Whitetip Reef Shark, Triaenodon obesus
The Whitetip Reef Shark, Triaenodon obesus, whose common Spanish name is cazón coralero trompacorta, is a member of the Requiem Shark or Carcharhinidae Family, known collectively as tiburónes gambuso in Mexico. Globally, this fish is the only species in the genus Triaenodon and it is found in all Mexican oceanic waters.
The Whitetip Reef Sharks have slender bodies. 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 Sharks are the most common sharks in coral reefs. They are found on or near the bottom in clear water at depths between 25 and 1,080 feet. They reach a maximum of 2.1 meters (6 feet 11 inches) in length and 18.3 kg (40 pounds) in weight. 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, Elacatinus 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 two-year cycle after a 10 to 13-month gestation period. Each female produces approximately 12 pups in her lifetime. Pups are born in the water column and measure 52 cm (20 inches) to 60 cm (24 inches) in length. They have slow growth rates compared to other requiem sharks reaching sexual maturity in eight or nine years. They have a lifespan of up to twenty-five years with females living longer than males.
The Whitetip Reef Sharks are one of the most common sharks in the Pacific being more common in the western Pacific. 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).
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 Cigua Toxin. 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. From a conservation perspective they are currently considered Near Threatened which is attributed to decreasing global populations and unregulated global fishing pressure. They have a long reproduction cycle and a limited habitat preference making them vulnerable to overfishing.
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 meters (4 feet 10 inches).