Plasticity in the morphometrics and movements of an Antarctic apex predator, the leopard seal

Abstract

Animals that display plasticity in behavioral, ecological, and morphological traits are better poised to cope with environmental disturbances. Here, we examined individual plasticity and intraspecific variation in the morphometrics, movement patterns, and dive behavior of an enigmatic apex predator, the leopard seal (Hydrurga leptonyx). Satellite/GPS tags and time-depth recorders were deployed on 22 leopard seals off the Western Antarctic Peninsula. Adult female leopard seals were significantly larger (454±59 kg) and longer (302±11 cm) than adult males (302±22 kg, 276±11 cm). As females were 50% larger than their male counterparts, leopard seals are therefore one of the most extreme examples of female-biased sexual size dimorphism in marine mammals. Female leopard seals also spent more time hauled-out on land and ice than males. In the austral spring/summer, three adult female leopard seals hauled-out on ice for 10+ days, which likely represent the first satellite tracks of parturition and lactation for the species. While we found sex-based differences in morphometrics and haul-out durations, other variables, including maximum distance traveled and dive parameters, did not vary by sex. Regardless of sex, some leopard seals remained in near-shore habitats, traveling less than 50 kilometers, while other leopard seals traveled up to 1,700 kilometers away from the tagging location. Overall, leopard seals were short (3.0±0.7 min) and shallow (29±8 m) divers. However, within this general pattern, some individual leopard seals primarily used short, shallow dives, while others switched between short, shallow dives and long, deep dives. We also recorded the single deepest and longest dive made by any leopard seal—1, 256 meters for 25 minutes. Together, our results showcased high plasticity among leopard seals tagged in a single location. These flexible behaviors and traits may offer leopard seals, an ice-associated apex predator, resilience to the rapidly changing Southern Ocean.

Estimating reproductive costs in marine mammal bioenergetic models: a review of current knowledge and data availability

“…For example, a recent study by Feyrer et al (2020) using stable isotope analysis of teeth showed that lactation durations of northern bottlenose whales (Hyperoodon ampullatus) were 3 to 4 years instead of the previous best estimate of at least 1 year, which was a minimum estimate based on the presence of milk and prey in the stomach of a one-year old calf (Benjaminsen and Christensen, 1979). Satellite telemetry data from a single leopard seal (Hydrurga leptonyx), a species where lactation durations are unconfirmed but speculations range from 10 days to 8 weeks (Southwell et al, 2003), provides preliminary support for a 2-week lactation duration (Kienle et al, 2022). In North Atlantic right whales, the use of genetic identification revealed that at least two calves never observed on the foraging grounds with their mothers survived, indicating successful weaning as early as 7.5 to 8.0 months of age on the northbound migration (Hamilton et al, 2022) A particular challenge in estimating total lactation costs is that there is a high degree of intraspecific variation in lactation durations in some species.…”

Genetic diversity and demographic history of the leopard seal: a Southern Ocean top predator

“…Despite being a top predator, recent studies have shown broad intraspecific variability with regard to diet, which is quite diverse and varies seasonally [68]. Variability is also observed in diving behavior [69], hunting strategies [70], the use of ice floes [71] and movements [29]. In fact, the traditional notion that leopard seals are exclusively found in the Antarctic has also recently been rejected [19].…”

“…To date, published genetic analyses of leopard seals are limited [25,26] and descriptions of key demographic parameters such as N E are lacking. [27,28] and can disproportionally impact ecosystems [29]. For example, leopard seals have consumed an estimated 69.3% of all Antarctic fur seal pups (Arctocephalus gazella) born annually at Cape Shirreff in the north Antarctic peninsula since 2010, contributing to the rapid collapse of this regional population [28].…”

Initial insights into leopard seal moult in Aotearoa New Zealand

“…As leopard seals (Hydrurga leptonyx), rāpoka | popoiangore | poipopiangori | popoikore (hereafter 'leopard seals') are primarily found in the remote Antarctic pack ice and sub-Antarctic Islands (Laws 1977;Rogers 2013), the effects of climate change on sea ice (including pack ice) may have considerable implications for their activity (Meade et al 2015). External tracking devices applied to the pelage, such as glued tags, have assisted in monitoring leopard seal activity (Rogers et al 2005;Krause et al 2016;Kienle et al 2022), but their usage is limited by the loss and replacement of pelage during the annual moult (e.g. Rogers et al 2005;Kienle et al 2022).…”

“…External tracking devices applied to the pelage, such as glued tags, have assisted in monitoring leopard seal activity (Rogers et al 2005;Krause et al 2016;Kienle et al 2022), but their usage is limited by the loss and replacement of pelage during the annual moult (e.g. Rogers et al 2005;Kienle et al 2022).…”