Sharks and Skates of Scotland Report: Blackmouth catshark (Galeus melastomus)

Habitat 

Around the coast of the UK, Black mouth catsharks (G. Melastomus) have been recorded along continental shelves and slopes at depths of ~100 m – 1000 m (Ellis et al., 2005; Neat et al., 2015), however they have also been found in shallower waters (55 m) and as deep as 2000 m elsewhere (Abella et al., 2015., Clarke et al., 2016). The species occurs in relatively high numbers in the fjordic systems of west Scotland. Black mouth catshark were found to use the cold-water coral reef habitat to the East of Mingulay, in the Outer Hebrides, as a spawning ground. The abundance of Black mouth catshark was found to be six times higher next to the Mingulay Reef Complex compared to sites further away, and eggs were repeatedly found nested in live corals at a narrow depth range of 165 – 172 m (Henry et al., 2013). ‘Spawning sites’ in the Mingulay Reef were found to face N to ~ NW on the leeward side of prevailing SSW to NNE currents, which likely reduced the risk of eggs drifting away (Henry et al., 2013). This site now forms part of the East Mingulay Protected Area, where demersal trawling, dredging and seine netting are prohibited according to the Inshore Fishing (Prohibition of Fishing and Fishing Methods) (Scotland) Order 2015. 

Biology and Ecology

Black mouth catshark are a small species, with a maximum total length of 90 cm, and are relatively fast-growing and early-maturing (Neat et al., 2015). In the Rockall Trough, the size at first maturity was estimated to be 55.6 cm (TL) for males and 59.7 cm (TL) for females. Black mouth catsharks are estimated to live for up to 10 years (Moore et al., 2013; Neat et al., 2015). The sex ratio of males to females caught in the Rockall rough was 1:1 (Moore et al., 2013; Neat et al., 2015). Studies in the Mediterranean found that females can hold 1-12 egg capsules in their oviducts, with sizes varying from 38 × 14 mm to 55 × 20 mm (Metochis et al., 2018). As is typical for catsharks (family: Scyliorhinidae), the right ovary is functional while the left is vestigial; however, both uteri are functional (Metochis et al., 2018). Off the coast of Portugal, mating and egg deposition occur year-round, with two reproductive peaks in winter and summer (Costa et al., 2005). The results of several studies indicate that Black mouth catsharks in the Atlantic attain a larger total length and a larger size at first maturity than those caught in the Mediterranean. In addition, egg cases from female Atlantic Black mouth catsharks are typically larger than those from Mediterranean females. This may be due to differences in food availability between the Mediterranean and the Northeast Atlantic (Metochis et al., 2018). Black mouth catsharks are generalist predators that feed on decapod crustaceans, cephalopods, euphausiids and mesopelagic fish. Dietary studies indicate that as they mature, the diet shifts from predominantly cephalopods and euphausiids, to decapod crustaceans and finally to a more generalist diet (Fanelli et al., 2009, RodríguezGarcía et al., 2024). Additionally, population-genetic analysis suggests differences between Scottish Black mouth catsharks and those found in the Mediterranean Sea and in Atlantic waters off Portugal (Crescenzo et al., 2022). A northward shift in species distribution from the Celtic-Biscay shelf is suggested by data collected between 1997 and 2020, which may indicate a response to changes in ocean temperatures or alterations in population numbers (Le Luherne et al., 2024). 

Human interactions 

Black mouth catsharks are often caught as bycatch of demersal trawl, gillnet and longline fisheries over much of their range, and larger individuals may have been landed for human consumption (generally further south, although see prohibitions from 2025). Rates of discarding can be high, but variable, and there are no data for the survival rates of Black mouth catsharks caught in fisheries (ICES, 2024). In some areas, they may also have been landed by creel/pot fishers and used as bait, especially in whelk and brown crab fisheries (ICES, 2018). The species may be of importance to recreational fisheries in some areas, including off the west coast of Scotland (Henry et al., 2013). This species is currently assessed over two management units by ICES (i) Celtic Seas and west of Scotland (Subarea 6 and Divisions 7.a–c and 7.e–j), and (ii) Bay of Biscay and Atlantic Iberian waters (Subarea 8 and Division 9.a). Advice is provided by ICES every 2 years. The last assessments of catsharks were published in 2023, covering the years 2024 and 2025, and were based on the MSY (maximum sustainable yield) approach. In 2023, ICES advised that for ICES subareas 6 and 7 “catches in each of the years 2024 and 2025 should be decreased by no less than 30% compared to the average catches in 2020-2022” (ICES 2024).