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Shark Nurseries in the Ten Thousand Islands |
 Failed Residential
Development Permanently
Altered the Natural
Sheetflow
In the 1960's, a large residential neighborhood just north of the Ten Thousand Islands was planned. A network of roads and 58 canals were built, but the project was later abandoned. The failed development permanently altered the natural sheetflow, or supply of fresh water, to the bays and estuaries of the Ten Thousand Islands. The new canal system directed freshwater runoff down one central canal to the Faka Union Bay and out to sea. Studies indicate a distinct decrease in salinity values in this bay (8-12 ppt), and a significant increase in salinity in two adjacent estuaries, which provide an important nursery habitat for sharks and other marine life. In order to improve the distribution of fresh water throughout the Ten Thousand Islands estuaries, land purchased by the State of Florida is now being restored by the South Florida Water Management District. Upon completion, freshwater flow out of the Faka-Union Canal is expected to be reduced by approximately 99%. |
 Effects of Restoration on Shark Populations
Sharks utilize shallow, protected estuarine bays to give birth to their young. These back bays provide young sharks with a bountiful food supply and protection from potential predators, such as larger sharks. In order to gain an understanding of shark nurseries and distribution before, during and after the restoration of the Ten Thousand Islands watershed, RBNERR researchers began collecting shark demographic data on a monthly basis starting in 2000.
This is possibly the first study ever to address the effects of restoration on shark populations. They sample the three bays adjacent to the canal, one bay per night each month, using a monofilament gill net and baited long lines. A donated houseboat is used as home base, and staff sets up the nets and lines two hours before sunset, watching closely until two hours after sunset. Armed with mosquito netting and gloves, researchers retreive the sharks upon capture.
Once in the boat, each shark is weighed, measured, tagged and released. Water conditions, including temperature and salinity, are documented each night. Bull sharks (Carcharinus leucas) are more tolerant of low salinities than other sharks, and freely move from marine to freshwater locations. According to the data so far, 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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