The humpback smooth-hound (''Mustelus whitneyi'') is a species of

houndshark The Triakidae or houndsharks are a family of ground sharks, consisting of about 40 species in nine genera. In some classifications, the family is split into two subfamilies, with the genera ''Mustelus'', '' Scylliogaleus'' and '' Triakis'' in t ...

and a part of the

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

Triakidae. The most noticeable difference between ''Mustelus whitneyi'' and its relatives, is the slight curvature, causing a "humpback" appearance located in front of its primary dorsal fin. It is found on the

continental shelves A continental shelf is a portion of a continent that is submerged under an area of relatively shallow water, known as a shelf sea. Much of these shelves were exposed by drops in sea level during glacial periods. The shelf surrounding an island ...

of the

tropical The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...

southeast

Pacific The Pacific Ocean is the largest and deepest of Earth's five oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is bounded by the cont ...

, from

Peru Peru, officially the Republic of Peru, is a country in western South America. It is bordered in the north by Ecuador and Colombia, in the east by Brazil, in the southeast by Bolivia, in the south by Chile, and in the south and west by the Pac ...

to southern

Chile Chile, officially the Republic of Chile, is a country in western South America. It is the southernmost country in the world and the closest to Antarctica, stretching along a narrow strip of land between the Andes, Andes Mountains and the Paci ...

, between

latitude In geography, latitude is a geographic coordinate system, geographic coordinate that specifies the north-south position of a point on the surface of the Earth or another celestial body. Latitude is given as an angle that ranges from −90° at t ...

s 3° S and 54° S. These sharks are demersal feeders but range from depths between . Humpback smooth-hound sharks are small sharks, reaching a maximum size of in total length. ''Mustelus whitneyi'' typically feed on teleosts and invertebrates in the benthic and pelagic ecosystems, most important prey being the peruvian anchovy. These humpback smooth-hound sharks are placental viviparious sharks, meaning that the embryo forms inside the mother tethered by the placental cord. The threats currently causing population decline to humpback smooth-hound sharks surround issues with local fisheries and management.

Description

The humpback smooth-hound is a small shark growing to a length of up to in total length for males and for females, with a maximum size of ."Tollo comun (Mustelus whitneyi)" (in Spanish). Retrieved 2023-04-13. It has a sturdy body with a moderately long, broad, sharply angled snout and large eyes, set widely apart. The mouth is fairly long and the upper lip furrows are longer than the lower ones. The teeth have a main pointed cusp and sometimes smaller subsidiary ones. The first dorsal fin is approximately triangular and the trailing edge is fringed with bare, dark-coloured collagen rods known as ceratotrichia. The pectoral fins are large and the pelvic fins moderately so. The caudal peduncle is short and the lower lobe of the tail fin is hardly curved in adults. The color of this shark is plain grey or greyish-brown without any spots or barring. The main difference between humpback smooth-hounds and others in its family, as mentioned before, is the slight curvature located directly behind the head, causing a "humpback" appearance. The humpback smooth-hound is streamlined in many different aspects. First being that the humpback smooth-hound has a almost completely cylindrical body allowing the animal to dive through the water. The shape of the primary dorsal fin reduces friction drag in the water, allowing the animal to move without exerting as much energy. Finally, the upper caudal lobe is disproportionately larger than the lower caudal lobe. This allows the shark to quickly and easily change direction.

Distribution and habitat

The humpback smooth-hound is found in the southeastern Pacific Ocean off the coast of Peru and Chile, between 1°N and 45°S. Although, the humpback smooth-hound is found within this range; it is rarely found in Chile, and mainly concentrated in Peru.Gonzalez-Pestana, Adriana; J, Carlos Kouri; Velez-Zuazo, Ximena (2016-04-12). "Shark fisheries in the Southeast Pacific: A 61-year analysis from Peru". Its depth range is between but it is most common between . ''Mustelus whitneyi'' is classified as a shark living in the marine neritic habitat, meaning it can be found in coastal waters. The shark is both a demersal and pelagic feeder, often found in coastal waters at the continental base, near the seabed, or on rocky shores. Due to their presence in both

benthic The benthic zone is the ecological region at the lowest level of a body of water such as an ocean, lake, or stream, including the sediment surface and some sub-surface layers. The name comes from the Ancient Greek word (), meaning "the depths". ...

and

pelagic The pelagic zone consists of the water column of the open ocean and can be further divided into regions by depth. The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or water column between the sur ...

habitats humpback smooth-hounds play an important ecological role in transferring resources between the two. The sharks act as mobile links for nutrients and resources through the methods of predation and waste release.

Biology and ecology

Humpback smooth-hound sharks are placental

viviparous In animals, viviparity is development of the embryo inside the body of the mother, with the maternal circulation providing for the metabolic needs of the embryo's development, until the mother gives birth to a fully or partially developed juve ...

sharks, placental meaning that the sharks develop inside the body in a placental sac connected to the mother. The minimum gestation for these sharks was 7 months however gestation is likely to last 10–11 months. The female humpback smooth-hounds then have on average, 10 pups per litter measuring at birth. Humpback smooth-hound sharks feed on a variety of organisms in both the benthic and pelagic coastal ecosystems. The main components of their diet include:

bivalves Bivalvia () or bivalves, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of aquatic molluscs (marine and freshwater) that have laterally compressed soft bodies enclosed by a calcified exoskeleton consis ...

cephalopod A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...

gastropods Gastropods (), commonly known as slugs and snails, belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda (). This class comprises snails and slugs from saltwater, freshwater, and from the land. Ther ...

, and

teleost Teleostei (; Ancient Greek, Greek ''teleios'' "complete" + ''osteon'' "bone"), members of which are known as teleosts (), is, by far, the largest group of ray-finned fishes (class Actinopterygii), with 96% of all neontology, extant species of f ...

s. They might also feed on crustaceans such as

crab Crabs are decapod crustaceans of the infraorder Brachyura (meaning "short tailed" in Greek language, Greek), which typically have a very short projecting tail-like abdomen#Arthropoda, abdomen, usually hidden entirely under the Thorax (arthropo ...

s and

mantis shrimp Mantis shrimp are carnivorous marine crustaceans of the order Stomatopoda (). Stomatopods branched off from other members of the class Malacostraca around 400 million years ago, with more than 520 extant species of mantis shrimp known. All li ...

s. A very important prey species of the humpback smooth-hound is the Peruvian anchovy, a small pelagic schooling fish. The humpback smooth-hound sharks are one of the top predators in their ecosystems therefore they have large ecological impacts. First being that these sharks regulate prey dynamics and populations through predation. Secondly, these sharks modify and influence prey behavior and physiology. Also, the decline in these predators can cause an increase in

and other prey species biomass. This increase can trigger cascading effects in the pelagic ecosystem. Humpback smooth-hound sharks specifically act as mobile links for resources between the benthic and pelagic environments they in habitat. By the methods of predation, excretion, and defecation the sharks transport nutrients and other resources between these two ecosystems. Specifically in the benthic habitats Humpback smooth-hounds physically alter the habitat through their predation. Because they prey on mollusks or other infaunal organisms they physically and biologically alter the sediment of the habitat, which can facilitate the penetration of oxygen in sediments and affects the nitrogen cycle. Their method of predation also causes more prey and resources to be accessible for many other species.

Status and threats

The humpback smooth-hound is fished for human consumption in Chile but more particularly in Peru, where it is more common. The Peruvian fisheries are the main threat to the population decline through directly removing these sharks and indirectly through bycatch. The unsustainable harvest causing population decline is shown in the Peruvian gillnet fisheries and the trawl fisheries in Ecuador which the Humpback is mainly caught as bycatch, and discarded. Along with the

spotted houndshark The spotted houndshark (''Triakis maculata'') is a houndshark of the family Triakidae found in tropical waters in the eastern Pacific Ocean off the coast of South America. It usually grows to a length around . The reproduction of this houndshark ...

(''Triakis maculata'') and the

speckled smooth-hound The speckled smooth-hound (''Mustelus mento'') is a houndshark of the family Triakidae. It is found on the continental shelf of the eastern Pacific, between latitudes 0° and 54° S, at depths between . It can reach a length of . Collectively ...

(''Mustelus mento''), it is known as "tollo" in its local fisheries, and of the three species it is the humpback smooth-hound that is the main target of the tollo fishery in Peru, which masks the true catch of humpback smooth-hound causing more individuals to be unsustainably removed. Landings averaging 11,000 tons of tollo per year were made in that country between 1965 and 1989, but quantities caught diminished thereafter. A minimum size requirement of was set in 2001 but was pitched so low as to have limited conservation effect. This is because this requirement does not protect the mature individuals which reproductively contribute to the population size and growth. The humpback smooth-hound is the 4th most captured of all sharks and the most captured of all demersal organisms. The fishery overexploitation is the cause of >80% reduction in population size of humpback smooth-hound sharks. The

International Union for Conservation of Nature The International Union for Conservation of Nature (IUCN) is an international organization working in the field of nature conservation and sustainable use of natural resources. Founded in 1948, IUCN has become the global authority on the stat ...

(IUCN) has rated the status of the humpback smooth-hound as being

critically endangered An IUCN Red List critically endangered (CR or sometimes CE) species is one that has been categorized by the International Union for Conservation of Nature as facing an extremely high risk of extinction in the wild. As of December 2023, of t ...

due to overexploitation.

References

External links

* {{DEFAULTSORT:smooth-hound, humpback humpback smooth-hound Western South American coastal fauna Taxa named by Norma Victoria Chirichigno Fonseca humpback smooth-hound