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Examining the role of area closures for the protection and conservation of an overexploited coastal shark species


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McAllister, JD 2014 , 'Examining the role of area closures for the protection and conservation of an overexploited coastal shark species', PhD thesis, University of Tasmania.

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Area closures have become increasingly popular in the management of marine resources
and in helping to rebuild overexploited species, yet their effectiveness rely on a sound
understanding of key animal behaviours such as movement and residency, which for
many highly mobile species remains largely unknown. The nursery areas of school
shark (Galeorhinus galeus) have been protected throughout southern Australia since the
1960s in an effort to re-build severely overfished stocks. Only recently have there been
signs of recovery in the population, however, a limited understanding of how and when
G. galeus utilise protected nurseries makes it difficult to evaluate the role and
effectiveness of these areas in current stock re-building and management strategies.
Throughout this thesis, acoustic telemetry and stable isotope analysis together with
more traditional catch rate surveys are used in a series of studies to address these
limitations in our current understanding of G. galeus early life history, by examining the
population dynamics and ecology of this overfished species and several other
chondrichthyan species in a protected nursery area in southeast Tasmania.
The first seasonal longline fishing surveys since the 1990s revealed young-of-the-year
(YOY) and juvenile G. galeus continue to occupy protected nursery areas during
summer and autumn, as was the case in the 1990s. However, longline catch rates
indicated that abundances of YOY G. galeus may have increased or at least have
remained stable since sampling in 1991-97, but are likely still below those of historic
handline catches in 1947-52. A re-analysis of historic research survey data indicated
that variations in YOY abundance in this nursery reflected modelled stock declines
through the history of the fishery, suggesting that continued monitoring of YOY
abundances may provide an alternative to fishery dependent tools for monitoring trends
in overall stock recovery.
Acoustic telemetry was used to better understand ontogenetic differences in site fidelity,
habitat preferences and seasonal use of protected nursery areas by YOY and juvenile
(1+) G. galeus. Both age classes showed a distinct seasonal pattern of occurrence in the
refuge area with most departing the area during winter and only some YOY returning the following spring. Whilst nursery areas continue to function and provide important
habitat for the offspring of G. galeus, evidence of YOY and juveniles emigrating from
these areas within their first 1-2 years and the fact that few YOY (33%) return suggest
these areas may only afford protection for a more limited amount of time than
previously thought. These results suggest that adopting a multi-facet management
approach incorporating conventional fisheries management (e.g. catch limits) with area
closures is critical to ensuring long-term conservation outcomes and recovery for this
Integration of acoustic telemetry with a novel application of stable isotope analysis was
used to determine movement behaviours and the separation of parturition sites within a
nursery area. YOY captured from an estuary historically considered an important
pupping site for G. galeus had enriched δ13C and δ15N and were distinctly separated
from those captured in an adjoining coastal embayment suggesting that individuals were
born at either site and remained within their birth sites for an extended period. This
conclusion was supported by acoustic tracking which showed that YOY G. galeus
remained in the estuary for 3-4 months after parturition before migrating to the coastal
Stable isotope analysis and acoustic telemetry were also integrated with traditional catch
rate surveys to examine how various chondrichthyan species (three sharks, three rays
and one chimera) and a common teleost coexist in an important pupping area for G.
galeus with limited predation risk. Dietary partitioning was evident between species
which had high spatial overlap. In contrast species which were competing for similar
dietary requirements often foraged in different habitats. These results demonstrate that
resource partitioning strategies play an important role in shaping the dynamics of shark
nursery areas, ecological mechanisms that must be maintained in developing strategies
to enhance the recovery of G. galeus.
Together these studies provide a greater understanding of how nursery areas are utilised
by G. galeus and chondrichthyans in general. This study demonstrates the value of
integrating multiple sampling methodologies to improve the resolution and
understanding of key animal behaviours needed to evaluate and refine the effectiveness of current area closures and enhance our efforts to conserve and promote the recovery of overexploited marine resources.

Item Type: Thesis - PhD
Authors/Creators:McAllister, JD
Keywords: chondrichthyan ecology, conservation ecology, nursery areas, acoustic telemetry, stable isotopes
Copyright Holders: The Author
Copyright Information:

Copyright 2014 the author

Additional Information:

Chapter 3 appears to be the equivalent of a pre-copyedited, author-produced PDF of an article accepted for publication in ICES Journal of Marine Science following peer review. The version of record, Jaime D. McAllister, Adam Barnett, Jeremy M. Lyle, and Jayson M. Semmens, 2015, Examining the functional role of current area closures used for the conservation of an overexploited and highly mobile fishery species, ICES Journal of Marine Science, First published online: May 8, 2015, 1-11 is available online at: 10.1093/icesjms/fsv079

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