Abundant deep-water catshark with a black mouth and a crest of enlarged denticles
The Blackmouth catshark (Galeus melastomus) is a species of catshark belonging to the family Scyliorhinidae. They are common in the northeastern Atlantic Ocean from Iceland to Senegal and the Mediterranean Sea and down to the Azores. It is typically found over the continental slope at depths of 66–12,630 feet, on or near muddy bottoms. It is characterized by the black interior of its mouth, and a marbled pattern of pale-edged brownish saddles or blotches along its back and tail. There is also a prominent saw-toothed crest of enlarged dermal denticles along the upper edge of its caudal fin.
Family: Scyliorhinidae – Catsharks
Common Name– Ground Sharks
Common Name– Catsharks
Status: IUCN Red List LEAST CONCERN
Average Size and Length: Each egg case measures 6×3 cm, however the size of an egg case varies by location, so some may be smaller. Mature males have been recorded at between 34-42 cm/1.1-1.4 feet. Mature females have been recorded at between 39-45 cm/1.3-1.5 feet. The longest recorded is 90 cm/3 feet (this may be a misidentified species). Females do grow typically larger than males.
Average Weight: The maximum weight on record is 3.1 pounds.
Current Rare Mythical Sightings: Constantine Samuel Rafinesque briefly described the Blackmouth catshark in his 1810 Caratteri di alcuni nuovi generi e nuove specie di animali e piante della Sicilia: con varie osservazioni sopra i medesimi, wherein he referenced the distinctive black interior of its mouth (from which the specific epithet melastomus is derived). No type specimen was designated.
The oldest documented Blackmouth catshark fossils come from the northern Apennines and date to the Lower Pliocene (5.3–3.6 Ma).
Teeth and Jaw: The mouth cavity and lining are blackish. The mouth forms a short, wide arch, and has moderately long furrows around the corners. The upper and lower jaws contain around 69 and 79 tooth rows. Each tooth is small, with a narrow central cusp flanked by one or two smaller cusplets on either side.
Head: They have a long, pointed snout comprising roughly 6–9% of the total length. The anterior rim of each nostril bears a large triangular flap, which divides the nostril into incurrent and excurrent openings. The eyes are large, and are horizontally oval and equipped with nictitating membranes. Beneath each eye is a subtle ridge, and behind is a small spiracle.
Denticles: There is a distinct crest of enlarged dermal denticles along the upper margin of the tail. The skin is very thick and covered by well-calcified dermal denticles.
Tail: The precaudal tail or caudal peduncle is laterally compressed, with the end of the anal fin very close to the caudal fin. The tail is elongated. The caudal fin comprises around a quarter of the total length; the upper lobe is low with a ventral notch near the tip, while the lower lobe is indistinct.
Demographic, Distribution, Habitat, Environment and Range: The Blackmouth catshark can be found in the northeastern and northwestern Atlantic and Mediterranean Sea from southwestern Iceland and Trondheim, Faeroes, the British Isles, and Norway, south to Senegal and the Azores (64°N – 14°N, 19°W – 36°E). They are found on the continental shelves and upper slopes on the bottom in muddy environments. It is possible that the youngest sharks generally inhabit shallower water than the older juveniles and adults, but many studies differ on this theory.
Considered demersal, they can be found at depths of 490–4,590 feet. However, it has been documented from water as shallow as 66–82 feet in Norway, and as deep as 7,550–12,630 feet in the eastern Mediterranean. The depths at which it is most common vary between regions, for example 980–1,640 feet in the Bay of Biscay, 1,300–2,600 feet off Portugal, 1,600–2,600 feet in the Strait of Sicily, 3,300–4,600 feet in the Catalan Sea, and 4,920–6,000 feet in the eastern Mediterranean. Water temperature does not appear to be an important factor. (Ragonese, S.; G. Nardone; D. Ottonello; S. Gancitano; G.B. Giusto & G. Sinacori (2009). “Distribution and biology of the Blackmouth catshark Galeus melastomus in the Strait of Sicily (Central Mediterranean Sea)“. Mediterranean Marine Science. 10 (1): 55–72) (Olaso, I.; F. Velasco; F. Sánchez; A. Serrano; C. Rodríguez-Cabello & O. Cendrero (2005). “Trophic relations of lesser-spotted catshark (Scyliorhinus canicula) and blackmouth catshark (Galeus melastomus) in the Cantabrian Sea”. Journal of Northwest Atlantic Fishery Science. 35: 481–494.
Diet: They mainly feed on a wide variety of prey that includes bottom invertebrates like shrimp, cephalopods, and also fish like lanternfish, bristlemouths, dragonfishes, and moras. The most significant prey species generally reflect what is most available in the environment, so the availability of prey may differ by location; they have adapted to be quite flexible and opportunistic. Adults favor relatively large fish prey and have been known to take other sharks and rays and smaller members of the same species.
The stomachs of some Blackmouth catsharks have found to contain pieces of animals too large for a single shark to overwhelm, suggesting that it may sometimes attack in groups. Scavenging has been infrequently documented, including of human refuse.
Known predators of the Blackmouth catshark include the Kitefin shark (Dalatias licha) and the European Flying squid (Todarodes sagittatus).
Aesthetic Identification: The Blackmouth catshark has a pattern of 15-18 dark saddles, blotches and circular spots on the back and the tail. There are white edges to the fins. They have a long anal fin reaching or extending past the lower caudal origin. The ventral side is whiteish. They are slender, and slim-bodied. There are five pairs of gill slits, with the fifth pair over the pectoral fin bases. The two dorsal fins are roughly equal in size and placed far back on the body: the first originates behind the midpoint of the pelvic fin bases and the second behind the midpoint of the anal fin base. The pectoral fins are large, while the pelvic fins are small and low, with angular margins. The anal fin is much larger than either dorsal fin; its base measures 13–18% of the total length and greatly exceeds the distance between the pelvic and anal fins, or between the dorsal fins.
Biology and Reproduction: They are oviparous having up to 13 egg cases per female; however, 1–4 per oviduct is typical. The number of eggs laid annually per female has been estimated at between 60 and 100, increasing with female size. Only the right ovary is functional in mature females.
Mating and egg-laying happens year-round. Reproductive activity is highest in winter and summer, though not all studies have found such a seasonal pattern. The eggs are deposited on muddy substrates in relatively shallow water.
Each egg case is vase-shaped and has a slight flange along the lateral margins; the anterior end is squared off, with a pair of stubby, coiled horns at the corners, while the posterior end is rounded. The surface of the case is somewhat translucent, smooth, and glossy. It is golden brown in color when first laid, and becomes dark brown in sea water.
Maturation size varies between geographical regions, and is generally larger in the Atlantic than in the Mediterranean.
A 2005 phylogenetic analysis that included five Galeus species, based on mitochondrial and nuclear DNA, found that G. melastomus forms a clade with G. murinus, apart from the clade of G. eastmani, G. gracilis, and G. sauteri. (Iglesias, S.P.; M.H. du Buit & K. Nakaya (2002). “Egg capsules of the deep-sea catsharks from the eastern North Atlantic, with first descriptions of the capsule of Galeus murinus and Apristurus aphyodes (Chondrichthyes: Scyliorhinidae)“.
Parasites that have been documented from this species include the tapeworm Ditrachybothridium macrocephalum and the protist Eimeria palavensis.
Behavioral Traits, Sensing and Intelligence: Its visual (they have very large eyes) and electroreceptive systems are adept at tracking moving, bioluminescent prey. It is nomadic in nature and may be found alone or in groups.
When foraging, the Blackmouth catshark swings its head from side to side to employ its senses more effectively. It likely relies mainly on vision and electroreception to find food, and less on smell. As in most sharks, its visual acuity is greatest along the median horizontal plane. The lens and cone cells of its eyes are large, allowing smaller or farther objects to be discerned from the background. The rod cells of its eyes are most sensitive to the wavelengths emitted by bioluminescence, which is exhibited by most of the organisms it hunts. For electroreception, the Blackmouth catshark has a high number of ampullae of Lorenzini that are evenly arranged, which enhances spatial resolution and is best suited for localizing fast-moving prey. (Fanelli, E.; J. Rey; P. Torres & L. Gil de Sola (2009). “Feeding habits of blackmouth catshark Galeus melastomus Rafinesque, 1810 and velvet belly lantern shark Etmopterus spinax (Linnaeus, 1758) in the western Mediterranean“. Journal of Applied Ichthyology. 25 (S1): 83–93.) (Bozzanao, A.; R. Murgia; S. Vallerga; J. Hirano & S. Archer (2001). “The photoreceptor system in the retinae of two dogfishes, Scyliorhinus canicula and Galeus melastomus: possible relationship with depth distribution and predatory lifestyle“. Journal of Fish Biology. 59 (5): 1258–1278.).
Speed: They are more than likely slow swimming, yet active. It often cruises just above the sea floor, possibly taking advantage of the ground effect to save energy. It has also been seen resting motionless on the bottom.
Blackmouth Catshark Future and Conservation: They are currently of least concern. They are common among their range. They are taken as bycatch, but are of very low commercial value. Most are deposited back.
Some fisheries, such as those off Portugal and Italy, hold and utilize a small subset of the largest individuals for human consumption fresh or dried and salted, and for leather. The fishing fleet of Viareggio, Tuscany reported landing 1,500 pounds in 2005. In the northeastern Atlantic, this shark is being increasingly targeted by fishers following the decline of other deep-water sharks.
According to the IUCN, off Corsica, Sicily, and southern Portugal, and in the Ionian, southern Adriatic, and Aegean Seas, most of the Blackmouth catsharks captured are immature, suggesting there has been a negative impact of fishing pressure, however they remain plentiful.
Blackmouth Catshark Recorded Attacks on Humans: Not a threat to humans.