Milk shark (Rhizoprionodon acutus)

IUCN Red List Status: Least Concern

The Milk Shark is a small, tropical species that inhabits the shallow waters of beaches and estuaries along the coasts of Africa, Southeast Asia, and Australia.

Reportedly, Milk Sharks can travel into freshwater habitats.

This species is probably not migratory, and populations off the coast of Indonesia are genetically distinct from populations off the coast of eastern Australia.

Because of its small size of only 5-5.5 ft (152-168 cm), the Milk Shark is not considered a threat to humans.

Milk Sharks eat small fishes, cephalopods, and invertebrates.  They are eaten by larger sharks such as Blacktip Sharks and could be an important prey item for large marine mammals as well.

Milk Sharks are viviparous, meaning pups are nourished by a placental connection during gestation.  Female Milk Sharks are pregnant for one year before giving birth to litters of 1-6 pups that range in length from 9.8-15.4 in (25-39 cm). 

Off the coast of Oman in the Indian Ocean, Milk Shark litters often have twice as many female pups as male pups, but off the coast of Senegal in the Atlantic, litters have the same number of male and female pups.

Milk Sharks are commonly captured by gillnet and trawl fisheries.  Sometimes the fins and meat are prepared for human consumption, but mostly this species is used for fish meal.

Despite being heavily exploited, Milk Shark populations do not appear to be in danger of extinction.

Milk Sharks may be resilient to over harvesting because they are relatively fast growing, reach maturity at a small size, and produce a litter of pups every year without taking a break between reproductive cycles.

Silky shark (Carcharhinus falciformis)

IUCN Red List Status: Near Threatened

-       The silky shark is an open ocean distributed shark found around the world in tropical waters

-       Often found in waters of depths ~650-1650 feet (200-500 meters), and around island systems

-       In the Gulf of Mexico, this species reaches up to ~11 feet (330 cm) and can live for 22+ years

-       Silky shark reach maturity at 7-8 feet (215-246 cm)

-       Females typically have 6-12 pups every 1-2 years, with a 12-month gestation period

-       The silky shark is piscivorous, which means they feed on fish, such as mullets, sea catfish, albacore, and yellowfin tuna

-       This species is one of the top targeted and incidentally captured sharks, particularly in purse seine fisheries

-       Purse seine fisheries involves fishermen setting nets around a fish aggregating device (FAD), and drawing the bottom of the nets together to form a purse shape, therefore capturing the fish under the FAD

-       They are taken for the meat for consumption, fins for soup, skin for leather, and liver for liver oil

-       Given the highly migratory nature of this shark, and it’s exposure to pelagic fisheries, international management measures are recommended by IUCN to aid in better data collection and conservation of the silky shark

Caribbean reef shark (Carcharhinus perezi)

IUCN Red List Status: Near Threatened

-       As it’s name suggests, this is a reef-dwelling shark found in the Caribbean and the tropical Western Atlantic

-       This species is the move common reef shark in the Caribbean

-       Often found associated with the bottom near drop offs, Caribbean reef sharks are generally found within ~100 ft (30m) depth, but have been recently found to dive to depths of ~1240 ft (378 m)

-       Pups are born at ~2-2.5 ft (60-75 cm), and individuals can grow up to ~10 ft (295 cm)

-       Pups are developed by placental viviparity (remember what this is??), and females reproduce every other year (biennially)

-       This species feeds on reef fishes and sometimes other elasmobranchs too!

-       This species is harvested for it’s meat for consumption, skin for leather, fins for soup, and liver for oils

-       Also valued within tourism as it is often featured in shark feeding/diving tours

-       This species may additionally be impacted by coral reef habitat degradation

Puffadder shyshark (Haploblepharus edwardsii)

IUCN Red List Status: Near Threatened

-The puffadder shark is sandy colored, with seven red-brown saddle markings on its back, and spotted

-This South African species was previously thought to range along most of South Africa’s coastline, but a recent assessment indicated that it’s range is actually much smaller, and located in heavily fished and polluted waters

-This species’ habitat selection is very site specific, found in inshore waters located in kelp forests, reefs, and sandy bottom habitats

-Feeds on crustaceans, cephalopods, and bony fishes

-The puffadder is oviparous, laying 2 eggs at a time, with no clearly defined breeding season

-Size of reproductive maturity ranges from ~1 ft (325 mm) to ~1.5 ft (450 mm)

-The puffadder lives to 22 years

-This species is displayed in aquaria

-The main threat to this species is capture on recreational fishing gear, in which it is caught as bycatch

Pyjama shark (Poroderma africanum)

Photo by Photo Leon Van Dijl

IUCN Red List Status: Near Threatened

This coastal species has a restricted range to the Southeast Atlantic and western Indian Ocean off of South Africa

Found in the intertidal region to depths up to ~300 feet (100 meters)

Individuals in this species reach maturity at lengths of 2.5-3 feet, and maximum sizes reach up to ~3 feet

The pyjama shark reproduces year round, and size of pups are ~0.5 feet

Reproductive mode is oviparous, in which females lay eggs that sit on the bottom of the ocean until hatching

This is a more social shark species, with individuals gathering and resting in caves and bottom structure on reefs and kelp beds

Preferred prey items include bony fishes, hagfish, invertebrates, and primarily cephaolopds

This species is caught as bycatch in local fisheries including inshore longline, gillnet, and beach-seine gear

Species will also readily take a baited hook if targeted, and is regularly caught by recreational anglers, and often release

The pyjama shark is rarely taken for human consumption, and sometimes taken for lobster bait

This species is hardy and regularly survives capture on fishing gear

Bronze whaler (Carcharhinus brachyurus)

Photo by Eben Human

IUCN Red List Status: Near Threatened

This species is a large coastal shark

The range of the bronze whaler has been challenging to define due to identification confusion with other species, particularly the dusky shark

This species is not naturally abundant anywhere, although it is widespread globally, found in warm-temperate and subtropical waters of the Gulf of Thailand, Mediterranean, northeast Atlantic, southwest Atlantic, Indian Ocean, and the western coast of South Africa

Readily found in shallow water, bays, and surf zones, as well as brackish water (do you know what “brackish” means?)

This species feeds on cephalopods and fishes, and juveniles feed on jellyfishes and benthic crustacean

Maximum sizes may reach ~11.5 ft (350 cm)

Maximum age is still unknown (perhaps one of our Gills will describe it one day!)

Bronze whaler nursery areas are large and poorly described, and overlap with nurseries for dogfish, school shark, and smooth hammerhead

Gestation of young is about 12 months, and pups are born at ~2 ft (60 cm)

Reproduction is by viviparity, with the placenta of the pup attached to a yolk sac

This species sometimes swims in school of hundreds of individuals

Stock structure is not known for any fished population

Soupfin shark (Galeorhinus galeus)

IUCN Red List Satus: Vulnerable

This species is located world-wide in temperature waters

Also commonly known as the “tope”, “school”, and “snapper” shark!

Reaches sizes up to 6 feet, and maturity around 4.5 feet

Mainly demersal, meaning they are often associated with the ocean floor, and recorded to move to depths of 550 meters (~1800 feet)

The larger the soupfin shark female, the more pups she will carry

Spawning occurs once per year, with a 12-month gestation period

Often this species migrates in schools in coastal waters

Opportunistic feeders that eat small fishes, crabs and other invertebrates

This species is aplacental viviparous, also called ovoviviparous…..based on your previous newsletters, do you remember what this means? J

This species is heavily exploited in certain areas of the world for its liver, flesh, and fins…hence it’s name

Common thresher (Alopias vulpinus)

IUCN Red List Status: Vulnerable

The IUCN status of “vulnerable” for the common thresher is due to a combination of moderate levels of global targeted fishing, large levels of misreporting of mortality rates in bycatch events, and the general life history characteristics of this species which makes it hard to recover from exploitation

Serious population declines in areas where heavy fishing occurs have been reported, such as in the eastern Pacific gillnet fishery, where landings reportedly were reduced 73% within a 6-year period in the 1980s

These circumglobal sharks are highly valued for meat (for consumption) and fins, and is an important species in recreational fisheries

This species is found in tropical to cold-temperate seas, has a tolerance for cold waters, and possesses an anatomy that supports regional endothermy, the ability to harness and retain metabolically-generated heat to warm certain areas of the body (a characteristic shared by only certain sharks, such as the white and shortfin mako sharks)

This species has 2-4 pups per liter, and reproduction is viviparous, with the pups being nourished in utero by a placental connection; oophagy has been shown to occur as well, where sibling pups will eat eggs while still in the uterus

This species, along with other thresher species, are easily identified by the elongated upper lobe of the caudal fin, which the sharks use for hunting small bait fish – the lobe is used like a whip, and the targeted bait fish will be hit by the threshers tail, stunned, and subsequently eaten by the hunting thresher shark

Maximum sizes for this species range from ~13.5-18 feet total length, but this includes the elongated caudal fin

This species are thought to live for at least 24 years, and maybe up to 50 years

Porbeagle Shark (Lamna nasus)

IUCN Red List Status: Vulnerable

Wide ranging coastal/pelagic shark in temperate and cold-water environments

This shark is a congeneric (species of the same genus) to the salmon shark, which is located in the northern Pacific Ocean

Porbeagle and salmon sharks are the only two species in genus Lamna, and both possess specialized anatomy and physiology for life in cold-water environments, and along with other members of Family Lamnidae, like the white shark and shortfin mako, are regionally endothermic.  Do you remember what this is? J

Distinct populations are located in the western North Atlantic and eastern North Atlantic, with little exchange between them, although there was one documented trans-Atlantic migration

This species has high commercial value, which has resulted in high longline targeting of this species

Such fisheries impacts, combined with low reproductive capacity, has resulted in over-exploitation and population declines, resulting in the IUCN classification of “vulnerable” on a global scale

In the Northwest Atlantic fishery, intensive targeting in the 1960s resulted in most of the biomass being harvested in six years

Little is known about pupping locations for any population

Maximum sizes of 355cm (11.5ft)

Reproduction is oophagous (with larger individuals feeding on eggs/developing young in utero), and litter sizes typically 1-5 pups

Thought to live up to 26 years, and mature between 8 (males) and 13 (females) years

The porbeagle shark is currently being considered for listing under the Endangered Species Act

Cookie cutter shark (Isistius brasiliensis)

Cookie cutter shark

Isistius brasiliensis

IUCN Status: Least Concern

This species only reaches up to 50 cm (1.6 ft) total length

Occasionally caught as bycatch in longlines and trawls

Found in temperate and tropical environments

This is a deepwater oceanic shark, and makes vertical migrations from 1000 m (~3000 ft) during the day to near the surface at night, and has been documented as deep as 3700 m (~12,000 ft) deep

Not much is known about its biology or population numbers

The cookie cutter is ovoviviparous, with 6-12 pups per litter that develop within the uterus and are nourished by large yolk sacs

This species leaves a characteristic, cookie-shaped, bite mark on larger fishes and marine mammals, for which this shark was given its name!

The species makes these unique bites using their suctorial lips and strong jaws to attach to the side of their prey, sink their lower teeth into the flesh, and then twist their bodies to cut out a conical chunk of flesh from their larger prey item

Their feeding behavior is aided by unique dentition, where the teeth on the upper jaws are small and thorn-like, and the teeth on the bottom jaw are much larger and triangular; the teeth along each jaw are also interconnected, so that teeth are shed all at once and replaced as a single unit

The cookie cutter shark is also bioluminescent!!  They possess thousands of photophores (light-emitting organs) along the edges of their scales, that cover the entire ventral (underside) surface of their bodies, with the exception of a band lacking photophores around the throat

Bioluminescence is common in deep water organisms, and is thought to aid in camouflaging prey silhouettes from predators

Whale shark (Rhincodon typus)

IUCN Red List Status: Vulnerable

The whale shark is a “cosmopolitan” species, meaning it is found throughout most of the world, in tropical and warm temperate seas

Found in deep waters, coastal waters, and coral reef systems

The whale shark is the largest fish in the sea!

This species undertakes large-scale migrations, often spanning multiple years and thousands of miles

Whale sharks can also dive very deep during these migrations

Whale sharks are ovoviviparous….do you remember what this means? J

Females can carry around 300 embryos, and pups have been measured at ~2 feet total length (total length measures tip of snout to tip of caudal tail)

It is thought that whale sharks grow up to 15 meters (49 ft), but have been reported up to 20 meters  (66 ft)

Whale shark length of gestation, birth locations, and reproductive frequency are still not understood

Whale sharks are one of three shark species that filter feeds….do you know the other two?

Unlike the other two species, the whale shark doesn’t use forward motion for feeding all the time, but also will hang vertically in the water column and use suction feeding to obtain food

Even though whale sharks are the largest fish, they have been held at several aquariums around the world, which has allowed for a greater understanding of their biology and behavior

The whale sharks has been targeted within harpoon and entanglement fisheries, and is valued for it’s fins and meat for consumption

Ecotourism groups that enable swimming with whale sharks are increasing in number around the world, and in some cases hold more economic value than whale shark fisheries

Blackfin gulper shark (Centrophorus isodon)

Photo by Andy Murch

IUCN Red List Status: Data Deficient

This is a rare, deepwater species of dogfish, found in the Indian and Pacific Oceans

Recorded at depths of 2,530 ft (779 meters)

This is a small shark, reaching max sizes of ~3 feet (93 cm) total length

This species of shark has a black mouth and tongue!

Related species have experienced population declines and been quite vulnerable to fishing pressures, highlighting the need for more data on these sharks

Size at maturity is unknown, and many other aspects of biology are unknown as well

Reproduction is ovoviviparous (remember what this is?), and the number of young is low, perhaps only producing 1-2 embryos per litter

Perhaps you will be the scientist to discover more important data about this species!

Dusky shark (Carcharhinus obscurus)

IUCN Red List Status: Vulnerable

This is a large coastal-pelagic shark found in temperate and warm-temperate waters

Found in surface waters down to depths of ~1,300 feet (400 meters)

Nurseries for this species have been found off the KwaZulu-Natal coast of South Africa, New Jersey to South Carolina in the United States, and Australia’s southwest coast

Adults are among the largest of their genus, reaching up to ~12 feet (360 centimeters), and live up to 40-50 years

This species eats other fish, elasmobranchs, and cephalopods (octopus, squid, and cuttlefish), with one observation of a group of 10-20 dusky sharks attacking a humpback whale calf in South Africa!!

Pups are born at sizes up to ~3.3 feet (100 centimeters), with litter sizes from 3-16 individuals

Dusky sharks are viviparous, meaning the young are nourished through a placental connection, and the young develop for 22 months in the mother

This species actually has a three-year reproductive cycle in which one litter is produced, and given the low litter sizes, dusky sharks have a very low rate of population increase

Given this low “fecundity” (the ability to produce young), dusky sharks are particularly vulnerable to overfishing, among the most vulnerable of all vertebrates

This species is highly valued for both it’s fins and meat

Dusky sharks have been caught as targeted catch and bycatch, in both commercial and recreational fisheries, and are particularly vulnerable to capture stress, making recovery rates, upon release, low

Initial declines of this population in the Northwest Atlantic (NWA) began with overfishing in the recreational and longline fisheries in the 1970s-80s, leading to dusky sharks being placed on the prohibited fishing list in 2000

This species’ population in the NWA are one of the more depleted shark stocks

Recently considered for the Endangered Species Act, but it was determined that management plans put in place for this species are successfully helping stock in NWA avoid extinction, bringing some good news to this historically overfished stock

Megamouth shark (Megachasma pelagios)

IUCN Red List Status: Data Deficient

This shark is considered perhaps the most exciting discovery of a new shark species in the twentieth century

First discovered in 1976!

Since discovery, only ~100 individuals have been seen

Specimens of the species are rarely encountered

Can grow as large as ~24 feet (7.2meters)

 Habitat range thought to be circumtropical, but this shark is rare throughout its range

Has been found in locations such as Brazil, Senegal, Taiwan, Western Australia, Japan, Hawaii, and USA (California)

Has been found in waters as shallow as 16 feet (5m), but has been found in epipelagic and deep waters as well

Known prey items are euphausiid shrimp (krill), copepods, and jellyfish

One tagged and tracked individual revealed that this species is not dependent on forward motion to breath, and can gill-pump for respiration

Mode of reproduction still unknown but is probably aplacental viviparity with oophagy (uterine cannibalism)

The megamouth is caught rarely as incidental bycatch in various pelagic and coastal fisheries

This species has only recently been satellite tagged in Taiwan, to learn more about its ecology

Blacktip shark (Carcharhinus limbatus)

IUCN Red List Status: Near Threatened

Found in warm-temperate, subtropical, and tropical waters worldwide

This species is seen in waters off of beaches, and in bays, estuaries, coral reefs, and river mouths

Blacktips eat primarily bony fishes, and also crustaceans such as shrimp and crabs

Populations in southern USA and South Africa exist with males and females in segregated groups of the population

Blacktip reproduction is placental viviparity (Quiz! Do you remember what this is?), and females produce 4-11 pups per liter, with gestation lasting 11-12 months

Females have a 1 year rest after reproducing, which makes their reproductive cycles 2-years

Pups are born at 1.7- 2 feet (53-65 cm) total length

Adults reach up to 9 feet (275 cm) total length

Found near inshore waters, with inshore nursery areas, which makes this species particularly vulnerable to fishing and habitat alteration

Frequently caught in recreational and commercial fisheries

Fins are highly marketable, and meat is desirable for consumption

Known for the behavior of jumping from the water and rotating in the air

Often confused with the spinner shark, owing to this behavior and a very similar morphology!

Bull shark (Carcharhinus leucas)

Photo by Bill Eastwick

IUCN Red List Status: Near Threatened

Uniquely identified as a species of shark that can exist in freshwater for long periods of time, the bull shark can be found in tropical and subtropical habitats

The bull shark has been found large distances (several thousand miles!) up freshwater rivers, such as the Amazon, Ganges, and Mississippi (as far north as Illinois!) Rivers

 Rarely targeted within fisheries, although caught as bycatch

Because this species is often found in freshwater, this puts them at unique risk to be exploited by freshwater fishing and habitat modification

This species has numerous common names, depending on the location, and include names such as Zambezi Shark, Swan River Shark, and Lake Nicaragua Shark

Commonly reach sizes up to 8.5 feet, but reported up to 13 feet

This species is responsible for a number of attacks on humans

Bull sharks are also well adapted to be on display in aquariums

Typically found in waters less than 30meters, but up to 150meters

This species is viviparous, with pups being nourished through a placental connection to the mother, resulting in live birth after gestation, which is 10-11 months

Spiny dogfish (Squalus acanthias)

IUCN Red List Status: Vulnerable

Small bodied sharks, reaching sizes up to about 3.5 feet, but reported up to 5 feet

Spiny dogfish have a spine on the leading edge of each dorsal fin, and white spots along their flank

Often found associated with the bottom of the ocean and swimming in large schools, segregated by size and sex

There is little mixing between different populations, but it does occur

Spinys are ovoviviparous, which means the pups develop in the mother’s uterus, and are nourished from egg sacks

These sharks don't have typical shark teeth, they have flat tooth pallets that facilitate crunching through invertebrate shells when feeding

Pups develop throughout a gestation period of 18-22 months, which is among the longest for any animal

Spiny dogfish eat various small fishes and invertebrates

This species reaches maturity late in life, produces few young, and often many pregnant females can be caught in fishing gear at the same time due to aggregating behavior; taken together, these characteristics make this species particularly vulnerable to overfishing

Blue shark (Prionace glauca)

IUCN Red List Status: Near Threatened

An abundant oceanic species, the blue shark is widespread throughout temperature and tropical waters

Reaches sizes up to 12.5 feet

Gestation of pups is 9-12 months

Relatively fast growing, with maturation around 4-6 years and a higher fecundity, with litters of about 35 pups

Often caught as bycatch (or, incidental catch) by fishing gear, with numbers reported up to 20 million individuals annually

Not a desirable fish for consumption

There are no population assessments for this species, and so the trend of population sizes in light of the impact of fisheries, is unknown, with the exception of a 20% population decline reported in the North Pacific between 1970s and early 1990s

Estimated to grow as old as 20 years

The blue shark is a highly migratory fish that exploits similar habitats such as the mako and white shark, but lack the anatomical/physiological adaptations that help the later two species exploit colder water temperatures and be highly migratory – blue sharks are a mystery in this regard!

Numerous trans-Atlantic migrations have been reported, and it’s proposed these are accomplished by slow swimming and taking advantage of ocean current systems

Mating documented in the north-western Atlantic, and pupping in the north-eastern Atlantic

Lemon shark (Negaprion brevirostris)

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IUCN Status: Near Threatened

Distributed coastally within the Atlantic and Pacific Oceans, including Gulf of Mexico

These sharks may enter fresh water but have not been found too far into river systems

Usually found around structures such as coral and mangrove systems

Gestation is 10-12 months, and females can give birth to 4-17 pups

Can reach sizes up to 12 feet, ages greater than 30 years, and maturity occurs at about 7.5 feet (12-13 years)

Localized consistent nursery areas, such as in Bimini, Bahamas, used by juveniles have allowed for extensive research of this species to be performed

Lemons have been targeted by both recreational and commercial fisheries, and fins fetch a very high price

This species is commonly held in aquariums, and also used extensively for research purposes

Will feed on fish, crustaceans, and mollusks

Reproduction mode is viviparous

Basking shark (Cetorhinus maximus)

IUCN Red List Status: vulnerable

Maximum length may be up to 36 feet, making them the second largest shark!

Have very large gills slits which almost completely encircle the head

Thought to live up to 50 years

Highly migratory and found in northern and southern hemispheres in warm temperate waters, often close to land, or associated with continental shelves

Recently it was shown that migrations can be transequatorial, with some sharks tagged off of Cape Cod moving into Southern Hemisphere waters near South America!

One of three filter-feeding, plankton-eating sharks

Often deep in the winter, and in surface waters in the summer, feeding on plankton

This surface behavior is what gives the name “basking”, as in basking in the sun!

Vulnerable due to capture as bycatch

In the same classification order group as the white shark and mako species