A rarely seen dolphin that lives in deep waters off Hawaii washed ashore on Maui last weekend.

The 9-foot-long, 800-pound male Risso’s dolphin was found dead on a rocky shoreline near Paia, Hawaii Pacific University biology professor Kristi West said Thursday.

A necropsy indicated the dolphin had pneumonia and heart disease. His stomach had firm masses that may have been cancerous. Researchers found a clear plastic bag in his esophagus but do not believe the bag contributed to his death.

West and other researchers are conducting further tests to determine why the dolphin died.

Risso’s dolphins are found in waters around the world. Off Hawaii, they’re generally seen only in waters 13,000 to 16,000 feet deep.

Scientists estimate about 2,000 Risso’s dolphins live around the main and Northwestern Hawaiian Islands.

West said strandings like this help scientists understand marine mammals they don’t know much about.

"They’re a huge source of information on these deep divers that we never see," she said.

A Risso’s dolphin was stranded in Hawaii in 2007, in the area of Maalaea Bay on Maui. But that dolphin was still alive and swam away when a shark came near.

The last time one of the dolphins was stranded in Hawaii and scientists had an opportunity to examine it was in the late 1980s.

While the recent dolphin’s esophagus wasn’t inflamed, West said food could have eventually pushed the plastic bag into the dolphin’s stomach. This could have blocked the dolphin’s digestive tract or deprived the stomach of room for nutritious food.

She said the bag is a reminder of the reach of human debris.

West leads a Hawaii Pacific University team that removes marine mammals stranded in the islands and conducts necropsies on them.