Red tide likely killed whale shark that washed up on Sanibel

Chad Gillis | The News-Press

Show Caption Hide Caption An introduction to red tide Red tide is a harmful algal bloom that can sicken or even kill local wildlife. It also causes respiratory issues in humans and other animals.

A whale shark that washed up on a Sanibel beach over the weekend likely died due to red tide poisoning.

Biologists at the Florida Wildlife Research Institute in St. Petersburg examined various tissue samples and found that all contained Karenia brevis, or red tide.

"This does not indicate why it died, but because researchers had measured similar and higher levels than that in live fish caught in bloom areas, and given the high concentrations of Karenia brevis in that area and the large fish kills in that area, it’s fair to say it may be red tide," said Michelle Kerr, FWRI spokeswoman. "But we don’t know for sure. We may never know."

A strong red tide has lingered along the Southwest Florida coast since October, at times stretching from Tampa Bay to the Florida Keys.

Several fish kills have been reported in Lee and Collier counties, and areas like Sarasota are seeing effects too.

Hundreds of sea turtles plucked from Southwest Florida waters this year are thought to be red tide victims as well.

More: Hundreds of sea turtles washing up dead on SWFL beaches; red tide likely killer

The cause of death for the whale shark will be listed as "natural," as red tide is a natural event, although water quality scientists say the blooms are more intense, more frequent and longer-lasting because of human activities like farming and development.

Connect with this reporter: Chad Gillis on Twitter.

How can you help?

Call the Florida Fish and Wildlife Conservation Commission at (800) 636-0511 to report a fish kill and (888) 404-3922 to report sick, injured or dead sea turtles, manatees and dolphins.