Sharks and Skates of Scotland Report: Deep-water skate (Rajella bathyphila)

An extract from the Sharks and Skates of Scotland Report.

Deep-water skate - Rajella bathyphila (Holt and Byrne, 1908) 

Note: This species is rarely observed in deep-water scientific surveys and occasionally recorded in deep-water fisheries. As such, there is limited data available on population size and trends (Dulvy and Walls, 2015). For example, only 10 individuals were caught in total in Scottish deep-water surveys in the Northeast Atlantic between 1998-2013 (ICES, 2018b). May be difficult to distinguish from the Bigelow’s skate (Rajella bigelowi), and the two species may be sympatric. There is also identification confusion with Rajella fyllae (Dulvy and Walls, 2015). 

Population status

Scotland and Northeast Atlantic: Stable. This species is mainly known from sporadic records from local deepwater fisheries and is rarely encountered by deepwater research trawl surveys (Ebert and Stehmann 2013; Dulvy and Walls, 2015). 

Global: Increasing. An overall annual rate of increase of 8.7% is consistent with an estimated median increase of 835% over three generation lengths (40.5 years) for Newfoundland and Labrador Shelf survey of mature individuals over the period 1996–2018. Due to this index of abundance and the level of fisheries this skate is exposed across the rest of its range, the population is expected to be increasing (Dulvy et al., 2020).

Conservation listings

• IUCN Red List Global: Least Concern (assessment 20 June 2019)
• IUCN Red List Europe: Least Concern (assessment 17 October 2014)
• CITES: Not listed
• CMS: Not listed
• OSPAR: Not listed

Range and distribution 

Deep-water skate is found in the North Atlantic from the northeastern USA and Scotian shelf, Canada north to the Davis Strait, Greenland, Iceland and the Mid-Atlantic Ridge, Faroe Islands, and Rockall Trough (Gordon and Duncan, 1989; Ebert and Stehmann 2013, Dulvy and Walls, 2015; Last et al. 2016; Dulvy et al., 2020).  

Habitat 

Deep-water skate are found on deeper continental slopes and abyssal plains over both hard and soft substrate, at depths ranging from 600 – 2300 m, but mostly occur in water deeper than 1400 m with a temperature range of 2.5 – 4.0^oC (Stehmann and Bürkel 1984, Ebert and Stehmann 2013; Dulvy and Walls, 2015).  

Biology and Ecology

Relatively little is known about the biology of Deep-water skate. They reach a maximum size of 95 cm total length (TL); males mature at 65–75 cm TL and female size-at-maturity is unknown (Ebert and Stehmann 2013, Last et al. 2016). Reproduction is oviparous (Ebert and Stehmann 2013, Last et al. 2016). Females lay approximately 40 eggs per year, and the young hatch after several months at 12 cm TL (Ebert and Stehmann 2013, Last et al. 2016) (Dulvy and Walls, 2015; Dulvy et al., 2020). The length of time taken to hatch is likely to vary with water temperature; for example, slower embryonic development is expected in colder water.  

Human interactions

Historically, Deep-water skate were occasionally taken as bycatch in local deep-water trawl fisheries, for example, those that operate in the Rockall Trough. Today, bycatch and discards are unlikely due to the introduction of general measures to protect deep-water elasmobranchs (i.e. ban of certain net fisheries below 600 m, and trawls below 800 m) (ICES 2024).