The oceans of planet Earth might seem endless in their capacity to sustain life. Up next, a scientist talks about why this "blue frontier" might be disappearing -- on today''s Earth and Sky.
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Great White Shark

DB: This is Earth and Sky. Ransom Myers of Canada''s Dalhousie University is lead author of a recent study about the big predators of the ocean -- like marlins and great white sharks.
JB: His study shows that in the last 50 years, over 90% of this sort of fish has vanished. Meyers told us why these large fish might go the way of the dinosaurs.

Myers: I think the analogy that I think of is, that if you go back to the Pleistocene, when humans developed hunting techniques to hunt large animals, whenever humans arrived in a continent --North America, South America, Australia -- you had a tremendous loss of bio-diversity of the large animals... The same pattern is repeating now, I believe, but it''s just beginning as we exploit the ocean....

DB: Meyers said that by using the latest technology, fishermen can catch almost down to the last fish.

Myers: Remember, we''ve killed off woolly mammoths and mastodons using nothing more than sharpened stones attached to sticks. And the human mind''s the most powerful weapon ever devised [laughs], so we can certainly do the same thing in the sea, which means that we have to fish in a responsible and sustainable manner.

JB: For more -- come to earthsky.org. Thanks to the National Oceanic and Atmospheric Administration and to the National Fish and Wildlife Foundation. We''re Block and Byrd for Earth and Sky.