Five northern right whale dolphins died after being stranded on Santa Rosa Island last Friday.

According to the Santa Barbara Museum of Natural History’s vertebrae zoology staff, four of the dolphins were already deceased after washing ashore on the island, which is approximately 35 miles southwest of Santa Barbara. The dolphins showed some visible bruising, which was mostly likely due to rolling in the surf.

Although officials performed a necropsy on the three dolphins, the cause of death is still unknown. Samples taken from the dolphins will be used for further analysis and the test results will be released in a few months.

The four recovered dolphins were all males, and each weighed at least 200 pounds. Northern right whale dolphins are typically six to 10 feet in length and weigh up to 250 pounds. They typically travel in groups of 100 to 200 dolphins and can swim at speeds of 22 miles per hour.