The human impact on the size of fish

SAN FRANCISCO (KGO) -- Most fishermen are disappointed if they don't come back with the biggest fish possible. But research shows catching only the biggest and throwing the smaller ones back may be speeding up their evolution - and that could be a very bad thing.

When UC Santa Cruz researcher Chris Darimont tells a fish story -- it's not about the big one that got away -- it's about the smaller ones being left behind.

"So when you take a lot of a population and take preferentially the largest, this sets in motion evolutionary process and future generations get even smaller," said Darimont.

In other words, both sportsmen and commercial fishers try to catch the biggest fish and throw the rest back. That leaves behind smaller, less hearty specimen. And since smaller fish tend to have more trouble reproducing -- the few offspring they do have are also smaller.

"To people and to harvesting industries that depend on especially these fish stocks, it's an important issue because in essence many of these commercial fisheries are harvesting away their future bounties," said Darimont.

Darimont says the same is true of land animals that are hunted, and plants that are harvested. But, the news is not all bad.

"There are solutions, and that would be to more closely mimic natural predators and that would require two activities: one taking far fewer individuals in a population each year and foregoing our taste for the largest, our preference for the largest," said Darimont.

But, making a change like that would mean a major cultural shift among people who hunt and fish professionally, as well as those who do it for sport.

"Culturally, if you think of fishing derbies or boone and crocket trophy hunting clubs, it's so engrained in our culture to preferentially target the largest. So that's a huge barrier," said Darimont.

Darimont has received angry e-mails from sportsmen and women who feel that he's attacking hunting and fishing. He says that's not true, he's just advocating changes in the way we do it so that the impact on wildlife is not as harmful.

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