Thursday, July 24, 2014

Dolphins in the coastal Everglades

By Postdoctoral Scientist Dr. Jeremy Kiszka
As the humidity returns, the thermometer rises and the afternoon thunderstorms water south Florida, we are reminded that the dry season has come to an end.  Over the months that spanned the dry season, however, our lab has been investigating dolphins in the Florida Coastal Everglades and associated areas of Florida Bay to answer questions about their behavior, movements and diets. 
We have been keeping a particularly close eye on the dolphins in the waters of the Shark River, Tarpon Bay, Oyster Bay, Joe River, and a 200 km2 stretch of coastal waters spanning east from Cape Sable to the Buttonwood Keys.  In May, three surveys have were conducted to increase sample sizes in Shark River and in Florida Bay, that will allow us to better understand the foraging ecology and ecological roles of dolphins in these areas.  With the 12 new biopsy samples collected we are up to about 35 samples and various analyses are underway, including stable isotopes to determine what and where dolphins are eating and persistent organic pollutants (e.g. PCBs, DDT) and Mercury (Hg). Preliminary results of stable isotope carbon and nitrogen analyses reveal that bottlenose dolphins feed in either coastal marine waters, as well as throughout river systems of the Everglades, from brackish to freshwater environments.
During our expeditions to the Everglades we have been able to observe some very interesting and unique behaviors of dolphins including strand feeding, mud ring feeding (solitary and in groups) and side swimming (in very shallow waters).  Biopsy samples taken from these animals may give us new information about diets specific to these feeding styles and behaviors. 

During mud ring feeding, a dolphin swims in a circle around a school of mullet while creating a ring of mud with its tail.  The mullet try to jump over the ring of mud and dolphins can catch them out of the air!

The nicks and cuts out of the dorsal fins help us identify individuals.

An osprey grabs a meal.

Some dolphins love to forage right next to - or even under - mangrove trees!