Finetooth Shark, Carcharhinus isodon
Finetooth Shark, Carcharhinus isodon. Fish caught off the beach in Sebastian, Florida, March 2021. Length: 1.27 m (4 feet 2 inches). Catch, photograph, and identification courtesy of Ben Cantrell, Sebastian, Florida.
Finetooth Shark, Carcharhinus isodon. Fish caught off the beach in Sebastian, Florida, March 2021. Length: 1.30 m (4 feet 3 inches). Catch, photograph and identification courtesy of Ryan Crutchfield, Tampa, Florida.
Finetooth Shark, Carcharhinus isodon. Fish caught from coastal waters off Sanibel Island, Florida, February 2021. Length: 1.27 m (4 feet 2 inches). Catch, photograph and identification courtesy of Marc Eberlein, Grand Rapids, Michigan.
The Finetooth Shark, Carcharhinus isodon, is a member of the Requiem Shark or Carcharhinidae Family, that is known in Mexico as tiburón dentiliso. They are named for their small fine needle-like teeth. Globally, there are thirty-five species in the genus Carcharhinus, of which seventeen are found in Mexican waters, seven in the Atlantic, four in the Pacific, and six in both the Atlantic and Pacific Oceans.
The Finetooth Shark has a small slender streamlined body. They are a dark blue-gray dorsally transitioning to white ventrally. Their fins are not marked and There is a white band on their sides and their fins are not marked; the undersides of their pectoral fins are pure white. Their head has a pointed snout with large round eyes that have nictitating eyelids. Their mouth is broadly rounded in the front with well-defined labial furrows around the corners that is equipped with finely pointed 12 to 15 rows of needle-like teeth that are similar on both jaws. The top and bottom teeth are symmetrical and narrowly pointed with the lower teeth being smooth and the upper teeth being weakly and irregularly serrated. Their anal fin has a deeply notched rear margin; their caudal fin has a straight upper edge, is strongly asymmetrical with a well-developed lower lobe and has a narrowly rounded tip; their first dorsal fin is high and triangular with a pointed apex with a short rear tip that originates before the rear tips of the pectoral fins with a slightly convex front margin and concave rear margin with pointed tips; the second dorsal fin mid-sized with a short rear tip and originates over the anal fin; their pectoral fins are small and narrow with pointed tips; and, their pelvic fins have narrowly rounded tips. They are covered with small overlapping dermal denticles. They have very long gill slits along the base of the first dorsal fin with the last two over the pectoral fins. They do not have the interdorsal ridge found in similar sharks. They have 5 pairs of gill slits, the last two originating over the pectoral fin base.
Finetooth Sharks are a coastal species found in large schools in shallow water bays and coastal lagoons at depths up to 20 m (65 feet). The move into deeper waters with this range during colder months. They are also known to make seasonal migrations of several hundred miles when water temperatures drop below 20oC (68oF) seeking warmer waters. They reach a maximum of 1.9 m (6 feet 3 inches) in length with females being slightly larger than males. As of January 1, 2023, the International Game Fish Association world record stood at 4.08 kg (9 lbs O oz) with the fish caught in coastal waters off South Carolina in July 2012. The Finetooth Shark fast swimming aggressive predators that are known to hunt in the surf zone in packs during daylight hours on small fishes including mackerels, Atlantic menhaden, and mullets and various invertebrates including crustaceans and squid. In turn they are preyed upon by various larger sharks. Reproduction is viviparous and involves a two-year cycle with a 12-month gestation period and litter sizes of 2 to 6 that are born as miniature adults. Parturition occurs in shallow water. At birth, the pups measure between 51 cm (20 inches) and 64 cm (2 feet 1 inch) in length and the remain in shallow bays and coastal lagoons for extended periods of time to avoid predation. The females are slower growing and live longer than the males. They have lifespans of up to fourteen years.
The Finetooth Shark is a resident of Mexican waters of the Atlantic Ocean but has a limited distribution being found along the west coast of the Gulf of Mexico from the Texas border south to Veracruz.
The Finetooth Shark are similar to and easily confused with the Atlantic Sharpnose Shark, Rhizoprionodon terraenovae (spotting on the sides), the Blacktip Shark, Carcharhinus limbatus (black tipped fins), the Lemon Shark, Negaprion brevirostris (same sized dorsal fins), and the Spinner Shark, Chacharhinus brevipinna (black tipped fins).
From a conservation perspective the Finetooth Shark is currently classified to be of Least Concern, with stable, widely distributed populations. The United States has banned the use of gillnets to catch these fish. They remain poorly monitored and unregulated. They are utilized in some parts of their range as a human food fish, but are small in stature. They are caught by commercial fishermen as a by-catch by floating longlines and drift gillnets. They are caught by recreational anglers from shore. Their long-term viability is currently threatened by overfishing, low reproductive rates and inshore habitat destruction caused by human developments. They are not known to be aggressive towards humans.