By: Sarah Latshaw
Boat strikes, which can destroy floats and cut crab trap lines, can lead to derelict crab traps. Derelict crab traps – crabs traps that become lost or abandoned – are a threat to wildlife, can degrade habitat, and become a navigation hazard. These traps may “ghost fish” for years, capturing and killing prey like crabs, diamondback terrapins, and many fish species. Many groups have worked to reduce the number of derelict crab traps through removal efforts, but some projects – like the one I observed – aim to prevent crab traps from becoming derelict in the first place.
As a former field biologist, I was excited to get out of the office to check out the South Carolina Department of Natural Resources (SCDNR) study on crab trap float loss. Supported by funding from the NOAA Marine Debris Program and National Fish and Wildlife Foundation, the goal of this study is to identify the float rigging designs that can prevent loss of crab traps from boat strikes, as well as conduct surveys to better understand a commercial crabber’s trap loss rate.
Often teased as being over prepared – I decided to pack light instead for the supposedly warm, sunny day out on the water. Soon after hopping on the boat, however, the downpour began. We motored back to the marina and took shelter until the rain slowed. While the researchers pulled out their rain coats and pants I, kicking myself for leaving my gear behind, embarrassingly donned a clear, plastic $2 poncho I found in my car. Rookie mistake for an old-hand.
Once the rain slacked off, we headed to the research site on the Stono River near Charleston, SC to test the durability of the crab trap floats riggings the researchers assembled. Some floats were round and made of polystyrene foam that seems to explode into pieces when hit by a boat propeller. (Don’t worry, the biologists work diligently to remove all float debris from the river). Other floats were the shape of bullets and made of a spongy-type foam that seems to slice apart but not explode when hit by a boat propeller. Additionally, some float configurations had PVC to protect the line added above the float or below the float, and some had no PVC at all.
So what float configuration works best at preventing lost traps? That’s exactly what researchers at the SCDNR are trying to figure out. During my visit SCDNR evaluated multiple float configurations, by attaching each float rigging to a 10 lb. weight and then running over it with their boat at high speed. Every time the researchers ran over a buoy, they documented damage to the float and line. They continued to run over the floats (and documenting the damage) until each float had been run over 30 times, or until the float was no longer functional or attached to the line. Any debris left by the float was immediately cleaned up.
From their findings, SCDNR researchers will produce recommendations for recreation and commercial crabbers on float configurations that reduce crab trap loss. Moreover, results from the survey will help characterize the annual crab trap loss rates in South Carolina. The project is ongoing – stay tuned for results from their findings in the coming year.