This phenomenon is not unique to Marco Island. Immediately adjacent but distinct communities of bottlenose dolphins occupying the near shore waters of the open gulf or the waters behind barrier islands has previously been documented in Sarasota Florida.
While the insights about Marco Island’s dolphins come from observation, Anna B. Sellas, (University of California, Santa Cruz), Randall Wells (Sarasota Dolphin Research Program) and Patricia E. Rosel were able to demonstrate this phenomenon in Sarasota using DNA analysis. In a 2005 paper they wrote,
“Using mitochondrial DNA and nuclear microsatellite markers, significant population differentiation was detected between Sarasota Bay residents and bottlenose dolphins sampled in nearshore coastal gulf waters. This result is surprising given the short geographical distance between these areas and the lack of obvious geographical barriers to prevent gene flow.” 1
The ‘population differentiation was significant but not complete; the communities are not completely separate. The authors noted,
“a significant amount of male-biased dispersal between the coastal gulf and Sarasota Bay,” confirming research that has shown resident males to have “wider ranging patterns and more frequent interactions with dolphins of neighboring areas than resident females.”
I’ll write about this tendency of some of the area’s males to cross this invisible boundary in a another post or, better yet, you can poke around in the database yourself and see if you can find evidence of this.
Robyn and I conducted two more surveys in the same area in our own boat on the 12th and the 13th. You can see the results of those trips in Trips page. I haven’t entirely finished the photo analysis yet but they appear to follow the same pattern with a few exceptions: three dolphins from the Big Marco Pass Community to the north showed up in sightings. This is to be expected – as I quoted Dr. Randall Wells in The Distribution of Dolphins in Southwest Florida there is a mosaic of overlapping communities along the coast of Florida. In this case the range of a pair of males pair of males (Captain Jack and Trixie) encompasses both areas and they had been recorded in Goodland as far back as 2012. An adult female named Rangle was also seen (with a new calf!)
NEW DOLPHINS ADDED
Finally, as we are in the exciting stage of filling out the Goodland and Open Gulf catalogues, a lot of dolphins new to The Dolphin Study were added during this survey. In honor of the contribution of our hosts, Captain Sarah and Eco Endeavors, we named three new dolphins referencing them – Endeavor; Tiger Lily, the name of one of their boats and Indiana – That’s where Sarah is from; also she named a dog that.