Changes in cetacean occurrence in the Salish Sea: Anomalous sightings in southern Puget Sound
Calambokidis, J. Huggins, D. Lambourn, S. Jeffries, J. Evenson, B. Diehl, J. Oliver, and B. Hanson. 2011. Changes in cetacean occurrence in the Salish Sea: Anomalous sightings in southern Puget Sound. Proceedings of the 2011 Salish Sea Ecosystem Conference, 25-27 October 2011. Vancouver, BC.
In the last few years, several unexpected species have been sighted and stranded in southern Puget Sound. This has included the return of one species, the harbor porpoise, that used to be common but had disappeared for many decades from Puget Sound before returning in recent years, and the occurrence of three species since 2010 that are either unknown or extremely rare this far north. In 2010, two Bryde’s whales and two bottlenose dolphins were sighted alive and then were documented to have died several weeks to months later. The two Bryde’s whales included the January 2010 sighting and stranding of a 39’ immature female, and the November-December 2010 sighting and subsequent stranding of a 34’ immature male with several serious injuries from an apparent ship collision (thought to have occurred weeks or months earlier). In the eastern North Pacific, Bryde’s whales have not to our knowledge been documented north of southern California and are considered a tropical species. The two bottlenose dolphins included: 1) an animal sighted early June 2010 which then is suspected to have died in mid-July when a decomposed dolphin was found stranded near Steilacoom, and 2) the December 2010 sighting of another live bottlenose dolphin seen repeatedly and then found dead on 31 January 2011 at the Nisqually Delta. Necropsies were conducted of but tissue decomposition prevented determination of cause of death of either of the bottlenose dolphins. Bottlenose dolphins have only been documented stranded twice before in Washington State prior to these two animals and typically do not occur north of central California. While any one of these occurrences would be unusual but perhaps just a chance occurrence, the presence of four warm water species coming alive into Southern Puget Sound in a one year period suggested there was a connection between these events. Additionally, starting around 2007, numerous harbor porpoise were sighted at multiple locations throughout southern and central Puget Sound, an area where they had been common in the 1940s but had been virtually absent from for at least the last 40 years. While the return of this species may be positive, it has also resulted in the death of a number of these animals due to entanglement in nets. We explore some of the factors that may have contributed to these changes in occurrence of marine mammals in the Salish Sea.