May 11, 2007

Yaana has moved closer to the mouth of Bahia San Blas.

May 10 - La Plata River

Yaana continues to move through relatively deep waters outside the mouth of Bahia San Blas.

Did you know that Franciscana dolphins are also sometimes referred to as La Plata River Dolphins? Though they look like some river dolphin species, this is a misnomer. Tthey have similar features as compared to the true river dolphins (long beaks, large flippers, small eyes, for example), they have arrived there from a different evolutionary path, and they are mostly a marine species. La Plata refers to the large estuary of the La Plata River that separates Argentina from Uruguay, and falls near the midpoint of the species’ range (19oS to 42oS).

May 9 - Yaana wins the marathon...

And then there was one...

One day after achieving our 60 day goal for tracking, Yaana is the only Franciscana continuing to send signals. She remains outside the mouth of the bay. Both Lea and Roberto had used about 60% of their possible transmissions, and battery strength was still good at the time of their final transmissions.

This suggests several possibilities:

1. shedding of the tag, as designed/planned,
2. damage to the tag, such as antenna breakage (Wildlife Computers had made the antennae a bit weaker but more flexible this year) that precludes transmissions,
   
3. loss or movement of attachment pins leading to repositioning of the tag on the fin such that the seawater switch is unable to function, or
   
4. loss of the animal (to sharks, orcas, fishing gear, etc.).

Observations of the animals, with photographic documentation of dorsal fins, will be crucial to trying to figure this out, looking for tags and for animals with marks from where the tags used to be attached. Pablo's team should be on the water soon to do this.

May 8 - Two Months

Today marks the 2-month point, our target for tag duration. In essence, three of the four tagged dolphins have provided data for the two months. They have thus far demonstrated limited movements in, or in the vicinity of, Bahia San Blas comparable to those of the Franciscana dolphins tagged previously in Bahia Samborombon. This supports a change in the way researchers think about Franciscana dolphin home ranges and behavior.

May 7 - Where is Lea?

Roberto remains deep inside the bay, and Yaana is still outside the mouth of the bay.

We have not received any signals from Lea over the past two days. This is not necessarily unexpected. We are just about at the two-month point that we had targeted for tracking. In addition, Lea's tag attachments were modified in an experiment to refine the design to release sooner. Last year, the tags stayed on some of the dolphins longer than we wanted them to. Pablo's next trip to San Blas is extremely important to find and photographically document the tagged dolphins and the conditions of the tags and attachments. Dr. Bordino emailed yesterday to say he plans to be out there getting photos next week.