Family : Carcharhinidae
Text © Sebastiano Guido
English translation by Mario Beltramini
The Lemon shark ( Negaprion brevirostris Poey, 1868) belongs to the subclass of the Elasmobranchii, cartilagineous fishes, order of the Carcharhiniformes and to the family Carcharhinidae, whose dorsal fin has no spines whilst the tail has an upper lobe greatly more developped than the lower one.
Like all Carcharhiniformes it has a nictitating membrane on the eyes, five gill slits, a couple of dorsal fins and one anal fin.
The name of the genus comes from the Latin word “negatio” (denial) and from the Greek “prion” (saw), hence not serrate teeth, whilst that of the species, brevirostris recalls us that its snout is short. The vulgar name of lemon shark refers to the colour tending to yellow of the fish.
It is present along the western and eastern coasts of USA, descending the Atlantic from New Jersey almost up to Argentina and the Pacific from California to Ecuador. Consistent groups exist also on the western African coasts of Senegal and Ivory Coast. A quite similar population, characterized by teeth more acuminate and thin ( Negaprion acutidens Rüppell, 1837) is conversely present in the tropical Indo-Pacific. Both species love shallow waters, from the surface to the 90 metres of depth.
The Negaprion brevirostris lives in the temperate and tropical coastal waters, including the brackish waters and the mangroves, where settles when young, with sporadic and short incursions in some river where however will stay for limited times.
The depth range it loves varies from 0 to 90 m preferring the sandy bottom where hunts the typical animals, such as soles and rays. Frequently, in little distubed zones, it may be met in numerous schools intersecting with their fins the surface.
The average length is of 2,40 metres, whilst the longest measured specimen reached the 3,40 metres with a weight of 183 kilos.
The main characteristics, when met under water, are a certain corpulence in the fore part that contrasts with a thinner terminal part of the body, where the second dordal fin is almost of the same size as that of the first.
The eye is clear, with vertical pupil, well forward on the snout where, all around, abound the Ampullae of Lorenzini that serve for sensing the electromagnetic fields produced by the preys. The mouth, harmonius with the size of the snout, has a double row of thin and sharp teeth bent forward comparable, though decidedly less threatening, than those abounding in the smile of the Sand tiger shark (Carcharias taurus).
The body, stocky ahead and slender behind, has dark back with a yellowish dominant that fades gradually to reach the ventral belt, of creamy white colour. Two long pectoral fins with dark margin are located just after the gills and sustain a body that with the pushing of the long upper lobe of the tail would tend to make it sink. The caudal peduncle gets fairly narrow in respect to the body. Just before its beginning departs specularly the second dorsal fin with dimensions almost the same as the first and the anal fin.
On the back, in retracted position, dominates the robust first dorsal fin. The tail is heterocercal, with long upper lobe.
Even if not considered as a man-eater, at times it may attack for pure curiosity. With the divers usually appears indifferent, getting closer probably for testing them, and at times it can attack, but it is sufficient to lean against the tip of its snout to have it passing under the diver’s body and giving up the attack. It mainly eats fishes and, less, crustaceans and mollusks it can dig out even from under the sand. It often loves, in fact, to stay in numerous groups on sandy bottoms where at times it is possible to find it lying. In these cases a diver that gets closer very calmly and holding the breath has good chances of shooting a macrophotography.
The mating (always in shallow waters and under a polyandry regime) and the gestation lead to the birth of a limited number heirs (averagely a dozen) that the female, placental viviparous, will deliver after ten-twelve months. The young, when born, are of about sixty centimetres and frequent the mangroves and low waters till when they reach a reassuring size for their own safety.
The population is in sharp decline due to the barbaric practice of the shark finning, and for the use of the meat, the leather and of the oil gotten from the liver. The resilience of the species is very low and the time of redoubling of the population can exceed the 14 years. The vulnerability index if very high, being of quota 87 on a scale of 100.
Hypoprion brevirostris Poey, 1868.