Why Florida Gulf Coast University researchers are following dead fish to track red tide on Sanibel

When you think red tide, dead fish probably come to mind, along with coughing and respiratory issues, but for one group, it’s the size and the science behind the algal blooms that matter.

While anyone looking for a beach day on Sanibel tries to avoid the dead fish, a team from FGCU’s Water School is looking for them.

“We’re measuring some of the dead fish counts after the red tide bloom, see which species were affected what like magnitude was the like fish, biomass and everything like that, basically how many fish in the local area died,” said Michael Kratz, an FGCU grad student.

This is an ongoing study that started after Hurricane Ian.

“So we’re basically setting up little areas with tape measures. So it’s standardized, and then measuring the fish within that and trying to find areas that represent the beach kill,” Kratz said.

“It’s also a historical record-keeping thing where you don’t know how bad the red tide is unless you quantify the impact of the red tide,” said Rick Bartleson, a Sanibel Captiva Conservation Foundation research scientist.

“This has probably been the least severe,” said Kratz. Researchers are seeing lower fish kill counts compared to October last year. “We were counting areas like 30 by 10, we were getting like 700 fish sometimes. So it was really high density.”

The number of fish that wash up and wash away can change day to day based on the winds, but this team has a tool to track them as well. It’s called eDNA.

“So eDNA stands for environmental DNA. Basically, we can use specific regions of DNA that we know are conserved, like in fish, and we can use that to ID different fish species just by taking water, so we don’t actually have to see the fish in person,” said Kratz.

Red tide toxins kill or injure more than just fish, birds, manatees, sea turtles, and many more feel its effects.

As of Thursday, there was a red tide health alert in place for Blind Pass, Gasparilla Island State Park, and on Sanibel at Tarpon Bay Road and Lighthouse beaches.