Six-gill Sawshark

About the Six-gill Sawshark

The Sixgill Sawshark, the only member of the genus Pilotrema, is a sawshark of the family Pristiophoridae.

Biology:

Presence of 6 pairs of gill slits highlights this genus among sharks; outside Hexanchiformes order, Pilotrema is the only shark with more than 5-gill slits. Unlike other saw sharks, the barbs on this shark’s rostrum continue onto the sides of the head. Its barbels are also closer to its mouth than in other species. Females reach a maximum size of over 136 cm /4 ft 5.5 inlong, and males reach a size over 112 cm/3 ft 8.1 in long. These sharks, like other saw sharks, are ovoviviparous, which are animals that develop inside eggs that hatch inside the mother’s body, leading to a live birth. They are thought to breed annually, giving birth to around five to seven pups per litter. They come to inshore pupping grounds to give birth. The pups are around 35 cm/1 ft 1.8 in at birth, and they later mature at around 83 cm/2 ft 8.7 in if they are male, and around 110 cm/3 ft 7.3 if they are female.

By using their sensitive barbels and electric sense, sixgill sawsharks are able to find their prey and then incapacitate them with their rostrum. Their known diet includes small fish, crustaceans, and squids.

Habitat:

Offshore benthic and epibenthic species on the warm-temperate and subtropical continental shelves and upper slopes of southern Africa and Madagascar at 37 m/121 ft to at least 500 m/1,640 ft, with apparent tropical submersion northeastwards along its range and onto the uppermost slopes. Bimodal distribution in South Africa Cape waters may be linked to restricted habitat.

Conservation:

Because of their deep habitat, sixgill sawsharks are not considered a threat to people.

The species is caught as bycatch of demersal trawlers and possibly in the South African hake longline fishery. It is inherently susceptible to capture in trawls as the saws are easily entangled in nets. In South Africa, trend analysis of research trawl surveys in fished areas over 26 years from 1991–2016 indicate a population increase over the past three generation lengths (33 years). Over the last decade, effort in South African fisheries has decreased with less than 1 t annually of Warren’s Sixgill Sawshark captured. It is a possible bycatch in fisheries off the coast of southern Mozambique and catches should be monitored. There is no evidence of population decline and Warren’s Sixgill Sawshark is not suspected to be close to reaching the population reduction threshold and it is assessed as Least Concern.

The utilization of Warren’s Sixgill Sawshark is unknown, but it may be retained for meat when captured. Warren’s Sixgill Sawshark was listed in South Africa as a Threatened or Protected Marine Species in 2017, however this only pertains to capture without permits and it can still be captured by commercial and recreational fishers licenced under the Marine Living Resources Act 1988 (DEA 2017). A number of marine protected areas (MPAs) occur across its range, including: Agulhas Bank Complex MPA, iSimangaliso MPA, and the uThukela MPA in South Africa, and Ponta do Ouro Partial MPA in southern Mozambique. Further research is needed on population size and trends, life history, and catch rates.

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Six-gill Sawshark Gallery