A large, slender requiem shark. Snout long. First dorsal low, with a rounded apex. First dorsal base approximately half way between pectoral fin and anal fin. Pectoral fins long and thin. Dorsal coloration shades of blue and grey; darker blue on top, brighter blue with metallic hues on the flanks. Ventrum white.
Maximum length 383cm. Size at birth 35-44cm.
Sub-tropical and temperate seas. The blue shark is an oceanic species that is rarely found inshore. Surface to 1000m. Generally found deeper at warmer latitudes.
Blue sharks are present across all temperate and subtropical oceans.
The blue shark has the highest known population growth rates among pelagic sharks; it matures young and has large litters. It is caught globally as target and bycatch in commercial and small-scale pelagic longline, purse seine, and gillnet fisheries, although most of the take is bycatch of industrial pelagic fleets in offshore and high-seas waters. Generally, Blue Sharks are retained for the fins, although the demand for meat is likely increasing. The steepest population declines have occurred in the North and South Atlantic, with lesser declines in the Indian Ocean, and increases in the Pacific. The weighted global population trend estimated a median decline of 7.3%, with the highest probability of <20% reduction over three generation lengths (30–31.5 years). However, due to uncertainty in some of the regional estimated trends, inferred steep historic declines in the Mediterranean Sea, high levels of unregulated exploitation, and high levels of international trade in meat and fins, experts estimated a global population reduction of 20–29% over three generation and the Blue Shark is assessed as Near Threatened (nearly meeting Vulnerable A2bd).
Citations and References
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 10 October 2020.
A viviparous species with yolk-sac placenta. The blue shark is one of the most prolific sharks with up to 135 pups per litter. 50-80 pups is not uncommon. Gestation is approximately 12 months.
Blue sharks are opportunistic feeders that will predate on whatever is readily available. Diet usually consists of squid and schooling bony fishes such as anchovies, sardines, and herring. Will also consume crustaceans, and small sharks.
Blue sharks are highly migratory ocean wanderers. Tagging studies have recorded them making trans-Atlantic crossings. Due to their oceanic nature, not much is known about their seasonal behavior other than movements towards cooler latitudes when ocean temperatures climb. Blue sharks are known to segregate by gender and size.
Reaction to divers
Inquisitive but not normally aggressive. In baited situations, blue sharks will remain next to divers for many hours even after the bait has been exhausted.
In the Eastern Pacific there are baited snorkeling trips that leave from Cabo San Lucas in Baja. The water there is usually extremely clear. The appearance of blue sharks is seasonally dependent, with the greatest number of blue sharks present in February and March. Day trips generally attract multiple blue sharks and shortfin mako sharks. Towards late March, blue shark numbers decrease but there is a greater opportunity to see smooth hammerheads. Big Fish Expeditions runs trips in early March when there is an opportunity to see all three species at once.
In San Diego, there are a couple of operators running blue and mako trips. Makos are a bit hit and miss but the blue shark activity is fairly consistent.
Off Rhode Island and Massachusetts in the northwest Atlantic, there are well established operators offering blue shark and mako shark trips over the summer months when the gulf stream moves closer to shore.
Off Pico Island in the Azores, there is a popular blue shark snorkel/dive which consistently attracts a small number of sharks over the summer. The operators also run trips to Princess Alice Bank which is the best spot to see large Chilean Devilrays.
During the summer months, there are a couple of operators in the UK offering blue shark dives. On rare occasions, porbeagle sharks have been known to make an appearance.
Off of the Western Cape in South Africa, there is an excellent blue and mako shark dive that attracts more blues than I have seen anywhere else in the world. One year I estimate we had more than 100 blue sharks in attendance. To reach the right temperatures and find the best water clarity, the boat has to go about 2hrs away from shore into the South Atlantic. Not surprisingly, this is a weather dependent dive, but one that should not be missed when conditions permit.
Shortfin Mako Shark Makos have a very similar coloration and they are often seen in the same areas as blue sharks. However, they are easily distinguished by their conical snout, exposed rows of curved teeth, and lunate caudal fin.
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