Abundant Killer Whale Population

ABSTRACT

Life history parameterization is foundational to population monitoring, particularly for long‐lived species under targeted management schema. In the eastern North Pacific, multidecadal photographic identification studies have facilitated the estimation of life history parameters for several distinct populations of fish‐eating “Resident” killer whales ( Orcinus orca ater ). However, to date, comparable estimates have not been generated for the increasingly abundant West Coast Transient (WCT) population of mammal‐eating “Bigg's” killer whales ( Orcinus orca rectipinnus ), despite their designation as “Threatened” under the Canadian Species at Risk Act. We used over 50 years of photographic identification data to estimate life history and reproductive parameters for WCT for the first time and compared our estimates to those previously published for sympatric Resident killer whale populations. Several aspects of WCT life history were consistent with Resident killer whales: mean age of first successful recruitment in WCT was 15.2 years (SE = 0.4), while average WCT calving interval was 4.88 years (SE = 0.13), yielding average annual fecundity of 0.20 calves per mature WCT female per year. However, WCT showed potential evidence of decreasing age at first recruitment (regression slope = −0.07, p  = 0.08), were the only population examined to exhibit decreasing calving intervals over the course of their study period (1972–2024), and had the lowest calf mortality of any killer whale population assessed in this study. While shared evolutionary lineage conserves many aspects of life history among killer whales, these potential differences may be associated with ongoing WCT population growth over the last 5 decades and could reflect ecological conditions, including increasing prey abundance, within their core range.