Monday, March 14, 2016

Shark Migration Patterns

Sharks are apex predators in the marine ecosystem and they regulate the populations of the species below their food chain.  There are 465 known species of sharks. Sharks have skeleton that is made out of cartilage, which is a tissue that is lighter than bone. They have five to seven gills and multiple rows of teeth that continue to grow all the time. Little is known about the shark migration patterns Knowledge of the habitat and migration pattern of large sharks are important because they can assess the effectiveness of large predator Marine Protected Areas (MPAs), know the vulnerability to fisheries and environment, and have control over shark and human interactions.

In a recent study 18 adult bull sharks 195-283 cm in length were tagged and tracked from 10-22 months. It was found that 16 of the sharks showed temporally and spatially variable residency patterns combined with migration events. Ten sharks had a coastal migration with 8 of them returning to the study site.  During the migration the sharks moved at a rate of 2-59 km.d-1 and traveled distances between 450-3760 km. In spring and winter is when the sharks were found migrating in lower latitudes. There was found to be a significant negative correlation between residencies and mean monthly sea temperature at the study site. This showed that seasonal change is major factor in migration patterns and directions. Future research that could occur would to be to find out if reproductive and foraging activity could influence the migration patterns.

In another study one of the top three sharks; the tiger shark, migration patterns were studied.  There were 33 tiger sharks tagged and tracked long Australia and the Coral Sea. Satellite tags were used to study habitat use and movement among habitats across the Coral Sea. A few sharks showed one-year residency in Chesterfield and along the Great Barrier Reef. In coastal barrier reefs, tiger sharks were short lived and each one displayed a unique pattern of swimming. From 2009-20013 14 tiger sharks had wide ranging along the Coral Sea with eight shark moving back into “normal movement”. They studied concluded that the islands along chesterfield were an important habitat for the tiger sharks. There was no explanation about why there was wide ranging along the Coral Sea. There also needs to be future research on why the Marine Protected Areas (MPA) are popular for tiger sharks. The MPAs only provide brief protection to the sharks from other larger sharks. The amount of food present along the reefs could play a factor.

A graduate student, Tellman, studied the migration patterns of the blacktip shark and results were found to be like clockwork. Every winter in the Atlantic coast of Florida thousands of blacktip sharks are found. Tellman monitored the shark migration from a small airplane along the Palm Beach Coast for three winters. There was winter where she photographed 12,000 blacktip sharks during a single flight.  Each year it was found that the blacktips swim towards bays and estuaries in the Southeastern coast to mate and give birth. The juveniles will reach maturity in shallow nursery grounds away from the adults. The blacktips were found to swim in ocean temperatures from 22 to 24 degrees C. This has been slowly changing due to climate change. As the ocean heats up the warmer waters moves to higher latitudes causing the sharks to change their migration patterns.  This can cause some negative affects such as beach closures and more shark attacks. Last year the black tip migration lined up with spring break causing all the spring break travelers to be kicked off of the beach. Also the black tips were blamed for 20 percent of the unprovoked shark attacks in Florida according to the International Shark Attack File maintained by the Florida Museum of Natural History. Future research could be done to see if climate change is really having an effect on the migration patterns of the blacktips.

Daly, R., Smale, M. J., Cowley, P. D., & Froneman, P. W. (2014). Residency Patterns and Migration Dynamics of Adult Bull Sharks (Carcharhinus leucas) on the East Coast of Southern Africa. Plos ONE, 9(10), 1-11. doi:10.1371/journal.pone.0109357

Lipske, M. (2014). Shark-Swarming Season. National Wildlife (World Edition), 52(2), 1.

Werry, J. M., Planes, S., Berumen, M. L., Lee, K. A., Braun, C. D., & Clua, E. (2014). Reef-Fidelity and Migration of Tiger Sharks, Galeocerdo cuvier, across the Coral Sea. Plos ONE, 9(1), 1-18. doi:10.1371/journal.pone.0083249

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