Oceanic white tip sharks

6/29/2016

Shark Week 2016 is in full swing, and they are showcasing one of our favorite sharks: the oceanic whitetip (Carcharhinus longimanus). Sound familiar? Our "Behind the Fins" shark scientist Cassandra Ruck studied them for her MSc degree!

They're slow-moving, but don't let that fool you. They are aggressive and dominate in feeding frenzies, and are known to frequent shipwrecks and air crashes. It is one of the top three common oceanic sharks, which also include the blue shark (Prionace glauca) and the silky shark (Carcharhinus falciformis), meaning while all of these sharks face population declines, you could bump into them while out in the open ocean!

These large pelagic sharks inhabit tropical and subtropical waters. They are normally a brown to olive-yellow colour with white smatterings on its fins and a creamy underbelly. What distinguishes this animal from other sharks are its long, rounded, white-tipped fins. It's these same fins that are highly valued for shark fin soup.

Unlike many sharks, it is not diurnal and is active both during the day and night. And, despite being a solitary animal, these animals have paparazzi follow them: pilot fish, dolphinfish and remora linger, in search of food scraps. Mainly patrolling the top part of the water column, they feed on pelagic cephalopods, teleosts, sea turtles, birds, etc.
Whitetips follow schools of tuna or squid, and trail groups of cetaceans such as dolphins and pilot whales, scavenging their prey (some have even been seen swimming in pilot whale feces). Its an opportunistic feeder and therefore has a varied diet.

And with varied diets come unique teeth! The upper jaw has broad, triangular, serrated teeth while the ones on the bottom jaw are pointed and only serrated at the tip. You can see this in the picture on the left by David Fleetham. Groups of this species form usually when they all sniff out a particularly promising meal. They are a competitive, stubborn predator that exploits the meal at hand.

Oceanic whitetip sharks can grow to be quite large, with some reaching 3.5-4 m (11-13 ft); most are > 3m (10 ft). The maximum weight for this species, that has been recorded, is 167.4 kg (370 lbs). Males mature at around 1.7-1.9 m (5.7-6.5 ft) while females mature at 1.8-2.0 m (5.9-6.6 ft), both at around 6-7 years. Although females then to be larger than males, there doesn't seem to be a segregation by sex/size.

Mating season for these animals depends on where they are located! It's early summer in the NW Atlantic and SW Indian Ocean, and females in Pacific have observed to have embryos all year round! Oceanic white tips are viviparous, and have a gestation period of one year. Litter sizes can vary from one to 15 pups.

Famed oceanographic researcher Jacques Cousteau once said the oceanic whitetip was "the most dangerous of all sharks." Despite Jaws giving great white sharks quite a bad rap, oceanic whitetips are suspected to be responsible for many fatal attacks on humans, as a result of predation on survivors of shipwrecks or crashed aircrafts.

These aren't recorded, though, and therefore the oceanic whitetip does not have the highest number of recorded incidents. #Finfact: In the torpedoing of USS Indianapolis on July 30th 1945, these sharks are believed to be responsible for many, if not all, attacks on the survivors who survived the explosion. HOWEVER, most reportedly died from exposure to the elements rather than from shark attacks.

Due to fishing pressure for its fins and large quantities of bycatch, the oceanic whitetip shark classified as Vulnerable (VU) on the IUCN. However, it has been labeled as Critically Endangered by the IUCN in the NW and central Atlantic Ocean due to decreased catches, indicating substantial population declines. The fishery of this animal is inadequate in may places, and therefore there is insufficient data to say exactly what the fisheries are doing to population size.

Although there is no oceanic whitetip shark conservation program/effort, data is trying to be collected on population declines, which can help point future conservation measures in the right direction.

what are your thoughts on this shark?

glossary

Cephalopods: The most intelligent, mobile, and largest of all molluscs. These include: squid, octopuses, cuttlefish, the chambered nautilus, and their relatives.
Cetaceans: Widely distributed and diverse clade of carnivorous, finned, aquatic marine mammals.
Cosmopolitan: Worldwide distribution.
Diurnal: Daily.
Fecundity: The natural capability to produce offspring.
Gestation: The period in which a fetus develops, beginning with fertilization and ends at birth.
IUCN: International Union for Conservation of Nature.
Teleost: Bony fishes.
Pectoral fins: Fins located behind the gills on either side.
Pelagic shark: Live in the open waters of the seas and oceans.
Pup: Give birth to baby sharks (pups).
Pups: Baby sharks.
Viviparous: Eggs hatch inside the female's body and the babies are fed by a placenta which transfers nourishment from the mother to the babies (via an umbilical cord which is connected to the baby shark behind the between the pectoral fins).