Daggernose Shark

The daggernose shark gets its name from its elongated, triangular pointed snout. They are requiem sharks from the family Carcharhinidae and the sole surviving member of their genus.

These sharks were first described in 1839 by German biologists Johannes Peter Müller and Friedrich Gustav Jakob Henle. In a German publication translating – ‘Description of Plagiostomes’, the two biologists named the species oxyrhynchus (from the Greek’ oxys), meaning sharp or pointed.

Daggernose Shark Scientific Classification

Kingdom Animalia
Phylum Chordata
Class Chondrichthyes
Order Carcharhiniformes
Family Carcharhinidae
Genus  Isogomphodon
Scientific Name Isogomphodon oxyrhynchus

Description

Adult male daggernose sharks can reach a length of 4.6 ft, whereas females have been recorded to be up to 5.2 ft long. The largest individual captured weighed about 29 lbs.

The upper side of these sharks is generally gray or grayish-brown with a lighter white underside. They have no distinguishable color patterns in their body or fins.

They have a long pointed snout that is flat and triangular. Nictitating membranes, which are a third protective layer, cover their small, circular eyes. They have small nostrils which lack any extending nasal skin flaps.

The mouths of these sharks contain short, deep furrows at the corners. There are tooth rows numbering 49–60 in the upper and 49–56 in the lower jaws, respectively. The upper teeth have serrated edges, while the lower teeth are smooth. Every tooth consists of one narrow straight cusp.

They have a powerful body consisting of a pair of broad, sizeable pectoral fins shaped like paddles, which emerge just under the fifth-gill slit. The back of the pectoral fin bases gives origin to the first dorsal fin. In contrast, the second one (about 1.5 times taller than the first) is located in front of the anal fin.

The anal fin is small and has a deep notch in its margin situated in the back. The caudal peduncle has a crescent-shaped gap and succeeds the caudal fin, whose lower lobe is well developed.

Where do they live

The geographical distribution of the daggernose sharks is not extensive as other sharks, with most of their numbers found along the northeast South American coast. The sharks have been spotted in the waters of the central west Atlantic Ocean and the Caribbean Sea. They are located along the shores of Venezuela, Trinidad, Suriname, Guyana, French Guiana, and northern Brazil.

These sharks inhabit muddy and shallow coastal waters, such as estuaries and river mouths with high turbidity and depths of 13-131 feet. Females swim in greater depths as compared to males. The daggernose prefers a habitat consisting of a humid, tropical climate, drainage by rivers (like the Amazon), water salinity levels of 20-34 ppt, and tidal amplitudes measuring up to 23 feet.

Behavior

Dietary

The daggernose sharks have long jaws and sharp teeth, which help them capture schooling fishes such as herrings, catfishes, croakers, and anchovies.

Reproductory

These sharks are viviparous (they give birth to live young). A placental connection forms out of the depleted egg yolk after the developing embryos finish consuming the yolk. Gaseous exchange and nourishment take place via this placental connection. The entire rainy season (six months) marks the period when mating and birth usually take place. Changes in environmental conditions can make the female shift the time of its reproductive cycle by up to four months.

Pregnancy lasts an entire year, resulting in a litter size consisting of 2-8 pups every alternate year. The number of offspring does not depend upon the female’s size. Pups measure 15-17 inches at the time of birth. Male sharks take 5-6 years to reach the age of sexual maturity when they are 41 inches long, whereas female sharks maturewhen they at 6-7 years of age at a length of around 45 inches.

The general lifespan of these sharks is seven years for males and twelve years for females.

The Brazilian state of Maranhão is an example of an important shallow coastal nursery where the female sharks prefer to give birth.

Adaptations

To hunt and swim effortlessly in their preferred choice of murky sediment-laden waters, the tiny eyes of these sharks are not of any help. Therefore, they rely heavily on their olfactory receptors and sensory organs in their snout.

Interactions with humans

Their small size and tiny teeth do not pose a threat to humans.

These sharks are caught in small numbers by local fisheries in Trinidad, Guyana, Suriname, French Guiana, and northern Brazil during the dry season. Although found in commercial markets, their meat has not been considered a good source of food.

Due to its low reproductive rate and limited distribution, factors that can lead to depletion of their numbers during overfishing, the IUCN has listed these sharks as Critically Endangered. In places like Brazil, intense fishing pressure has resulted in the survival of only 10% of their numbers compared to the previous decade.

Conservation schemes and the proper monitoring of fisheries should be implemented effectively, as recommended by the IUCN.

Sources

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