Current global population size, post-whaling trend and historical trajectory of sperm whales

Abstract

The sperm whale lives in most deep ice-free waters of the globe. It was targeted during two periods of whaling peaking in the 1840’s and 1960’s. Using a habitat suitability model, we extrapolated estimates of abundance from visual and acoustic surveys to give a global estimate of 736,053 sperm whales (CV = 0.218) in 1993. Estimates of trends in the post-whaling era suggest that: whaling, by affecting the sex ratio and/or the social cohesion of females, reduced recovery rates well after whaling ceased; preferentially-targeted adult males show the best evidence of recovery, presumably due to recruitment from breeding populations; several decades post-whaling, sperm whale populations not facing much human impact are recovering slowly, but populations may be declining in areas with substantial anthropogenic footprint. A theta-logistic population model enhanced to simulate spatial structure and the non-removal impacts of whaling indicated a pre-whaling population of 1,949,698 (CV = 0.178) in 1710 being reduced by whaling, and then then recovering a little to about 844,761 (CV = 0.209) in 2022. There is much uncertainty about these numbers and trends. A larger population estimate than produced by a similar analysis in 2002 is principally due to a better assessment of ascertainment bias.

Priorities for ecological research on cetaceans in the Galápagos Islands

“…Long-term outcomes (years to decades) Target species Unlike pinnipeds, for which population assessments have been conducted on a regular basis throughout Galaṕagos (e.g., Paéz-Rosas et al, 2021), very few studies have reported population assessments for cetaceans in Galaṕagos (Palacios and Forney, 2008;O'Hern et al, 2017;Whitehead and Shin, 2022), and there is no formal ongoing program for monitoring cetacean populations. Yet, baseline information on demographic parameters, such as density, abundance, survival, and recruitment, is essential for understanding population status and dynamics, and to unravel the relative importance of competition and predation in structuring the local cetacean community relative to the influences of environmental variability.…”

Genomics reveals the role of admixture in the evolution of structure among sperm whale populations within the Mediterranean Sea

“…Worldwide and for up to three centuries, this species was the focus of two intensive hunting periods (Whitehead, 2002). From a pre‐whaling abundance of over 1 million, today there are an estimated 844,761 individuals (Whitehead & Shin, 2022) and they are now globally classified as Vulnerable on the IUCN red list (Taylor et al, 2019).…”

“…From a pre-whaling abundance of over 1 million, today there are an estimated 844,761 individuals (Whitehead & Shin, 2022) and they are now globally classified as Vulnerable on the IUCN red list (Taylor et al, 2019). Range-wide population genetic studies of sperm whales have identified several key features.…”

Unraveling site fidelity and residency patterns of sperm whales in the insular oceanic waters of Macaronesia

“…Sperm whales are globally classified as Vulnerable by the International Union for Conservation of Nature, with an unknown worldwide population trend (Taylor et al, 2019), with recent studies indicating a global population of 844 761 individuals (Whitehead & Shin, 2022). This species was extensively hunted worldwide since the 18 th century, growing from a shore-based enterprise to industrial whaling that only ceased in the 1980s.…”

“…This species was extensively hunted worldwide since the 18 th century, growing from a shore-based enterprise to industrial whaling that only ceased in the 1980s. This caused a decrease of 68% in the global population, with males being more heavily targeted (Whitehead, 2002;Whitehead, 2018). Due to the low reproduction rates of these long-lived mammals, the populations of sperm whales are still recovering.…”