One of the most distinctive individuals of a small group of common dolphins in the southern Puget Sound was found dead near Johnson Point in Olympia on 15 January 2020. The 7’7” adult male, named Big Back Notch due to the missing piece on the trailing edge of its dorsal fin, was first documented in the region in June of 2016 and had been sighted numerous times over the last few years. The last live sighting of this dolphin was on 23 December 2019, when it appeared to be active, although a skin condition that had been observed several months earlier had worsened. An examination was conducted by biologists and volunteers from Cascadia Research and the Department of Fish and Wildlife over the holiday weekend. The cause of mortality could not be clearly determined from the exam; preliminary findings include thin (but not emaciated) body condition and no evidence of recent feeding, internal indications of initially coming ashore alive, and a large number of worn, broken and missing teeth that suggest this was likely an older individual. The cause of the skin condition, which was extensive, is unknown at present. Samples were collected for a variety of analyses and we hope to have a better understanding of what happened to this animal as the results become available.
Sightings and strandings of common dolphins, which typically inhabit warmer waters, have been increasing in the Pacific Northwest over the last 10-15 years. Several live dolphins have stayed within the Puget Sound for months, and in the case of Big Back Notch and a few other individuals, years. Cascadia Research is interested in tracking the behavior and movements of these animals while they are in the region—if you see some of these or other unusual dolphin or whale species, please contact our office at 360-943-7325. A video to help you identify dolphin and porpoise species can be found here.
As this is a stranding of a known individual, we are including some images of the last 3.5 years of encounters while he and his companions have been inhabiting the southern Puget Sound.