Today we are going to discuss one of the many species of pelagic shark. First you may ask, what does pelagic mean? Simply put, pelagic just means that the organism in question lives in open water, not too close to shore. But the ocean is a big and varied habitat, so scientists decided to distinguish between two different categories of pelagic fish. There are coastal pelagic fish which tend to live in sunlit waters above the area surrounding large landmasses where the sea is shallow compared to the open ocean – an area known as the continental shelf. Then there are oceanic pelagic fish which prefer to live in waters below the continental shelf. Some species can inhabit both the oceanic and coastal pelagic zones because of the changing stages of their life cycles. Today’s Featured Creature, the Blue Shark, Prionace glauca, is typically oceanic pelagic and can be found at the surface to about 1150 feet below temperate and cooler tropical waters.
The Blue Shark is recognizable by its slender body and long pointed pectoral fin. The snout is also long and conical. As highly observant and sharp witted scientists, you readers have probably guessed the Blue Shark is named for the dark blue coloration on the upper part of the shark. However, this shark isn’t blue all over. The underside is white, which may bring back to your mind an adaptation we’ve discussed in a previous post known as counter shading. (Give yourself a high-five if you remembered counter shading!
A counter shaded coloration pattern helps the Blue Shark blend in the water as they hunt. Their prey includes pelagic octopus, cuttlefish, squid, other invertebrates and bony fish. Even though this species usually hunts for food, these sharks are often opportunistic. Opportunistic feeders will eat whatever they find that can fit in their mouth. They have been witness feeding on dead marine mammals and plucking fish from gill nets. Gill nets hang vertically in the water so that fish get trapped in it by their gills. This is one of the major issues that threatens Blue Shark populations.
Some of the causes for decline in Blue Shark populations are bycatch, recreational fishing, and commercial fishing. There currently exist regulations on the amount of shark meat that can be caught on commercial longlines on the east coast of the United States. Blue shark meat does not keep very long, and so to circumnavigate the regulations, unscrupulous fishermen will cut the fins off and throw the shark back. Thankfully, citizens have rallied, especially in California, and have taken great steps to help further protect sharks like the Blue Shark by outlawing finning and Shark Fin Soup and promoting sustainable seafood awareness. Talk to your family about ways you can get involved locally with ocean and shark protection projects!
Join us next week as we look at a shark with a highly unique shape.
Edited by KC O’Shea
Photography: Doug Perrine and AndyMurch