Blackmouth Catshark aka Galeus melastomus

Blackmouth Catshark

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Common Names: Blackmouth catshark.

Scientific Binomial: Galeus melastomus.

Family: Scyliorhinidae.

Identification: An intricately patterned species. Reddish-brown above with a row of 15-18 rounded brown blotches circled in white along flank. Fins may have bluish dark tips and white trailing edges. Ventrum off white.
Pectoral fins large. Pelvic fins low but long. Anal fin extremely long - extending to caudal fin origin or beyond. Enlarged denticals present on upper margin of caudal fin.
Eyes large. Mouth cavity pigment dark - hence common name. Teeth tricuspid - lateral cusps much smaller than central cusp.

Blackmouth Catshark

Size: 90cm maximum (female). 61cm (male).

Habitat: Rocky, sandy or muddy substrates on outer continental shelf. Usually remains on bottom or close to it. Mostly found between 200-500m. Listed as occurring between 55-1000m but regularly encountered in certain Norwegian fiords between 25-40m even when no chum is used.

Distribution: The blackmouth Catsharks is present in the Northeast Atlantic Ocean and Mediterranean Sea. From the Faroe ISlands and Southern Norway southward to the Azores and Senegal.

Behavior: Often rests on the substrate.

Diet: Hunts for bottom dwelling invertebrates (shrimps, cephalopods, etc) and lanternfish.

Reproduction: Oviparous, laying up to 13 egg cases.

Conservation Status: The IUCN lists the Blackmouth Catshark as LEAST CONCERN. However, this species is taken as bycatch by demersal trawls and longlines throughout large areas of its geographic range. It is generally discarded, but is retained and utilised in some areas.

- Northeast Atlantic
Although a large portion of the population of G. melastomus avoided most of the commercial fishing pressure associated with the 1970s deepwater trawl fishery for Blue Ling (Molva dypterygia) in the northeast Atlantic at >600 m, it is concerning to note that mature individuals of this species are found at similar depths to the shallowest depth range of this fishery, and that commercial deepwater trawl vessels are now targeting these sharks. The targeting of mature individuals of this species may lead to similar detrimental impacts experienced by other deepwater species in this area (Crozier 2003).

Off the south coast of Portugal (Algarve), this species is captured in high quantities as bycatch of the bottom trawl fishery that targets the Norway Lobster (Nephrops norvegicus), Red Shrimp (Aristeus antennatus) and Deepwater Pink Shrimp (Parapenaeus longirostris), and by the near bottom longline fishery that targets European Hake (Merluccius merluccius), Conger Eels (Conger conger) and Wreck Fish (Polyprion americanus). In both fisheries, most captured specimens are discarded (Coelho et al. 2005). Most specimens are captured and returned to the sea alive, but usually with severe injuries (due to the long trawling periods or hooks) that are likely to impair their survival. However, declines in traditional target species during the last few years mean it is likely that fisherman are now landing larger quantities of alternative species, such as this catshark, so it may be increasingly retained and sold.

- Mediterranean
The species is caught as bycatch by trawl nets and bottom longlines on slope bottoms. The species appears to suffer greater fishing mortality in the Ionian, south Adriatic and Aegean Seas, compared to along the coasts of Morocco, Spain, France and around Crete. Length Frequency Distributions (LFD) show that along the coasts of Morocco, Spain, France and around Crete specimens were mostly larger than 30 cm (78% of the total), while only 23% of the specimens around the coasts of Corsica, Sicily and in the Ionian, South Adriatic and Aegean Seas were over 30 cm (Serena et al. 2005).

It seems that this species suffers relatively moderate effects from fishing pressure in the south Ligurian and northern Tyrrhenian sea, although it is an important bycatch of the Norway lobster Nephrops norvegicus fishery.

G. melastomus constitutes a significant portion of the bycatch of the Viareggio fleets fishing efforts, but most of the individuals are discarded due to the limited market demand and low commercial value. Only a fraction of the larger individuals (TL>40 cm) are landed at Viareggio (about 700 kg in 2002) (Abella and Serena 2005). Considering the depths at which G. melastomus is caught (250800 m) and the observed poor condition of the individuals immediately after their capture, it is likely that only a small fraction of the discarded individuals survive. However, it should be noted that the fishing grounds for the Viareggio fleet coincide only partially with the areas where G. melastomus is known to be abundant, and that higher densities of this species are found in deep waters off northern Corsica, where the fishing pressure is moderate. These areas could therefore act as a refuge for this species (Abella and Serena 2005).

In the Alboran Sea, where this species is very abundant, G. melastomus is the most important bycatch species in the recently developed bottom trawl fishery targeting the Deepwater Shrimp (Aristeus antennatus) (Torres et al. 2001).

The recently developed ban on bottom trawling below depths of 1,000 m in the Mediterranean Sea probably offers this species some refuge from fishing pressure.

Photographs: Namsen and Trondheim Fiords in Western Norway.

Blackmouth Catshark

Similar species: The only other catshark with similar markings and an overlapping range is the African Sawtail Catshark - Galeus polli. This species has large greyish blotches, less intricate markings overall and is shorter and relatively more robust. Its range overlaps with the blackmouth Catshark in Northwest Africa.

Reaction to divers: This species rests on the bottom for long periods of time. Easy to get close to after a slow, non-threatening approach.

Diving logistics: Although normally found in water too deep for recreational diving, in certain Norwegian fiords e.g. Namsen Fiord and Trondheim Fiord, run-off at the surface creates a layer of silty water that significantly lowers the light level in the water below it.

In these areas, blackmouth catsharks and other deepwater species, come much closer to the surface than elsewhere.
Blackmouth Catsharks can often be seen when exploring certain reefs within these fiords but they are even easier to see and approach when bait is introduced.
Big Fish Expeditions offers yearly Deep Shark Safaris in Norway. Usually in October.

References:

Serena, F., Mancusi, C., Ungaro, N., Hareide, N.R., Guallart, J.,Coelho, R. & Crozier, P. 2009. Galeus melastomus. The IUCN Red List of Threatened Species 2009: e.T161398A5414850. http://dx.doi.org/10.2305/IUCN.UK.2009-2.RLTS.T161398A5414850.en. Downloaded on 12 December 2018.

BLACKMOUTH CATSHARK