Leopard Sharks - Interesting Facts and Features

Leopard Sharks – Interesting Facts and Features

Leopard shark (Triakis semifasciata) is an amazing sea creature that earned its name from the black saddle-like stripes on its back which many believe resembles that of leopard. This shark belongs to the family of Triakidae, usually found in estuaries in the eastern Pacific Ocean, from Oregon to the Gulf of California. Leopard shark is a small shark that rarely grows more than four or five feet with the heaviest weighing only about 40 pounds.

Scientific Classification

Kingdom – Animalia
Phylum – Chordata
Class – Chondrichthyes
Order – Carcharhiniformes
Family – Triakidae
Genus – Triakis
Species – T. semifasciata

Leopard Shark Typical Behavior

Leopard sharks show social interactions. They tend to travel in schools segregated by gender and size. That is, smaller males of leopard sharks travel together, a behavior also popular among their juveniles. These schools, when tracked by researchers, shows that some leopard sharks reside in specific areas. While others tend to roam around throughout coastal regions.

Warm coastal waters increase the rate of digestion in these sharks and accelerate gestation. These sharks have a trait they share with nurse sharks which is their ability to rest on the seafloor. They are also capable of pumping water through their gills, a unique trait that most sharks are unable to do. When searching for food, leopard sharks emerge at night in large groups to hunt for prey.

Naming and Development History of Leopard Sharks

The leopard shark’s first scientific name was Triakis californica, a name coined by British zoologist John Edward Gray in 1851. However, Gray’s taxonomic name was invalid because the group designated was not sufficiently described for recognition. Thus, referred to as “nomen nudum” in taxonomy.

Later on, an American ichthyologist William Orville Ayres, in December 1854 gave a lecture describing leopard sharks as Mustelus felis which was part of the first scientific description of these species. The first reprinting of Ayres’s lecture was in a San Francisco newspaper called “The Pacific”. And, later in the journal Proceedings of the California Academy of natural sciences.

A French scientist afterward, in 1855 published another description of these species naming them Triakis semifasciata. Even with M. felis being the senior synonym, an error in the dates of publication led to the wide use of T. semifasciata as leopard sharks scientific name. Due to the long-standing error, Triakis semifasciata came to be the recognized valid name i.e. “nomen protectum”. As such, Mustelis felis invalidated as “anomen oblitum”.

The semi in the specific name comes from a Latin word which means “half”. Similarly, is fasciatus which means “banded” describing the dorsal pattern of saddle-like markings on their body. Some old books or literature may refer to these sharks as catshark or trigger shark.

Natural Habitat and Range of Distribution

Leopard sharks usually occur in the temperate continental waters of Coos Bay, to the tropical waters of Mazatlán in Oregon, Gulf of California and Mexico. They prefer Sandy or muddy flats within enclosed estuaries and bays. They can also inhabit near rocky reefs and beds along the open coast. Leopard sharks most times swim in school, they generally swim close to the bottom and are rampant in the intertidal zone to a depth of 13ft (3.9 m). However, these sharks can sometimes swim in great depths as deep as 299ft (91.1 m).

These amazing sharks are migratory fish and would leave their coastal habitats in winter and later return in early spring. Research in Tomales bay showed that leopard sharks migrate when the temperature of the water drops below 10 to 12 degrees Celsius. Some leopard sharks have been documented to swim as far as 62.1 miles (100 kilometers). Though, many others prefer to remain in a localized area for most of their lives.

Leopard sharks usually inhabit shallow waters of estuaries, bays, and sometimes patrol the kelp forest, staying near the bottom. Leopard sharks rarely go to water more than 65 feet (19.8 m) deep. During extreme times, they follow high tide to feed on shallow mudflats, then move out when the water recedes again.

There is genetic divergence across its range due to the low level of dispersal. As such, leopard sharks in areas such as Humboldt Bay tend to be larger and produce fewer offspring compared to others in areas like Baja California.

How to Identify Leopard Sharks

Leopard sharks are beautiful, slender sharks with short, broadly rounded snout. Their first dorsal fin is fairly large and the origin is from their inner margins’ pectoral fins. The second pectoral fin is almost as large as the first pectoral fin and their anal fins are smaller when compared to the remaining two. Their pectoral fins are triangular and wide. They have a well-developed caudal fin lower lobe in adults and less than half of the length of the upper lobe in juvenile with a hard-ventral notch near the tip.

Teeth Arrangement

These sharks produce tooth set ridges that overlap between tooth rows. This result in large flattened and ridged surface on the upper and their lower jaws. This type of Dentition is called the “pavement method”.

They have a well-developed triangular flap of skin in front of their nares. Leopard sharks have a large oval eye with a protective third eyelid. The lines of their mouth are strongly curved and the furrows of their mouth extend to both jaws (upper and lower jaws). And, on the lower jaw, the furrow is long enough to meet at the midline.

They have tooth rows number of about 41 – 55 in their upper jaw and 34 – 45 in their lower jaw. Each tooth has a bit oblique, smooth-edged cusp at the center. Their teeth arrangement is into the flat-like surface with their ridges overlapping. They have 1-2 cusplets on either side of their jaws.

Coloration

Leopard sharks have unique coloration, consisting of black saddles and large black spots on a silvery to bronzy gray background running along the back of their body. Their adults usually have more spots and saddles with lighter centers compared to the juveniles. They have a plain and whitish underside.

What are leopard sharks’ growth rates and size?

Leopard sharks’ average length is about 3.9 – 4.9 ft (1.2 – 1.5 m). Their males grow up to about 4.9 ft (1.5 m) and the females grow up to about 5.9 ft (1.7m). On the other hand, the recorded heaviest weighing leopard shark weighed 41 Ib (18.5 kg). Their pups are born at a size of 9 to 10 inches (22.8 to 25.4 cm) and they reach maturity at a size of 3 to 3.5 ft that is about 1m length.

Behavioral Attributes of the Leopard Shark

Leopard sharks are active swimmers that swim with a strong undulating motion. As a result, they would usually cruise in or just beyond the surf zone. Leopard sharks are nocturnal creatures hunting at night, and they prefer to lie at the bottom of the river. Often, leopard sharks follow the tide onto mudflats to look for food in Tomales Bay and elsewhere. But they retreat fast enough to prevent from being stranded or trapped as the water recedes.

Leopard sharks usually form large schools segregated by age and sex. These schools are nomadic and are often suddenly in an area for a few hours and then, vanish just as quickly. When observed in captivity, bigger sharks tend to dominate the younger ones through light nips to their Pectoral fins.

In the summer, a large association of female leopard sharks assemble in estuaries and shallow bays and then disperse at night. When these female sharks follow the warmest patches of water, they can raise their temperature up to about 3 degrees Celsius. They take advantage of this heat to help hasten their growth and that of their gestation period. This association doesn’t often last because of the periodical switching between different sites causing them to scatter all over.

Adaptations for Survival

Leopard sharks have small numerous red blood cells that allow them to process oxygen more efficiently. This is an adaptation for scrounging enough oxygen in deoxygenated estuary environments. Also, they have eyes that contain few cone cells due to the murky water environment they live in. Spots and saddles on their body which gives them their unique name help them camouflage when they swim along the ocean floor.

Leopard sharks’ Diet

Leopard sharks are natural bottom feeders. These sharks have a mouth that is flat on the underside of their head and opens downward. Most sharks have un-terminal mouth except megamouth sharks and a whale shark. Leopard sharks’ diet naturally includes shrimps, crabs, Octopus and fat innkeepers.

When hunting, they skim above the sandy surface, picking up clam siphons, crabs, fish eggs, and hot-dog-shaped fat innkeeper worm. Leopard sharks mutilate their prey by only eating parts of the animals they ingest, leaving aside others. Larger leopard sharks prefer eating more of fish and lesser crabs. Other food materials found in the stomach of this shark species include bat rays, smoothhound sharks, and octopuses.

How do Leopard sharks Catch Preys Buried in Sand?

Leopard sharks have been seen, swimming stealthily above the sand just to get at preys like clam sticking out their siphon two or three inches above the bottom. If leopard shark is quick enough to grab siphon in its teeth and pull them out of the sand, It can get the whole clam in the process, but sometimes the clam senses predators and pull its siphon back to safety.

When the shark realizes the siphon has been tucked back in by the clam, it shovels its nose into the sand and twists it. Sometimes, while unearthing a pile of sands, the shark might be lucky enough to get a worm or worms for the trouble.

Leopard Sharks’ Predators

When in juvenile, leopard sharks are prey to larger sharks like the great white shark, and the broadnose seven-gill shark. Leopard sharks have been found on some occasions ambushed by a broad nose Nseven-gill shark on a tidal mudflat in Humboldt bay. When they become adults, they are still prone to predators like a white shark (Carcharodon) because of their relatively small size.

Parasites of Leopard sharks

These sharks have animals that depend on them for food. They are tapeworms Lacistorhynchus dollfusi, phyllobothrium riseri, paraorygmatobothrium barber, Achtheinus oblongatus and copepods Echrogaleus eoleoptratus.

Leopard Sharks’ Lifespan

These sharks can live up to about 30 years.

Roles in the Ecosystem

Leopard sharks are important predators in the ecosystem. Also, bigger sharks and humans hunt down their species.

Mating and Reproduction

Leopard sharks are aplacental viviparous with their yolk sac sustaining their developing embryo. In the northern areas where these sharks are common, the females use sloughs and bays as their nursery areas. While in the south, they give birth to their pups in open areas. The known breeding grounds of this species are Tomales Bay, Humboldt Bay, San Francisco, Bodega Bay, Elkhorn Slough, Catalina Harbor, San Diego Bay.

They give birth within the range of 1-37 pups annually between March and July, mostly between April and May. There is also one unique thing about their mating, that is multiple males can father a litter with only one mother. In places like San Francisco bays and Humboldt, their females give birth to their pups in beds of eelgrass that will serve as shelter and food for them.

However, females of leopard sharks in Catalina harbor, give birth on flats in 3.3 feet (1m) of water with their backs and dorsal fins exposed. Their pups stay in shallower water of about 12 inches (30cm) in depth.

System of Mating

Their males reach reproductive maturity at 7 to 13 years while their females reach it at 10 to 15 years. Leopard shark’s female gives birth to 4 to 37 live pups. The pups become independent immediately they are born which means these sharks do not exhibit any parental care.

Mating in this species takes place in early summer; Pups of leopard sharks measure around 7.9 inches long. Each individual of leopard sharks varies in size especially the bigger ones, they tend to grow slowly after reaching maturity.

Harm to Humans

Leopard sharks’ flesh possesses a high level of mercury. Mercury is a toxic element, an industrial pollutant that gets into waters through runoff and rain. Scientists in 1975, analyzed five livers of leopard sharks and in all of the five, they found a high level of mercury. Also, in yet another research in 1975, scientists investigated pollutants in different fishes from San Francisco Bay. And, in all of the eight investigated are very high levels of mercury in their tissues that could cause serious harm to humans upon consumption.

Leopard sharks get exposed to this pollutant because they spend most of their time feeding in the mud and sand. However, the great life span of this species means that mercury takes time to build up in them. There are no studies yet conducted to check whether a high level of mercury in leopard sharks affect them. But human consumption of this species is a bad idea, especially the ones caught in San Francisco.

History

Leopard sharks are ancient species whose fossilized specimens date back one million years.

Home range

These sharks travel up to about 2 km to find food. There have not been any recorded cases of them defending their territories. Some leopard sharks are known to be nomadic while some reside in one particular area for long.

Communication

Leopard sharks use their sense of smell and their unique eyesight to navigate through their surroundings and catch their Preys. Like every other shark, leopard sharks’ eyes contain cones, rods, and horizontal cells. The concentration of cones is lesser than that of rods.

As a result of the high concentration of rod cells in their eyes, the short wavelength can penetrate their retinas. This allows them to see in dimmer light since leopard sharks are nocturnal beings. These are an adaptation to support their lifestyle and help them navigate better in deep waters.

These sharks also use their sense of smell through the flow of water over their nares. For instance, fishes give off a particular odor when they feel excited. And, leopard sharks can easily detect like this through their nares. Also, female leopard sharks give off sex pheromone which their males can easily detect. This sex pheromone is to indicate that the female leopard shark is ready to mate.

Threats to Humans

Although leopard sharks are predators, there has only one recorded attack on humans. Thus, the record involved a spearfisher in 1959 who caught a fish and leopard shark traced the smell of the fish to the fisherman. There was no fatal injury to the human. In all leopard sharks are not large nor aggressive.

Caring for Leopard Sharks in Captivity

Leopard sharks do well in public aquariums and zoos. They are fond of rocky reef structures and kelp forest habitats. Leopard sharks are not picky eaters; therefore, are easy to feed. They would eat varieties of fish, crustaceans, and squid when in captivity. These sharks can live up to 30 years if taken care of properly.

Threats and Conservation/IUCN List

Threats

These sharks live close to shore and they have light firm meat that tastes really delicious which makes them very popular among fishermen. Consequently, spearfishers and anglers catch about 140 tons of leopard sharks every year in California. There is also a small commercial fishery that brings about 30 tons of leopard sharks per year in California.

Although, this is moderately light fishing considering they are common species. But, leopard sharks take a long time to grow (about a decade). Students have indicated that leopard sharks could be vulnerable to overfishing if the fishing rate is not curbed. Therefore, there is now a size limit for fishing leopard sharks which is 35.8 inches (91cm) long for anglers. Thus, fishing leopard sharks that are lesser than the size limit is illegal if they are from California waters.

Conservation

On the IUCN (International Union of Conservation of Nature) Red List, the Leopard shark (Triakis Semifasciata) appeared as “Least Concern” (LC).

They have a stabilized number by the conservation acts enforced by the government of California. Leopard sharks have lost some of their habitats due to degradation by development, pollution, and agriculture. The problem leopard sharks are currently facing is overexploitation by fishing. To curb this issue, gillnets have been banned along the California coast in water shallower than 361 feet (110 m).

Some types of fishing gear for coastal fishing has also been restricted by the state of California to ensure the safety of these sharks. The Government has limited the rate of commercial harvesting and aquatic trade of leopard sharks to a minimum size of 18.1 inches (46 cm) for rays and sharks.

Recreational fishermen are limited to a total number of three sharks longer than 91 cm. Due to low genetic exchange, small geographical range, delayed maturity, long gestation period, leopard sharks are regarded as vulnerable by researchers. Leopard sharks are one of the three species under the management authority of the National Marine fisheries service through the pacific and National Ocean-Atmosphere Administration (NOAA).

Side Note:

Research carried out on leopard shark’s DNA define 7 unique population that are separated geographically. Most leopard sharks that are found in waters Off Mexican cast have little difference in their genes. Especially with those that are found along the coast of California. The ones that are found off the coast of California have more genetic information that is common to each other. The Isolated aggregation of leopard sharks found in Humboldt Bay has more unique genetic characteristics.

In 2007, a ring of smugglers who tried to snuggle young leopard sharks out of California and sell as pet fish stores or to some private buyers have been arrested and fined close to a million-dollar. The fine was used to restore the San Francisco bay habitat.

Domestication

Humans have not been able to domesticate any of these sharks.

Can I Keep Leopard Sharks as Pet?

These species can thrive in human care but they are not good pets. Although they are relatively small when compared to other sharks, they still require a huge aquarium to thrive. Unless you are a shark expert and you have the extensive resources to run a public aquarium, these sharks are probably not the right choice of pet for your home aquarium.

Fun Facts About Leopard Sharks

  1. These sharks are generally non-threatening to humans although there was an unprovoked attack on a diver in Trinidad Bay, California.
  2. Leopard Sharks and Piked dogfish on observation engage in a unique feeding strategy. The two sharks swim at the surface with their mouths open in a counter-clockwise direction.
  3. Leopard sharks live in water that is less than 20 feet deep.
  4. These sharks have a tooth pattern called “pavement-toothed”
  5. Leopard sharks are skittish in behavior.
  6. Leopard sharks lack swim bladder (a sac-likee organ that fish use to fine-tune their buoyancy).
  7. These sharks can have up to 55 teeth in their upper jaw and 40 or more in their lower jaw.
  8. Leopard sharks are social sharks that congregate in groups of similar gender or age to search for food together.
  9. These sharks prey, specialists, they go for specific prey especially when that prey is very abundant.
  10. They follow incoming tide into mudflats to feed on hidden animals.

Further Reading