Franciscana dolphins, a species of small dolphin found only in the coastal waters of Argentina, Uruguay, and Brazil, continue to be killed in large numbers in artisanal fishing nets.  Little is known about their biology and behavior, beyond what has been gleaned from fishing bycatch.  In 2005, following several training sessions for Argentine researchers in Sarasota Bay, Pablo Bordino of AquaMarina and Wildlife Trust initiated a collaborative field project with the Sarasota Dolphin Research Program and Disney’s Animal Programs to begin to study the ranging patterns of these tiny dolphins in the waters of Bahia Samborombon, in Buenos Aires Province, Argentina.  The research team, composed primarily of Argentine researchers, students, and veterinarians, attached small VHF transmitters to the dorsal fins of three dolphins – the first time this species had ever been tagged.  Tracking from a lighthouse and other shore vantage points suggested that the dolphins were much more localized in their movements than had been thought previously, but the location data from primarily shore-based tracking were very imprecise. 
      In 2006, we built upon this pilot study by using small satellite-linked tags to provide more precise location information, over a longer period of time.  Four dolphins were tagged in Bahia Samborombon, and they were tracked over periods ranging from one week to 261 days.  The satellite-linked tracking confirmed the patterns suggested from 2005, with all four dolphins remaining within an area of less than about 25 km distance from the capture-release sites. 

Figure 1.  Three franciscana dolphins surface in Bahia San Blas in March 2007.

      In March 2007, we moved our operations several hundred km to the south, to Bahia San Blas, in northern Patagonia (Figure 1).  We tagged another four franciscana dolphins (Figure 2) with satellite-linked transmitters, and tracked them for periods as long as six months.  The San Blas dolphins showed the same degree of site fidelity as the Samborombon dolphins, moving from inside the bay to waters immediately outside, and returning (Figure 3).  They also showed the same significant tidally-related movement patterns, being found farther inside the bay on high tides, and towards the mouth or outside on low tides.

Figure 2.  Franciscana dolphin “Marta” during tagging in March 2007.

      Such a high degree of site fidelity at multiple sites along the Argentine coast, consistent with the findings from ongoing genetic research by PhD student Martin Mendez, should provide important guidance to Argentine wildlife managers as they determine how best to protect this species – it is a very different picture from the original management scheme of wide-ranging movements along the entire coast of the country.
      Funding from Disney will support additional tagging in Bahia San Blas in 2008, this time with satellite-linked transmitters with time-depth recorders that will allow us to learn more about how the dolphins use the water column, and to determine if fishing nets set at specific depths might be more likely to entangle the dolphins.

Figure 3.  Positions of franciscana dolphin “Yaana” over six months of satellite-linked tracking.