The dusky catshark (''Bythaelurus canescens'') is a species of

shark Sharks are a group of elasmobranch cartilaginous fish characterized by a ribless endoskeleton, dermal denticles, five to seven gill slits on each side, and pectoral fins that are not fused to the head. Modern sharks are classified within the ...

belonging to 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 ...

Pentanchidae Pentanchidae, the deepwater catsharks, is a family of sharks belonging to the order Carcharhiniformes Carcharhiniformes ( from Classical Greek ' (karcharos) 'sharp/jagged' and ' (rhinos) 'nose', plus Latin ''forme'' 'shape'), commonly known a ...

, the deepwater catsharks. This shark is endemic to the southeast Pacific Ocean, off the coasts of Peru and Chile. It grows to a maximum length of , and is

oviparous Oviparous animals are animals that reproduce by depositing fertilized zygotes outside the body (i.e., by laying or spawning) in metabolically independent incubation organs known as eggs, which nurture the embryo into moving offsprings kno ...

like many other

chondrichthyans Chondrichthyes (; ) is a class of jawed fish that contains the cartilaginous fish or chondrichthyans, which all have skeletons primarily composed of cartilage. They can be contrasted with the Osteichthyes or ''bony fish'', which have skeletons ...

in the Indo-Pacific.

Ecology

''Bythaelurus canescens'' is deep-sea shark, generally located between depths of . It lives primarily on mud on the upper continental slopes, but can also be found on rocky bottoms. It is an important

mesopredator A mesopredator is a predator that occupies a mid-ranking trophic level in a food web. There is no standard definition of a mesopredator, but mesopredators are usually medium-sized carnivorous or omnivorous animals, such as raccoons, foxes, or ...

, and is often caught it shrimp trawl nets in northern and central Chilean coasts. Sometimes ''B. canescens'' makes up to 20.3% of the total catch. In spite of this, little is known about it because it is often thrown back without further consideration. Trophic ecology studies are often done on ''B. canescens t''o obtain a general overview of their diet.

Diet Studies

Much of what is known about the ecology and predicted behavior of the dusky catshark is known due to studies of stomach samples. Their most important prey were reported to be the squid '' Loligo gahi'', the

siphonophore Siphonophorae (from Ancient Greek σίφων (siphōn), meaning "tube" and -φόρος (-phóros), meaning "bearing") is an order within Hydrozoa, a class of marine organisms within the phylum Cnidaria. According to the World Register of Marine ...

'' Sulculeolaria quadrivalvis'', and the bony fishes '' Muggiea atlantica'' and ''Coelorhynchus fasciatus''. Overall, the bulk mass consumed consisted of siphonophores. Other prey options such as octopus or crustaceans would depend on environmental availability, making the dusky catshark a general bentho-

demersal The demersal zone is the part of the sea or ocean (or deep lake) consisting of the part of the water column near to (and significantly affected by) the seabed and the benthos. The demersal zone is just above the benthic zone and forms a layer o ...

predator that eats what fits in its mouth. Its diet is similar to those of other Scyliorhinidae sharks in the Chilean deep sea which are opportunistic hunters. It is also possible it undergoes vertical migration while following its food source. In a separate study, the deep-sea shrimp '' Heterocarpus reedi'' is reported to be the main food source for ''B. canescens'', which is to be expected as dusky catsharks are often caught in the ''H. reedi'' nets. Its diet was again found to consist mostly of benthic prey sources. However, there is still some data lacking as most ''Bythaelurus canescens'' specimens caught are juveniles; adults tend to live at deeper depths of around 1000 meters. At an active methane seep off the coast of Chile, ''Bythaelurus canescens'' was reported to be one of the top predators, with a highly variable diet.

Reproduction

Like many sharks, ''Bythaelurus canescens'' reproduces using complex egg capsules which are deposited on the sea floor or attached to rocks and corals. Scyliorhinid shark eggs are vase-shaped, and are carried two at a time, one in each uterus. The capsules are light yellow-brown, and darken to brown after fixation to the sea floor. The capsule is slightly translucent, elongated and flattened, and ridged lengthwise, with a long tendril extending from each corner. Fixation occurs by two of the four tendrils, with two strong, coiled posterior tendrils designed to hold onto substrate. Development occurs after the egg has been laid, with no aid from the parents.

References

{{Taxonbar, from=Q2615551 dusky catshark Fish of Chile Fauna of Tierra del Fuego Western South American coastal fauna dusky catshark dusky catshark