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NOAA Scientists Work to Quantify, Mitigate Effects of "Ghost" Crab Traps
The blue crab is an iconic species of the Chesapeake Bay. The bay's blue crab fishery—the nation's largest—uses traps as the primary method of harvest. But every year, commercial fishermen might lose up to 30 percent of these traps each year after the traps' float lines are severed by boat propellers, chafed due to wave action, or moved by strong currents. Without floats, watermen are unable to find these traps.
Quantifying Derelict Traps
To quantify the number of derelict traps throughout the Chesapeake and to evaluate the direct effects of derelict traps on blue crabs and other estuarine species, the NOAA Chesapeake Bay Office, with support from the NOAA Marine Debris Program, conducted field work and research in the Maryland portion of the bay. The densities of derelict crab traps were quantified and examined using side-scan sonar, ground-truthing surveys, and a diver-based survey.
The survey results indicate that derelict traps appear to be ubiquitous in areas where the commercial hard crab trap fishery is active. The total number of derelict traps in the Maryland Bay is estimated to be more than 84,500 traps.
A Measurable Source of Unaccounted Fishing Mortality
To determine the effects of derelict traps, scientists deployed and monitored experimental crab traps, revealing that blue crab and a variety of by-catch species continue to be captured and killed even after bait in the trap is gone. Experimental traps continued to capture species for the entire study, indicating that derelict traps last for at least 14 months.
White perch had the highest mortality of all by-catch species and seem to be highly susceptible to derelict traps; other by-catch species included oyster toadfish, spot, pumpkinseed, Atlantic menhaden, Atlantic croaker, American eel, sheepshead, and black sea bass. Scientists estimate blue crab mortality is 20 crabs per trap per year.
Potential for Mitigation
The study's final report notes that although there are currently no management regulations in place to reduce ghost fishing by derelict traps, there are options to reduce the effects and potentially reduce the numbers of derelict traps in the Bay. These include modifications to the traps to help living resources escape from derelict traps, developing management strategies to reduce crab trap losses, and retrieving traps once they become derelict.
The NOAA Chesapeake Bay Office is working with partners on a similar study in Virginia. Information collected by NOAA will help scientists and managers work with industry to determine the best combination of approaches to reduce the loss of crab traps in the Chesapeake Bay.