Our first group of dolphins today included 3 adults and 1 calf. The calf spent time running around our boat checking us out while the adults spread out across a shallow sea grass bed (<1m depth) and performed a really cool feeding behavior called “mud plume feeding”.
Mud plume feeding involves creation of a U shaped plume of mud in the water column. Dolphins do this with a down stroke of the fluke near the top of the sea grass. Sediment on the sea grass then becomes suspended. Same way that it does if you are new to diving or snorkeling and kick near the bottom.
|U shaped mud plume produced by bottlenose dolphin. Bottom of U is towards the right side of the photo. Opening at top of U is towards the left side of the photo.|
|Bottlenose dolphin lunging through a mud plume to capture fish.|
There are some really interesting characteristics about this behavior. When lunging through the plume, they usually (>90% of the time) lunge on the right side. We do not know why this is the case, but the same thing has been noted for bottlenose dolphins that strand feed (stranding on the right side). Dolphins in the community near Key West also usually travel very close to one another (no more than a body length apart usually), unless they are mud plume feeding. When mud plume feeding they spread up to 400m apart. Animals in the group will continue to move with one another across the shallows, but with a lot of space between them. They also usually follow specific tidal states as the tides move across the sea grass flats. So they continue to travel in between creating the plumes.Key West dolphins will perform this behavior for hours at a time. Sometimes stopping to socialize for a short time. Sometimes coming close to one another for a while traveling to another location further on the flat, then spreading out again for more mud plume feeding.
We are currently investigating whether performing this feeding behavior gives the dolphins that use it any advantage when feeding over sea grass beds, when compared to those that don't use the behavior.
For more information about mud plume feeding, please see the link to our paper about it on our web site: http://tropicaldolphin.org/Lewis_and_Schroeder_2003.pdf