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Genetic connectivity of a coastal apex predator: The population genetic structure reveals a potential spatial isolation of Fijian bull sharks, Kerstin Glaus [et al.]

Genetic connectivity of a coastal apex predator: The population genetic structure reveals a potential spatial isolation of Fijian bull sharks, Kerstin Glaus [et al.]

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which aims to understand the drivers of spatial isolation and the distinct genetic signatures in

bull sharks from Fiji.



307



Global genetic inventory of the Silky Shark

(Carcharhinus falciformis), the shark finning

industry, and DNA fingerprinting

Derek Kraft



∗ 1,2



1



Melanie Hutchinson (International Fisheries Program NOAA) – International Fisheries Program 1845

Wasp Blvd, Honolulu, HI 96818, United States

2

Brian Bowen (HIMB) – Hawaii Institute of Marine Biology 46-007 Lilipuna Rd, Kaneohe, HI 96744,

United States



The pelagic silky sharks (Carcharhinus falciformis) occur in all oceans and are the second

most commonly harvested shark on the planet. Their habitat overlaps with commercial tuna

fisheries and they account for > 90% of the shark bycatch in tropical purse seine fisheries of

the western and central Pacific. Silkys’ are also one of the most abundant species in the shark

fin trade; contributing to a harvest estimated at 26-73 million sharks annually. As a result

of these non-regulated fisheries, this formally abundant shark has declined by > 85% in the

last 20 years, and is now listed as near-threatened and declining by IUCN. In the face of this

dramatic decline, there is little information on extraction rates or stock structure, which are

the basic units of wildlife life management. Here we provide a global genetic inventory of the

Silky shark to resolve populations and delineate stock structure. Subsequently this information

will be used as a baseline to identify the origins of Silky shark in the fin markets. We have

secured global sampling coverage with > 2,000 specimens. To quantify genetic structure, we

use restriction site-associated DNA polymorphisms (ezRAD) in whole genome scans. Once the

population structure of Silky sharks is resolved, this data is used to quantify gene flow on a

global scale. Finally over 1000 fin samples have been taken over four years from the shark fin

trade in China and will be compared to our global baseline, using a Bayesian mixed stock model.

This will allow the identification of sharks in the fin trade to both the species-level and oceanic

region of origin, providing a much-need scientific foundation for management plans. Given that

traditional extraction monitoring is not available, our assessment of stock harvest will happen

at the end point of the market supply chain.







Speaker



308



Ground truthing dermal denticles to

characterize shark assemblages on Palmyra

Atoll

Erin Dillon



∗† 1



, Kevin Lafferty 2,1 , Darcy Bradley 3 , Richard Norris 4 ,

Douglas Mccauley 1 , Aaron O’dea 5



1



University of California, Santa Barbara (UCSB) – Department of Ecology, Evolution, and Marine

Biology, University of California, Santa Barbara, CA 93106, USA, United States

2

U.S. Geological Survey (USGS) – Western Ecological Research Center, U.S. Geological Survey, Marine

Science Institute, University of California, Santa Barbara, CA 93106, United States

3

University of California, Santa Barbara (UCSB) – Bren School of Environmental Science and

Management, University of California Santa Barbara, Santa Barbara, CA 93106, USA, United States

4

Scripps Institution of Oceanography (SIO) – University of California San Diego, 9500 Gilman Drive,

La Jolla, CA 92093-0208, U.S.A., United States

5

Smithsonian Tropical Research Institute (STRI) – Balboa, Ancon, Panama



Assessing how and why predator assemblages vary over space and time is crucial for understanding ecosystem trophic structure and dynamics. Historical accounts often depict extremely

high densities of sharks that sharply juxtapose contemporary reports of shark abundance in

the same regions. Although this suggests that shark populations have declined, evaluating the

reliability of these anecdotes is challenging because detailed shark surveys began after the initial

degradation of marine ecosystems. Consequently, quantitative pre-exploitation shark baselines

are nearly nonexistent, so the magnitude and long-term trajectories of change in shark communities are unresolved. To meet this challenge, we are reconstructing historical shark communities

using dermal denticles, the small tooth-like scales covering elasmobranch skin, which accumulate

and are well-preserved in modern and fossil coral reef sediments. They can be extracted and

identified to reveal broad spatiotemporal patterns of relative shark abundance and diversity. To

extend the utility of the denticle record as a new paleoecological proxy, we assessed its fidelity

and resolution on Palmyra Atoll, a remote unfished U.S. National Wildlife Refuge in the central

Pacific where shark abundance is high and well-documented. Here, we evaluated the alignment

between denticle assemblages found in modern, time-averaged sediments collected from lagoonal

and backreef environments with visual, video, and capture-recapture shark survey data, while

also examining the extent of spatial patchiness in the denticle record across the atoll. We found

rank alignment between denticle abundance per kilogram sediment and censused shark abundance, and denticle diversity reflected known taxa on the atoll. Comparing the outputs of these

different survey methods as well as measuring and constraining potential biases of the denticle record can help standardize this tool, enabling comparisons between denticle assemblages

in congruent habitats across wide spatial areas. This new data source could provide unique

insight into shark communities before industrial fishing, facilitate assessments of the magnitude

and ecological consequences of shark declines, and help set more appropriate, region-specific

management targets.







Speaker

Corresponding author: erin.dillon@lifesci.ucsb.edu



309



How does a shark’s paradise become a fish’s

nightmare? Ecology and behaviour of reef

sharks at Fakarava, one of the world’s

biggest aggregations.

Johann Mourier



∗† 1



, Laurent Ballesta 2 , Charlie Huveneers 3 , Yannis

Papastamatiou 4 , Serge Planes 5



1



Centre de Recherche Insulaire et Observatoire de l’Environnement (CRIOBE) – CNRS : USR3278,

Ecole Pratique des Hautes Etudes – Universite de Perpignan, 58 Av. Paul Alduy - 66860 Perpignan

cedex, France

2

Andromede Oceanology – Andromede Oceanology – 7 Place Cassan, 34280 Carnon-Plage, France

3

Flinders University – Room 140, Biology Building, Sturt Road, Bedford Park, SA, 5042 South

Australia, Australia

4

Florida International University – 3000 NE 151st st, North Miami, 33181, United States

5

Centre de Recherche Insulaire et Observatoire de l’Environnement (CRIOBE) – BP 1013 - 98 729,

Papetoai, Moorea, French Polynesia



The extent of the global human footprint limits our understanding of what are natural baselines in the marine environment. Remote near-pristine areas provide some baseline expectations

for biomass and suggest that predators dominate, producing an ‘inverted biomass pyramid’. The

southern pass of Fakarava atoll – a Biosphere Reserve in French Polynesia – hosts more than 500

reef sharks, 2-3 times the biomass/ha documented for any other reef shark aggregations. This

huge biomass of predators makes the trophic pyramid inverted. Bioenergetics models indicate

the sharks require ˜ 90 tons of fish/year while the total fish production in the pass is ˜ 17

tons/year. Sharks may overcome low local energy availability by feeding on fish spawning aggregations and other subsidies transiting into the pass which concentrate energy from other local

trophic pyramids. Using a combination of cutting edge technologies, ongoing research aims to

investigate the natural shark hunting behaviour, feeding ecology, movement patterns and social

behaviour in a unique pristine reef to better understand the role of sharks on the local ecosystem

and how such concentrations of predators are maintained. Altogether, our preliminary findings

have important conservation implications for maintaining a balanced and healthy ecosystem.









Speaker

Corresponding author: johann.mourier@gmail.com



310



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