Bigeye sand tiger

11/19/2018

PIRO-NOAA Observer Program

The bigeye sand tiger (Odontaspis noronhai) is an extremely rare species in the Odontaspididae family. Found inhabiting continental margins and pelagic waters from 60–1,000 m (200–3,280 ft), reports from around the world suggest it may have a worldwide distribution.

The first ever known bigeye sand tiger was a female who measured about 1.7 m (5.6 ft) long that was caught off Madeira (an autonomous region of Portugal) in April 1941. Those who caught her weren’t actually fishing for sharks, but had longlines set for black scabbardfish (Aphanopus carbo)! Fascinated by their find, this specimen was preserved and mounted, and later was described scientifically by a German ichthyologist named Günther Maul. In 1955 Günther’s article for Notulae Naturae was published, where he gave it the name “noronhai” in honour of the late Director of the the Funchal Museum, Adolfo César de Noronha. At the time, the new species of sand tiger shark was labelled under the genus Carcharias, which at the time was used for this family. Odontaspis later came around to be established as a separate genus from Carcharias, and therefore all fell under that.

The species is most known from the Atlantic Ocean, found Madeira, Brazil, Texas, Florida, and the Mid-Atlantic Ridge. It has been captured at relatively shallow depths at night, suggesting that they may partake in daily diel vertical migration, rising from the depths at night to feed. According to some reports, these sharks are only captured during the springtime in Brazil, so perhaps there is some type of seasonal migratory movement occurring here?

They look similar to other sand tiger sharks, as in they are large, bulk, and have a bulbous snout. Their large orange eyes lack nictitating membranes, their mouth never fully closes due to their rows of needle-like teeth which are brown in colour. The species can get up to at least 3.6 m (12 ft) in length, and feeds on a variety of fish and squid. “Wait, you just glossed over the fact that they have ORANGE EYES?” Well, their size and color may suggest they spend most of their time in the mesopelagic zone – a place with little light.

One account of a this sand tiger noted that it was very aggressive, thrashing and snapping violently in and out of the water… but that’s also because it was caught and to be fair, we wouldn’t be docile if we were caught either. We know little about their reproduction methods and assume it is similar to those in its family meaning they are viviparous with their embryos feeding on unfertilized eggs during gestation (something called oophagy). The IUCN has assessed them as Data Deficient (DD).

WHAT DID YOU LEARN ABOUT THIS ANIMAL?

GLOSSARY

Continental shelf: Extends from a continent underwater, resulting in a shallow-water area.
Continental slope: The steep slope from a continental shelf to the ocean floor; usually around 20 km (12.4 miles) wide and made up of mud and silt substrate. It is an ideal area for deep sea fishing.
IUCN: International Union for Conservation of Nature.

Teleost: Bony fishes.
Oophagy: Sometimes called "oviphagy;" when developing embryos feed on unfertilized eggs.
Pectoral fins: Fins located behind the gills on either side.
Pup: Give birth to baby sharks (pups).
Pups: Baby sharks.

Viviparous with yolk-sac: Also known as aplacental viviparous and previously known as ovoviviparous/ovoviviparity; it is the production of eggs that are fertilised and hatch inside the female shark but the embryos lack a placental connection to the oviduct or uterus and so do not feed off the mother.