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Basking Sharks Face Low Genetic
Diversity Worldwide
August 04, 2006
Scientists studying mitochondrial DNA of basking
sharks, found in various oceans worldwide, have found very
little difference in their genetic makeup, according to a
paper published in the current online edition of Biology
Letters.
Measuring up to 33 feet long, the basking
shark (Cetorhinus maximus) is the second largest fish species
in the world, second only to the whale shark in size. Though
its size may conjure other images, the basking shark often
swims slowly from side to side near the surface of the world’s
oceans, filtering and eating small fish and plankton through
its large mouth.
This surface swimming behavior makes them
highly susceptible to harpoon fisheries. The species matures
slowly, has long gestation periods, and gives birth to few
offspring, which at more than five feet long are the largest
shark pups. They have been exploited in some fisheries for
meat, fins, liver oil, and cartilage.
Analyzing
samples from basking sharks found in the eastern and western
North Atlantic, Mediterranean Sea, Indian Ocean, and western
Pacific, a team of scientists from the United Kingdom, United
States, and New Zealand found surprisingly low genetic
diversity (? = 0.0013) across the globe and no significant
genetic differentiation between ocean basins.
“Such
low genetic diversity suggests the species has gone through
some type of population bottleneck event, and may indicate
reduced evolutionary potential to respond to environmental
changes. It is important that conservation and management
efforts take into account this low genetic diversity and
prevent its further erosion,” says Mahmood Shivji, Ph.D.,
co-author of the paper and director of the Guy Harvey Research
Institute at Nova Southeastern University in Florida, whose
work is partially funded by the Pew Institute for Ocean
Science.
Shivji and his colleagues conclude that while
some other shark species have low genetic diversity, none are
as low as the basking shark, whose effective genetic
population size is estimated to be roughly around 8,200 -
surprisingly low for a globally distributed species.
“This study confirms the vulnerability of the
little-studied but very important basking shark,” says Ellen
Pikitch, Ph.D., executive director of the University of
Miami’s Pew Institute for Ocean Science. “Maintaining the
genetic diversity of sharks is important to sustaining healthy
ocean ecosystems.”
The Guy Harvey Research Institute
(GHRI) is a scientific research organization based in Ft.
Lauderdale, Florida, at the Oceanographic Center of Nova
Southeastern University. GHRI was established in 1999 as a
collaboration between the renowned marine artist Dr. Guy
Harvey and NSU’s Oceanographic Center to provide scientific
information necessary to understand and save the world’s fish
resources and biodiversity from drastic, ongoing declines. For
more information, visit www.nova.edu/ocean/ghri.
The
mission of the Pew Institute for Ocean Science is to advance
ocean conservation through science. Established in by a
generous multi-year grant from the Pew Charitable Trusts; the
Pew Institute for Ocean Science is a major program of the
University of Miami’s Rosenstiel School of Marine and
Atmospheric Science For more information, visit
www.pewoceanscience.org.
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