Slippery Beast

What is it about eels? Depending on who you ask, they are a pest, a fascination, a threat, a pot of gold. What they are not is predictable. Eels emerged some 200 million years ago, weathered mass extinctions and continental shifts, and were once among the world's most abundant freshwater fish. But since the 1970s their numbers have plummeted. Because eels?as unagi?are another thing: delicious.