April Elasmobranch of the Month: The Blue Shark
Author Linda Weiss
The Blue shark is aptly named for its blue color. It is dark blue on top, transitioning to lighter blue on the sides before becoming white underneath. The blue shark has a slender and sleek build, with no interdorsal ridge. The top lobe of the caudal fin is larger than the lower lobe. Its pectoral fins are very long and slender and located in front of the dorsal fin. Its snout is long and conical shaped and its eyes are large. The teeth in the upper jaw overlap at the bases. They are triangle shaped, with curved tips and serrated edges. The teeth of the lower jaw are triangle shaped, though straight, more pointed and more finely serrated than the teeth of the upper jaw. Blue sharks can reach a length of 3.8 m (13 ft).
Habitat and Distribution
The blue shark is a highly migratory, pelagic species with a global range. It is found in tropical and temperate waters in all oceans. It inhabits waters at depths ranging from 0 – 350 m (1148 ft).
Blue Shark Distribution Credit: IUCN Red List
The diet of the blue shark is diverse. Its main prey are pelagic fish, such as hake, haddock, cod, mackerel, pollock, tuna and swordfish. It also consumes other fish, squid, birds, and seals. An opportunistic feeder, the blue will also feed on dead mammals, such as porpoises and whales.
For sharks, this species reaches sexual maturity quickly, around 5 years of age. Their reproduction is viviparous. Embryo are nourished by a yolk sac inside the female for a gestation period of 9-12 months. Live pups are born in an average-sized litter of 35, with litters typically ranging in size from 20-50 pups. 135 pups, is the largest litter size recorded. The newborns measure 40-51 cm (16-20 ft).
The IUCN Red List of Threatened Species currently lists the Blue shark as Near Threatened, with a decreasing population trend.
The biggest threat to the blue shark is the commercial fishing industry. An estimated 20 million are killed annually. The majority of those as bycatch on long-lines, in trawls and gill nets. They are also targeted for their large fins in the shark fin trade. The sport fishing industry also targets the blue shark for the fight and is generally released after it’s landed. They are the most prevalent species found in the world shark fin trade.
Blue Shark with a Hook Credit Ron Watkins
Fisheries and Ocean Canada
Marine Conservation Society
Shark Research Institute
The IUCN Red List of Threatened Species
Rigby, C.L., Barreto, R., Carlson, J., Fernando, D., Fordham, S., Francis, M.P., Herman, K., Jabado, R.W., Liu, K.M., Marshall, A., Pacoureau, N., Romanov, E., Sherley, R.B. & Winker, H. 2019. Prionace glauca. The IUCN Red List of Threatened Species 2019: e.T39381A2915850. https://dx.doi.org/10.2305/IUCN.UK.2019-3.RLTS.T39381A2915850.en. Downloaded on 11 April 2020.