Earthwatch Dolphin Monitoring Program 2004-2005
By Jason Allen, BS, Field Coordinator, SDRP

The Sarasota bottlenose dolphin community remains the most thoroughly studied free-ranging dolphin population in the world. We have been able to continue our year-round monthly monitoring of the Sarasota dolphin community during 2005 thanks largely to continuing support from Earthwatch Institute volunteers and NOAA Fisheries. We continue to address increasingly refined questions about the lives of these animals with the benefit of information gained through our intensive year-round studies of their distribution, social and reproductive patterns.

Photo-identification surveys were conducted on 101 days from November 2004 through October 2005 with the assistance of 33 Earthwatch volunteers from 16 states and five countries. These volunteers contributed over 2,000 hours to our project.

During this period, we had 481 group sightings that totaled 1,791 dolphins (including resighted animals). Monthly values were variable, but overall we averaged about five sightings and almost 18 dolphins per day (Figure 1). We had a high of 13 sightings in one day during a February 2005 survey and a high of 73 dolphins during a June 2005 survey. Our single largest dolphin group occurred on the 23rd of September and was composed of 30 known community members. These values have remained fairly consistent over the past several years (Figure 2). However, monthly averages of group size show that there were many more dolphins per sighting in the summer of 2005 than in the previous year (Figure 3). In addition, the proportion of sightings with 15 or more animals was much larger this summer compared to the previous ten years (Figure 4). This increase in group size seems to be correlated with the extensive red tide event that affected Sarasota Bay for 10 months starting in January, and becoming exceptionally severe this summer.

We documented the births of ten calves during the spring/summer of 2005 while monitoring the Sarasota dolphin community. Lightning had her sixth calf, while Pumpkin had her fifth. Other moms included Merrily (pictured below), Moonfin look-a-like, Square Notch, FB 127, FB 149, FB 167, and FB 175. Finally, the most significant addition to the Sarasota population this summer was the birth of Annie’s first calf. This represented the first known fifth-generation dolphin born into the Sarasota community. Though this calf’s grandmother and great-grandmother are dead, its 39 year-old great-great-grandmother is still seen in Sarasota Bay. Unfortunately, this newborn suffered the fate of most first-born calves in the Sarasota Bay area, and was lost shortly after birth.
Last year we reported that Rose and RP 27 had died, leaving behind one- and two-year-old orphans, respectively. During our capture-release efforts this year we performed a health assessment with both of these individuals and found that they are well and healthy. First time health assessments with Pup and Wanda’s 2002 calves, Murphy Brown’s 2003 calf, FB 234 and FB 189 (recent arrivals to Sarasota Bay), Yorik (observed since 1999), FB 193 (observed since 1990), and FB 195 (observed since 2002) also occurred this year.

During the past year, we lost two Sarasota Bay community members. FB 99 died from a stingray barb that punctured her body and then traveled through her aorta. Pumpkin’s 2002 calf, Seed, was also found dead on the 12th of September. Sadly, the necropsy showed that her spine was broken, most likely from a motor boat collision. Through our Earthwatch-sponsored surveys, we have accounted for over 90% of the Sarasota Bay community members during 2005. As of October 2005, the number of dolphins regularly using the waters surrounding Sarasota Bay stands at approximately 160 animals.
Once again, we would like to thank all of our Earthwatch Institute volunteers for their interest in, and support of, the Sarasota Dolphin Research Program.