Sea trout spawning sounds offer hope for lagoon

Vero Beach marine scientist Dr. Grant Gilmore was out on the lagoon last Tuesday night, wrapping up several months of research funded by a $25,000 grant from the Coastal Conservation Association.

When he lowered an underwater microphone to the bottom of the Indian River Lagoon between Fort Pierce Inlet and the 17th Street bridge, he was happy with what he heard: The spotted sea trout were making some serious whoopee.

Grant’s hydrophone picked up loud clickety-clacking, freight train-type noises some 10 feet below – signs that males and females were still enthusiastically propagating their species.

“The sound is directly proportional to eggs in the water column – the more sounds, the more eggs,” Gilmore, founder of Estuarine Coastal and Ocean Science (ECOS), told a small group of recreational anglers aboard Captain Paul Fafeita’s pontoon boat.  “It’s a barometer of water quality – not just spawning.”

Gilmore has been studying the spawning calls of fish in the 150-mile-long lagoon since he began his career at Harbor Branch Oceanographic Institute 40 years ago, mapping more than 100 sites where sea trout reproduce based on the sounds they emit from vibrations in their gas bladders. He visits those sites year after year at night from April through late September around the full and new moons.

Gilmore, who is widely considered the most eminent expert on fish species in the lagoon, zeroed in on sea trout because it’s an important recreational species and a prime indicator of overall lagoon health.

Gilmore believes the waters near Vero Beach are the most important spawning grounds left in the lagoon. That is due, in large part, to tidal flushing from the nearby Fort Pierce and Sebastian inlets that help maintain better water quality and seagrass growth here compared to the rest of the estuary.

This summer, Gilmore partnered with the Coastal Conservation Association of Florida – a statewide recreational fishing and research-support organization with more than 20,000 members – to expand his research. The CCA awarded him a $25,000 grant, purchased three complete hydrophone sets, and deployed three small teams – CCA members Gilmore taught to listen in on and identify fish spawning calls.

Andy Steinbergs of Vero Beach, chairman of the habitat committee for CCA Florida, is one of the newly-minted trout eavesdroppers.

Steinbergs said his group will continue to listen in on trout next season, feed the information to Gilmore and “let him tell us whether the stocks are getting better.  CCA represents families and fishermen and we want to make sure our grandkids get to fish.”

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