Crossing lines: a multidisciplinary framework for assessing connectivity of hammerhead sharks across jurisdictional boundaries - PubMed (original) (raw)

Crossing lines: a multidisciplinary framework for assessing connectivity of hammerhead sharks across jurisdictional boundaries

A Chin et al. Sci Rep. 2017.

Abstract

Conservation and management of migratory species can be complex and challenging. International agreements such as the Convention on Migratory Species (CMS) provide policy frameworks, but assessments and management can be hampered by lack of data and tractable mechanisms to integrate disparate datasets. An assessment of scalloped (Sphyrna lewini) and great (Sphyrna mokarran) hammerhead population structure and connectivity across northern Australia, Indonesia and Papua New Guinea (PNG) was conducted to inform management responses to CMS and Convention on International Trade in Endangered Species listings of these species. An Integrated Assessment Framework (IAF) was devised to systematically incorporate data across jurisdictions and create a regional synopsis, and amalgamated a suite of data from the Australasian region. Scalloped hammerhead populations are segregated by sex and size, with Australian populations dominated by juveniles and small adult males, while Indonesian and PNG populations included large adult females. The IAF process introduced genetic and tagging data to produce conceptual models of stock structure and movement. Several hypotheses were produced to explain stock structure and movement patterns, but more data are needed to identify the most likely hypothesis. This study demonstrates a process for assessing migratory species connectivity and highlights priority areas for hammerhead management and research.

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Conflict of interest statement

The authors declare no competing financial interests.

Figures

Figure 1

Figure 1. Locality map showing the scope of the asessment region across Australasia and Indonesia.

The map shows the countries and major regional features discussed during the assessment. Figure created using ArcGIS 10.2.1.

Figure 2

Figure 2

Indicative distribution of: (A–C) scalloped hammerhed (triangles) and (D–F) great hammerhed (circles) sharks for sex and size categories from sampled locations. (A,D) adult females, (B,E) adult males, (C,F) immature and neonate individuals of both sexes. Insets show indicative distribution of neonates. Grey shading denotes spatial grids where fishing and sampling effort occurred. Note: more detailed information on fishing effort is not available due to confidentiality provisions of data-sharing agreements and fisheries monitoring programs. Data for scalloped hammerheads from PNG presented in Fig. 4. Spatial information for Indonesia was not available. Figure created using ArcGIS 10.2.1.

Figure 3

Figure 3

Size frequency distributions of scalloped hammerheads recorded in fisheres catches in Australia (A), Indonesia (B) and Papua New Guinea (C) showing the low numbers of adult females in Australian waters but occurrence in Indonesia and Papua New Guinea. Dotted lines indicate size at maturity for males (light grey) and females (dark grey).

Figure 4

Figure 4. Distribution of scalloped hammerheds in Papua New Guinea.

(A) adult females, (B) adult males, (C) immature and neonate individuals of both sexes. Insets denote neonates (pentagons). Dashed line represents the edge of the continental shelf – North Bismark Plate. Figure created using ArcGIS 10.2.1.

Figure 5

Figure 5. Conceptual population structure model of scalloped hammerhead sharks in Australasia.

TS indicates the Torres Strait land bridge, GoC is the Gulf of Carpentaria, NT is the Northern Territory, Figure created using ArcGIS 10.2.1 and biogeographic features added using Adobe Photoshop CC2015.

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