Lagenorhynchus acutus (Atlantic White-sided Dolphin)  

The Atlantic white-sided dolphin has a limited distribution in the cool temperate and subarctic waters of the North Atlantic. They prefer the continental shelf regions to the west of the Outer Hebrides, although they tend to move closer to the coast during summer months.

Additional Information
Hebridean Whale and Dolphin Trust
Cetacean Research & Rescue Unit