It’s clear that summer has arrived in the Outer Banks when colorful beach umbrellas dot the beaches, local restaurants and stores are bustling, and trailers are lined up at boat ramps to launch a variety of boats laden with excited boaters.
Just as the Outer Banks beaches and towns come alive during the summer, life in the Outer Banks sounds pick up as well. As the sound waters warm in the spring, fish move back into their summer habitats along with dolphins, osprey, and pelicans. During the summer, bottlenose dolphins are abundant throughout Roanoke Sound, the body of water that separates Nags Head from Roanoke Island. Since 2008, the Outer Banks Center for Dolphin Research has studied the dolphins in Roanoke Sound to learn more about their ecology, behaviors and population size. As time goes on, it becomes more apparent that not all dolphins are first time visitors to Roanoke Sound. Just as the Outer Banks has visitors that travel to the area year after year, Roanoke Sound has dolphin “regulars” as well. Read on to learn about how we track our seasonal residents in the sound and how the ability to identify these individuals can contribute to their conservation.
Sighting a group of dolphins can be an exhilarating experience. From far away, one might see a dorsal fin peek above the surface of the water, a blow rush up into the air, or a lot of splashing. However, at closer look, one might be able to distinguish dolphins of different sizes (adults, juveniles, or calves) and even have the ability to discern markings on the dorsal fins. Dorsal fin markings are common on bottlenose dolphins, and approximately half of the dolphins in Roanoke Sound have some type of distinctive marking on the fin, whether it may be a notch, nick, or series or cuts, or something more distinguishing such as a sliced fin or missing a fin altogether. Many dorsal fin markings are natural due to general wear and tear on the fin and interactions with other dolphins. Other markings may result from entanglement in fishing line or boat strikes, however, all markings may get more exaggerated over time. Dolphins use their dorsal fin for regulating body temperature and balance; however, the dorsal fin is a key tool for researchers to identify individual dolphins and track them over time, gaining valuable glimpses into their lives.
Researchers use a technique known as photo-identification to identify and track individual dolphins. Via boat-based surveys, researchers photograph each dolphin’s dorsal fin and match these photos to a catalog. (Photo-id catalog software was originally based upon human fingerprinting software!) Any dorsal fin matched to the catalog builds the sighting history for that dolphin. If a dorsal fin is not matched, it is added to the catalog as a new individual and builds our catalog which currently numbers greater than 1,100 dolphins seen in Roanoke Sound since 2008.
Over time, it seems that certain dolphins return to Roanoke Sound every summer. Dolphins such as Onion, Skylar, Fatlip, and Sequoia along with at least 40 others appear to be “summer residents,” visiting Roanoke Sound between the months May and September each year. Observing these dolphins year after year has given us insight into the population, or stock, they likely belong to, male behaviors, and female calving, and some of the trials that dolphins may face throughout their lives. Many of these “summer residents” are also consistently observed in the Beaufort/Cape Lookout, North Carolina area during other times of the year as well as Virginia Beach/Norfolk, Virginia. Sighting patterns indicate that these dolphins likely belong to a small estuarine stock, numbering at just over 800, and moving seasonally throughout central North Carolina and southern Virginia throughout the year. Onion had first been observed in Roanoke Sound in 1997 and Cape Lookout in the late 1980s, and last observed in Roanoke Sound in 2019. As Onion was already likely an adult at the time of his first sighting, this would lead us to conclude that these dolphins may live long life spans of 40 years or more as has been observed in other populations.
Frequent sightings have also given us insight into whether dolphins may be males or females. Adult males may form strong pair bonds for ecological and reproductive benefits. The ability to discern individual dolphins has allowed us to recognize this type of behavior in Roanoke Sound. Numerous long-term pair bonds lasting at least 10-20 years, such as between Onion and Pinchers, 708 and Sequoia, and Sprite and Cola, have been observed by OBXCDR researchers as well as researchers in Cape Lookout. Females are identified by the presence of a dependent calf and many females, such as Fatlip, Double Scoop, and Madi, have been seen raising calves to independence and then raising their younger brothers or sisters. Calves have been seen leaving their moms and “moving out” anywhere from 3 years old to 8 years old or more (in the case of Tinkerbell, Wendy’s calf). Calf survival and time to independence can give insight into how healthy the population is. A population that is doing well would not be rushed to quickly reproduce and females would be able to spend time raising their calves.
In the fall, as the water cools, the dolphins typically move out of Roanoke Sound and our research season draws to a close. The sound becomes quieter without the dolphins, as does life on land with vacations coming to an end and children returning to school. However, the valuable information that we learn about the dolphins each summer can contribute to their conservation as we process our data, compare notes with other researchers, and piece together years of observations. Bottlenose dolphins in North Carolina are not threatened or endangered, but they are protected under the federal Marine Mammal Protection Act. Dolphins may face challenges such as pollution or entanglement. Follow this tips to do you part to help to conserve our local dolphins:
- Refrain from feeding wild dolphins. Dolphins are excellent hunters and feeding them can be dangerous to both dolphins and people. It is also illegal under the Marine Mammal Protection Act.
- Maintain a distance of at least 50 years while viewing wild dolphins from a boat. This reduces disturbance to the group and makes for a better viewing experience.
- Dispose of your trash in designated areas as littering can be harmful to wildlife.
- Report all marine mammal stranding to the local marine mammal stranding response network: Northern OBX Beaches/Currituck/Hyde County, (252) 455-9654; Cape Hatteras National Seashore, 252-216-6892.
