Tagging and tracking of Franciscana dolphins in Argentina: Year 2
By Randall Wells and Pablo Bordino

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 adult female 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 42 days of 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 (two adult females, two juvenile males) were tagged, and they were tracked over periods ranging from one week to 261 days, with three of the four dolphins reaching or exceeding the desired 2-month minimum tracking duration. The four dolphins confirmed the patterns suggested from 2005.

The movements of all four dolphins remained within an area of less than about 25 km distance from the capture-release sites, and most positions were within only a few kilometers (see sample map below). The fact that two of the dolphins tracked for 6-8 months remained in the same area hints at year-round residency to the shallow waters of the bay. Such a high degree of site fidelity 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. Future research will attempt to determine movement patterns in other parts of the species' range.

Movements of adult female Franciscana dolphin "Chica" during 15-22 November 2006 in southern Bahia Samborombon, Buenos Aires, Argentina. Water depths are in meters.