BEAUMONT An investigation into the deaths of 68 dolphins that washed ashore between Sabine Pass and Galveston this spring turned out to be inconclusive, an official said.

Heidi Watts of the Texas Marine Mammal Stranding Network said the dolphins' bodies were too decomposed to determine what killed them.

The National Oceanic and Atmospheric Administration declared an "unusual mortality event" and opened a special investigation after the dolphin corpses came ashore in Galveston and Jefferson counties in March.

Watts said the review included testing of genetics and testing for toxins and high chlorophyll. She said she has asked federal officials to close the case.

The 68 dolphins that washed ashore in March represented a spike from the nine dead dolphins discovered in March 2006 and 11 in March 2005. Scientists worried that a decline in dolphin health could indicate problems in the health of the ocean.

The next stranding season starts Jan. 1.