Last year we reported on long-term site fidelity patterns of dolphins in the Charlotte Harbor and Pine Island Sound (CHPIS) study area from a dataset that spanned 1982-2007. We found that out of 1,157 individuals identified in the study area, 604 individuals were observed over 5 years or more (343 of these individuals were seen over 10 years or more). Prior to 2001, multi-week surveys were done only in summer during 1990-1994 and in 1996 in the CHPIS region. Between 2001 and 2006 we conducted multi-week surveys in both summer and winter months (summer 2001-2004 and 2006, winter 2002-2004) to determine abundance trends and seasonal residency in the study area. In Sarasota Bay, just to the north of CHPIS, five generations have been observed year-round. Therefore we were interested to know if the animals were also present in the CHPIS study area year-round. We identified 828 individuals that met our analysis criteria, and 479 (58%) of these were observed in both a winter and a summer field season.
Two hundred and fifty three (31%) were observed only in summer, while 95 (11%) were observed only in winter. If we exclude dolphins seen only once, and therefore likely not residents, (127 summer/67 winter) the percentage of year-round residents increases to 76%. These findings indicate that the waters of Charlotte Harbor and Pine Island Sound are important to bottlenose dolphins both long-term and year-round. These year-round residency findings track well with what we have observed with abundance estimates. Preliminary estimates show that dolphin abundance in the CHPIS study area is consistent from summer to winter and even after a Category 4 hurricane struck the area in August 2004.
Funding sources that contributed to this long-term project include: Mote Scientific Foundation, the Chicago Zoological Society, Harbor Branch Oceanographic Institution’s “Protect Wild Dolphins” program, Mote Marine Laboratory, the National Marine Fisheries Service, Dolphin Biology Research Institute, and Earthwatch Institute.