Bigeye Sand Tiger

The bigeye sand tiger is a deep mid-ocean dwelling shark belonging to the family Odontaspididae. These rare mackerel sharks may have a worldwide distribution. However, most of their numbers are found in the southern Pacific and Atlantic Ocean.

The species was first described in a 1955 article for Notulae Naturae by a German ichthyologist named Günther Maul, in honor of Adolfo César de Noronha-the late Director of the Funchal Museum. Maul described the species of a 5.6 feet female specimen caught in Madeira in April 1941.

Bigeye Sand Tiger Scientific Classification

Kingdom Animalia
Phylum Chordata
Class Chondrichthyes
Order Lamniformes
Family  Odontaspididae
Genus Odontaspis
Scientific Name Odontaspis noronhai

Description

Mature males grow to a length of 7.2 feet, with the largest specimen measured at 12 feet. In contrast, mature females reach to a size of 10.7 feet.

Their color ranges from a dark reddish-brown to chocolate brown. An occasional black trailing margin is sometimes visible on their fins. Moreover, their first dorsal fins may often appear white towards the tip . They have a set of big rounded eyes that are dark orange with vertical greenish pupils that lack nictitating membranes. There are small spiracles present behind their eyes.

Their head has a large, bulbous snout and a vast mouth whose corners extend behind their eye level. The floors of their mouth, gill arches, and the area around the jaws have several black patches. Their jaws can be highly protruded, with 34–43 tooth rows in the upper and 37–46 tooth rows in the lower jaw. There are 0-2 rows of tiny teeth at the midpoint of their upper jaw and 2-4 rows of tiny teeth at the midpoint of their lower jaw. Their teeth are narrow, exposed, and consist of a singular cusp surrounded by a smaller cusplet on both sides. The bigeye sand tigers have five pairs of gill slits.

They have a pair of medium-sized pectoral fins that have rounded tips. The first dorsal fin is large, located near the pectoral fins. In contrast, the second dorsal fin, half the size of the first dorsal fin, originates over the base of the pelvic fins. The anal fin is smaller than the second dorsal fin. The upper origin of the caudal fin is also where a crescent notch in the caudal peduncle is visible. The upper lobe of the caudal peduncle consists of a deep dent near the tail, while the lower lobe is short but prominently seen. .

Their skin has dermal denticles that overlap each other and are made of three horizontal ridges that lead to marginal teeth.

Where do they live

The bigeye sand tiger is found across tropical and warm-temperate regions of the southern Pacific and Atlantic waters. These sharks are generally spread across southern Brazil, Texas, eastern Florida, and the Mid-Atlantic Ridge.

This species has been found at depths of 200 – 3280 ft. They inhabit continental and insular shelves near the seafloor and in mid-water. They swim to the upper parts of the water column at night to feed and return to the depths where even sunlight fails to reach during daytime.

Behavior

Dietary

These sharks generally feed on bony fishes and squids, and other mollusks.

Reproductory

The species follows a viviparous mode of reproduction where eggs are present in the form of enclosed capsules in the uterus, where they eventually hatch. Inside the egg, the embryos sustain themselves by feeding on unfertilized eggs, a process called oophagy. Females, upon maturation, have two functional uteri and a single functional ovary.

Males undergo sexual maturation when they are about 7.2-0.5 ft long. In contrast, females reach sexual maturity when they are almost 10 feet long.

Adaptations

These fish are mesopelagic, i.e., they dwell in the middle of the ocean, where they hunt and feed. Their big eyes and dark, patchy skin help them adapt to these waters.

Interactions with humans

These sharks are harmless unless provoked or captured. There has been a report of the shark acting aggressively and thrashing out when it was on the way to being captured. Their numbers are so rarely spotted that they are of no commercial importance.

Although these deep water fishes are sometimes caught accidentally in tuna longlines and gillnets, their numbers face no threat of depletion, which is why the IUCN has listed the sharks as a ‘Least Concern’.

Sources

 

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