Milk shark
Encyclopedia
The milk shark is a species
of requiem shark
, family
Carcharhinidae, whose common name
comes from an India
n belief that consumption of its meat promotes lactation
. The largest and most widely distributed member of its genus
, the milk shark typically measures 1.1 m (3.6 ft) long and can be found in coastal tropical waters throughout the eastern Atlantic and the Indo-Pacific
regions. Occurring from the surface to a depth of 200 m (656.2 ft), this species is common near beaches and in estuaries
, and has been recorded swimming up river
s in Cambodia
. Juveniles are known to inhabit tidal pools and seagrass
meadows. The milk shark has a slender body with a long, pointed snout and large eyes, and is a nondescript gray above and white below. This shark can be distinguished from similar species in its range by the long furrows at the corners of its mouth, and 7–15 enlarged pores just above them.
Among the most abundant sharks within its range, the milk shark feeds primarily on small bony fishes but also takes cephalopod
s and crustacean
s. In turn, it often falls prey to larger shark
s and possibly marine mammal
s. In common with other members of its family
, this species is viviparous with the developing embryo
s sustained by a placenta
l connection. Females give birth to 1–8 young either during a defined breeding season
or throughout the year, depending on location. The reproductive cycle is usually annual but may be biennial or triennial. Large numbers of milk sharks are caught by artisanal
and commercial fisheries
in many countries for meat, fins
, and fishmeal. Despite this, the International Union for Conservation of Nature (IUCN) has assessed this species as being of Least Concern
, because its wide distribution and relatively high productivity seemingly allow present levels of exploitation to be sustained.
published the first scientific description of the milk shark, as Carcharias acutus (the specific epithet means "sharp" in Latin
), in his 1837 Fische des Rothen Meeres (Fishes of the Red Sea). It has since been listed under several different genera, including Carcharhinus
and Scoliodon, before finally being placed in the genus Rhizoprionodon via synonymization
with the type species
, R. crenidens. As Rüppell did not mention a type specimen, in 1960 Wolfgang Klausewitz designated a 44 cm (17.3 in) long male caught off Jeddah
, Saudi Arabia
as the lectotype
for this species.
The common name
"milk shark" comes from a belief held in India
that eating this shark's meat enhances lactation
. Other names for this species include fish shark, grey dog shark, little blue shark, Longmans dogshark, milk dog shark, sharp nosed (milk) shark, Walbeehm's sharp-nosed shark, and white-eye shark. A 1992 phylogenetic analysis by Gavin Naylor, based on allozyme
s, found that the milk shark is the most basal
of the four Rhizoprionodon species examined. The extinct R. fischeuri, known from Middle Miocene
(16–12 Ma) deposits in southern France
and Portugal
, may be the same as R. acutus.
, it is found from Mauritania
to Angola
, as well as around Madeira
and in the Gulf of Taranto
off southern Italy
. In the Indian Ocean
, it occurs from South Africa
and Madagascar
northward to the Arabian Peninsula
, and eastward to South
and Southeast Asia
. In the Pacific Ocean
, this species occurs from China
and southern Japan
, through the Philippines
and Indonesia
, to New Guinea
and northern Australia
. The milk shark likely once had a contiguous distribution by way of the Tethys Sea, until during the Miocene
epoch when eastern Atlantic sharks were isolated from Indo-Pacific sharks by the collision of Asia and Africa.
Occurring close to shore from the surf zone
to a depth of 200 m (656.2 ft), the milk shark favors turbid water off sandy beaches and occasionally enters estuaries
. In Shark Bay
, Western Australia
, juvenile milk sharks inhabit seagrass
meadows composed of Amphibolis antarctica
and Posidonia australis
. Although some sources state that this species avoids low salinities
, it has been reported several times from fresh water
in Cambodia
, as far upstream as the Tonlé Sap
. Milk sharks may be found anywhere in the water column from the surface to the bottom. Off KwaZulu-Natal
, South Africa, its numbers fluctuate annually with a peak in summer, suggesting some form of seasonal movement
.
The largest member of its genus, off West Africa
the milk shark has been reported to reach 1.78 m (5.8 ft) and 22 kg (48.5 lb) for males, and 1.65 m (5.4 ft) and 17 kg (37.5 lb) for females, though there is uncertainty regarding the species identity of these specimens. Even if accepted, these figures are considered exceptional and most individuals do not exceed 1.1 m (3.6 ft) in length. Generally, females are heavier and attain a greater maximum size than males.
The milk shark has a slender build with a long pointed snout, large round eyes with nictitating membrane
s (protective third eyelid
s), and no spiracle
s. On each side of the head behind the corner of the jaw, there are usually 7–15 enlarged pores. The nostril
s are small, as are the adjacent triangular skin flaps. There are long furrows at the corners of the mouth on both the upper and lower jaws. The tooth rows number 24–25 in both jaws. The upper teeth are finely serrated and strongly oblique; the lower teeth have a similar shape, though the serrations are smaller and the tips curve gently upward. The teeth of juveniles are smooth-edged.
The broad, triangular pectoral fins originate below the third or fourth gill slit
s, and are no longer than the front margin of the first dorsal fin
. The anal fin is about twice as long as the second dorsal fin and preceded by long ridges. The first dorsal fin originates over the pectoral fin free rear tips, and the much smaller second dorsal fin originates over the last third of the anal fin base. The dorsal fins do not have a ridge between them. The lower lobe of the caudal fin is well-developed and the upper lobe has a ventral notch near the tip. This shark is plain gray, brown-gray, or purple-gray above and white below. The leading edge of the first dorsal fin and the trailing edge of the caudal fin may be dark, and the trailing edges of the pectoral fins may be light.
bony fishes. Occasionally squid
, octopus
, cuttlefish
, crab
s, shrimp
, and gastropods are also taken. In Shark Bay, the most important prey are silversides, herring
, smelt-whitings
, and wrasse
s; this is also the only local shark species that preys on the Waigeo seaperch
(Psammoperca waigiensis), found in seagrass beds avoided by other sharks. In the Gulf of Carpentaria
, it feeds mainly on halfbeak
s, herring, and mullets
, and is also a major predator of penaeid prawns
. Smaller sharks eat proportionately more cephalopods and crustaceans, switching to fish as they grow older.
Many predators feed on the milk shark, including larger sharks such as the blacktip shark
(Carcharhinus limbatus) and Australian blacktip shark
(Carcharhinus tilstoni), and possibly also marine mammal
s. Off KwaZulu-Natal, the decimation of large sharks by the use of gillnet
s to protect beaches has led to a recent increase in milk shark numbers. A known parasite of this species is the copepod
Pseudopandarus australis. There is some evidence that male and female milk sharks segregate from each other.
(on the left) and two functional uterus
es divided into separate compartments for each embryo
. The details of its life history vary across different parts of its range. Females generally produce young every year, though some give birth every other year or even every third year. Mating and parturition take place in spring or early summer (April to July) off western and southern Africa, and in winter off India
, Alternately, off Oman
parturition occurs year-round with a peak in spring. Parturition also occurs continuously in Australia
n waters; in the Herald Bight of Shark Bay, the number of newborns peaks in April and again in July. One proposed explanation for the lack of reproductive seasonality in these subpopulations is a lengthier and/or more complex reproductive cycle than has been detected (such as a period of dormancy
in embryonic development, though there is presently no evidence of this occurring). Females do not store sperm internally.
The litter size ranges from 1 to 8 with 2–5 being typical, increasing with female size. In Omanese waters females on average outnumber males in a litter by more than 2:1, and all-female litters are not uncommon. Similar but less extreme sex imbalances have also been reported from litters of milk sharks off Senegal
and eastern India. The reason for this imbalance is unknown, and it has not been observed in related species such as the Atlantic sharpnose shark
(R. terraenovae). Gestation
of the embryos takes around a year and proceeds in three phases. In the first phase, lasting two months to an embryonic length of 63–65 mm (2.5–2.6 in), the embryo relies on yolk for sustenance and gas exchange
occurs across its surface integument and possibly also the yolk sac
. During the second phase, which also lasts for two months to an embryonic length of 81–104 mm (3.2–4.1 in), the external gill
filaments develop and the yolk sac begins to be resorbed, the embyo ingesting histotroph (a nutritious substance secreted by the mother) in the meantime. In the third phase, lasting six to eight months, the depleted yolk sac is converted into a placenta
l connection through which the fetus receives nourishment until birth.
Young sharks are typically born at a length of 32.5–50 cm (12.8–19.7 in) and weigh 127–350 g (0.279987072974795–0.771617917647072 lb). There is an atypical record of a female, caught off Mumbai
, carrying a fetus only 23.7 cm (9.3 in) long that was already nearly fully developed, long before gestation was complete. Pregnant females make use of inshore nursery areas to give birth, taking advantage of the warmer waters and abundant food; known nursery areas include the Banc d'Arguin National Park
off Mauritania
, and Cleveland Bay and Herald Bight off Australia. In Herald Bight, large groups of small milk sharks can be found in shallow tidal pools, as well as in seagrass beds where they are sheltered from predators by the dense, tall vegetation. The sharks move out of these coastal embayments
when they mature.
Males and female milk sharks mature at lengths of 84–95 cm (33.1–37.4 in) and 89–100 cm (35–39.4 in) respectively off West Africa, 68–72 cm (26.8–28.3 in) and 70–80 cm (27.6–31.5 in) respectively off southern Africa, and 63–71 cm (24.8–28 in) and 62–74 cm (24.4–29.1 in) respectively off Oman. These discrepancies in maturation size may be a result of regional variation or incidental selection
from heavy fishing pressure. The growth rate for milk sharks off Chennai
have been calculated as 10 cm (3.9 in) in the first year, 9 cm (3.5 in) in the second year, 7 cm (2.8 in) in the third year, 6 cm (2.4 in) in the fourth year, 5 cm (2 in) in the fifth year, and 3–4 cm (1.2–1.6 in) per year from then on. The age at maturation is thought to be 2–3 years, and the maximum lifespan is at least 8 years.
The milk shark is harmless to humans because of its small size and teeth. Caught using longlines, gillnet
s, trawls, and hook-and-line, this shark is marketed fresh or dried and salted for human consumption, and is also utilized for shark fin soup
and fishmeal. Its abundance makes it a significant component of artisanal
and commercial fisheries
across its range. Off northern Australia, it ranks among the most common sharks caught in trawls, and comprises 2% and 6% of the annual gillnet and longline catches respectively. This species is also one of the most commercially important sharks caught off Senegal, Mauritania, Oman, and India. Some sport fishers
regard it as a game fish
.
The International Union for Conservation of Nature (IUCN) has listed the milk shark under Least Concern
; despite being heavily fished it has a wide distribution and remains fairly common. The reproductive characteristics of this species suggests that it is capable of withstanding a somewhat high level of exploitation, though not as much as the grey sharpnose shark
(R. oligolinx) or Australian sharpnose shark
(R. taylori). In the 1980s and early 1990s, stock assessments of the milk shark off India's Verval coast concluded that catches by gillnet and trawl fisheries were below the maximum sustainable level. However, these studies were based on methodologies that have subsequently been proven unreliable for shark populations. Moreover, fishing pressure in the region has increased substantially since the assessments were conducted.
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
of requiem shark
Requiem shark
Requiem sharks are a family, Carcharhinidae, of sharks in the order Carcharhiniformes, containing migratory, live-bearing sharks of warm seas such as the tiger shark, the blue shark, the bull shark, and the milk shark.The name may be related to the French word for shark, "requin", itself of...
, family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Carcharhinidae, whose common name
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
comes from an India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
n belief that consumption of its meat promotes lactation
Lactation
Lactation describes the secretion of milk from the mammary glands and the period of time that a mother lactates to feed her young. The process occurs in all female mammals, however it predates mammals. In humans the process of feeding milk is called breastfeeding or nursing...
. The largest and most widely distributed member of its genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
, the milk shark typically measures 1.1 m (3.6 ft) long and can be found in coastal tropical waters throughout the eastern Atlantic and the Indo-Pacific
Indo-Pacific
The Indo-Pacific is a biogeographic region of the Earth's seas, comprising the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the seas connecting the two in the general area of Indonesia...
regions. Occurring from the surface to a depth of 200 m (656.2 ft), this species is common near beaches and in estuaries
Estuary
An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....
, and has been recorded swimming up river
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
s in Cambodia
Cambodia
Cambodia , officially known as the Kingdom of Cambodia, is a country located in the southern portion of the Indochina Peninsula in Southeast Asia...
. Juveniles are known to inhabit tidal pools and seagrass
Seagrass
Seagrasses are flowering plants from one of four plant families , all in the order Alismatales , which grow in marine, fully saline environments.-Ecology:...
meadows. The milk shark has a slender body with a long, pointed snout and large eyes, and is a nondescript gray above and white below. This shark can be distinguished from similar species in its range by the long furrows at the corners of its mouth, and 7–15 enlarged pores just above them.
Among the most abundant sharks within its range, the milk shark feeds primarily on small bony fishes but also takes cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s and crustacean
Crustacean
Crustaceans form a very large group of arthropods, usually treated as a subphylum, which includes such familiar animals as crabs, lobsters, crayfish, shrimp, krill and barnacles. The 50,000 described species range in size from Stygotantulus stocki at , to the Japanese spider crab with a leg span...
s. In turn, it often falls prey to larger shark
Shark
Sharks are a type of fish with a full cartilaginous skeleton and a highly streamlined body. The earliest known sharks date from more than 420 million years ago....
s and possibly marine mammal
Marine mammal
Marine mammals, which include seals, whales, dolphins, and walruses, form a diverse group of 128 species that rely on the ocean for their existence. They do not represent a distinct biological grouping, but rather are unified by their reliance on the marine environment for feeding. The level of...
s. In common with other members of its family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
, this species is viviparous with the developing embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s sustained by a placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
l connection. Females give birth to 1–8 young either during a defined breeding season
Breeding season
The breeding season is the most suitable season, usually with favourable conditions and abundant food and water, for breeding among some wild animals and birds . Species with a breeding season have naturally evolved to have sexual intercourse during a certain time of year in order to achieve the...
or throughout the year, depending on location. The reproductive cycle is usually annual but may be biennial or triennial. Large numbers of milk sharks are caught by artisanal
Artisan fishing
Artisan fishing is a term used to describe small scale low-technology commercial or subsistence fishing practices. The term particularly applies to coastal or island ethnic groups using traditional techniques such as rod and tackle, arrows and harpoons, throw nets and drag nets, and traditional...
and commercial fisheries
Commercial fishing
Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often pursue fish far into the ocean under adverse conditions...
in many countries for meat, fins
Shark fin soup
Shark fin soup is a popular soup item of Chinese cuisine usually served at special occasions such as weddings and banquets, or as a luxury item in Chinese culture. The shark fins provide texture while the taste comes from the other soup ingredients.There is controversy over the practice of shark...
, and fishmeal. Despite this, the International Union for Conservation of Nature (IUCN) has assessed this species as being of Least Concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
, because its wide distribution and relatively high productivity seemingly allow present levels of exploitation to be sustained.
Taxonomy and phylogeny
The German naturalist Eduard RüppellEduard Rüppell
Wilhelm Peter Eduard Simon Rüppell was a German naturalist and explorer. Rüppell is occasionally transliterated to "Rueppell" for the English alphabet....
published the first scientific description of the milk shark, as Carcharias acutus (the specific epithet means "sharp" in Latin
Latin
Latin is an Italic language originally spoken in Latium and Ancient Rome. It, along with most European languages, is a descendant of the ancient Proto-Indo-European language. Although it is considered a dead language, a number of scholars and members of the Christian clergy speak it fluently, and...
), in his 1837 Fische des Rothen Meeres (Fishes of the Red Sea). It has since been listed under several different genera, including Carcharhinus
Carcharhinus
Carcharhinus is the type genus of the requiem shark family, Carcharhinidae.- Species :* Carcharhinus acarenatus * Carcharhinus acronotus...
and Scoliodon, before finally being placed in the genus Rhizoprionodon via synonymization
Synonym (taxonomy)
In scientific nomenclature, a synonym is a scientific name that is or was used for a taxon of organisms that also goes by a different scientific name. For example, Linnaeus was the first to give a scientific name to the Norway spruce, which he called Pinus abies...
with the type species
Type species
In biological nomenclature, a type species is both a concept and a practical system which is used in the classification and nomenclature of animals and plants. The value of a "type species" lies in the fact that it makes clear what is meant by a particular genus name. A type species is the species...
, R. crenidens. As Rüppell did not mention a type specimen, in 1960 Wolfgang Klausewitz designated a 44 cm (17.3 in) long male caught off Jeddah
Jeddah
Jeddah, Jiddah, Jidda, or Jedda is a city located on the coast of the Red Sea and is the major urban center of western Saudi Arabia. It is the largest city in Makkah Province, the largest sea port on the Red Sea, and the second largest city in Saudi Arabia after the capital city, Riyadh. The...
, Saudi Arabia
Saudi Arabia
The Kingdom of Saudi Arabia , commonly known in British English as Saudi Arabia and in Arabic as as-Sa‘ūdiyyah , is the largest state in Western Asia by land area, constituting the bulk of the Arabian Peninsula, and the second-largest in the Arab World...
as the lectotype
Lectotype
In botanical nomenclature and zoological nomenclature, a lectotype is a kind of name-bearing type. When a species was originally described on the basis of a name-bearing type consisting of multiple specimens, one of those may be designated as the lectotype...
for this species.
The common name
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
"milk shark" comes from a belief held in India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
that eating this shark's meat enhances lactation
Lactation
Lactation describes the secretion of milk from the mammary glands and the period of time that a mother lactates to feed her young. The process occurs in all female mammals, however it predates mammals. In humans the process of feeding milk is called breastfeeding or nursing...
. Other names for this species include fish shark, grey dog shark, little blue shark, Longmans dogshark, milk dog shark, sharp nosed (milk) shark, Walbeehm's sharp-nosed shark, and white-eye shark. A 1992 phylogenetic analysis by Gavin Naylor, based on allozyme
Allozyme
Variant forms of an enzyme that are coded by different alleles at the same locus are called allozymes. These are opposed to isozymes, which are enzymes that perform the same function, but which are coded by genes located at different loci....
s, found that the milk shark is the most basal
Basal (phylogenetics)
In phylogenetics, a basal clade is the earliest clade to branch in a larger clade; it appears at the base of a cladogram.A basal group forms an outgroup to the rest of the clade, such as in the following example:...
of the four Rhizoprionodon species examined. The extinct R. fischeuri, known from Middle Miocene
Middle Miocene
The Middle Miocene is a sub-epoch of the Miocene Epoch made up of two stages: the Langhian and Serravallian stages. The Middle Miocene is preceded by the Early Miocene....
(16–12 Ma) deposits in southern France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
and Portugal
Portugal
Portugal , officially the Portuguese Republic is a country situated in southwestern Europe on the Iberian Peninsula. Portugal is the westernmost country of Europe, and is bordered by the Atlantic Ocean to the West and South and by Spain to the North and East. The Atlantic archipelagos of the...
, may be the same as R. acutus.
Distribution and habitat
The milk shark has the widest distribution of any Rhizoprionodon species. In the eastern Atlantic OceanAtlantic Ocean
The Atlantic Ocean is the second-largest of the world's oceanic divisions. With a total area of about , it covers approximately 20% of the Earth's surface and about 26% of its water surface area...
, it is found from Mauritania
Mauritania
Mauritania is a country in the Maghreb and West Africa. It is bordered by the Atlantic Ocean in the west, by Western Sahara in the north, by Algeria in the northeast, by Mali in the east and southeast, and by Senegal in the southwest...
to Angola
Angola
Angola, officially the Republic of Angola , is a country in south-central Africa bordered by Namibia on the south, the Democratic Republic of the Congo on the north, and Zambia on the east; its west coast is on the Atlantic Ocean with Luanda as its capital city...
, as well as around Madeira
Madeira
Madeira is a Portuguese archipelago that lies between and , just under 400 km north of Tenerife, Canary Islands, in the north Atlantic Ocean and an outermost region of the European Union...
and in the Gulf of Taranto
Gulf of Taranto
The Gulf of Taranto is a gulf of the Ionian Sea, in southern Italy.The Gulf of Taranto is almost square, 140 km long and wide, and is delimited by the capes Santa Maria di Leuca and Colonna...
off southern Italy
Italy
Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...
. In the Indian Ocean
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
, it occurs from South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
and Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
northward to the Arabian Peninsula
Arabian Peninsula
The Arabian Peninsula is a land mass situated north-east of Africa. Also known as Arabia or the Arabian subcontinent, it is the world's largest peninsula and covers 3,237,500 km2...
, and eastward to South
South Asia
South Asia, also known as Southern Asia, is the southern region of the Asian continent, which comprises the sub-Himalayan countries and, for some authorities , also includes the adjoining countries to the west and the east...
and Southeast Asia
Southeast Asia
Southeast Asia, South-East Asia, South East Asia or Southeastern Asia is a subregion of Asia, consisting of the countries that are geographically south of China, east of India, west of New Guinea and north of Australia. The region lies on the intersection of geological plates, with heavy seismic...
. In the Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
, this species occurs from China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
and southern Japan
Japan
Japan is an island nation in East Asia. Located in the Pacific Ocean, it lies to the east of the Sea of Japan, China, North Korea, South Korea and Russia, stretching from the Sea of Okhotsk in the north to the East China Sea and Taiwan in the south...
, through the Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
and Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
, to New Guinea
New Guinea
New Guinea is the world's second largest island, after Greenland, covering a land area of 786,000 km2. Located in the southwest Pacific Ocean, it lies geographically to the east of the Malay Archipelago, with which it is sometimes included as part of a greater Indo-Australian Archipelago...
and northern Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. The milk shark likely once had a contiguous distribution by way of the Tethys Sea, until during the Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
epoch when eastern Atlantic sharks were isolated from Indo-Pacific sharks by the collision of Asia and Africa.
Occurring close to shore from the surf zone
Surf zone
As ocean surface waves come closer to shore they break, forming the foamy, bubbly surface we call surf. The region of breaking waves defines the surf zone. After breaking in the surf zone, the waves continue to move in, and they run up onto the sloping front of the beach, forming an uprush of...
to a depth of 200 m (656.2 ft), the milk shark favors turbid water off sandy beaches and occasionally enters estuaries
Estuary
An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....
. In Shark Bay
Shark Bay
Shark Bay is a World Heritage listed bay in Western Australia. The term may also refer to:* the locality of Shark Bay, now known as Denham* Shark Bay Marine Park* Shark Bay , a shark exhibit at Sea World, Gold Coast, Australia* Shire of Shark Bay...
, Western Australia
Western Australia
Western Australia is a state of Australia, occupying the entire western third of the Australian continent. It is bounded by the Indian Ocean to the north and west, the Great Australian Bight and Indian Ocean to the south, the Northern Territory to the north-east and South Australia to the south-east...
, juvenile milk sharks inhabit seagrass
Seagrass
Seagrasses are flowering plants from one of four plant families , all in the order Alismatales , which grow in marine, fully saline environments.-Ecology:...
meadows composed of Amphibolis antarctica
Amphibolis antarctica
Amphibolis antarctica, commonly known as Wire weed or Sea Nymph, is a seagrass found in coastal waters of southern and western Australia.-Description:...
and Posidonia australis
Posidonia australis
Posidonia australis is a species of seagrass that occurs in the southern waters of Australia. It is sometimes referred to as Fibreball Weed. The marine plant forms large meadows that are considered to be of high importance to the environmental conservation of the region...
. Although some sources state that this species avoids low salinities
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
, it has been reported several times from fresh water
Fresh Water
Fresh Water is the debut album by Australian rock and blues singer Alison McCallum, released in 1972. Rare for an Australian artist at the time, it came in a gatefold sleeve...
in Cambodia
Cambodia
Cambodia , officially known as the Kingdom of Cambodia, is a country located in the southern portion of the Indochina Peninsula in Southeast Asia...
, as far upstream as the Tonlé Sap
Tonlé Sap
The Tonlé Sap is a combined lake and river system of major importance to Cambodia.The Tonlé Sap is the largest freshwater lake in South East Asia and is an ecological hot spot that was designated as a UNESCO biosphere in 1997....
. Milk sharks may be found anywhere in the water column from the surface to the bottom. Off KwaZulu-Natal
KwaZulu-Natal
KwaZulu-Natal is a province of South Africa. Prior to 1994, the territory now known as KwaZulu-Natal was made up of the province of Natal and the homeland of KwaZulu....
, South Africa, its numbers fluctuate annually with a peak in summer, suggesting some form of seasonal movement
Fish migration
Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousands of kilometres...
.
Description
West Africa
West Africa or Western Africa is the westernmost region of the African continent. Geopolitically, the UN definition of Western Africa includes the following 16 countries and an area of approximately 5 million square km:-Flags of West Africa:...
the milk shark has been reported to reach 1.78 m (5.8 ft) and 22 kg (48.5 lb) for males, and 1.65 m (5.4 ft) and 17 kg (37.5 lb) for females, though there is uncertainty regarding the species identity of these specimens. Even if accepted, these figures are considered exceptional and most individuals do not exceed 1.1 m (3.6 ft) in length. Generally, females are heavier and attain a greater maximum size than males.
The milk shark has a slender build with a long pointed snout, large round eyes with nictitating membrane
Nictitating membrane
The nictitating membrane is a transparent or translucent third eyelid present in some animals that can be drawn across the eye for protection and to moisten it while maintaining visibility. Some reptiles, birds, and sharks have a full nictitating membrane; in many mammals, there is a small...
s (protective third eyelid
Eyelid
An eyelid is a thin fold of skin that covers and protects an eye. With the exception of the prepuce and the labia minora, it has the thinnest skin of the whole body. The levator palpebrae superioris muscle retracts the eyelid to "open" the eye. This can be either voluntarily or involuntarily...
s), and no spiracle
Spiracle
Spiracles are openings on the surface of some animals that usually lead to respiratory systems.-Vertebrates:The spiracle is a small hole behind each eye that opens to the mouth in some fishes. In the primitive jawless fish the first gill opening immediately behind the mouth is essentially similar...
s. On each side of the head behind the corner of the jaw, there are usually 7–15 enlarged pores. The nostril
Nostril
A nostril is one of the two channels of the nose, from the point where they bifurcate to the external opening. In birds and mammals, they contain branched bones or cartilages called turbinates, whose function is to warm air on inhalation and remove moisture on exhalation...
s are small, as are the adjacent triangular skin flaps. There are long furrows at the corners of the mouth on both the upper and lower jaws. The tooth rows number 24–25 in both jaws. The upper teeth are finely serrated and strongly oblique; the lower teeth have a similar shape, though the serrations are smaller and the tips curve gently upward. The teeth of juveniles are smooth-edged.
The broad, triangular pectoral fins originate below the third or fourth gill slit
Gill slit
Gill slits are individual openings to gills, i.e., multiple gill arches, which lack a single outer cover. Such gills are characteristic of Cartilaginous fish such as sharks, rays, sawfish, and guitarfish. Most of these have five pairs, but a few species have 6 or 7 pairs...
s, and are no longer than the front margin of the first dorsal fin
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
. The anal fin is about twice as long as the second dorsal fin and preceded by long ridges. The first dorsal fin originates over the pectoral fin free rear tips, and the much smaller second dorsal fin originates over the last third of the anal fin base. The dorsal fins do not have a ridge between them. The lower lobe of the caudal fin is well-developed and the upper lobe has a ventral notch near the tip. This shark is plain gray, brown-gray, or purple-gray above and white below. The leading edge of the first dorsal fin and the trailing edge of the caudal fin may be dark, and the trailing edges of the pectoral fins may be light.
Biology and ecology
One of the most (if not the most) abundant near-shore sharks within its range, the milk shark feeds mainly on small benthic and schoolingShoaling and schooling
In biology, any group of fish that stay together for social reasons are said to be shoaling , and if, in addition, the group is swimming in the same direction in a coordinated manner, they are said to be schooling . In common usage, the terms are sometimes used rather loosely...
bony fishes. Occasionally squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
, octopus
Octopus
The octopus is a cephalopod mollusc of the order Octopoda. Octopuses have two eyes and four pairs of arms, and like other cephalopods they are bilaterally symmetric. An octopus has a hard beak, with its mouth at the center point of the arms...
, cuttlefish
Cuttlefish
Cuttlefish are marine animals of the order Sepiida. They belong to the class Cephalopoda . Despite their name, cuttlefish are not fish but molluscs....
, crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s, shrimp
Shrimp
Shrimp are swimming, decapod crustaceans classified in the infraorder Caridea, found widely around the world in both fresh and salt water. Adult shrimp are filter feeding benthic animals living close to the bottom. They can live in schools and can swim rapidly backwards. Shrimp are an important...
, and gastropods are also taken. In Shark Bay, the most important prey are silversides, herring
Herring
Herring is an oily fish of the genus Clupea, found in the shallow, temperate waters of the North Pacific and the North Atlantic oceans, including the Baltic Sea. Three species of Clupea are recognized. The main taxa, the Atlantic herring and the Pacific herring may each be divided into subspecies...
, smelt-whitings
Sillaginidae
The Sillaginidae, commonly known as the smelt-whitings, whitings, sillaginids, sand borers and sand-smelts, are a family of benthic coastal marine fishes in the order Perciformes. The smelt-whitings inhabit a wide region covering much of the Indo-Pacific, from the west coast of Africa east to Japan...
, and wrasse
Wrasse
The wrasses are a family, Labridae, of marine fish, many of which are brightly colored. The family is large and diverse, with over 600 species in 82 genera, which are divided into nine subgroups or tribes....
s; this is also the only local shark species that preys on the Waigeo seaperch
Waigeo seaperch
The Waigeo seaperch is a species of marine fish in family Latidae of order Perciformes. The only species of genus Psammoperca, it is native to tropical coastal waters from the Bay of Bengal south through Indonesia to northern Australia and north through the Philippines and the South China Sea to...
(Psammoperca waigiensis), found in seagrass beds avoided by other sharks. In the Gulf of Carpentaria
Gulf of Carpentaria
The Gulf of Carpentaria is a large, shallow sea enclosed on three sides by northern Australia and bounded on the north by the Arafura Sea...
, it feeds mainly on halfbeak
Halfbeak
The halfbeaks are a geographically widespread and numerically abundant family of epipelagic fish inhabiting warm waters around the world. The family Hemiramphidae is divided into two subfamilies, the primarily marine Hemiramphinae and the freshwater or estuarine Zenarchopterinae...
s, herring, and mullets
Mullet (fish)
The mullets or grey mullets are a family and order of ray-finned fish found worldwide in coastal temperate and tropical waters, and in some species in fresh water. Mullets have served as an important source of food in Mediterranean Europe since Roman times...
, and is also a major predator of penaeid prawns
Penaeidae
Penaeidae is a family of prawns, although they are often referred to as penaeid shrimp. It contains many species of economic importance, such as the tiger prawn , whiteleg shrimp, Atlantic white shrimp and Indian prawn. Many prawns are the subject of commercial fishery, and farming, both in marine...
. Smaller sharks eat proportionately more cephalopods and crustaceans, switching to fish as they grow older.
Many predators feed on the milk shark, including larger sharks such as the blacktip shark
Blacktip shark
The blacktip shark is a species of requiem shark, family Carcharhinidae. It is common to coastal tropical and subtropical waters around the world, including brackish habitats. Genetic analyses have revealed substantial variation within this species, with populations from the western Atlantic Ocean...
(Carcharhinus limbatus) and Australian blacktip shark
Australian blacktip shark
The Australian blacktip shark is a species of requiem shark, family Carcharhinidae. It is one of the two most abundant shark species in commercial gill-net catches off northern Australia . Black markings on the tips of both dorsal fins, and the pectoral and lower caudal fins distinguish C...
(Carcharhinus tilstoni), and possibly also marine mammal
Marine mammal
Marine mammals, which include seals, whales, dolphins, and walruses, form a diverse group of 128 species that rely on the ocean for their existence. They do not represent a distinct biological grouping, but rather are unified by their reliance on the marine environment for feeding. The level of...
s. Off KwaZulu-Natal, the decimation of large sharks by the use of gillnet
Shark net
A shark net is a submerged net placed around beaches to reduce shark attacks on swimmers.Shark nets do not offer complete protection but work on the principle of "fewer sharks, fewer attacks". They reduce occurrence via shark mortality. Reducing the local shark populations is believed to reduce the...
s to protect beaches has led to a recent increase in milk shark numbers. A known parasite of this species is the copepod
Copepod
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...
Pseudopandarus australis. There is some evidence that male and female milk sharks segregate from each other.
Life history
Like other requiem sharks, the milk shark is viviparous; females usually have a single functional ovaryOvary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
(on the left) and two functional uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
es divided into separate compartments for each embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
. The details of its life history vary across different parts of its range. Females generally produce young every year, though some give birth every other year or even every third year. Mating and parturition take place in spring or early summer (April to July) off western and southern Africa, and in winter off India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
, Alternately, off Oman
Oman
Oman , officially called the Sultanate of Oman , is an Arab state in southwest Asia on the southeast coast of the Arabian Peninsula. It is bordered by the United Arab Emirates to the northwest, Saudi Arabia to the west, and Yemen to the southwest. The coast is formed by the Arabian Sea on the...
parturition occurs year-round with a peak in spring. Parturition also occurs continuously in Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
n waters; in the Herald Bight of Shark Bay, the number of newborns peaks in April and again in July. One proposed explanation for the lack of reproductive seasonality in these subpopulations is a lengthier and/or more complex reproductive cycle than has been detected (such as a period of dormancy
Diapause
Diapause is the delay in development in response to regularly and recurring periods of adverse environmental conditions. It is considered to be a physiological state of dormancy with very specific initiating and inhibiting conditions...
in embryonic development, though there is presently no evidence of this occurring). Females do not store sperm internally.
The litter size ranges from 1 to 8 with 2–5 being typical, increasing with female size. In Omanese waters females on average outnumber males in a litter by more than 2:1, and all-female litters are not uncommon. Similar but less extreme sex imbalances have also been reported from litters of milk sharks off Senegal
Senegal
Senegal , officially the Republic of Senegal , is a country in western Africa. It owes its name to the Sénégal River that borders it to the east and north...
and eastern India. The reason for this imbalance is unknown, and it has not been observed in related species such as the Atlantic sharpnose shark
Atlantic sharpnose shark
The Atlantic sharpnose shark, Rhizoprionodon terraenovae, is a requiem shark of the family Carcharhinidae, found in the subtropical waters of the northwestern Atlantic Ocean between latitudes 43° N and 25° S,-Habitat:...
(R. terraenovae). Gestation
Gestation
Gestation is the carrying of an embryo or fetus inside a female viviparous animal. Mammals during pregnancy can have one or more gestations at the same time ....
of the embryos takes around a year and proceeds in three phases. In the first phase, lasting two months to an embryonic length of 63–65 mm (2.5–2.6 in), the embryo relies on yolk for sustenance and gas exchange
Gas exchange
Gas exchange is a process in biology where gases contained in an organism and atmosphere transfer or exchange. In human gas-exchange, gases contained in the blood of human bodies exchange with gases contained in the atmosphere. Human gas-exchange occurs in the lungs...
occurs across its surface integument and possibly also the yolk sac
Yolk sac
The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals...
. During the second phase, which also lasts for two months to an embryonic length of 81–104 mm (3.2–4.1 in), the external gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
filaments develop and the yolk sac begins to be resorbed, the embyo ingesting histotroph (a nutritious substance secreted by the mother) in the meantime. In the third phase, lasting six to eight months, the depleted yolk sac is converted into a placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
l connection through which the fetus receives nourishment until birth.
Young sharks are typically born at a length of 32.5–50 cm (12.8–19.7 in) and weigh 127–350 g (0.279987072974795–0.771617917647072 lb). There is an atypical record of a female, caught off Mumbai
Mumbai
Mumbai , formerly known as Bombay in English, is the capital of the Indian state of Maharashtra. It is the most populous city in India, and the fourth most populous city in the world, with a total metropolitan area population of approximately 20.5 million...
, carrying a fetus only 23.7 cm (9.3 in) long that was already nearly fully developed, long before gestation was complete. Pregnant females make use of inshore nursery areas to give birth, taking advantage of the warmer waters and abundant food; known nursery areas include the Banc d'Arguin National Park
Banc d'Arguin National Park
The Banc d'Arguin National Park lies in Western Africa on the west coast of Mauritania between Nouakchott and Nouadhibou. The World Heritage Site is a major breeding site for migratory birds. A wide range of species include flamingos, broad-billed sandpipers, pelicans and terns. Much of the...
off Mauritania
Mauritania
Mauritania is a country in the Maghreb and West Africa. It is bordered by the Atlantic Ocean in the west, by Western Sahara in the north, by Algeria in the northeast, by Mali in the east and southeast, and by Senegal in the southwest...
, and Cleveland Bay and Herald Bight off Australia. In Herald Bight, large groups of small milk sharks can be found in shallow tidal pools, as well as in seagrass beds where they are sheltered from predators by the dense, tall vegetation. The sharks move out of these coastal embayments
Bay
A bay is an area of water mostly surrounded by land. Bays generally have calmer waters than the surrounding sea, due to the surrounding land blocking some waves and often reducing winds. Bays also exist as an inlet in a lake or pond. A large bay may be called a gulf, a sea, a sound, or a bight...
when they mature.
Males and female milk sharks mature at lengths of 84–95 cm (33.1–37.4 in) and 89–100 cm (35–39.4 in) respectively off West Africa, 68–72 cm (26.8–28.3 in) and 70–80 cm (27.6–31.5 in) respectively off southern Africa, and 63–71 cm (24.8–28 in) and 62–74 cm (24.4–29.1 in) respectively off Oman. These discrepancies in maturation size may be a result of regional variation or incidental selection
Artificial selection
Artificial selection describes intentional breeding for certain traits, or combination of traits. The term was utilized by Charles Darwin in contrast to natural selection, in which the differential reproduction of organisms with certain traits is attributed to improved survival or reproductive...
from heavy fishing pressure. The growth rate for milk sharks off Chennai
Chennai
Chennai , formerly known as Madras or Madarasapatinam , is the capital city of the Indian state of Tamil Nadu, located on the Coromandel Coast off the Bay of Bengal. Chennai is the fourth most populous metropolitan area and the sixth most populous city in India...
have been calculated as 10 cm (3.9 in) in the first year, 9 cm (3.5 in) in the second year, 7 cm (2.8 in) in the third year, 6 cm (2.4 in) in the fourth year, 5 cm (2 in) in the fifth year, and 3–4 cm (1.2–1.6 in) per year from then on. The age at maturation is thought to be 2–3 years, and the maximum lifespan is at least 8 years.
Human interactions
Gillnet
Gillnetting is a common fishing method used by commercial and artisanal fishermen of all the oceans and in some freshwater and estuary areas. The gillnet also is used by fisheries scientists to monitor fish populations. Because gillnets can be so effective their use is closely monitored and...
s, trawls, and hook-and-line, this shark is marketed fresh or dried and salted for human consumption, and is also utilized for shark fin soup
Shark fin soup
Shark fin soup is a popular soup item of Chinese cuisine usually served at special occasions such as weddings and banquets, or as a luxury item in Chinese culture. The shark fins provide texture while the taste comes from the other soup ingredients.There is controversy over the practice of shark...
and fishmeal. Its abundance makes it a significant component of artisanal
Artisan fishing
Artisan fishing is a term used to describe small scale low-technology commercial or subsistence fishing practices. The term particularly applies to coastal or island ethnic groups using traditional techniques such as rod and tackle, arrows and harpoons, throw nets and drag nets, and traditional...
and commercial fisheries
Commercial fishing
Commercial fishing is the activity of catching fish and other seafood for commercial profit, mostly from wild fisheries. It provides a large quantity of food to many countries around the world, but those who practice it as an industry must often pursue fish far into the ocean under adverse conditions...
across its range. Off northern Australia, it ranks among the most common sharks caught in trawls, and comprises 2% and 6% of the annual gillnet and longline catches respectively. This species is also one of the most commercially important sharks caught off Senegal, Mauritania, Oman, and India. Some sport fishers
Recreational fishing
Recreational fishing, also called sport fishing, is fishing for pleasure or competition. It can be contrasted with commercial fishing, which is fishing for profit, or subsistence fishing, which is fishing for survival....
regard it as a game fish
Game fish
Game fish are fish pursued for sport by recreational anglers. They can be freshwater or marine fish. Game fish can be eaten after being caught, though increasingly anglers practise catch and release to improve fish populations. Some game fish are also targeted commercially, particularly...
.
The International Union for Conservation of Nature (IUCN) has listed the milk shark under Least Concern
Least Concern
Least Concern is an IUCN category assigned to extant taxon or lower taxa which have been evaluated but do not qualify for any other category. As such they do not qualify as threatened, Near Threatened, or Conservation Dependent...
; despite being heavily fished it has a wide distribution and remains fairly common. The reproductive characteristics of this species suggests that it is capable of withstanding a somewhat high level of exploitation, though not as much as the grey sharpnose shark
Grey sharpnose shark
The grey sharpnose shark, Rhizoprionodon oligolinx, is a requiem shark of the family Carcharhinidae, found in the tropical waters of the Indo-West Pacific Oceans between latitudes 30° N and 18° S, from the surface to 36 m...
(R. oligolinx) or Australian sharpnose shark
Australian sharpnose shark
The Australian sharpnose shark, Rhizoprionodon taylori, is a requiem shark of the family Carcharhinidae, found in the tropical waters of the western Pacific Ocean off Papua New Guinea and northern Australia between latitudes 8° N and 28° S, from the surface to 110 m. Its length is up to...
(R. taylori). In the 1980s and early 1990s, stock assessments of the milk shark off India's Verval coast concluded that catches by gillnet and trawl fisheries were below the maximum sustainable level. However, these studies were based on methodologies that have subsequently been proven unreliable for shark populations. Moreover, fishing pressure in the region has increased substantially since the assessments were conducted.