Leopard Seal Distribution and Diet
From Vagrant to Resident: occurrence, residency and births of leopard seals (Hydrurga leptonyx) in New Zealand waters
“In contrast to previous reports that leopard seals (Hydrurga leptonyx) are rare vagrants to New Zealand, we show that this species is a regular member of the marine fauna of this region. We present a first analysis from the New Zealand Leopard Seal Database – an extensive collation of 2,711 records of leopard seals within New Zealand between 1200 and 2018. Of these records, 51.2% (n = 1,408) were photographic. Leopard seal sightings have increased over time and been reported in all seasons and regions of New Zealand. Sightings are predominantly of adult individuals of good or excellent body condition, which differs to previous hypotheses
suggesting that leopard seals visiting New Zealand shores are primarily juvenile animals in poor health condition. A total of 176 unique individuals have been identified in the New Zealand Leopard Seal Catalogue between 2014 and 2018 and preliminary results indicate that numbers per annum have continued to increase over time. Three leopard seal births and a number of juvenile animals (34% of the NZ records) have been documented. Considering the information presented here and the current definitions in the New Zealand Threat Classification System, the threat status of leopard seals within New Zealand waters should be reclassified from Vagrant to Resident.”
— Hupman et al., 2020
“Unlike other southern continents where leopard seals (Hydrurga leptonyx) are considered vagrant visitors from Antarctica, sightings of leopard seals in New Zealand have been increasing, resulting in a re-classification from a vagrant to resident speciesin 2019. However, their ability to adapt to northerly environments still remains relatively unknown. Assessments of leopard seal body condition within this northern part of their range is one way in which scientists can understand their health status and thereby adapt strategies to protect populations. Preceding this study research investigating body condition of leopard seals often-employed invasive and costly techniques that carried risk to seals and researchers. This thesis presents four non-invasive procedures to examine body condition of leopard seals found in New Zealand waters, designed to assist with understanding their health status following such a substantial habitat shift. A body condition scoring system allocated leopard seal sighting records into body condition groups based upon presence/absence of bony protrusions and identified that sighting records of New Zealand leopard seals (n=80) were predominantly in Good condition (71.25%). Using these body condition groups, machine learning classifiers were successful in predicting sighting records of New Zealand leopard seals into Good, Moderate and Poor body condition using differences in body shape defined by photogrammetry. Whilst highest classification accuracy was obtained using photographic measurements of body width and Linear Discriminant Analysis (87.5%), an Artificial Neural Network based on leopard seal silhouettes (81.25%) was also identified as being suitable for examining body condition New Zealand leopard seals due to its ability to utilise large, complex datasets and flexibility with lower quality images. Methodologies developed here were enabled by a large photograph library collated by citizen scientists and volunteer researchers and can potentially be applied to assess the body condition of leopard seals in other regions as well other pinniped species.”
— Warren, 2021
“Leopard seals (Hydrurga leptonyx) are top-order predators that prey on a wide variety of species including crustaceans, cephalopods, fishes, birds, and pinnipeds. While multiple diet studies have been conducted worldwide, there are no previous accounts of leopard seals predating on chondrichthyans. As part of a wider study on the diet of leopard seals in New Zealand (NZ) waters, researchers and citizen scientists recorded 39 observations of predation and collected 127 scats (166 total records) between 1942 and 2019. Predation on chondrichthyans was detected in 23.1% (n = 9) of observations of predation and 7.1% (n = 9) of scats (the latter via morphological examination and DNA sequencing). From both observations of predations and scats, three chondrichthyan species or genus were identified; elephantfish (Callorhinchus milii), ghost sharks (Hydrolagus spp.) and spiny dogfish (Squalus acanthias). While this is the first published record of leopard seals feeding on chondrichthyans, the relatively high frequency of occurrence within our NZ records, and that certain individuals appeared to target this type of prey, indicates that these species could constitute a substantial, or important, part of the diet for some leopard seals in this region. As chondrichthyans form an important part of the NZ marine ecosystems, our recognition of an additional top-order predator of these species contributes to understanding the overall health of, and future impacts of predators on, the wider NZ marine ecosystem.”
— van der Linde et al., 2021
“Despite the ecological importance of leopard seals (Hydrurga leptonyx) as apex marine predators, little is known about their reproductive biology. To address this paucity, we reviewed leopard seal birth and pup records and applied a standardised age-class classification system to differentiate between births/newborns (offspring ≤ 14 days old) and pups (> 14 days but < 6 months old). We compiled 19 birth/newborn and 141 pup records and examined their occurrence by month, region, substrate, birth-specific attributes (i.e. birth observations, fresh umbilicus or placental), standard length, weight, presence of mother, presence of lanugo, sex, status (e.g. born alive) and fate. These records indicate that leopard seal births occur between September and December, with peak records from September to November, whilst pup records peaked between August and December. The regions with the most birth/newborn records were the sub-Antarctic Islands (31.6%) and Chile (31.6%), followed by Antarctica (15.8%), New Zealand (15.8%) and the Falkland Islands (5.3%). Pups were recorded predominantly in the sub-Antarctic Islands (54.6%), followed by the Antarctic (42.6%), Chile (2.1%) and Australia (0.7%). Whilst leopard seal birth records were predominantly on ice, they were also found on terra firma. The northernmost published leopard seal birth records occurred in New Zealand whilst the northernmost published leopard seal pup records occurred in Australia. This study contradicts the long-standing hypothesis that leopard seals only give birth on Antarctic pack ice, and instead, here we indicate that 84.2% and 57.4% of collated leopard seal birth and pup records, respectively, occur outside of Antarctica. Our records illustrate the importance of northern regions as part of the leopard seal’s range. We emphasise the need to conduct research focused on the reproductive biology of this keystone species throughout its range and that future management of leopard seal populations should also consider their northern range.”
— van der Linde et al., 2022
