Adult oysters are seen in Harpswell in this May 18, 2017, file photo. Credit: Linda Coan O'Kresik

Maine has recently lifted long closures of several shellfish harvest sites due to the potentially fatal biological toxin known as red tide.

The Portland Press Herald reports this year’s closure remained in place for three months in parts of southern Maine, nearly three times as long as the typical four to five weeks.

Jeff Nichols, a spokesman for the Maine Department of Marine Resources, said the department hasn’t determined the cause of the longer red tide season.

Nichols said in the last seven years the state has relied upon precautionary closures, which means harvest areas are closed at the first sign of toxins instead of when toxins reach a certain level.

Darcie Couture, a marine scientist who once worked for the state, criticized this approach for not balancing public health with industry needs.