Browsing by Author "Bilgmann K"

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    A Matter of Scale: Population Genomic Structure and Connectivity of Fisheries At-Risk Common Dolphins (Delphinus delphis) From Australasia
    (Frontiers Media S.A., 2021-02-16) Barceló A; Sandoval-Castillo J; Stockin KA; Bilgmann K; Attard CRM; Zanardo N; Parra GJ; Hupman K; Reeves IM; Betty EL; Tezanos-Pinto G; Beheregaray LB; Möller LM; Jensen MP
    An understanding of population structure and connectivity at multiple spatial scales is required to assist wildlife conservation and management. This is particularly critical for widely distributed and highly mobile marine mammals subject to fisheries by-catch. Here, we present a population genomic assessment of a near-top predator, the common dolphin (Delphinus delphis), which is incidentally caught in multiple fisheries across the Australasian region. The study was carried out using 14,799 ddRAD sequenced genome-wide markers genotyped for 478 individuals sampled at multiple spatial scales across Australasia. A complex hierarchical metapopulation structure was identified, with three highly distinct and genetically diverse regional populations at large spatial scales (>1,500 km). The populations inhabit the southern coast of Australia, the eastern coast of Australia, New Zealand, and Tasmania, with the latter also showing a considerable level of admixture to Australia's east coast. Each of these regional populations contained two to four nested local populations (i.e., subpopulations) at finer spatial scales, with most of the gene flow occurring within distances of 50 to 400 km. Estimates of contemporary migration rates between adjacent subpopulations ranged from 6 to 25%. Overall, our findings identified complex common dolphin population structure and connectivity across state and international jurisdictions, including migration and gene flow across the Tasman Sea. The results indicate that inter-jurisdictional collaboration is required to implement conservation management strategies and mitigate fisheries interactions of common dolphins across multiple spatial scales in the Australasian region.
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    Establishment of a stable isotope database for New Zealand fur seal breeding colonies using δ13C and δ15N in pup vibrissae
    (Taylor and Francis Group on behalf of the Royal Society of New Zealand, 2025-05-21) Galbraith D; Chilvers BL; Bilgmann K
    The New Zealand fur seal/kekeno (Arctocephalus forsteri, NZFS) is native to Aotearoa/New Zealand. Its original range included the entire coast of mainland New Zealand, and offshore and subantarctic islands. The NZFS has gradually recolonised much of its former range after being almost extirpated by hunting, however, little is known about species dispersal in the non-breeding season. Stable isotope analysis (SIA) can trace foraging ecology and migration in marine mammal species. Isotopic niche width can be described statistically and provides ecologically relevant information on diet and potentially foraging location. Otariid pup vibrissae (whiskers) can be used as proxies for maternal foraging as they provide a sequential record of nutrient intake derived from maternal milk. In this study, vibrissae from NZFS pups were collected from seven established breeding areas around the coast of New Zealand. A stable isotope database of δ13C and δ15N was established for each breeding colony, and isotopic niche widths estimated. Isotopic niche widths were largest at Open Bay Islands and Cape Foulwind. Results were discussed in light of previous oceanographic and NZFS diet and foraging studies. Colonies are not likely to be sufficiently isotopically distinct for pups to be identified to their colony of origin.