Spotted...!?

A survey from Aberystwyth on September 28th revealed an unusual dolphin. Unfortunately it was not very cooperative, but in appearance it could have been taken for a juvenile bottlenose on its lonesome.

According to the crew, it had emerged quite close to the front of the boat initially, reported to bear an unusual coat of little dark speckles. The boat was called to a sudden halt, but at the speed we were going, it seemed the dolphin was more than spooked and it did not return again. We paused for several minutes, eyeing the ripples and drifts of tides, but no sign.

"It didn't look like a Tursiops," our lead watcher affirmed. I couldn't argue; there was something unusual about the one that got away, but it wasn't overly, strikingly different to a usual bottlenose. But there was another group of dolphins very similar, belonging to the Stenella genus. Its closest member, the Atlantic spotted dolphin, normally inhabits seas beyond the Mediterranean. She wasn't immediately confident that it was one, and for good reason: it was a major rarity anywhere in the north Atlantic.

Of course they then look to me. "Did you get any pictures?" they ask, for which I can't offer an optimistic reply.  No internet information exists on Atlantic spotted dolphin in the UK, or even in Franc. It was not the first possible spotted dolphin reported this year, though none of the reports had been confirmed or photographed, a fate that this one will also share. 

Considering the rare and vagrant Cetaceans known in the UK in the past, it is hardly impossible. Birds are the best example of vagrancy, we've seen "megas" that have flown thousands of kilometres from their native range from western Asia, Africa and America. The UK's sole record of ancient murrelet, a central Pacific bird that will not fly over land except in hurricanes, would have traveled all up the Pacific Coast, along the Arctic Ocean, down the Atlantic through Greenland and all the way over the North Sea to reach the UK. So then the question is why has the spotted dolphin, something which by rarity is hardly comparable to some foreign birds, has not been "officially" seen in the UK before? 

This question is far more easy to answer. The extreme similarity of the Atlantic spotted dolphin to the bottlenose dolphin by default makes it susceptible to being highly overlooked. I saw our dolphin from no more than 100 metres off, albeit silhouetted, but I never would have given it a second look. If it wasn't for the markings, I doubt anyone would have raised an eyebrow. Most dolphins are seen far out to sea, and even binoculars or telescopes might not be enough to see the details. The only truly obviously diagnostic difference are in the spotted markings, which are tricky to see unless in close proximity, and you need a boat for that, and the sacred license to approach them in the first place. 

The issue with many sightings is that well-marked bottlenose, especially if only a dorsal view is seen, could be mistaken. This is supported by the issue that markings usually increase in density as they travel up the animal, so the back could easily be as spotted as the confusion species in question (but if it were to breach, then the rest of it would be obviously unspotted; spotted dolphins should be equally spotted all over except for juveniles).  

It is also worth noting that unlike birds, their complete territory is far harder to survey, and for the most part impossible from land. A speculation was that warming seas could encourage them further north. The eBird report exists here.


*(bearing in mind this is a bit of a generalization, as many dolphin pods are in fact not tolerant of boats at all even in Wales).

**Dedicated surveys only allow a maximum of 5 minutes with each encounter before we must move on, whether it is to keep the survey going or to reduce interference with the animal's natural behaviour.