Leopard Seals (Hydrurga leptonyx) in New Zealand Waters Predating on Chondrichthyans

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.

Genetic characterisation of the spiny dogfish Squalus acanthias in the Adriatic Sea: evidence for high genetic diversity and an Atlantic–South Pacific origin

Spiny dogfish Squalus acanthias is a widely distributed, highly migratory mesopredatory shark that is extremely sensitive to overexploitation. Because of unregulated targeted and incidental capture and a lack of enforceable management in the Mediterranean Sea, the spiny dogfish subpopulation has declined by at least 50% in the Mediterranean Sea over the past 75–105 years, and is regionally classified as endangered. In this study we sampled 124 spiny dogfish in the northern-most part of the Mediterranean (i.e. the Adriatic Sea) to: (1) assess levels of genetic diversity using 13 microsatellite loci and mitochondrial (mt)DNA (NADH dehydrogenase subunit 2 (ND2) gene); and (2) infer its evolutionary placement while assessing further possible genetic divergence across the Atlantic and Pacific Ocean basins based on ND2. Analysis of mtDNA revealed 12 unique haplotypes and a high level of genetic variation in the Mediterranean region, whereas results from microsatellite markers showed significant genetic heterogeneity and a fine-scale stock structuring involving both sexes. The findings support an Atlantic–South Pacific origin for the spiny dogfish in the Adriatic Sea, with little or no present-day connectivity with the Atlantic population. Consequently, this commercially exploited and regionally endangered coastal shark in the Adriatic Sea should be considered as a separate management unit, with implementation of regional protective management plans.