Acoustically Triggered Buoyless Lobster Trap Recovery System

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Project Type: 

Students Involved:

Hayden Turner UNH - Department of Mechanical Engineering
Jud DeCew UNH - Department of Mechanical Engineering
Darryn Goldsmith UNH - Department of Electrical and Computer Engineering
Scott Brimlow UNH - Department of Mechanical Engineering

Faculty Advisors:

Kenneth Baldwin UNH - Department of Mechanical Engineering

The Buoyless Lobster Trap (BLT) is an acoustically triggered retrieval mechanism for deep water lobster trawls. The system manipulates a rotary solenoid to discharge a buoy, connected to a line, to the surface from the ocean floor. The BLT is made up of three integrated subsystems: the electronics, release and winding mechanism. The design goal was to keep the system simple and use an existing trap as a vehicle for all the components.

The BLT system will replace the current fishing practice indiscernibly. The system will completely eliminate the need for fixed gear, which will minimize marine mammal entanglements. The BLT is a simple, robust, inexpensive and reliable means of accommodating the ALWTRP supplicated by the Department of Commerce. The ALWTRP is the Atlantic Large Whale Take Reduction Plan, which seeks the reduction of mammal fatalities due to commercial fishing practices.

The BLT prototype exploited a Hummingbird Fish Finder to act as the system transponder that will project the sound wave from the surface vessel to the trap on the ocean floor. The hydrophone was poached from a previous project and the ideal frequency is 160 kilo Hertz. The Hummingbird transmits a signal at 200 kilo Hertz that does not overlap the hydrophone's frequency band so amplification and manipulation of the signal is very inefficient. The final BLT will demand identical sensitivity and operating frequencies of the transponder and hydrophone.

The sea faring portion of the system is made from a converted lobster trap so that handling of traps on deck will not change. Dysfunctional traps are readily available to the fisherman so that the total cost of the system can be reduced. The system hydrophone protrudes out of the trap about two inches due to its origin, which creates a stacking problem. The final system will be constructed so that no portion of the system extends beyond the boundaries of the lobster trap. This will protect the contents.

The BLT is a simple device that can be operated by any person, no matter what his or her background. Simply pressing the button will dispatch the signal and the rest is analogous to the present lobster trawl hauling technique. Maintenance for the system consists of changing the batteries a couple of times a year. The estimated cost per unit is $315, and each string of traps should have at least two, for safety reasons. These units will replace conventional commercial lobster trawling practices without creating an undue burden to the industry and virtually eliminate the danger to whales.


Available from the National Sea Grant Library (use NHU number to search) or NH Sea Grant


  • BLT: acoustically triggered buoyless lobster trap recovery system (1999). Hayden Turner, Jud DeCew, Darryn Goldsmith and Scott Brimlow. Advisor: Ken Baldwin.