State biologists say hundreds of fish that have turned up dead near Davis Islands were not killed by the massive algae bloom that has plagued Tampa Bay all summer.
Instead, what killed all those sheepshead, spotted sea trout, catfish and lizardfish was a lack of oxygen in the water caused by poor flushing action from nearby canals, according to experts from the Florida Wildlife Research Institute in St. Petersburg.
Biologists first heard reports of the fish kill last weekend, then headed out to check it.
They observed a variety of fish species floating along Bayshore Boulevard, as well as south and west of Davis Islands, Hillsborough County Environmental Protection Commission scientist Richard Boler wrote in an e-mail Friday.
The institute scientists checked the waters along Erie Avenue, Riviera Bridge Drive and the Davis Island Yacht Club beach. They didn't find anything at the beach, they said, but the other two locations were another story.
"The water analysis showed low dissolved oxygen readings at the first two locations only," the institute scientists wrote in their report. "These two canals are poorly flushed systems where dissolved oxygen levels can be depleted, resulting in fish kills."
But they found no sign that the fish kill was caused by Red Tide or by the gigantic algae bloom first detected back in June.
That bloom is one of the largest in the bay's history, stretching 14 miles. The bloom was most likely fueled by pollutants — fertilizers, yard waste and animal feces — that were washed into the bay from the rains that hit the region in recent months. The summer's heat has helped spur the explosive growth of the microscopic algae.
A similar bloom in Tampa Bay last year killed catfish, menhaden, pinfish, triggerfish, puffer fish, spadefish, stingrays, blue crabs, brittle stars and small Florida crown conchs. At night the blooming algae absorb all the oxygen in the water, leaving none for any fish nearby, and the fish suffocate.