A large pygmy sperm whale carcass that washed up by the Morris Island lighthouse near Charleston Friday was too decomposed to say what killed it, researchers concluded.

The whale stranding follows a string of 13 bottlenose dolphin carcasses since late February. A marine mammal stranding crew was in Charleston Harbor on Monday recovering another dolphin carcass. But the pygmy sperm carcass is only the second whale to wash up on a South Carolina beach this year. A dwarf sperm whale was discovered in January.