Derelict crab pots are fishing gear that has been lost or abandoned, creating unseen hazards for boaters and death traps for marine life like diamondback terrapins and blue crabs. Since 2019, DESG coastal ecologist Kate Fleming has led the effort to collect these ghost crab pots from Inland Bays tributaries, removing more than 200 of them so far with the help of Trembanis, his students, and dozens of volunteers. The effort has identified hundreds more waiting to be collected, and researchers suspect there are thousands still yet to be found. The removal project will continue in the area of the Indian River in January 2022, and researchers can use all the help they can get.

“We have about doubled the number of people that have expressed interest in bringing personal boats to come out and remove pots,” Fleming said. “To leverage their assistance, we need more sonar expertise.”

Dave Walter of Milton, an ocean engineer who now works for the U.S. Department of Energy, said helping with the crab pot removal effort was exactly why he came to learn more about the sonar devices.

Earlier this fall, Walter and 17 other people attended a virtual session to learn more about the capabilities of consumer-grade fish finders like those made by Humminbird or Garmin, which typically cost $1,500 and up (way, way up, in some cases).

A handful of the participants in the virtual fish finder training joined sonar expert Vince Capone with Black Laser Learning, Fleming and Trembanis on the water Saturday, Sept. 18, to get some hands-on experience in using the devices for more than finding fish.

“A lot of people who have these units don’t know how to use them beyond basic stuff,” said Fleming. “This is an opportunity to get more information they can apply to use them better.”

“Fish finders” are underwater devices that use sound waves that ping off the bottom surface of waterways and collect data about what lies beneath, from large metal objects like crab pots to ripples on the seafloor caused by currents and storms. Researchers can also use the data collected by the equipment to map marine habitats, as is being done in a graduate student project currently focusing on changes at Herring Point.

During the Sept. 18 training, students, professionals, recreationalists, private citizens and future volunteers learned how to work with sonar devices, by interpreting the images that pop on to the screen and learning to record and interpret the data they collect. They practiced by setting waypoints where instructors had placed crab pots in the water as they slowly traveled in a pontoon boat around the boat basin off Pilottown Road across from the University of Delaware’s Hugh R. Sharp Campus in Lewes. The data collected can also show users where they’ve already been, so they don’t have to boat blindly if they’re searching for something specific.

Instructors, including oceanography graduate students Grant Otto and Jennifer Repp, showed attendees how to record data, which can then be saved for future reference and even shared with researchers like Fleming and Trembanis. Like the National Oceanic and Atmospheric Administration mantra, “Map once, use many times.”

“It’s all about creating images with sonar,” Capone said. “You’re literally taking acoustic pictures of the bottom.”

Not only can sonar be used for finding fish and underwater obstacles, but it can also play a helpful role in more dire situations, such as missing people, drowning cases and even to find evidence discarded in the water.

Last summer, two swimmers went missing off of Bowers Beach, and Leipsic Volunteer Fire Company Deputy Chief Mike Greco, who attended the event on Saturday, wondered whether more side-scanning sonar capabilities could have helped with that search effort.

But he also came to learn more about the devices from a scientific perspective as an employee of the Delaware Department of Natural Resources and Environmental Control (DNREC). Working DNREC’s trawl surveys, which monitors fish and shellfish populations, there are times the trawl equipment gets hung up on stuff at the bottom of a waterway.

Sonar can help “ground truth” obstacles like those seen during trawls, Greco said.

For the derelict crab pot project, it is the opposite approach, with sonar making the initial find of possible pots and later removal confirming, and correcting, the problem. Walter, the boater who came to the September training specifically to help with the project, is hoping everyone who benefited from the training might be able to play a part.

“Now that they know how to operate these and know what something looks like on the bottom, maybe something that’s not supposed to be there, they can call the right authorities and hopefully have it fixed,” Walter said. “It’s like playing detective.”

For more information about the upcoming derelict crab pot removal effort or to volunteer, visit deseagrant.org/derelict-crab-pots or contact Fleming at kfleming@udel.edu.