Wednesday, February 23, 2011

Bottlenose dolphins, a summary of 2010's photo-ID effort

Cut, Genie, Big A, Scarf & Matrix

During 2010 we had 116 days of encounters with Bottlenose dolphins (Tursiops truncatus). On 49 of these days (i.e. 42%) we took pictures for photo-ID purpose. This resulted in 1700 photos out of which 201 animals could be distinguished (some from both sides and others from one side only). Of these animals, 134 (i.e. 67%) were photographed only on one occasion, 32 (i.e. 16%) on two different occasions and 35 (i.e. 17%) of them were photographed on three or more different occasions.26 % of the 35 animals that had been sighted on at least three different occasions 2010, had been sighted previously (the earliest matching photos were taken in 2005).
In order to get a picture of the dolphins associations to each other, animals were noted to be associated if photographed together on at least three separate occasions. This resulted in 27 of them being associated, divided into five different groups (spanning from a pair up to 11 individuals). Some of them were pretty “tight” like in the case of the group around “Six”, a physically challenged dolphin, that is easy to make out from the others due to a stiff vertebral column. Six of the nine animals in this group had been seen together in former years as well. Other groups were more loosely aggregated, like the individuals that were seen around “Big A” (our most photographed individual that was seen on 12 different occasions).
To study the dolphins using photo-ID is time consuming and at times difficult, but more so, fun and important. In this way we are able to better estimate the amount of animals passing by and the amount of animals staying around all year. By studying our resident animals we are better equipped to evaluate factors that might impact this population. As I see it, it is our responsibility to do so.

No comments:

Related Posts Plugin for WordPress, Blogger...