Common dolphin dubbed “Big Back Notch” found dead in Olympia

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.

Long-beaked common dolphin found 15 January, 2020.
Big Back Notch, during our last live encounter with him on 23 December, 2020. It was evident at that time that is skin condition was much worse than during previous encounters.

Lesions are visible on the head.
In this image, you can see the advanced stage of the skin condition, covering much of the body. You can also see the distinctive notch at the base of the dorsal fin, which gave Big Back Notch his name.

 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.

The first boat based encounter with the common dolphins in Drayton Passage, 11 November, 2016. It was during this encounter when Big Back Notch received his name.

Big Back Notch, and one of his companions with Mt. Rainier and Chambers Bay in the background, 11 June, 2017.
Big Back Notch showing only old scarring on his flank in the image from 03 July, 2018. This provides a clear view of his distinctive dorsal fin that allowed him to be easily identified, even in poor quality images.
Big Back Notch surface feeding on anchovies near Herron Island in Case Inlet, 03 July 2018.
Big Back Notch breaching in Bud Inlet, 6 August, 2018. Old scarring evident, no recent skin issues apparent.
Big Back Notch, Top Notch and Cinco bowriding on 06 October, 2018. Our best opportunities to check out the body condition of the dolphins occur when they decide they want to bowride for a few minutes.