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...
