Dead whale shark in Florida washes up on beach; red tide likely killer

A whale shark was found dead on a Sanibel Island and was likely killed by the red tide, scientists said. (iStock)

A dead whale shark that recently washed up on a beach on Sanibel Island in Florida was likely killed by the current red tide bloom, wildlife officials said.

The bloom occurs when “colonies of algae — simple plants that live in the sea and freshwater — grow out of control while producing toxic or harmful effects on people, fish, shellfish, marine mammals, and birds,” according to the National Ocean Service.

Tissue samples taken from the whale shark indicate it was infected by the Karenia brevis organism, which produces the brevetoxins that can harm and, in some cases, kill sea life.

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The current red tide bloom in southwestern Florida is the longest, continuous bloom in more than a decade, scientists said this week.

In addition to the whale shark, the bloom has stranded nearly 100 sea turtles on the beaches, more than 50 of which were dead.

“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," Michelle Kerr, a spokeswoman for the Florida Wildlife Research Institute, told the Naples Daily News of the whale shark’s death.

The higher concentration of the toxins, the more likely it is that large sea creatures -- such as a whale shark -- can be affected by the bloom, Dr. Richard Bartleson, a research scientist with the Sanibel-Captiva Conservation Foundation, told Fox News.

A low concentration of the Karenia brevis organism is considered to be 10 cells per liter of water, while a high concentration -- which has the ability to kill fish -- typically starts at 500,000 cells per liter.

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Some marine and water quality scientists have argued that the abnormally high concentration of Karenia brevis is linked to human activities such as farming. Many of the chemicals used in fertilizer -- such as phosphorus and nitrogen -- reach the ocean via surface runoffs that occur after a rainstorm or hurricane. These chemicals provide the “perfect nutrients” to worsen the bloom, Bartleson said.