Population Connectivity of the Highly Migratory Shortfin Mako (Isurus oxyrinchus Rafinesque 1810) and Implications for Management in the Southern Hemisphere

Shannon Corrigan,Gavin J P Naylor,Andrew D Lowther,Julian G Pepperell,Barry D Bruce,John R Hyde,Geremy Cliff,William T White,Rima W Jabado,Lindsay Marshall,Dovi Kacev,Luciano B Beheregaray,Malcolm P Francis,Nuno Queiroz,Simon Goldsworthy ,Gonzalo Mucientes ,Alan J Foulis ,Clinton Duffy ,Sanine P Wintner ,Paul Rogers

doi:10.3389/fevo.2018.00187

Abstract

In this paper we combine analyses of satellite telemetry and molecular data to investigate spatial connectivity and genetic structure among populations of shortfin mako (Isurus oxyrinchus) in and around Australian waters, where this species is harvested in recreational and commercial fisheries. Mitochondrial DNA data suggest matrilineal substructure across hemispheres, while nuclear DNA data indicate shortfin mako may constitute a globally panmictic population. There was generally high genetic connectivity within Australian waters. Assessing genetic connectivity across the Indian Ocean basin, as well as the extent that shortfin mako exhibit sex biases in dispersal patterns would benefit from future improved sampling of adult size classes, particularly of individuals from the eastern Indian Ocean. Telemetry data indicated that Australasian mako are indeed highly migratory and frequently make long-distance movements. However, individuals also exhibit fidelity to relatively small geographic areas for extended periods. Together these patterns suggest that shortfin mako populations may be genetically homogenous across large geographical areas as a consequence of few reproductively active migrants, although spatial partitioning exists. Given that connectivity appears to occurring at different scales, management at both the national and regional levels seems most appropriate.

Highlights

Implementing practical and effective management for highly migratory species (HMS) of pelagic sharks is challenging because they have vast ranges that are often spatiotemporally dynamic
The vast ranges of pelagic HMS make it challenging to assess population connectivity at spatial scales that are appropriate for informing policy
We aimed to address knowledge gaps regarding connectivity among populations of highly migratory shortfin mako from the Southern Hemisphere, in and around Australian waters

Summary

Introduction

Implementing practical and effective management for highly migratory species (HMS) of pelagic sharks is challenging because they have vast ranges that are often spatiotemporally dynamic. Some HMS of pelagic sharks move among favorable foraging, breeding, and pupping grounds, sometimes using specific migration pathways (Hueter et al, 2005; Kinney and Simpfendorfer, 2009; Chapman et al, 2015). Recognizing such movement patterns is important for devising suitably scaled management plans, when a species range spans multiple, or extends beyond, national jurisdictions (Worm and Vanderzwaag, 2007). Propensity to migrate is multifaceted and different movement types variously influence population persistence This means that management plans for HMS must consider more than their mobility. Regions may be genetically homogenized by a few reproductively active migrants despite considerable spatial partitioning (Waples, 1998; Gagnaire et al, 2015)

Objectives

Methods

Results

Conclusion