In the waters surrounding St. Thomas and St. John, U.S. Virgin Islands, we conducted an assessment of the causes and effects of lost fish traps. We evaluated fish mortality, trap fouling and degradation, and assessed the efficiency of autonomous underwater vehicles in detecting and verifying derelict traps in a coral reef ecosystem. We estimate that, of the approximately 6,500 traps located in the area, 650 traps are lost each year, totaling an estimated annual fish market loss of $34,000.
Why We Care
Generations of fishermen in St. John and St. Thomas have used traps to catch fish and lobster. While traps are efficient and relatively cost effective, they can move during storms; become snagged by passing boats and dragged to other areas; and be vandalized, stolen, or abandoned. In addition to the economic forfeiture, lost traps pose boating and navigational hazards as well as major threats to marine life and habitats. Moreover, lost or abandoned traps continue to collect fish, a casualty known as ghost fishing. Because the extent of the problem and its ecological and economic impacts were unknown, this project was initiated to begin defining the scope, causes, and impacts of derelict fishing traps in St. John and St. Thomas.
What We Did
We mapped fishing effort in St. John and St. Thomas, documenting the number and type (fish or lobster) of traps being used, and their specific locations. Trap use had not been characterized at this scale for this region.
We collected information from local fishermen about trap discarding practices and locations where traps had been lost in the past. Our partners ran field experiments to quantify fish death in controlled derelict traps and to assess trap degradation. We tested the U.S. Navy’s autonomous underwater vehicles (AUVs) equipped with sidescan sonar to evaluate their ability to detect derelict traps in and adjacent to various complexities of coral reefs.
What We Found
Approximately 6,500 traps were used in the region, and the total annual loss rate was estimated to be 10 percent. Traps from the primary commercial fishery were primarily found in deep water locations on the south shores of St. John and St. Thomas. An unknown fishing group targeted shallow waters. The mortality of fish held in experimental derelict traps was 5 percent, with an estimated $30,000 to $40,000 in annual catch loss.
Our experimental traps at 10 meters moved considerably (up to 150 meters) by a hurricane; movement before the storm was negligible. Traps at 20 meters were not moved by the hurricane. Fish movement was not impaired in traps with escape panels open, and mortality was rare. Some experimental derelict traps provided structure for juvenile fish species. In many cases, abandoned traps had been colonized by benthic organisms, including stony corals. AUVs were successful at identifying traps in low relief habitats.
We are pursuing partnerships to continue AUV surveys to fully quantify derelict fish trap abundance in the study area. We hope to use the AUV to verify potential archaeological sites such as shipwrecks.