By Jessica Taylor | Correspondent
As any visitor and local knows, the Outer Banks has amazing seafood. Local restaurants offer fresh shrimp, fish, crabs and scallops prepared in a myriad of ways: broiled, fried, on sandwiches or as entrees. However, we aren’t the only ones who enjoy the area’s abundance of local seafood.
Bottlenose dolphins frequent the Outer Banks’ ocean beaches year-round but move into the Roanoke Sound from April through October to feast on the summer fish. In fact, the Roanoke Sound is considered an important foraging and nursery area for dolphins due to its plentiful food supply and shallow waters free of predators.
Bottlenose dolphins are known to be opportunistic in terms of their food and the ways they catch it. Even though they almost always feed exclusively on fish, they’re resourceful when it comes to getting a meal. Hungry dolphins have learned to herd fish against structures, flip fish into the air with their tail flukes (a behavior known as fish whacking), strand themselves temporarily on the beach to eat the fish that wash up with them and even carry marine sponges on their rostra (noses) to dig in the sand to search for fish.
Many of these behaviors are learned and complex, which leads us to believe that mothers pass the techniques on to their calves as a form of tradition and culture.
The Roanoke Sound is so special for hungry dolphins due to the type of fish in the sound. Bottlenose dolphins may be opportunistic hunters but prefer specific species of fish. Living in the water, dolphins are very acoustically oriented and focused on sound. They seem to prefer sound producing (or soniferous) fish. A hungry dolphin is more likely to catch a fish it can hear; they use a technique called passive listening to more easily sneak up and catch these fish. During the summer, Roanoke Sound teems with loud and noisy fish, such as croaker and spot.
Although we see lots of feeding behavior in the Roanoke Sound, it is very rare to see a dolphin capture a fish. The water in the Roanoke Sound is shallow but not very clear, so underwater video is not much use for seeing a dolphin in a successful pursuit. The Outer Banks Center for Dolphin Research (OBXCDR) conducts boat-based dolphin surveys in the Roanoke Sound and uses photo-identification to monitor the identities and behaviors of the dolphins. During our surveys, we can observe feeding behavior and habitat use, but it is difficult to see in the field exactly what the dolphins are eating.
In order to learn more about their foraging ecology, we collaborate with the North Carolina Marine Mammal Stranding Response team. The team responds to stranded marine mammals, such as dolphins, whales or seals, that wash up on the beach. Even if a stranded dolphin has died, there is still a wealth of information that can be learned, including its diet. The stranding response team may conduct a necropsy (an animal autopsy), which includes an analysis of the stomach contents. Dolphins have three stomachs, and the majority of the prey contents can be found in the first stomach, the forestomach. The last part of a fish to be digested is the ear bone, also known as an otolith. Different types of fish have different looking otoliths. Scientists can identify the fish species a dolphin was recently eating by finding these otoliths.
The OBXCDR is also collaborating with the stranding response team on new ways to learn about what dolphins eat. For example, UNC doctoral student and OBXCDR summer intern, Meggan Alston, is examining whether the prey remains contained in dolphin stomachs is a useful way of determining what dolphins are eating. The more we understand what dolphins eat and when, the more scientists will learn why the Roanoke Sound is important to dolphins, especially from April through October. If your food migrated, wouldn’t you follow your food, too?
Better understanding dolphin feeding patterns benefits people, too. Dolphins are important indicators of environmental health, and their presence or absence gives us insight into how healthy the fish populations are in an area. Since people and dolphins may be interested in catching the same types of fish, it’s possible for dolphins to be attracted to fishing gear. If you are ever fishing and dolphins approach your line, it is best to pull your line in and fish somewhere else. Although they may not broil or fry their food, we know these creatures enjoy the summer seafood offerings of the Outer Banks just as much as we do. The more we study the dolphins, the more we’ll know how precise their menu really is.