Hundreds of fish -- possibly thousands -- were washed up along several miles of Anna Maria Island shoreline, a grim discovery for dozens of early Christmas Day beachgoers.

A red tide bloom was suspected, the Manatee County Sheriff's Office said. But recent water samples taken in Southwest Florida by the Fish and Wildlife Conservation Commission gave no indication of a threat.

There was a trace of red tide in samples Dec. 15-17 in Lee County. The only other red tide were low to medium blooms in parts of the Keys.

Another possibility was discarded bycatch from a mullet run, and mullet thrown overboard after their roe was harvested, local residents said.

The fish were evenly distributed in a zone stretching at least 3 miles -- from "three piers" in Bradenton Beach to north of Manatee Avenue in Holmes Beach. The beaches were stench-free at 7:30 a.m. but that didn't last long.

The FWC's next red tide report is scheduled Jan. 2. Fish typically die when exposed to 250,000 red tide (Karenia brevis) cells per liter of water, according to the FWC. A medium-sized bloom is 100,000 to 1 million cells per liter. The FWC said the mortality threshold varies with bloom concentration and exposure.

In 2013, 276 manatees perished because of red tide, according to state records.

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