Study results: 1,570 potential derelict traps off the NH Seacoast

1,570 Potential Derelict Lobster Traps located during 4 days of Derelict Fishing Gear Sidescan Sonar Survey: Portsmouth, NH and the Isle of Shoals

Rozalia Project for a Clean Ocean conducted a 4 day sidescan sonar survey to locate derelict fishing gear around the coastal waters of Portsmouth, NH and the Isle of Shoals on the behalf of the Blue Ocean Society for Marine Conservation, NH Sea Grant and UNH Cooperative. The Sonar survey was conducted as part of the Marine Debris to Energy Project, a NOAA funded project to detect and remove marine debris along the coastline from southern Maine to northern Massachusetts. The Sonar survey was also supported by Optima Bank, Portsmouth, NH and the Kittery Point Yacht Yard, Kittery, ME.

METHOD:

The survey was conducted from Rozalia Project's 60ft sailing research vessel American Promise utilizing a Tritech Starfish sidescan sonar towed from the starboard quarter of the vessel at speeds ranging from 1.9-4.3 knots, in depths of water from 20-135 feet.

The aim of the survey was to locate derelict fishing gear and investigate it's volume and geographical distribution, in this case predominantly derelict lobster traps (pots)

Potential derelict lobster traps were identified on the sonar image by the following criteria: red dots=potential derelict trap, blue dots=active trap. The following examples are from the sonar survey:

1:    Groups of 3 or more lobster traps clumped together in close proximity:

2: Trap line of 3 or more with v shape or large deformation of the multi-trap line:

3: Individual traps with no active gear nearby:

4: Trap lines with no active lobster buoys within the Starfish’s range:

When potential derelict lobster traps where viewed on the sonar display, a snapshot was taken from the sonar image. In addition, waypoint locations and track information were recorded on an iPad utilizing Navionics charting software with snapshot time, waypoint number, track number, track start and finish GPS positions and track start and finish times recorded on data sheets.

RESULTS

1: Portsmouth Harbor/Piscataqua River Entrance (Fort Constituition to Gunboat Shoal): 

• 30.18 potential derelict traps per mile
• 9 tracks totaling 11.1nm were surveyed with 335 potential derelict lobster traps located

2: Gunboat Shoal to Rye Ledge:

• 102.86 potential derelict traps per mile
• 9 tracks totaling 10.14nm were surveyed with 1043 potential derelict lobster traps located

3: Isle of Shoals:

• 25.95 potential derelict traps per mile
• 7 tracks totaling 7.4nm were surveyed with 192 potential derelict lobster traps located

Survey totals:

• 1,570 potential derelict lobster traps located
• 28.64 miles of ocean were surveyed
• 296 waypoint locations of potential derelict traps recorded on sonar

CONCLUSION

1. Clumps/groups of lobster traps are often located at substantial terrain changes, for example, from sand to rock ledge (see below – ledge off Rye Harbor):

2. A higher volume of potential derelict lobster traps exists within 1.0 mile of the coast.  Density of inshore tracks  = 72.8 pdlt/mile
3. A higher volume of potential derelict lobster traps exists in proximity of highest density of active fishing gear (recommend ROV survey to confirm accuracy of sonar survey in these high density active trap areas).
4. A lower volume of potential derelict lobster traps exists offshore beyond 1.0 mile of the coast. Density of offshore tracks = 37.7 pdlt/mile.
5. A lower volume of potential derelict lobster traps exists in areas of lowest density of active gear (Isle of Shoals, and offshore tracks).
6. Derelict lobster traps are not static, during the survey, American Promise re-surveyed a shipwreck that was part of a 2008 Sonar Survey (below). During the 2008 survey the top of the wreck was covered by over 20 derelict traps. During our 2011 survey, the sonar image shows a wreck with no derelict lobster traps on it, just an active trap line to its port side. More research is needed on what moves the traps around (storms, draggers?) and where they go.

In the opinion of the Rozalia Project, the waters of coastal New Hampshire and the Isle of Shoals have a significant amount of derelict fishing gear on the sea floor with several inshore (within 1 mile of coast) locations where it has accumulated that would make removal of the derelict fishing gear feasible.