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Conservation Status of Sharks, Rays, and Chimaeras in the Arabian Sea and Adjacent Waters, Jabado Rima [et al.]

Conservation Status of Sharks, Rays, and Chimaeras in the Arabian Sea and Adjacent Waters, Jabado Rima [et al.]

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Direct evidence of contemporary sex-biased

reproductive dispersal in threatened river

sharks.

Pierre Feutry ∗ 1 , Oliver Berry 2 , Peter Kyne 3 , Richard Pillans 4 , Richard

Hillary 1 , Peter Grewe 1 , James Marthick 5 , Rasanthi Gunasekera 1 ,

Floriaan Devloo-Delva 1 , Nicholas Bax 1 , Mark Bravington 1

1



CSIRO – Oceans and Atmosphere, Castray Esplanade, Hobart 7000, Tasmania, Australia, Australia

CSIRO – Oceans and Atmosphere, PMB 5, Floreat 6014, Western Australia, Australia, Australia

Charles Darwin University – Research Institute for the Environment and Livelihoods, Charles Darwin

University, Ellengowan Drive, Darwin 0909, Northern Territory, Australia, Australia

4

CSIRO – Oceans and Atmosphere, 41 Boggo Road, Dutton Park 4102, Queensland, Australia,

Australia

5

University of Tasmania – Menzies Institute for Medical Research, University of Tasmania, 17

Liverpool Street, Hobart 7000, Tasmania, Australia, Australia

2



3



Measuring population connectivity is a critical task in conservation biology. While genetic

markers can provide reliable long-term historical estimates of population connectivity, scientists

are still limited in their ability to determine contemporary patterns of gene flow, the most practical time frame for management. Also, contrasting results from mitochondrial nuclear DNA

markers are often interpreted as evidence of sex-biased reproductive dispersal. However, differences in genetic drift in mitochondrial and nuclear genes is an equally valid explanation. This

approach combining mitochondrial and nuclear genes has been used in many chondrichthyes

species and sex-biased reproductive dispersal is now suspected to be a common feature in this

class, although it has never been formally demonstrated.

Here, we tackled these two issues by developing a new approach that only requires juvenile

sampling at a single time period. To demonstrate the usefulness of our method, we used the

Speartooth shark (Glyphis glyphis), a critically endangered species of river sharks found only in

tropical northern Australia and southern Papua New Guinea.

Contemporary adult and juvenile shark movements was estimated with the spatial distribution of kin pairs across and within three river systems. Over 200 full- and half-sibling pairs were

identified. Full-sibling pairs were only captured within the same river suggesting that juveniles

remain in the natal river for some time. Out of the 121 cross-cohort HS pairs, 103 were captured within the same river system, indicating that in most cases at least one parent returned

to reproduce in the same river system across breeding seasons. The remaining 18 cross-cohort

HS pairs were shared between the Adelaide and the Alligator Rivers showing that at least one

parent had moved between these rivers. The comparison of the mitochondrial haplotypes of

these 18 pairs of juveniles revealed that males were most likely to be that parent.

This is the first direct evidence of sex-biased reproductive dispersal in chondrichthyes and we

showed that accounting for juvenile river fidelity and female philopatry is important in popula∗



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287



tion structure analysis and that targeting sampling in nurseries and juveniles aggregation should

be included in the genomic toolbox of threatened species management.



288



Evidence for rapid recovery of shark

populations within a coral reef marine

protected area

Conrad Speed



∗ 1,2



, Mike Cappo 3 , Mark Meekan



1,2



1



Australian Institute of Marine Science (AIMS Perth) – Indian Ocean Marine Research Centre, The

University of Western Australia (MO96), 35 Stirling Hwy, Crawley Western Australia 6009, Australia

2

Global FinPrint Project (FinPrint) – The University of Western Australia (MO96), 35 Stirling Hwy,

Crawley Western Australia 6009, Australia

3

Australian Institute of Marine Science (AIMS Townsville) – Australian Institute of Marine Science

PMB 3, Townsville MC Townsville 4810, Queensland, Australia, Australia



There is limited evidence on the rate at which reef shark populations can rebound from overexploitation, the baselines that might signify when recovery has occurred and the role of Marine

Protected Areas (MPAs) in aiding this process. We surveyed shark assemblages at Ashmore Reef

in the north-west of Western Australia using baited remote underwater video systems (BRUVS)

in 2004 prior to enforcement of MPA status on the coral reef and then again in 2016 after eight

years of strict enforcement of the MPA. We found an increase in the relative mean abundance

of the most common reef shark, Carcharhinus amblyrhynchos from 0.16 ± 0.06 individuals/hr1 in 2004 to 0.74 ± 0.11 individuals/hr-1 in 2016, a change that was also accompanied by

a shift in the community assemblage of sharks to greater proportions of apex species (from

7.1% in 2004 to 11.9% in 2016) and reef sharks (from 28.6% in 2004 to 57.6% in 2016), and a

decrease in the relative abundance of lower trophic level species (from 64.3% in 2004 to 30.5%

in 2016). Abundances and trophic structure of the shark assemblage at Ashmore Reef in 2004

resembled those of the Scott Reefs, where targeted fishing for sharks still occurs, whereas in

2016, abundances and trophic structures had recovered to resemble those of the Rowley Shoals,

a reef system that has been a strictly enforced MPA for over 25 years and receives negligible

fishing pressure. The rapid shift in abundance and community structure coincident with strict

enforcement of the MPA at Ashmore Reef has occurred at a rate much greater than predicted

by demographic models, implying the action of compensatory processes in recovery. Our study

shows that shark communities can recover rapidly after exploitation in a well-managed MPA.







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289



Gigantothermy in whale sharks – tracking

the behavioural strategies of a

homeothermic ectotherm

Mark Meekan



∗ 1



, Randall Davis†



2



1



Australian Institute of Marine Science (AIMS Perth) – Australian Institute of Marine Science The

UWA Oceans Institute (M096) 35 Stirling Hwy Crawley 6009, Western Australia, Australia, Australia

2

Texas AM University Galveston Campus – Texas AM University Galveston Campus P.O. Box 1675

Galveston, Texas 77553, United States



Whale sharks (Rhincodon typus) are a tropical, warm-adapted species that feeds on dense

aggregations of prey in the deep scattering layer (300-500 m depths) during the day. Feeding

using the gill in this deep, cold water has the potential to cool the body of a whale shark very

quickly. We developed a model of heat loss and gain from the gill as a means of understanding

and predicting patterns of vertical movement in this species. Using this model and extensive

time-depth and water temperature data from recovered Splash tags, we show how whale sharks

have effectively become homeothermic ectotherms, maintaining stable and high (23-25oC) body

temperatures despite feeding in deep, cold water. This has been achieved through a range of

behaviours that include basking both before and after descents to the deep scattering layer

and by partitioning time between warm surface water and deep cold water. Environmental heat

gained by basking and time in shallow water is stored by a body plan adapted for gigantothermy.

The strategy invoked by whale sharks provides insights into the evolution of filter-feeding in large

marine vertebrates over the last 150 million years.









Speaker

Corresponding author: davisr@tamug.edu



290



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