For years, our private dolphin tours around Hilton Head Island have showcased the beauty of the common bottlenose dolphin (Tursiops truncatus). On these boat tours, we’ve often marveled at the differences between the offshore and coastal dolphins, particularly in their sizes. However, recent studies reveal that these variations are not mere distinctions within a species; instead, they point to a unique subspecies named Tamanend’s bottlenose dolphin (Tursiops erebennus).
A Historical Dive: Tamanend’s bottlenose dolphin has a history dating back to 1865 when the first specimen was recorded in New Jersey. Named after a chief of the Lenape Delaware nation, this species remained overlooked for over a century. Initially, observed physical differences were attributed to environmental factors. Yet, as science advanced, studies of western North Atlantic dolphins unveiled significant variations, both physically and genetically, between offshore and coastal variants.
Revealing Tamanend’s Dolphin: The most noticeable difference between offshore and coastal dolphins lies in their size. Coastal dolphins can reach up to 8 feet, while offshore counterparts surpass 12 feet. Over the past decade, scientists meticulously studied their skulls and vertebral columns, leading to a groundbreaking revelation – Hilton Head Island’s dolphins are not just common bottlenose dolphins; they belong to a unique subspecies, Tamanend’s bottlenose dolphin.
Distinguishing Cranial Features: To differentiate between the two, we look at the shape of their skulls. Offshore dolphins have a flat top, an elongated bone near the eye, a noticeable bump at the back, a wider front part of the mouth bone when seen from below, and a back edge forming a right angle to the skull’s length. Coastal dolphins, in contrast, have a higher front top, a shorter bone near the eye, no noticeable bump at the back, a narrower front part of the mouth bone when seen from below, and a back edge forming an acute angle to the skull’s length.
Vertebral Column Analysis: The study identified clear differences in the number of vertebrae in the spinal column of coastal and offshore dolphins. More vertebrae provide stability for fast maneuvers in oceanic dolphins, while fewer vertebrae allow slower and more precise movements in complex coastal waters. During a private dolphin tour, you can witness the remarkable flexibility of the Tamanend bottlenose spinal column. This adaptation is particularly evident as they engage in strand feeding along the mud banks of Hilton Head.
Ecological Implications: These distinctive features have ecological implications, suggesting different feeding ecologies and habitat preferences. Coastal dolphins, with their smaller size, feed on nearshore sciaenid fishes, while offshore dolphins, being larger, opt for deep-sea fish and squids. Skull scarring from the parasitic nematode Crassicauda also differs between the ecotypes, indicating distinct feeding behaviors.
Genetic Confirmation: Genetic analyses further affirm the distinctiveness of Tamanend’s bottlenose dolphin. Coastal dolphins exhibit a unique genetic profile, while offshore dolphins share genetic similarities with counterparts worldwide. The offshore ecotype shows higher genetic diversity, indicating a broader distribution.
Conservation Implications: Understanding the unique characteristics and genetic makeup of Tamanend’s bottlenose dolphin has crucial conservation implications. Recognizing these dolphins as a distinct subspecies ensures targeted conservation efforts, emphasizing the importance of preserving both coastal and offshore habitats to sustain these unique populations.
As we welcome the new year, let’s embrace the exciting revelation of Tamanend’s bottlenose dolphin around Hilton Head Island. The more we learn about these incredible creatures, the better equipped we are to protect and appreciate the rich biodiversity that thrives in our oceans. So, the next time you embark on a private dolphin tour, remember, you might just be in the presence of a Tamanend’s bottlenose dolphin, a unique and fascinating species that calls Hilton Head Island home.