Please use this identifier to cite or link to this item: http://hdl.handle.net/2440/120349
Type: Thesis
Title: An integrated approach to assess pupping areas and natal origins in a Conservation Dependent shark, Galeorhinus galeus Matthew N.
Author: McMillan, Matthew N.
Issue Date: 2018
School/Discipline: School of Biological Sciences
Abstract: Knowledge around reproductive movements and habitat use can be central to understanding the life histories of animal populations. Such knowledge can be especially important for managing recovery of populations depleted by human over-exploitation and habitat degradation. In marine environments, clarifying animal movements and habitat use can be difficult given the practical and logistical constraints of studying them. For my research I therefore integrate diverse techniques to cast light on reproductive movements and habitat use of the Conservation Dependent school shark Galeorhinus galeus, where conventional methodologies have left important knowledge gaps unanswered. A national rebuilding plan for the species highlighted a lack of knowledge around whether all female G. galeus migrate to historically identified pupping areas around Tasmania and Bass Strait in the south-eastern range of the species as current management assumes. Alternatively, reproductive movements and habitats may be more varied in extent and location, including pupping areas in South Australia to the northwest where aggregations of pregnant females occur. My overarching aim was to assess the spatial distribution of G. galeus pupping areas in southern Australia and the extent of shared natal origins among populations. I use: (1) element signatures in calcified shark vertebrae that derive from water chemistry and diet in birth areas as natural tags to test whether sharks from different populations recruit from common or different pupping areas, (2) energetic analyses to assess constraints on pup dispersal from pupping areas and whether pups caught in South Australia could feasibly have dispersed from known pupping areas around Tasmania and Bass Strait, and (3) satellite archival tags to track movements of pregnant G. galeus tagged in South Australia to assess pupping movements and the spatial distribution of likely pupping areas. My findings increase our knowledge of the extent and plasticity of reproductive movements and areas used by G. galeus and address several assumptions, on which current management is based, that conventional techniques such as mark-recapture studies and genetic investigations had left open to speculation. A review of elasmobranch vertebral chemistry analysis and ground-truthing laboratory experiments establish the utility of shark vertebrae as sources for natural tags. Element signatures were consistent among related time-resolved portions of the same and adjacent vertebrae, while commonly used bleach preparation did not affect element signatures for a range of elements, validating use of elasmobranch vertebrae as biogenic archives for microchemistry analyses. Post-natal element signatures from three cohorts of juvenile and sub-adult G. galeus were compared between populations in South Australia and Bass Strait. Signatures differed among populations, indicating use of different pupping areas and not supporting the previous assumption of uniform female migrations to common pupping areas. Bioenergetic analyses established an energy budget and assessed constraints on dispersal of G. galeus pups from pupping areas. High energetic costs of growth, small energy reserves, and low concentrations of energy storage lipids relative to adults indicated a trade-off prioritising growth over dispersal in pups. Newborn pups in South Australia are shown to likely be born locally rather than migrants from distant, traditionally identified pupping areas. Satellite archival tagging of pregnant females found that some remained resident in South Australia over the pupping season (November–January), some migrated to the region of known pupping areas around Tasmania and Bass Strait, and one migrated to New Zealand. Given that a single mixed stock is known to exist, this indicates partial female migration with likely pupping areas stretching from the Great Australian Bight to New Zealand that are far less spatially constrained than assumed. This thesis therefore achieved its main aim of assessing whether the spatial distribution of G. galeus pupping areas and uniformity of female migratory behaviour in southern Australia conformed to current assumptions. Furthermore, it confirmed South Australia is a reproductively important area for school shark. Allocation of resources to future study of reproductive behaviours and habitats in South Australia would better inform management and enhance prospects for successful recovery of the species.
Advisor: Gillanders, Bronwyn
Dissertation Note: Thesis (Ph.D.) -- University of Adelaide, School of Biological Sciences, 2018
Keywords: Migration
pupping areas
fisheries management
microchemistry
tagging
energetics
conservation biology
Provenance: This electronic version is made publicly available by the University of Adelaide in accordance with its open access policy for student theses. Copyright in this thesis remains with the author. This thesis may incorporate third party material which has been used by the author pursuant to Fair Dealing exceptions. If you are the owner of any included third party copyright material you wish to be removed from this electronic version, please complete the take down form located at: http://www.adelaide.edu.au/legals
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