User:Margojd/Cape elephantfish

Background

Elephantfish are known for their slow-evolving genome and are often used as a reference point for evolutionary studies. The Cape elephantfish, Callorhinchus capensis, are most closely related to two other species of elephantfish, C. callorynchus of South America and C. milii of southern Australia and New Zealand.1

Description
The Callorhinchus capensis, more commonly known as the Cape Elephantfish based off of their elongated snouts used to sift through benthic sediments1, belongs to the Chondrichthyes class, along with sharks and rays. This class is composed of fish that have skeletons primarily composed of cartilage. However, they differ from sharks and rays because they exhibit a tooth plate instead of individual teeth and have tissue covering their gills. The Elephantfish is typically a silver or bronze color with scale-less skin and an arched caudal fin. The Callorhinchus capensis typically reaches a maximum length of about 4 ft (from 10 cm at hatching), and a weight of 5.3 kg.2 They typically can live up to 10 years and reach maturity in only 3 to 5 years.1

Distribution
Callorhinchus capensis can be found mainly in the Southeast Atlantic, from Namibia to the Cape and Natal in South Africa. Within the ocean and shallow bays, Elephantfish are found from close inshore to the continental slope. They are a bottom-dwelling marine species, living over sandy and muddy sediment. They are most commonly found in depths from 10 to 370 m within the bounds of the neritic zone. However, younger fish are found in shallow water, less than 50 m in depth.

Cape Elephantfish are thought to be nomadic, but they have an annual inshore migration for breeding with other individuals.2

Reproduction
In the summer months, mature Elephantfish migrate inshore to mate and lay eggs. They lay their eggs in shallow, sheltered bays. Cape Elephant fish are oviparous: they reproduce by laying eggs, and can lay two egg cases at a time with up to 22 eggs.5 The eggs are left to germinate in the sediments for roughly 6 to 8 months.1 Physically, males uniquely develop two sets of pelvic region protrusions and a tentaculum located on top of their skulls all in addition to typical internal reproductive structures. Females do not develop such obvious external exhibits of sexual maturity but have been observed to increase in size and weight. In a study done by Freer and Griffiths (1993), it was found to be very common that one of the ovaries in many individuals did not develop at the age of maturity. Additionally, female individuals also exhibit semen plugs that prevent the ability to reproduce and must be lost beforehand. Cape Elephantfish are estimated to live up to nine years. The species has reverse sexual dimorphism, females are typically larger than males. Males mature at 3 years, with a length of 50 cm. Females mature at age of 4-5 years with an average of 70 cm in length.

Diet
Elephantfish typically eat benthic invertebrates that include, crustaceans, bivalves, polychaetes, gastropods, fish, sea urchins, and black mussels. The Elephantfish predators include seals and larger sharks. They use their elongated snout to sift through benthic sediments to hunt for food.

Fishing
C. capensis is generally caught for specialized usage in small-scale, South African fisheries as fillet white fish and to be dried, the overall amount of which can reach around 800 tons per year off the southwest coast of Africa.7 A large portion of this sum is bycatch from trawl fishing on the south and west coasts of Africa, the contents of which typically include many immature individuals as most of the trolling occurs within the nursery grounds close to the shoreline. Even including the unintentional bycatch, they are ecologically safe fish for fisheries since the high fecundity rate and early maturity support a constant and sufficient replenishment of populations.7 Like all fished populations, C. capensis is subject to overexploitation in the event that juvenile populations in shallower waters are targeted and the population declines due to a decrease in sexually mature individuals. To avoid such exploitation, the types of nets permitted to catch      C. capensis have changed over time to accommodate the changing population densities of this species and others of higher target over time.7

Predation
The top predators of C. capensis include fur seals and sharks.7