Naturalist Fact: Lemon Shark

Lemon sharks are one of the most common shark species in the waters surrounding LSSI. (photo: Albert Kok)

Lemon sharks are one of the most common shark species in the waters surrounding LSSI. (photo: Albert Kok)

Negaprion brevirostris are known as lemon sharks because of their light brown to yellowish skin, which helps them blend in with the sandy ocean bottoms. Although identifying sharks is often difficult, lemon sharks are fairly easy due to their coloration and the fact that their two dorsal fins (top fins) are about the same size, unlike most sharks. They also have a blunt snout, flattened head and stocky body. These sharks grow to a maximum length of about 11 feet and weight of over 400 pounds.

Lemon sharks live in shallow waters preying upon bony fish, rays, and sometimes crustaceans. Females give birth at about 6-7 years of age from April through September. There are 4-17 pups in each litter, and the pups are 24-26 inches long at birth. The lifespan of lemon sharks is estimated at about 25 years. Lemon sharks do well in captivity and experiments on lemon sharks have shown they learn as quickly as some mammals and remember things for at least 6 months without reinforcement. This is a very social shark species. They are often seen in groups and have a structured hierarchy system based on size and sex. They generally don’t show any aggressive behavior with each other and coordinate in groups for hunting purposes in places that the hierarchy is strictly followed.

Although lemon sharks are among the world’s largest shark species, they are rarely dangerous to humans. The International Shark Attack File has only reported 10 unprovoked bites by lemon sharks, none of which were fatal.

The lemon shark is targeted by commercial and recreational fishermen along the US Atlantic Ocean, Caribbean, and in the eastern Pacific Ocean. Their fins are highly prized and exported to Asia for shark fin soup. Their skin may be used for leather and their meat can also be consumed, all of which make this shark very marketable. There is some concern that populations in the western north Atlantic and eastern Pacific Ocean are declining due to over-fishing.

This is one of the most common shark species in the waters surrounding LSSI. You can catch them in the surf from March to November with heavy tackle and large cut bait. They should be released as quickly as possible once landing them to reduce stress on the fish.

Lemon-shark-(30)

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Naturalist Fact: Bonnethead Shark

Bonnetheads (Sphyrna tiburo) are the smallest species of the hammerhead family reaching an average size of 3-5 feet.  This shark can be distinguished from other hammerheads by its rounded, shovel-shaped head.  They are found in the Western Atlantic and Eastern Pacific oceans.  Unlike most sharks, they have molar-like teeth at the back of the jaw for crushing their prey such as hard-shelled invertebrates, crabs, shrimp, mantis shrimp, snails, cephalopods, as well as small bony fishes.  Their feeding behavior involves swimming across the seafloor, moving its head in arc patterns like a metal detector, looking for minute electro-magnetic disturbances produced by prey hiding in the sediment.  Studies of a colony of captive Bonnetheads revealed that this species has surprisingly complex behavior, body language and social organization.  18 Bonnethead body postures and movement patterns were identified including head shakes, back hunching, puffing out the gill pouches, jaw snapping, hitting other Bonnetheads, circling head-to-tail in lines of up to five, and (in males) clasper flexing.  Half of these appeared to regulate social activities.  A subtle, size-related dominance hierarchy was also noted among the sharks, with submissive individuals giving way to dominants as little as 5% longer than themselves.  This suggests they have a keen awareness of their own size relative to that of others sharing their environment.  Bonnetheads give birth to live young with a gestation period of 4 to 5 months, which is the shortest gestation period of all sharks.  Females reach sexual maturity when about 2 1/2 feet long.  They give birth in late summer or early fall to litter sizes of 8 to 16 pups.  During this time, the females lose their desire for food, which prevents them from feeding on their pups.  Males move to a different location, also an adaptation to avoid feeding upon their own young.  Bonnetheads are the only sharks known to exhibit sexual dimorphism, which is where male and female adults look different from one another.  Adult females have a broadly rounded head, whereas males possess a distinct protuberance at the top of the head.  In 2001 at a zoo in Nebraska, a female Bonnethead produced a pup in a tank containing three other females, but no males.  It was concluded after DNA testing that the reproduction was by parthenogenesis, a form of reproduction in which an unfertilized egg develops into a new individual. This type of asexual reproduction had been seen before in bony fish, but never in cartilaginous fish such as sharks, until this documentation.  The Bonnethead, with its early age at maturity and high litter size and population growth rates are very abundant and therefore considered a species of lesser concern.

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