Bull Sharks

Nursery Habitat Tracking

In 2001, the Center for Shark Research began studying the habitat use of newborn and juvenile bull sharks (Carcharhinus leucas) in the Caloosahatchee River, in Southwest Florida. The river is the connector between Lake Okeechobee and the Gulf of Mexico. Because of its attachment to the lake, the river has been substantially modified over the last 100 years. One such modification is dams, which have been built to regulate water flow from the lake down the river. The opening and closing of dams throughout the year coincides with changes in the river's salinity, which can in-turn affect the animals in the river.

Bull sharks can spend extended periods of time in freshwater. This ability makes them ideal subjects for a study monitoring habitat use within the river based on fluctuating salinities created when upriver locks and dams are opened and closed. In this study, bull sharks are tagged with radio transmitters that can be "read" by acoustic receivers placed in the river. An array of 23 acoustic receivers cover roughly 20 miles of the river, from the mouth where it feeds into San Carlos Bay to a point upriver near the Interstate 75 overpass. 

The receivers, which can detect transmitter signals up to 800 meters away, are spaced in such a way as to maximize listening coverage.  Although all data are preliminary, some bull sharks have remained within the river for the first two years of their lives. 

 

 

2005 interns Meredith Penland and Brooke Stanford release a bull shark with a transmitter attached into the Caloosahatchee River. 

 

 

 

 

 

 

 

In addition to bull sharks, the acoustic receiver array within the river has allowed us to monitor movements of other species, such as the cownose ray (Rhinopterus bonasus) and the endangered smalltooth sawfish (Pristis pectinata).

 

 

 

 

Former University of South Florida graduate student Angela Collins prepares to tag and release a cownose ray into the river study site.