Poachers' nets killing sharks off Texas coast

Sharks may be the scariest predators in the water, but they are no match for fishermen. Florida is ordering a ban on fishing for certain sharks, and it turns out they're disappearing all over the Gulf. CBS News correspondent Anna Werner went out to sea on the trail of the vanishing sharks of Texas.

Five miles east of South Padre Island, game warden James Dunks and his crew search a crime scene stretching over 3,000 square miles, looking for leads.

"We're looking for anything that's floating on the surface, whether it would be a Coke bottle, milk jug, any type of Styrofoam," he said.

A milk jug is a makeshift buoy for gill nets set by Mexican fishermen who come into U.S. waters illegally to catch red snapper and sharks. The nets they use are banned in Texas.

"Why are they so bad?" Werner asked Dunks.

"Nets indiscriminately catch anything," he said. "If a fish swims into a gill net, it's gonna die."

In September, Dunks found a gill net nearly three miles long, filled with dead sharks. "It was almost impossible to count," he said.

One net held 3,000 juvenile sharks -- an entire generation.

"I've never seen that much devastation in one piece of net," Dunks said.

It's the use of those nets that has decimated fish stocks in Mexican waters.

"We have caught some of these fishermen from south of the border in the past," said Dunks, "and we've asked them, 'How come you all keep coming across?' And they will tell you, 'There are no fish left in Mexico.'"

Now what should be Mexico's problem has become one for U.S. authorities -- and the fishing and tourist industries.

Boats that Mexican fishermen use are called pangas. They're light, and they're fast. So nimble, authorities have a hard time catching them.

Coast Guard Lt. Joshua Sagers oversees the crews who chase the poachers. "It's a game in which I would say the advantage is on their side," he said.

"Realistically, you can't catch them all," asked Werner.

"I would say as we're resourced now -- we don't get 100 percent."

On an average day, there are just four boats to patrol 3,000-square miles of ocean.

"Basically what it boils down to is they are trying to make money off of our resources," said Dunks. "And we're doing everything we can to stop them."

But when they do stop them, it's often just a brief interruption. Their boats are confiscated and they're sent back to Mexico. Then they come north again to fish once more.