Sharks and Skates of Scotland Report: Longnose velvet dogfish (Centroselachus crepidater)

Habitat 

Longnose velvet dogfish live on or close to the seabed along the underwater slopes off continents and islands, typically at depths of 200–2,000 m, with most records occurring deeper than 500 m (Finucci et al., 2020), as well as on seamounts (Neat et al., 2015). Survey data from the Northeast Atlantic (Rockall Trough) indicate that Longnose velvet dogfish is most abundant at depths greater than 900 m, with a peak occurrence between 750 and 1,050 m depth (Neat et al., 2015).

Biology and Ecology

Longnose velvet dogfish are a long-lived, late-maturing deep-water shark species that are poorly studied. They are medium sized, and in the Northeast Atlantic, can grow to a maximum total length of about 105 cm, with females attaining a greater length than males (Ebert and Stehmann, 2013; Blasdale et al., 2015). In the Rockall Trough, the size at first maturity was estimated to be 57.2 cm TL for males (~ 9 years old) and 75.4 cm TL for females (~20 years) (Moore et al., 2013). The species are viviparous, and uterine fecundity ranged from 1 to 9 embryos (Nolan and Hogan, 2003). The size at birth ranges from about 28 to 35 cm (Ebert and Stehmann, 2013), and Longnose velvet dogfish do not appear to have a defined breeding season (Nolan and Hogan, 2003). The species has a non-continuous reproductive cycle (meaning the periods of vitellogenesis (yolk accumulation) and gestation (pregnancy) occur consecutively, not at the same time, this results in a "resting" or non-pregnant period for the female after giving birth, and before her ovaries are ready for the next ovulation, extending the full cycle to every two or three years (biennial or triennial), rather than annual) with no seasonal trends in maximum ovum diameter or gonadosomatic index (Daley et al., 2002). Gestation length is unknown, but it has been suggested that with follicle development, gestation and a resting phase the reproductive cycle is likely to be at least two years (Francis et al., 2018; Irvine et al., 2006; Simpfendorfer & Kyne, 2009). Unvalidated estimates suggest Longnose velvet dogfish may live to 54 years (Daley et al., 2002; Sarah Irvine CSIRO Marine Research, unpublished data). Deep-water survey data from the Rockall Trough show that sex ratio of males to females in the area was 1.5:1. A full range of sizes and maturities (including late-stage pregnant females) were present suggesting that all life-history stages are found in the Rockall Trough (Neat et al., 2015). Dietary studies found that Longnose velvet dogfish mainly feed on micronekton (fauna 2–20 cm in size) in the vicinity of the seabed (Mauchline and Gordon, 1983), with mesopelagic fishes and squids also recorded (Dunn et al., 2010). 

Human interactions 

There is currently no targeted fishery for this species. Since 2010 there has been a zero TAC in European waters for Longnose velvet dogfish and from 2015, the species has been prohibited from ICES division 2a and subarea 4 which was extended in 2021 to all European waters in 2021 (ICES, 2024). Since the introduction of general measures to protect deep-water elasmobranchs (ban of static net fisheries below 600 m and trawls below 800 m), bycatch and discards are thought to be relatively low (ICES 2024). Where the species is occasionally incidentally caught, discards will occur, with the discard mortality thought to be high (Moura et al., 2018; Finucci et al., 2020). The species is offered some refuge from fisheries because a large proportion of the population occurs at depths beyond the limit of deepwater fisheries in the Northeast Atlantic.