Bull sharks
Project Leader: Juerg Brunnschweiler
Background
Juerg Brunnschweiler with a satellite tag
Bull sharks (Carcharhinus leucas) have a worldwide distribution in coastal and freshwater habitats with frequent sightings in some areas, yet many aspects of their behaviour and ecology remain a mystery. With a lack of knowledge about local population structures, reproduction sites and the migratory routes to and from these areas, it has been impossible to draw up any meaningful conservation plans.
The Bull Shark Tagging Programme was initiated in 2003 and has been co-funded by SOSF since 2004. The initial pilot study in the Bahamas tested the feasibility of studying movement patterns and habitat use of bull sharks with state-of-the-art pop-up satellite archival tags (PSAT). The pilot study revealed that bull sharks, residing in a relatively small area close to Walker’s Cay for most of the year, would leave the site in the spring and travel as far as the eastern coast of the US. This is the first indication of movement of bull sharks between the Bahamas and the Florida coast, underscoring the need for international co-operation in shark conservation.
Since 2004, the main field site of the Bull Shark Tagging Programme is located in the South Pacific. The scope of the project is now much broader and includes other shark and fish species inhabiting the Shark Reef Marine Reserve in Fiji. Here, up to eight different species of sharks can be encountered on a regular basis making it an excellent reef for studying free-ranging sharks and other reef fishes in their natural environment.
The Bull Shark Tagging Programme was initiated in 2003 and has been co-funded by SOSF since 2004. The initial pilot study in the Bahamas tested the feasibility of studying movement patterns and habitat use of bull sharks with state-of-the-art pop-up satellite archival tags (PSAT). The pilot study revealed that bull sharks, residing in a relatively small area close to Walker’s Cay for most of the year, would leave the site in the spring and travel as far as the eastern coast of the US. This is the first indication of movement of bull sharks between the Bahamas and the Florida coast, underscoring the need for international co-operation in shark conservation.
Since 2004, the main field site of the Bull Shark Tagging Programme is located in the South Pacific. The scope of the project is now much broader and includes other shark and fish species inhabiting the Shark Reef Marine Reserve in Fiji. Here, up to eight different species of sharks can be encountered on a regular basis making it an excellent reef for studying free-ranging sharks and other reef fishes in their natural environment.
Aims & objectives
The main aim of the Bull Shark Tagging Programme is to better understand the behaviour and ecology of bull sharks. Besides this, the long term goal of the project is to establish the Shark Reef Marine Reserve as a prime site for shark research and to produce scientific data that will help towards the conservation of the various shark and fish species that regularly visit the marine reserve. In order to implement meaningful conservation measures, basic biological data such as population sizes and dynamics, habitat use, nursery and mating grounds, and small- and large-scale movement patterns must be known.
One particularly important aspect of the project in Fiji is the investigation of shark behaviour as a response to a tourist shark feeding dive. Feeding of elasmobranches has become a popular means by which tourists and tourism operators can facilitate close observation and interaction with sharks and rays in the wild. Feeding wild sharks is a controversial issue and has received a lot of public and media attention.
One particularly important aspect of the project in Fiji is the investigation of shark behaviour as a response to a tourist shark feeding dive. Feeding of elasmobranches has become a popular means by which tourists and tourism operators can facilitate close observation and interaction with sharks and rays in the wild. Feeding wild sharks is a controversial issue and has received a lot of public and media attention.
In the field
The project uses the full spectrum of telemetry techniques, ranging from direct observation of sharks and fish in their natural habitat to acoustic and satellite telemetry, as well as genetics and local ecological knowledge.
The following projects are currently underway in Fiji:
• the Bull Shark Tagging Programme investigates large- and small-scale movements of bull sharks using satellite and acoustic telemetry as well as direct observation of the sharks in their natural environment. Whereas the large-scale movement studies are principally aimed at identifying and eventually protecting the bull shark nurseries in the rivers, the small-scale movement research is aimed at determining the optimum size and geographical extension of the protected area. We aim at testing several hypotheses linking the periodic disappearance of the bull sharks in spring/early summer to their birthing and mating cycles
• exploring local and traditional ecological knowledge along all of Fiji's major rivers. Local and traditional ecological knowledge have the potential to improve community-based coastal resource management by providing baseline data such as information about the presence, behaviour and ecology of species inhabiting these environments. Our major aim is to explore the potential of local and traditional ecological knowledge to identify shark river habitats in Fiji, to learn how locals regard and use sharks, and to capture ancestral legends and myths that shed light on the relationship between local people and these animals
• maintaining an exhaustive database about the shark dives. This is the backbone of the research into population dynamics, life cycles, inter- and intra-specific interactions and questions pertaining to the shark diving industry, namely the effects of the shark diving operators’ activities on the animals and the optimum procedures one ought to adopt in order to ensure a maximum of safety.
The following projects are currently underway in Fiji:
• the Bull Shark Tagging Programme investigates large- and small-scale movements of bull sharks using satellite and acoustic telemetry as well as direct observation of the sharks in their natural environment. Whereas the large-scale movement studies are principally aimed at identifying and eventually protecting the bull shark nurseries in the rivers, the small-scale movement research is aimed at determining the optimum size and geographical extension of the protected area. We aim at testing several hypotheses linking the periodic disappearance of the bull sharks in spring/early summer to their birthing and mating cycles
• exploring local and traditional ecological knowledge along all of Fiji's major rivers. Local and traditional ecological knowledge have the potential to improve community-based coastal resource management by providing baseline data such as information about the presence, behaviour and ecology of species inhabiting these environments. Our major aim is to explore the potential of local and traditional ecological knowledge to identify shark river habitats in Fiji, to learn how locals regard and use sharks, and to capture ancestral legends and myths that shed light on the relationship between local people and these animals
• maintaining an exhaustive database about the shark dives. This is the backbone of the research into population dynamics, life cycles, inter- and intra-specific interactions and questions pertaining to the shark diving industry, namely the effects of the shark diving operators’ activities on the animals and the optimum procedures one ought to adopt in order to ensure a maximum of safety.
Project Update: 2010
Funding from the Save Our Seas Foundation for 2010 allows the continuing investigation of the bull sharks’ horizontal and vertical movements as well as more targeted efforts to find out more about bull sharks in Fijian rivers. These data will help to better identify the ecological niche of this species as well as to hopefully get information on where they go when they are absent from the Shark Reef Marine Reserve.
Updates on and results from this project can be found at www.leucas.net and on the SOSF blog.
Updates on and results from this project can be found at www.leucas.net and on the SOSF blog.
Project Update: 2009
For the 2009 field season, it is planned to acoustically monitor additional bull sharks and expand the receiver array as well as tag four adult bull sharks with state-of-the-art pop-up satellite archival tags. The successful 27 day tagging of a female bull shark with a high rate pop-up X-Tag in 2008 (sponsored by the Save Our Seas Foundation) has produced a detailed dataset on the vertical movement of this species. With the support of the Save Our Seas Foundation, two high rate (depth and temperature readings every few minutes) and two standard X-Tags that will also collect light intensity values for subsequent geolocation will be attached to bull sharks at Shark Reef Marine Reserve Fiji in 2009.
Project Update: 2008
During 2008, more than 45 sharks – largely bull but also sicklefin lemon (Negaprion acutidens) and tiger (Galeocerdo cuvier) – have been acoustically tagged and some have been fed tags with sensors to collect stomach temperature data. Sharks equipped with acoustic tags have been picked up by several receivers placed on Shark Reef and surround reefs. Extensive field work has identified more than 30 individual bull sharks based on unique external markings, such as cut fins, body scars and body coloration. This will also enable the visual tracking of individuals over time – many of the sharks are known to have frequented the reef for several years. During 2008, tissue samples have also been collected from bull and grey reef sharks. These will form part a collaborative research program into the genetic structure of the species being carried out by another SOSF-funded project based in Florida.
Another interesting aspect of the project will be to hopefully solve the mystery of the disappearance of the bull sharks from the local reefs each year from October to January. A likely explanation is the movement to mating and/or nursery grounds. Anecdotal evidence suggests that female bull sharks give birth in and use freshwater rivers in Fiji as nursery grounds. For autumn 2008, there are plans to both externally tag and feed transmitters to pregnant and non-pregnant female bull sharks as well as male bull sharks before they disappear from Shark Reef, selected rivers in Fiji are being monitored with VR2 receivers.
Initial research carried out by Juerg Brunnschweiler and the SOSF team has already been instrumental in supporting efforts to have Shark Reef declared a no-take zone and developed as a self-sustained diving site as part of a marine protection program. This has now been sanctioned by the Fiji Department of Fisheries. Establishing Shark Reef as a prime site for shark research remains a key objective and will further enhance the ability to learn about and protect the marine species that inhabit this part of the South Pacific..
Another interesting aspect of the project will be to hopefully solve the mystery of the disappearance of the bull sharks from the local reefs each year from October to January. A likely explanation is the movement to mating and/or nursery grounds. Anecdotal evidence suggests that female bull sharks give birth in and use freshwater rivers in Fiji as nursery grounds. For autumn 2008, there are plans to both externally tag and feed transmitters to pregnant and non-pregnant female bull sharks as well as male bull sharks before they disappear from Shark Reef, selected rivers in Fiji are being monitored with VR2 receivers.
Initial research carried out by Juerg Brunnschweiler and the SOSF team has already been instrumental in supporting efforts to have Shark Reef declared a no-take zone and developed as a self-sustained diving site as part of a marine protection program. This has now been sanctioned by the Fiji Department of Fisheries. Establishing Shark Reef as a prime site for shark research remains a key objective and will further enhance the ability to learn about and protect the marine species that inhabit this part of the South Pacific..