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>> reporter: on this day at sea, the lemons keep coming. three black tips, too. the blood and tissue from these guys will be tested for concentrations of hydrocarbons from oil. they can be contaminated even if they never swim through the oil. >> the fishing area has been closed in the gulf of mexico because they dont want people to catch and eat that fish. i dont know if sharks got the memo. >> reporter: because its a natural predator, a reduced shark population impacts the balance of nature. th...