Blackmouth Catshark: Galeus melastomus

Family: Scyliorhinidae
Common name(s)

Blackmouth Catshark.

Identification

Slender body. Snout pointed. First dorsal origin approximately level with pelvic fin insertion. First and second dorsal fins of equal size, with a pointed apexes. Pectoral fins large. Anal fin very long; extending from level of first dorsal insertion to origin of caudal fin. Caudal fin has a distinct row of enlarged dermal denticles along upper margin. Dorsal coloration predominantly brown with a vivid pattern of large and small brown circles, edged in white. Circles form rows extending from head to tip of tail. Larger animals have more intricate patterns with a greater amount of circles within each row. Fins dark blueish-grey with vague pale circles and pale margins.

Size

Galeus melastomus is one of the largest sawtail catsharks. Maximum length 90cm (Compagno et al. 2005). This record is questionable since other researchers list vastly smaller maximum sizes of 62-67cm (Rey et al. 2002, Costa et al. 2005). Size at birth unknown.

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.

Conservation Status

LEAST CONCERN

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 fleet’s 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 (250–800 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.

Citations and References
Serena, F., Mancusi, C., Ungaro, N., Hareide, N.R., Guallart, J.,Coelho, R. & Crozier, P. 2009. Galeus melastomusThe IUCN Red List of Threatened Species 2009: e.T161398A5414850. https://dx.doi.org/10.2305/IUCN.UK.2009-2.RLTS.T161398A5414850.en. Downloaded on 13 October 2020.

Reproduction

An oviparous species, laying up to 13 egg cases. Egg production occurs year round. Hatching occurs mainly in spring and summer.

Diet

Hunts for bottom dwelling invertebrates (shrimps, cephalopods, etc) and small bony fishes including lanternfishes.

Behavior

Little is known about blackmouth catshark behavior. Forages over substrate in search of food, sometimes seen resting in areas where an abundance of food is available i.e. near fish and scallop farms.

Reaction to divers

Fairly easy to approach when resting on the sea floor. Will bolt if approached to quickly or aggressively.

Diving logistics

Rarely encountered south of Norway. 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 (such as velvetbelly lantern sharks), are found 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.

Similar species

Atlantic Sawtail Catshark Distinguished by less intricate markings including large blotches and saddles. Limited range from Spain to Northwest Africa, at depths between 330-790m.

African Sawtail Catshark Distinguished by blotchier flank markings and saddles. Range overlap from Morocco to Senegal. Found at depths between 159-720m.

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