Shark Nursery Assessment Program
Since 1999, research staff have been conducting monthly assessments to gain an understanding of fish population size and estuarine habitat use in relation to hydrologic restoration in the Ten Thousand Islands watershed. A monofilament gill net and baited long lines are used to catch sharks and sawfish for a database of community composition and age ranges. Using a donated houseboat as home base, researchers monitor the nets and lines from two hours before until two hours after sunset. Sharks and sawfish are carefully brought into the boat to be identified, measured, sexed, weighed and tagged before release so that we can continue to learn about habitat use as the fish age. Water conditions, such as temperature, dissolved oxygen and salinity, are also recorded.
An acoustic monitoring program is now underway to complement this assessment. Five acoustic receivers have been deployed in one of the bays in the Ten Thousand Islands study area. The receivers will record the presence of any sharks, sawfish or other large fish with an acoustic tag that swim within a several-hundred-meter radius. The receivers will also record basic information from tags in use by partnering institutions who are conducting similar research, including FWC and Mote Marine Laboratory. The data will be downloaded from the receivers each month as part of the reserve’s ongoing fisheries assessment and will help fill gaps in our collective understanding of predatory fish movement and habitat needs along the coast.
Why This Matters
Sharks utilize shallow, protected estuarine bays to give birth to their young. These back bays provide young sharks with plenty of food and protection from potential predators, such as larger sharks. To gain an understanding of shark nurseries and relative distributions before, during and after the restoration of the Ten Thousand Islands watershed, reserve researchers began collecting shark demographic data on a monthly basis in May 2000. This may be the first study ever to address the effects of restoration on shark populations.
Bull sharks (Carcharhinus leucas) are more tolerant of low salinities than other sharks, and freely move from marine to freshwater locations. Results to date indicate that bull sharks are by far the dominant species caught in the Faka Union Bay. Scientists hope to learn more about sharks by documenting the different types of sharks found in each location to determine how they react to changes in their environment.
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Shark Research Partnerships
Over the years Rookery Bay Reserve has worked with various research partners to broaden the applications of this shark assessment program. One collaborative project, facilitated by the Shark Foundation, entails collection of genetic samples that assist researchers with the University of Miami and Stonybrook University to determine possible linkages with other shark populations around Florida and the Caribbean. Another collaborative project assisted the Florida Aquarium, Georgia Aquarium, and Shedd Aquarium in their analysis of stress levels in sharks following capture.
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Shark Monitoring Also Tracks Sawfish
In 2002 and 2003, 11 juvenile sawfish were captured, tagged and released. Four of them were recaptures that were previously tagged. The growth data from all recaptures contributed to a publication/paper which showed a substantially faster growth rate than previous literature exhibited. Since 2012, 33 sawfish, including one possible adult female (15' in length), were captured, tagged and released. All sawfish except the one large female, were 8' long or less and assumed to be one or two years old. Southwest Florida estuaries are important nursery habitats for juvenile smalltooth sawfish. Sawfish are extremely dangerous and caution is paramount if you encounter any sized sawfish.
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