This week’s featured species is one of the most visually stunning shark species: the blue shark (Prionace glauca). With its brilliant blue skin, large eyes, sleek body and elongated pectoral fins, the blue shark is truly a sight to behold for any diver. The blue shark is the prime example of the fusiform shark body (Tricas, Deacon, Last, McCosker, Walker, Tayloer, 1997). The fusiform, or cigar-shaped, body features a body that has the greatest diameter approximately a third of the way back from the snout and tapers towards the tail. This form allows water to flow smoothly over the body and reduces turbulence along the skin (Tricas et al, 1997).
Blue sharks have incredible life histories. They are an oceanic species, spending their entire lives out in the open ocean. In the spring and summer months, large mature males are often found in the Western Atlantic where they mate with sub-adult females (Skomal, 2016). Blue shark mating can be incredibly vigorous and violent. Females have developed skin twice as thick as the males to protect themselves from the bite of the males; despite their thicker skin, females often present with deep scarring (Parker, 2008).
In early summer, females utilize the North American current and Gulf Stream to travel from the eastern coast of North America, across the Atlantic, to Europe (Parker, 2008). This trans-Atlantic journey can take the females a year to complete. During this time the females can store sperm inside their shell gland to fertilize their eggs over the next year (Skomal, 2016). Once along the European coast, the females will give birth to as many as 135 pups before returning to North American waters on the Canaries and North Equatorial currents (Parker, 2008). This transoceanic journey will take the sharks nearly 10,000 miles (16,000 km) to complete over several months to years. One blue shark was tagged off the coast of New York in August of 1990. It was recaptured off the Portugal in January of 2005 (Skomal, 2016). Two other sharks were tagged off the coast of New York, and with a few months were recaptured in Spain and Brazil (Angela, Angela & Recchi, 1997).
Spending their entire lives out in the open sea means blue sharks must be highly resourceful. Just as females have adapted to store sperm for long periods of time, so they do not waste a mating opportunity; blue sharks have also adapted some metabolic processes to reduce wasting energy between feedings. Blue sharks are ectothermic, meaning their body temperature is the same as the surrounding water (Angela, Angela, Recchi, 1997). Just as reptiles adjust their activities to their temperature, blue sharks adjust their level in the water column, and thus water temperature, to meet their activity needs. For example, after feeding, blue sharks often rise to the surface seeking warmer waters to assist in metabolic processes like digestion. Once digestion is complete, they descend back down into cooler waters in order to conserve energy (Carey, Scharold, & Kalmijn, 1990).
Over the last few decades, the global population of blue sharks has been on the decline, like many species of elasmobranchs, mostly due to over fishing (Frederico & Hassall, 1998). As a large species of shark, the blue shark has very few, if any, natural predators (Parker, 2008). However they are often caught on long lines set up to catch swordfish and tuna (Campana, Joyce,& Manning, 2009). As a highly migratory, transoceanic species, conservation efforts will require the international coordination on behave of the blue sharks (Skomal, 2016).
Monterey Bay Aquarium Research Institute (MBARI). (2014 August 14). Blue Shark [Video Clip]. Retrieved from https://www.youtube.com/
Length: Maximum of 13 feet (3.9 m)
Weight: 300-400 lbs (136-181 kg)
Depth: Surface to an excess of 1,800 feet (548 m)
Reproduction: Placental viviparity (also known as viviparous)
Gestation: 9 to 12 months
Litter Range: Huge variation! 4 to 135 pups
Home Range: Worldwide; found in warm tropical waters seasonally to temperate zones
Diet: Broad Range including schooling fishes, squid and invertebrates, small sharks, seabirds, carrion, marine mammals (including dead whales), and garbage
IUCN Status: Near Threatened
(Skomal, 2016; Parker, 2008; Stevens, 2009; Mojetta, 1997)
Thanks for checking out this week’s Featured Species! If you missed last week’s Featured Species, the goblin shark, be sure to check it out! Let me know what species you’d love to see featured next week by leaving me a comment. I’d love to know!
Remember you can make a difference for marine ecosystems by calling your Congress man or woman and tell them that you care about the quality of our waters! Sharks, rays, and other marine organisms cannot speak or be represented in Congress. They need your voice. Get involved and stand up for sharks. Until next time Finatics!
Featured Image Source
Conlin, M. (Photographer). (2011 April 11). Blue Shark (Prionace glauca). [Digital Image]. Retrieved from https://commons.wikimedia.org/wiki/File:Prionace_glauca_by_mark_conlin.JPG
Angela, P., Angela, A., & Recchi, A. L. (1998). Sharks!: Predators of the sea. Philadelphia, PA: Courage.
Campana, S. E., Joyce, W., & Manning, M. J. (2009). Bycatch and discard mortality in commercially caught blue sharks Prionace glauca assessed using archival satellite pop-up tags. Marine Ecology Progress Series, 387, 241-253.
Carey, F. G., Scharold, J. V., & Kalmijn, A. J. (1990). Movements of blue sharks (Prionace glauca) in depth and course. Marine Biology, 106(3), 329-342.
Frederico, L., & Hassall, G. (Eds.). (1998). Reader’s Digest Explores: Sharks (1st ed.). Reader’s Digest.
Mojetta, A. (1997). Sharks: History and biology of the lords of the sea. (E. McNulty, Ed.). San Diego: Thunder Bay Press.
Parker, S. (2008). The encyclopedia of sharks (2nd ed.). Buffalo, NY: Firefly Books Ltd.
Skomal, G. (2016). The Shark Handbook: The Essential Guide for Understanding the Sharks of the World. (2nd ed.). Kennebunkport, ME: Cider Mill Press.
Stevens, J. 2009. Prionace glauca. The IUCN Red List of Threatened Species 2009: e.T39381A10222811.
Tricas, T.C.; Deacon, K.; Last, P.; McCosker, J.E.; Walker, T.I.; Tayloer, L. (1997). The Nature Company Guides: Sharks and Rays. (L. Taylor, Ed.). Hong Kong: The Nature Company, Time Life Books.