Conservation of Endangered Great Hammerheads

The great hammerhead shark (Sphyrna mokarran) is a circumglobal species inhabiting warm temperate to tropical coastal waters. It occurs over continental and insular shelves, as well as adjacent deep waters and is thought to be highly mobile and migratory. The general life history pattern of S. mokarran is that of a long-lived (maximum estimated age 44 yrs), slow-growing, and late-maturing species. Observations and captures of S. mokarran have been repeatedly and frequently documented at our study sites in Florida and the Bahamas. Here we present a collaborative research project that combines telemetry and genetic data with modern analytical and ecological techniques to examine the conservation, habitat and space use of the endangered great hammerhead shark.
1. Movement patterns
- Gain a better understanding of the horizontal and vertical use of space by S. mokarran at two locations. For example, do they show localised movements and/or travel long distances? Do S. mokarran in Bimini and Florida represent an interconnected population or distinct sub-populations?
- Determine the amount of time S. mokarran spend within the Bahamas EEZ vs. US EEZ?
2. Habitat preferences
- Determine to what extent abiotic factors, such as depth or temperature influence S. mokarran habitat use i.e. do they show thermal preferences, surface orientated or deep diving behaviors?
3. Conservation status
- Provide various stakeholders (e.g. National Marine Fisheries Service) within our study locations with new species-specific recommendations, that have direct application in future research and management approaches for this species locally and globally.
S. mokarran are a target or bycatch species in a wide variety of fisheries throughout their range and substantial population declines are suspected to have occurred in many areas as a result of fishing. According to Clarke et al. (2006), hammerheads (Sphyrna spp.) are the second-most abundant species group in the international trade in fins. S. mokarran in particular are highly sought after because of their large fins which are prized in Hong Kong fish markets. Such declines and susceptibility have led to a global effort to enhance their management and conservation. In March of this year S. mokarran were added to CITES (Convention on International Trade in Endangered Species) Appendix II and were categorized as endangered by the IUCN (International Union for the Conservation of Nature) Red List. S. mokarran are also listed on Annex I, Highly Migratory Species, of the UN Convention on the Law of the Sea, which urges States to cooperate over their management. NOAA Fisheries Service HMS Division has also identified Florida’s coastal waters as Essential Fish Habitat (EFH) for many species of sharks. This includes S. mokarran, which was recently added by the Florida Fish and Wildlife Conservation Commission (FWC) to the list of shark species prohibited from harvest in Florida state waters. 
Clarke et al (2006) Global estimates of shark catches using trade records from commercial markets. Ecol Lett 9: 1115–1126.
Bimini: Since its inception in 1990 BBFS have encountered S. mokarran at various sites around the Bimini Islands. About 10 yrs ago we located an area where these sharks could be baited in for snorkelling experiences and to facilitate tagging and genetic sampling. Since then we have marked (N = 25) S. mokarran (12 males, 13 females; estimated total length range 200 - 350cm) with external dart tags, as part of the National Marine Fisheries Service (NMFS) cooperative shark tagging program. Many of these individuals have been re-sighted within the same week and/or month, with at least three sighted in multiple years and one this year tagged in 2010.
These early findings indicate to us that Bimini might be an important location or stop-off along a migratory path for these animals. Thus it is critical we take advantage of this unique opportunity to understand more about this elusive and charismatic species.
Florida: Since 2005 as part of our large coastal shark project we have tagged (N = 26; 8 male, 14 female) S. mokarran with NMFS external dart tags (estimated total length range 200 - 420cm). Of these (N = 5; 2 female, 3 male) were implanted with 7 year acoustic transmitters (see Research Techniques Biotelemetry) and monitored through our receiver array (Hobe Sound to Boynton) and the Florida Atlantic Coast Telemetry array. Preliminary results indicate that all S. mokarran survived our tagging procedure and were detected at receivers near Jupiter Inlet with two detected ~300km North at Cape Canaveral.
Pop-up Satellite archival tags (PSATs) for tracking - S. mokarran in Bimini will be equipped with PSATs (Research Techniques - Biotelemetry). PSATs are used to chronicle or ‘archive’ the habitat preferences, horizontal and vertical movements, fishery interaction, and post-release mortality rates of a variety of pelagic animals. Such detailed information can be used to contribute to the conservation of our target species, by informing stakeholders (e.g. fisheries managers) of our findings.
Acoustic trackingS. mokarran from Bimini, Bahamas and Jupiter Inlet, Florida will be equipped with acoustic transmitters (Research Techniques - Biotelemetry). These will provide important fine scale resolution to S. mokarran movements. At our study sites (Bimini and Jupiter Inlet) we have existing receiver arrays for the tracking of other large coastal species. Using such arrays as well as active tracking techniques we will be able to determine local coastal movement patterns at a higher resolution than what we can derive from our PSAT tags. We will be able to assess the residency of S. mokarran to our coastal sites and also identify seasonal, diel patterns of habitat use.
Ancillary data collectionVery little is known about the basic biology and ecology of S.mokarran. We will therefore non-destructively collect tissue samples from specimens, when possible, for use in a variety of additional studies. Skin tissue, white muscle, red blood cells and blood plasma will be sampled and used for chemical tracer studies of the species diet and ecological role, as well as for genetic studies of population structure. Finally, all specimens will be fitted with external dart tags to facilitate long term recognition of individuals, establishing the potential to assess long term movements and measurements of growth rates.
Principal Investigator
Dr. Tristan Guttridge - Cardiff University, UK
Dr. Samuel H Gruber - University of Miami, US
Dr. Demian D Chapman - Stony Brook University, US
Dr. Dean R Grubbs - Florida State University, US
Dr. Steve T Kessel - Windsor University, CAN
Jill Brooks - Carleton University, Ottawa, CAN
Lucy Howey-Jordan (Scientific Liason: Microwave Telemetry), US
William Winram (Shark Publicist), CA
Close content
Open content