Sharks and Skates of Scotland Report: Blue shark (Prionace glauca)

Habitat 

Blue sharks are an oceanic pelagic species found from the surface to depths of 1000 m (Rigby et al., 2019), although in Scotland they have been reported to 600 m (Baxter et al., 2011). They also occur in inshore waters where the continental shelf is narrow. They are highly migratory and move according to the location of their prey and their breeding cycle. There is little data on Blue shark in Scottish waters, but they are an oceanic species, regularly reported off the western coasts of the British Isles (Baxter et al., 2011) with occaisonal sightings in the North Sea.  

Biology and Ecology

Blue sharks have the highest known population growth rate potential of the pelagic sharks as they mature young and have large litters of pups. This large shark can reach a maximum of about 3.8 meters (TL), with the male maturing at 1.8-2.1m and females maturing at 1.8-2.2m (Rigby et al., 2019). Females in the Atlantic mature at around 5-6 years, with a generation length of 10 years and an age span of 15.5-16 years. Blue sharks give birth to live young (viviparous) and have a gestation period of 9-12 months (Rigby et al., 2019). They often produce 25-35 pups at a time, but litter size ranges from 4 to 135, and newborn pups measure 35-60 cm (TL). The species can reproduce every 1 to 2 years (Rigby et al., 2019). Juveniles tend to prefer areas with high primary production, where zooplankton and pelagic prey aggregate (Vandeperre et al., 2016). In the Southern Atlantic, reproduction is annual, and parturition occurs in cold, productive Southern waters (Mas et al., 2023). In general, Blue sharks are opportunistic predators feeding on fish and cephalopods, although a variety of other food has been found in their guts, including seabirds, elasmobranchs and cetaceans (possibly carrion) (Campana et al., 2016).  

Human interactions 

Blue sharks are thought to be the most heavily fished shark species in the world. They dominate the shark fin trade, and in 2014, nearly half of all shark fins imported into Hong Kong were from Blue sharks (Rigby et al., 2019). The shark meat itself is mostly discarded, but in some regions, it may be sold for human consumption (fresh, frozen or dried), including in southern Europe. Fisheries that target Blue sharks include commercial and small-scale pelagic longline, purse seine, and gillnet fisheries (Rigby et al., 2019). However, globally, the majority of catch comprises bycatch (discards) of the industrial pelagic fleets in offshore and high-seas waters (principally longline). Blue sharks can also be taken as bycatch by coastal longlines, gillnets, trammel nets, and sometimes trawls, especially in areas with narrow continental shelves (Rigby et al., 2019). Blue sharks are important to big-game recreational catch and release fisheries and are commonly caught by recreational anglers around the UK (Scotts, 2023). There are no measures fully regulating catches of Blue sharks in the North Atlantic. However, the International Commission for the Conservation of Atlantic Tunas (ICCAT) provided updated catch limit recommendations for the North Atlantic Blue shark stock in 2023 (entry into force June 2024), with the annual TAC set at 30,000t, and the UK restricted to 25t. The Convention on the Conservation of Migratory Species of Wild Animals (CMS) recommends taking precautionary, regionally coordinated action to ensure that Blue shark fisheries are sustainable throughout the shark’s migratory range (CMS, 2025). Measures that could help safeguard Blue shark populations include preventing overfishing via regional and national catch limits, improved reporting of catch and discard data, efforts to minimise bycatch mortality, and full implementation of all commitments agreed through international treaties (Rigby et al., 2019).