Centro de Estudios para la Conservación de Ecosistemas Marinos

Dolphins between sea and sky

February 25, 2017

The sea is like a mirror reflecting the soft grey sky. The horizon has dissolved. Everything around us is sea…. Only the gently sloping coastline with its lush vegetation provides a reference for our searching eyes. Several small grey dorsal fins break the mirror surface and leave small ripples. And then the show begins.

 

 Chilean dolphins make a spash in perfect seas (photo - Sonja)

 

Not that Chilean dolphins ever really put on an extravagant show (unlike the other three species of the same genus)! But this group, like many others we’ve encountered over the last days, is “buena onda”….Buena onda is one of my favourite chilenismos – roughly translated as good-natured/ having good vibes. It is the antithesis of my other favourite Chilean expressions: “fome” which is what Chilean dolphins usually are. Fome = boring/ troublesome encompasses all the frustration we usually experience with these difficult, elusive dolphins that often “no estan ni ahi” - i.e.are not willing to cooperate…

 

 Excitement and action - two Chilean dolphins get airborne  (photo - Lea).

 

The last days have been full of surprises. The weather has been great, Beaufort wind speeds of 0-2, perfect conditions to spot dolphins….. And by golly, have we spotted dolphins! Top count of the day was 15 different groups of Chilean and Peale’s dolphins, with roughly 40 Chilean dolphins and 25 Peale’s dolphins counted. That is certainly my all-time daily record for these two species by Chiloé standards. Not only have we found plenty of dolphins, more than expected, but we’ve also taken 100s of photographs of their dorsal fins to identify individual dolphins from natural markings. Most of the photos admittedly are rather crap, and go straight into the on screen rubbish bin. Even with a good, fast camera and lens Chilean dolphins are difficult subjects. They don’t bowride, but instead might pass your boat at close range but underwater, and then pop up facing away. For photo-identification to work we need nice splash-free dorsal fins perpendicular to the photographer’s lens so that marks on the trailing edge of the fin can be seen clearly in the photograph.

 

Everything that could possible be wrong for photo-ID..... (photo - Sonja)

 

Chilean dolphins surface in irregular fashion, so most of the time it’s a point and shoot process. Light conditions are often bad and contrast is often worse (dark fin against dark shadowy water). We need to shoot at high shutter speeds and with high ISO settings to capture sharp images of fast moving little objects.

 

 

Contrast!  A bad photo of a well marked individual with a big nick on the tip of the dorsal fin (photo - Sonja)

 

So imagine that you are playing a game of “catch the dolphin” in a dimly lit room, and the objects you have to capture are about 15cm in height (dorsal fin), are visible for less than 2 seconds, pop up in a 360 degree area at 1m to 50m distances from your boat, there can be four or five at the surface at the same time, and you need to try and capture all of them! Your tool to capture them is your camera’s view finder and the shutter button. It is fun, no doubt, but also frustrating ….

 

 

Silhouettes of Chilean dolphins - one unmarked fin (left) and one marked fin (right) (photo - Sonja)

 

I don’t think anyone has ever taken so many pictures of the sea surface…..and yet, amongst all the splashes and blurry shots there are enough good ones to allow identification of individual dolphins – for Chilean dolphins we’ve got around 30 marked individuals so far. Of course there are also many clean fins so for the overall population estimate we need to take into account that only a fraction of the dolphin population is identifiable – eyeballing the raw data suggests that around 1 in 3 dolphins bears useful natural identification marks in our current study area.

 

 Spot the dolphin tooth rake marks on the dorsal fin and back (photo - Sonja)

 

The origin of these marks can vary, but often result from interactions between dolphins. Unlike the often glorified and anthropomorphised views, it’s not all peaceful in dolphin societies. Dolphins squabble and can get quite physical with each other, leaving tooth rake marks on each other’s bodies. Some marks might be inflicted by other species, such as sea lions, which we’ve often seen feeding near the dolphins. Many dolphins bear long scratch marks on their bodies which we think were inflicted by sea lion canines in a possible dispute over access to fish. Dolphins also bear scars from interactions with humans. Luckily we do not see evidence of propeller scars (which might be a consequence of Chilean dolphins generally interacting less with boats than other dolphin species), but some line marks look suspiciously like potential marks from fishing nets. ….. But that’s a different blog entry…..

 

 Sonja in action (photo - Lea)

 

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