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

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Scyliorhinidae that is endemic to the southeast Pacific Ocean, off the coasts of Peru and Chile. It grows to a maximum length of 70 cm, and is

oviparous Oviparous animals are animals that lay their eggs, with little or no other embryonic development within the mother. This is the reproductive method of most fish, amphibians, most reptiles, and all pterosaurs, dinosaurs (including birds), and ...

like many other chondrichthyans in the Indo-Pacific.

Ecology

''Bythaelurus canescens'' is deep-sea shark, generally located between depths of 250–1260 meters. 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 mid-ranking predator in a trophic level, which typically prey on smaller animals. Mesopredators often vary in ecosystems depending on the food web. While there is no definitive measurement for mesopredators, they are usually ref ...

, 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 ''Doryteuthis gahi'', also known as the Patagonian longfin squid and Patagonian squid (Spanish: ''calamar patagónico''), is a small-sized squid belonging to the family Loliginidae. It occurs in coastal waters in the southeastern Pacific Ocean an ...

'', the siphonophore '' 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 of ...

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 Diel vertical migration (DVM), also known as diurnal vertical migration, is a pattern of movement used by some organisms, such as copepods, living in the ocean and in lakes. The word ''diel'' comes from the Latin ''dies'' day, and means a 24- ...

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

dusky catshark Fish of Chile Fauna of Tierra del Fuego Western South American coastal fauna dusky catshark dusky catshark {{shark-stub