by Erik Markusson

Created on: September 23, 2007   Last Updated: September 24, 2007

Sharks have skeletons made of cartilage instead of bone. Cartilaginous fish include sharks, skates, and rays. This group of fish also has another feature which makes them unique, an electroreceptive sense. Thus they can sense weak electrical currents through the water coming from living animals. However, this system is only effective at close range (3 ft.). Sharks and their relatives use this electroreceptive sense to help them in the final stages of feeding.

Many sharks are in extreme peril of becoming extinct. Researchers at Dalhousie University in Nova Scotia say since 1986 Atlantic shark populations have declined by over 50 percent. Similar declines are occurring around the world. Certain areas and species have experienced declines much more than that. For instance, since the 1950's oceanic whitetip sharks have declined by 99 percent in the Gulf of Mexico. In 2005 according to the World Conservation Union two dozen species were on the verge of extinction. Every year they add more and more shark species to the Red List of Threatened Species.
The primary reason for this decline is overharvesting. Sharks are sought after for the touted medicinal properties of their cartilage and liver oil. Another desirable product is shark skin which is used to make leather goods. They are also exploited for their fins to make shark fin soup, an increasingly widespread delicacy in Asia. Sharks also get caught up and die in nets meant to protect popular beaches from sharks. In addition to the commercial catch a significant number of sharks are also harvested unintentionally as part of the bycatch, the unwanted species caught amongst the intended fishing catch.
Between the annual catch of 100 million sharks and the resulting decline of their populations, it's evident that sharks need to be protected better. Perhaps the single biggest thing that needs to change is the size of commercial fishing fleets. At any one time there are 4 million vessels plying the oceans. This is too large for the ocean to sustain. Therefore, the commercial fleets should be reduced to more sustainable levels. The size of shark bycatch also needs to be reduced. There should also be a ban on long-line boats and restrictions on drift nets. Considering the perilous state that sharks are already in, the restrictions that exist should be made stricter. This should include lowering quotas and suspension of fishing in shark breeding grounds. In 2005, off the North Carolina coast the National Marine Fisheries

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