Squalus mahia – Malagasy skinny spurdog

Squalus mahia – Malagasy skinny spurdog ©FAO/M. Lipperi

The Malagasy skinny spurdog is a small-sized mesopelagic shark, with a particularly slender body, elongated and thin dorsal-fin spines, a narrow caudal fin, and a mostly white lower caudal-fin lobe featuring a black blotch near its base.

The discovery

The holotype of this species was collected on 17 September 2009 by J. Groeneveld aboard the research vessel Dr. Fridtjof Nansen off the coast of northern Madagascar. The specimen was captured using a trawl net deployed at a depth of approximately 250 m. Along with additional specimens collected off Madagascar and South Africa, it was sent to the South African Institute for Aquatic Biodiversity (SAIAB), a globally-recognized centre for aquatic biodiversity research.

The specimens were later analysed by two Brazilian scientists, S.T. de F.L. Viana and M.R. de Carvalho, together with SAIAB researcher M.W. Lisher. Their detailed examination involved comparing these samples to other co-occurring Squalus species to clarify the distinct characteristics and confirm the identification of this new species. This collaborative effort provided the foundation for its formal description and enhanced understanding of the region’s shark biodiversity.

Features and characteristics

The Malagasy skinny spurdog is a short-snouted dogfish, with a slender body, narrow caudal fin with pointed tips, and dermal denticles with slender crowns. It can be distinguished from its regional relatives, including S. acanthias and S. acutipinnis, by its mostly white ventral caudal lobe with a black blotch near the origin of the lower caudal fin.

Its colouration is grey on the dorsal side and white on the underside, extending from the pelvic fins to the base of the tail. The first dorsal fin is dark grey with a whitish base and blackish tip, with a slight white edge at the rear. The second dorsal fin is grey with a lighter base and blackish tip, edged with white at the back. Both dorsal fins feature a black mark below their spines. The caudal fin is grey with broad white areas near the lower edges, a black fork, and distinct black markings along the vertebral column and on both the upper and lower lobes.

Given the depth range and fishing gear used for its capture, the authors inferred that this species is mesopelagic, typically found at depths between 202 m to 390 m, with occasional records at 500 m. Its distribution suggests an affinity for warmer waters, likely linked to the Mozambique and Agulhas currents.

Squalus species, also known as spiny dogfishes, are equipped with sharp dorsal spines that act as a defence mechanism against predators. Unlike other sharks, Squalus species are characterized by inconspicuous low, close-set blade-like teeth in both jaws perfectly suited to slicing up prey too large to be swallowed whole.

Despite their small size compared to other sharks, Squalus species are efficient hunters. They primarily feed on fish, squid and crustaceans, using their sharp teeth to grasp slippery prey in the dimly lit depths of the ocean.

Squalus species are an important resource in global fisheries. They are harvested for their meat, fins, liver oil and even skin, making them valuable in various industries. These sharks are caught using trawls, gillnets and longlines, either targeted in their preferred depth ranges or captured as bycatch.

As is the case for most sharks, Squalus species have an impressive lifespan, with some species living for up to 70 years. Due to their slow growth, late maturity and low reproductive rates, they are highly vulnerable to overfishing. Population declines in some areas have led to management measures such as quotas and seasonal closures to promote sustainable practices. As mid-level predators, maintaining healthy Squalus populations is essential for marine ecosystem balance.

Geographical distribution

This species is found in the western Indian Ocean, ranging from the Socotra Islands and northern Madagascar down to Algoa Bay in the Eastern Cape of South Africa.