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Dusky Sandbar Comparison

Dusky Sandbar Comparison

Two common sharks that confuse fishermen and biologists alike are the dusky and sandbar sharks, Carcharhinus obscurus and Carcharhinus plumbeus. Because proper identification is vital to the success of our tagging program, we have in the past provided information that separates these two species from each other.

The sandbar and dusky sharks share many characteristics. The teeth are similar in number, size, and shape. Size of eyes, gills, mouth, and nostrils are also similar, as are most body proportions. There are differences in the shape, size, and location of the fins, although these features are subtle. The dusky's fins are proportionately smaller and swept back, whereas the fins of the sandbar are broader and the first dorsal is higher and originates further forward. The two sharks are easily separable when the skin is viewed through a 10X hand magnifier. The scales on the dusky shark are overlapping and shingle-like, while those on the sandbar shark are separated and more like cobblestones.

Sharks, like other animals, change shape and appearance as they grow and mature. Their bodies thicken, fins become relatively longer and distances between the fins appear to change as the sharks reach maximum sizes. As a consequence of these changes, young sandbar and dusky sharks look very similar even though the adults look quite different. The smaller sizes (3-4 feet total length) are most similar and nearly impossible to tell apart in the water. At 5 to 6 feet, the dusky is a trimmer shark than the sandbar, with sickle-shaped fins and a longer, lower caudal fin. The first dorsal fin on a 5 foot dusky is further back and more rounded than on one of 3-4 feet. The overall shape of the sandbar shark is less changeable with size, although the fins become slightly broader and the girth is proportionately larger than a dusky of the same size. Otherwise, sandbars keep the same husky shape from juvenile to adult. The maximum sizes reached by these species can also help to identify them. Sandbar sharks mature at 5-6 feet and rarely reach 8 feet or 200 pounds. Dusky sharks mature at 8 feet, reach 10-12 feet and several hundred pounds. Consequently, a 250+ lb. shark is definitely not a sandbar shark; it could be a dusky, but it should be keyed out in the Anglers' Guide to Sharks or other literature.

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(File Modified Sep. 13 2011)