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Annual Public Lectures Series > Ransom A. Myers
Scientists and Journalists:
Getting the Point Across
June 12-16, 2006
A World Without Sharks: Consequences of Global Loss of Ocean Preditors
Ransom A. Myers, Killam Chair of Ocean Studies, Dalhousie University
Summary of comments from June 13
The extinction of large mammals and flightless birds has been closely tied to the migration of humans, especially in North America and New Zealand. As humans, we have killed off most large land vertebrae, such as the giant sloth and mammoth, by hunting. This trend seems to now be repeating itself in the ocean. Ransom A. Myers, Killam Chair of Ocean Studies at Dalhousie University, addressed the results and consequences of overfishing as it pertains to ecological issues and the loss of large marine predators in his lecture on June 13, 2006, at the University of Rhode Island's Graduate School of Oceanography.
In the last five decades, there has been a 90 percent drop in the number of large marine fish predators around the continent of North America. Even predators such as the White Tip Shark, at one time thought to be the world's most common large vertebrate, have been seriously affected. The number of White Tip Sharks has decreased to one three-hundredth its former size off the southern US coast.
Native marine species in Nova Scotia, such as shad and halibut, once heavily populated the coast, but have now left completely. Walruses, Beluga whales, swordfish, and sharks, all animals that once were among the most populous in the area, are no longer present either.
Leatherback turtles have also suffered huge decreases in numbers as a result of overfishing in the last 50 years. Hammerhead shark abundance was reduced to less than one third it relative presence between the years 1995 and 1998. Additionally, all large shark populations have been significantly reduced across the globe, including sharks in the Mediterranean Sea.
The overfishing of the Newfoundland cod has been a very expensive project for Newfoundland, costing over $5 billion to counteract. However, the Newfoundland cod has not been added to the list of endangered species by the Canadian government.
Overfishing in the Gulf of Maine has had an immense impact on right whales, attributed mainly, by Myers, to the multitude of lobster traps in the area, which, he posited, are unnecessary. During the lobster-trapping season, the frequency of right whale sightings in the Gulf of Maine drops to almost zero, while the number in Nova Scotia decreases only slightly. In the 2003 season, lobster yields in Nova Scotia greatly outnumbered those in the Gulf of using far fewer traps.
Through this example, Myers indicated that an increased number of traps does not mean greater yields, and that fewer traps can help to lessen the impact of fishing on large marine predators.
With the vast reduction of large marine predators comes a steep increase in the abundance of middle-sized predators. Fishing, especially overfishing, poses a threat not only to desired catch, but also to other fish and seafloor habitats, all of which support marine ecosystems. Small fish and sea floor dwellers, such as cow-nose ray fish and soft shell clams, are starting to dwindle in number all along the North American east coast, a result of too many mid-sized predators. At the same time, small shark numbers have gone up dramatically.
According to Myers, if current trends in large predator reduction continue, giving the middle-sized predators the chance to expand, the survival or recovery of small fish and soft shell clams will be dangerously in question.
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December 4, 2007