Great Sharks

Large sharks (>2meters) are some of the most stereotypical and recognizable predators on earth.  We will use the term Great Sharks to descibe the 11 sharks that have been studied over the past forty years along the North American Atlantic Coast.  Species include sandbar sharks, great white, blacktip, tiger, scalloped hammerheads, bull, dusky, smooth hammerhead, sand tiger, great hammerhead, shortfin mako (Myers 2007).  A long term survey was produced by UNC Institute of Marine Sciences showing the drastic decline in large shark populations along the Atlantic Coast, from Cape Cod, MA to Cape Canaveral, FL from 1972 to 1975 (Myers 2007).  Sharks have been overexploited as demand has increased for their fins and meat as well as them being tragic victims of by-catch in many fishing industries.

 The 2007 report compiled surveys and other studies to show how these populations decreases have lead to increased abundance of skates and rays rays, both members of the suborder Batoidea.  Since the mid 1970's, the cownose ray (Rhinoptera bonasus) has experience the largest population increases (Myers 2007).  This natural phenomenon, known as mesopredator release, indicates that when apex predators are removed, species who where once considered prey (even though they themselves are predators to other species) dramatically increase in population (Carpenter).

Mesopredator  release has shown to have far reaching and adverse effects on ecosystems, as seen with the decrease in sharks and the subsequent increase in cownose ray population and densities along the Atlantic Coast.   This has lead to the enhanced predation of the bay scallop (Argopecten irradians), a staple in the ray's diets, as well as certain clams and oysters (Myers 2007).  Scallop populations reached such a unprecedented low that in 2004, North Carolina had to close scallop fishery that had flourished for over a hundred years.  The fisheries reopened in 2008, after 4 years and millions of dollars of potential profits lost (Estes 2011).   The industry remains very fragile and export looks for innovative ways to increase scallop production therefore reviving local economies along the coast.

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