August 7 - Tons of Transmissions!

Yaana continues her movements from the bay into the waters just outside the mouth.

After more than five months and 37,000 transmissions (half again as many as advertised), the transmitter is still indicating good battery strength. Some tracking weirdness over the weekend---we have been getting a larger number of satellite "hits", which may be indicative of Yaana spending more time at the surface, or may reflect really calm conditions; and the final location Saturday put her in the middle of the island! Hopefully this just indicates a bad position that will be resolved with additional CLS data processing... And if not, well, she has been a lot more aquatic since then, as you would expect...

June 25---Catching a Glimpse...

Yaana is outside the mouth of the bay.

Pablo's team saw a tagged dolphin yesterday, apparently with only one pin still holding the satellite tag onto the fin. Unfortunately, they were not able to get any photos of it, so we cannot determine for certain which dolphin it was. However, Yaana has spent time in the vicinity (near Northeast Sandbanks) on each of the past 3 days before moving offshore at night. Field conditions are very challenging---the extreme cold limits time on the water each day. (That is a shot of calm conditions---you can imagine how hard it is when things are far from ideal, as right now.)

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 1 - Getting Data

From west to east the dolphins are: Roberto, Lea, and Yaana has moved back into the bay.

I've gotten some questions from readers asking how we get the tags on the dolphins to create the daily maps that I am posting. It is hard work! The tagging research involves a team of about 40 people on 6-7 boats, and a long net that encircles 1-3 dolphins in shallow water (less than two meters deep). We then measure the dolphin, attach a satellite-linked transmitter to its dorsal fin, obtain a blood sample for health assessment, and release the dolphin---all within about 5-10 minutes! I am lucky to work with such a solid group. The photo on the left is of Yaana's release.

Follow-up work involves receiving downloads of dolphin positions over the computer back in the lab. We plan to initiate periodic observations of the dolphins in Bahia San Blas, in which team members will use small boats to find dolphins and photograph their fins with a digital camera with a telephoto lens, looking for nicks, notches, and tags. In fact, I mentioned last week that Dr. Bordino got some new funding to do this very soon. I am looking forward to posting some of the photos he gets.

April 26 - Where is Marta?

Unfortunately, our daily maps do not include Marta... We originally tagged four Franciscana dolphins, but lost the signal for one fairly early on.

We do not know why we lost Marta’s signal. There were some indications of a possible problem with the electronics of the tag over the last few days of transmission (the tag sends out function status reports periodically when it is working properly, in addition to location data). There are plenty of scenarios that might explain this: the tag could have come off (as it is designed to do if it should become entangled, for example), or sadly the dolphin could have been lost from the population. There are plenty of potential dolphin predators abound in Bahia San Blas. The town’s claim to fame is as a recreational shark fishing site. On our last day, we observed killer whales passing through the area where we had recently received signals from Marta. (I posted the orca picture on the left when we first started the blog.)

While we do not know why we lost the tag, I know the problem was not the battery... The tag indicated good voltage through its last status report. The tag is programmed to provide potentially 100 days of transmissions and we were nowhere near that point.

While it was not a battery problem, the way the tag is affixed to the dolphin is a bit more dicey. The tag is attached to the fin with plastic pins held on with corrosible metal nuts. These are designed to corrode in saltwater. Temperature and salinity will affect how fast this will happen, but it should take several months, at which point the tag will fall off the fin.

So...after all that, we just don't know what happened with Marta...

April 4, 2007 - Franciscana Dolphin Range

So...we are going to be posting these maps daily. But you might be wondering what they refer to... You can get a sense of where this place is from the project map below, but what is the area like? Well, Franciscana dolphins live in coastal waters and estuaries---areas where there is influence from rivers, but typically in full seawater. The species is found from Brazil, through Uruguay, to northern Patagonia in Argentina, so the species as a whole experiences a wide range of water temperatures, though more temperate than tropical. This year, we worked near the southern extent of the species’ range, in early autumn waters of about 65 degrees. Where we have worked with them, Franciscans seem to prefer habitats with sandy bottoms and murky waters (from the river influence).