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.

Saturday, February 12, 2011

Mystic creatures

Blainville's beaked whale

The whale god was with us yesterday. He both allowed a trip to the sea before the wind got up and he gave us whales. Not the easy kind to observe, but beaked whales of the genus Mesoplodon, “the mysteries of the sea” as very little is known about these "shy" creatures. They have been recorded to dive to more than 1500m and they are thought to be very sensitive to sounds pollution (one of the explanation of why beaked whales might end their lives upon beaches). We were in the middle of taking photos of a group of bottlenose dolphins when the vigia (lookout) called out the good news on the radio. I hardly dared getting excited as beaked whales might mean that we just get to try to see them. Anyhow, half an hour later three of them surfaced in the area and gave us the time to watch them take some four breaths before they disappeared again and then a little bit later two other animals (an adult and a juvenile) surfaced and gave us a few more minutes of observation. In all enough for us to see that they were Mesoplodon but not enough to distinguish what specie (i.e. unsure if we had M.bidens, M.europaeus or M.mirus). By then the wind was getting up and we headed back towards land. Saturday will be a day on land and by Sunday we hope to be out there again.

Saturday, February 5, 2011

One of those perfect days

"Dino" who swims together with "Sphinx"

Yes, it can rain in the Azores during the winter, but, most years, the weather is pretty ok from January onwards. This Thursday the weather was more like summer and the sea surface lay flat like a mirror. Therefore we were hopeful when we set of to sea. It also did not take long until we came across a small group of Bottlenose dolphins. Looking closer at their dorsal fins, we recognized one of them straight away, last time we saw this dolphin named "Sphinx", was in December last year ("Sphinx" had also then been part of a small group but that time we were not so lucky in getting photo-id's, this time we were more fortunate.) The Bottlenose dolphins seen here in the Azores can be either resident (staying around all year) or transient (passing through). The resident dolphins of the Azores are believed to belong to one and the same population. The group structure however, is rather complex as some individuals have very strong connections to each other or to a location while others come and go on a more loose basis. We have a few different groups that we have seen more frequently, however it would just be normal if some of these opted for another location during some time and that other group’s appeared in their place.

After this encounter we went further out and meet up with a big group of common dolphins (around 50-60). They were lovely, so chilled out as they flocked around us, even the mothers brought the calves to the boat to play. It warmed our souls to listen to their twittering whistles and as we slowly glided about in the sun, we smiled big and just enjoyed.
Unfortunately good things come to an end and we had to return.
But to our friends out there, See you next time and swim in peace!
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