Whitetip Reef Shark, Triaenodon obesus

Whitetip Reef Shark, Triaenodon obesus. Fish provided by the commercial fishermen of the greater Los Cabos area, Baja California Sur, May 2013. Length: 1.48 m (4 feet 10 inches).

The Whitetip Reef Shark, Triaenodon obesus, is a member of the Requiem Shark or Carcharhinidae Family,  and is known in Mexico as cazón coralero trompacorta. Globally, this fish is the only species in the genus Triaenodon and it is found in all Mexican oceanic waters of the Pacific Ocean.

The Whitetip Reef Shark has a slender body. Adults are grayish to brownish dorsally and transition to white ventrally with scattered randomly placed dark spots. Their caudal and dorsal fins have white tips. In some fish, the lower lobe of the caudal fin and the second dorsal fin also have white tips. Their anal and second dorsal fins are large and at least half as high as the first dorsal fin; their caudal fin has a lower lobe that is about half the length of the upper lobe and has a strong notch near the tip; their first dorsal fin is found well back on the body being closer to the pelvic fins than the pectoral fins; their pectoral fins are broad and triangularly-shaped and originate over the fifth gill slit. They lack the ridge between the two dorsal fins and the keels on the caudal base found in similar sharks. Their head is short and broad and has small oval eyes with vertical pupils and tubular skin flaps besides the nostrils. Their mouth has a distinct downward slant with short furrows at the corners and is equipped with 42 to 50 rows of teeth on the upper jaw and 42 to 48 rows of teeth on the lower jaw. Each tooth has a single narrow smooth-edged cusp at the center and is flanked by a pair of much smaller cusplets. Their skin is smooth to the touch.

The Whitetip Reef Shark is the most common sharks in coral reefs. They are found on or near the bottom in clear water at depths between 8 m (25 feet) and 330 m (1,080 feet). They reach a maximum of 2.1 m (6 feet 11 inches) in length and 23.3 kg (52 lbs) in weight. As of January 1, 2023, the International Game Fish Association world record stood at 23.3 kg (51 lbs 6 oz) with the fish caught in coastal waters off Tokyo in February 2019. During daylight hours they are found resting on the bottom. They are unique among requiem sharks in that they can remain motionless for long periods of time relying on ram ventilation to pump water over their gills, which allows them to breathe while stationary. They are gregarious by nature and can be found singly or in small groups arranged in parallel or stacked atop one another. They are nighttime predators forming groups that prey on bony fish (damselfish, eels, goatfish, parrotfish, snappers, surgeonfish, and triggerfish), crustaceans (crabs and spiny lobsters) and octopus but they can survive without food for up to six weeks. In turn they are preyed upon by the Galapagos Sharks, Carcharhinus galapagensis, the Giant Grouper, Epinephelus lanceolatus, the Silvertip Shark, Carcharhinus albimarginatus, and the Tiger Shark, Galeocerdo cuvier. They are known to be cleaned of parasites by the Banded Cleaning Goby, Tigrigobius digueti and the Mexican Hogfish, Bodianus diplotaenia. They have very limited home ranges and stay within a specific reef for months to years while returning to the same daytime locations. They are non-territorial and share their space with other species. Reproduction is viviparous with internal fertilization and each female delivering one to six pups on a 2-year cycle after a ten to thirteen month gestation period. Each female produces approximately twelve pups in her lifetime. Pups are born in the water column and measure 52 cm (20 inches) to 60 cm (2 feet 0 inches) in length. They have slow growth rates compared to other requiem sharks reaching sexual maturity in eight or nine years. They have lifespans of up to twenty-five years with females living longer than males.

The Whitetip Reef Shark is one of the most common resident sharks in the Pacific being more common in the western Pacific Ocean. In Mexican waters they are exceedingly rare with the fish photographed below caught 40 miles north of Cabo San Lucas documenting a significant northerly range extension for this species.

The Whitetip Reef Shark can be easily confused with the Silvertip Shark, Carcharhinus albimarginatus (larger body; larger first dorsal fin; small second dorsal fin; caudal fin with white margin and no white tip) and the Whitemargin Smoothhound, Mustelus albipinnis (large eyes; fins with white margins; caudal fin with large lower lobe).

From a conservation perspective the Whitetip Reef Shark is currently considered to be Near Threatened with decreasing global populations and unregulated global fishing pressure. They have a long reproduction cycle and a limited habitat preference making them vulnerable to overfishing. The Whitetip Reef Sharks are fished for food is some areas and are caught commercially by hand lines, gill nets, and bottom trawls but are known to contain ciguatoxin. They are not aggressive towards humans unless provoked. They are fearless and curious of divers. They can be hand-fed by divers and are now a target of the ecotourism diving business.