Environmental Branch

Sea Turtle Protection – Hopper Dredging

Deflector Information

• Contract Specifications
• Draghead Design Drawings
• Sea Turtle Population Trawling Surveys and Specifications
• Operating Procedures

General

The prototype deflector draghead shown here was developed by the Jacksonville District in conjunction with the Corps Waterways Experiment Station. The draghead, nicknamed the Ninja Turtle deflector, was mounted on the vessel McFarland and was tested at Fort Pierce Harbor using "mock" turtles made out of concrete and shaped like a turtle. These mock turtles were placed on the bottom at intervals. The prototype draghead had an 80% protection efficiency. Following the test, the McFarland was used at Canaveral Harbor entrance channel for a two-week period with no turtle takes. Since these tests proved to be successful, the design has become part of the Incidental Take Statement of the Regional Biological Opinion issued by the National Marine Fisheries Service for hopper dredging along the Southeastern United States coastline. Based on the concerns expressed by the NMFS, the Jacksonville District has committed to use the deflector on all its hopper dredging projects.

New Developments

The prototype was a rigid construction deflector. The problem with this draghead design was that it would only function properly at a minmum range of depths. Design changes were recommended by Mr. Phil Bates, Construction Operations Division, to make the design more flexible expanding the range of depths that the draghead could function properly. The design can be seen in the Design Drawings.

Operational Problems

The draghead has been successfully used at various locations within the Jacksonville District; Jacksonville Harbor, St. Augustine Harbor, Fort Pierce Harbor, Fernandina Harbor, and Palm Beach Harbor. Turtle takes of the green sea turtle have occurred during the final stages of dredging at Fort Pierce and Palm Beach Harbors because the draghead had not been firmly engaged with the bottom. At Tampa Harbor, it was suspected that turtles were taken when the hopper dredge was using its pumps through the draghead which were suspended in the water column in order to use the bow thrusters for turning the vessel. This could have been a design problem with the vessel used which was not common to all hopper dredges. Another problem could have been the starting of the pumps prior to engaging the draghead with the bottom. This is done to create suction so that the pumps can operate properly once the bottom is engaged. Additional operational conditions have been added to the project Specfications to alleviate or minimize this problem. These conditions were developed based on proper operation of the draghead.

Sea Turtle Population Surveys and Relocation

Pre-dredge sea turtle populaltion surveys were required by the previous Regional Biological Opinion. Surveys were conducted either by trawling or, in cases where trawling was not practicable, visual surveys. This gave the Corps and NMFS a idea of the levels of sea turtles in the navigation channel prior to the commencement of dredging. The new RBO eliminated that requirement because of the large amount of data generated. In areas, such as Tampa Harbor, this data gathering is still used. In addittion, should sea turtle take levels reach a threshold, trawling efforts are initiated and those turtles captured are tagged and relocated. This is done to move them out of harms way as well as determine movement in and out of the project area.