Sharks and Skates of Scotland Report: Leafscale gulper shark (Centrophorus squamosus)

Habitat 

Leafscale gulper sharks can be found in both demersal and pelagic habitats, at depths ranging from 0 – 2360 m (Ebert and Stehmann, 2013, Ebert et al., 2021). In the Rockall Trough they are found at relatively low abundance at depths of 500 and 1800m, peaking in abundance around 800 m (Neat et al., 2015). The species is highly migratory and can move hundreds of kilometres in several weeks along the continental slope waters. Females generally do not travel as far as males and might be philopatric (have a tendency to stay or habitually return to an area), (Veríssimo et al., 2012; Moura et al., 2014; Rodríguez-Cabello et al., 2016). The species appears to segregate by sex, size and maturity, with separation determined by factors such as depth and temperature (Moura et al., 2014). Seventy five percent of Leafscale gulper sharks caught mostly between 750 and 1000 m were male (O'Hea et al., 2020). Pregnant females tend to inhabit shallower and / or warmer waters (Moura et al., 2014). A number of pregnant females have been found off the Madeira Archipelago and Iceland, suggesting the areas are used as spawning grounds (Moura et al., 2014; Severino et al., 2009). Juveniles / neonates are rarely found in the Northeast Atlantic, larger immature sharks are generally found in deeper water than mature sharks (Moura et al., 2014).

Biology and Ecology

Leafscale gulper sharks are very long-lived and slow-growing. They are estimated to live for up to 70 years (Clarke et al., 2002) and can grow up to 166 cm TL (Weigmann 2016). The species is late to mature, with males maturing at 100 - 110 cm TL and females at 110 - 125 cm TL (Clarke et al., 2002; Ebert and Stehmann, 2013). Leafscale gulper sharks are aplacental viviparous and give birth to live young. They can produce 2 – 10 pups per litter, with newborns measuring between 35 – 43 cm TL (Severino et al., 2009). Sperm storage has been confirmed in females caught off New Zealand (Dutilloy and Dunn 2020). The stomach contents of 713 of Leafscale gulper sharks sampled in the Northeast Atlantic off Morocco consisted of teleosts, cephalopods, crustaceans, nematodes and condrichthians (Chimaera monstrosa and Dalatias licha), with teleosts having the highest relative importance of all the prey items identified (Nafia et al., 2023). 

Human interactions 

Leafscale gulper sharks were once an important component of mixed trawl fisheries, and mixed and directed longline and gillnet shark fisheries on continental slopes of the Northeast Atlantic (ICES, 2018), and both the flesh and the liver were sold. There is no longer a target fishery for this species following the introduction of a zero TAC for International waters in 2010 and All other waters in 2015. Vessels have been prohibited from landing the species in Scottish waters since 2012. The species is still taken as bycatch in mixed fisheries (trawl, long-line and gillnet), although this is thought to be relatively low (ICES, 2018). A study on discard survival of Leafscale gulper sharks captured on longlines at depths of 900 – 1100 m estimated a vessel mortality of 18.9% (when sharks in poor condition were included with those dead on retrieval). A subsequent tagging study of surviving Leafscale gulper sharks found that, of 9 sharks tagged successfully, three died within 5–10 weeks of release, and six survived for periods of at least 45–120 days. This corresponds to a mortality rate of 33% within 1-3 months post-capture (Rodríguez-Cabello and Sánchez, 2017). However, the study used much shorter soak times and slower haul speeds than would likely be encountered under normal commercial fishing conditions and therefore, mortality in these circumstances may be greater (ICES, 2024). Since 2021, Leafscale gulper shark has been a prohibited species in most of the Northeast Atlantic (ICES, 2024).