Beware when Redtide shows up in the Florida Keys, you may not want to eat the fish you catch

Redtide near shore


Have you ever heard of a Redtide? I’m sure if you fish on the west coast of Florida or in the Florida keys you have. It’s a kind of algae that’s harmful to fish, shellfish, birds, manatee and man.

Water temperature, salinity, currents and nutrients all play a role in the algae growing so fast that it produces an algae bloom. More than a hundred harmful strains of algae lay dormant under the silt and sand at the bottom of the ocean. Algae blooms happen all around the world and can occur in both fresh water and salt water. In the Florida Keys and the Gulf of Mexico the most likely time for this to happen is between the months of August and November when the waters are their warmest. Redtide has been seen here in every month of the year. It has to be a very large occurrence to last thru the cold winter months. They do occur each year in the offshore waters, 10 to 40 miles out in the Gulf of Mexico. It only becomes a problem when the wind and tides carry it to the coast. When the conditions are just right, the bloom can stay in the same area for months while moving up and down the coast line.

Here's a link for a satellite view of this event.

As the redtide grows, it gathers into dense red patches at the surface of the water. This species of algae has a red pigment that gives it the reddish color. These blooms aren’t always red. Sometimes they look green, brown, and sometimes purple. There have been some algae blooms where the water didn’t change color. Algae blooms have also been caused by the dust and iron particles blowing across the Atlantic Ocean on the trade winds from the Sahara Desert.

Redtide contains some of the most potent poison in nature. During high concentrations such as a bloom they release their toxins into the water. This toxin affects the central nervous system of fish. It can paralyze the fish and cause them to stop breathing. This can cause massive fish kills. They then wash ashore and become a health hazard as they lay there decaying. Birds such as cormorants, seagulls, turkey vultures and pelicans feast on the dead fish and become sick.

bad redtide

For man these algae blooms are responsible for the loss of millions of dollars in the commercial and recreational fishing industry and to the tourist trade. Man can also be affected physically by this phenomenon. When exposed you may have itchy eyes, coughing, sneezing, and tearing of the eye. It seems to readily effect those people with asthma. These symptoms are temporary and will go away a few hours after you’ve left the area of the bloom.

It’s all right to eat fish, crab , lobster and shrimp during a Redtide. The toxins aren’t absorbed into the edible meat of these creatures. The fish may not show any physical symptoms of being poisoned at first. So it’s up to you to decide if you want to eat a fish that may be sick or dying. Contaminated shellfish such as oysters and clams on the other hand will make you sick. Cold will feel hot and hot will feel cold. You’ll have the same symptoms as you do when you’re coming down with the flu. These symptoms can begin within minutes to a few hours after eating seafood contaminated with these toxins. To date no human has ever died from this.

redtide fish kill 2006

The worst Redtide event on record was from November 1946 thru the spring of 1947. It began near Naples and spread as far north as Sanibel Island then to Englewood by January. In spring it showed up in outer Florida Bay. A few months later it stretched all the way to Tarpon Springs. It killed an estimated 500 million fish.

Algae is phytoplankton. Most species are harmless and serves as the energy producers at the base of the food chain. Without algae higher life would not exist on this planet.

Even redtide is believed to be beneficial. It kills predators, this allows food species like crab to multiply. This has been going on for hundreds of years so it must have a purpose.

There’s lots of research going on with the scientists trying to find a way to predict when the next huge algae bloom will occur. But at the present time there’s no way to predict when the next Redtide will affect the fishing in the Florida Keys.



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