The cool December morning bites. The low tide wanes. Herons and egrets fly overhead. There’s a ruckus in the creek. I rush down to see two large bottlenose dolphins circling in the shallow waters, creating a bow wake as they move. All of a sudden there is an explosion of fish on the mud bank followed by the dolphins sliding sideways (both on their right side) up the bank, mouth open, catching the stranded fish.
This activity is known as strand feeding and is often attributed as unique to the Lowcountry (https://charleston.com/charleston-insider/video/what-is-strand-feeding). Strand feeding is a group effort by two or more individuals acting together to herd the fish onto shore. It is also a learned behavior, with mothers teaching their young on steep banks to make reentry into the water easier. That said, my first encounter with these behaviors came while kayaking along the Gulf Coast of the Everglades. Here a pair of dolphin first circled in the deeper water, then chased the fish onto a sandy opening among the mangrove roots and fed as do our Lowcountry dolphin on mud banks. One wonders: How did these distant populations learn the same technique for feeding?
In ecological systems, there exist many interactions among various species in an ecosystem. We are very familiar with predator-prey interactions (hawk-squirrel, alligator-turtle, and many more). E.P. Odum, often referred to as the father of modern day ecology, identified nine such interactions ranging from neutralism in which neither species is affected by the other, to mutualism where both species depend on each other for survival. In between lies the commensal interaction in which one species is benefited, the other unharmed or unaffected. As I watched the wading birds follow the dolphins along the creek bank, I noticed that they were catching small fish driven up the bank by the dolphins. In my mind, I classified the behavior as commensalism. It seemed that the dolphins were unaffected by the birds (the dolphins focused on the larger fish), while the herons and egrets benefitted from easy pickings of the smaller fish.
In these times of stress with the pandemic and other personal and global problems, I was delighted to witness this unique natural occurrence just in my backyard. This retired ecologist also enjoyed traveling down “memory lane” having reviewed ecological interactions from my dog-eared copy of “Fundamentals of Ecology” by E.P. Odum (Saunders Company, Philadelphia PA. 1971).
Laura Murray, Ph.D.
Marine Ecologist, Retired