Hook, line ... sinking the fish population?

Yet fish clearly benefit from pain medication, said aquatic veterinarian Scott Weber, a UC Davis professor who has operated on fish tumors, cataracts and other disorders with and without analgesia.

The fish that got pain medication returned to feeding and normal behavior much sooner than those that didn't, Weber said.

In the wild, it's incredibly difficult to design experiments that can fully assess the impacts of being caught and released, say those who spend their careers studying fisheries.

We have really good data on only five species – largemouth bass, walleye, striped bass, Atlantic salmon and rainbow trout, according to a 2005 study by Suski and co-author Steven Cooke.

That's out of an estimated 28,000 species of fish worldwide.

Mortality after release can range wildly, from zero to 89 percent, according to the 2005 study.

In California, about 95 percent of freshwater trout survive on release, with warm water fish such as catfish and bass doing better and anadromous fish such as salmon – which migrate from the sea to breed in fresh water – doing worse, said Dave Lentz, a senior fishery biologist with the state Department of Fish and Game.

"Catch and release has been successfully used for many decades," Lentz said, keeping fisheries far more robust than if all those fish had been taken home for food. In 2006, California issued more than 2 million recreational fishing licenses, and studies have estimated that recreational fishing pumps more than $5 billion into the economy.

Over the years, anglers have learned how to reduce death rates, choosing hooks, lures and other gear that put less stress on fish, and being especially careful when waters warm up and make fish more vulnerable.

"Fishers are keenly aware of these things," said Chris Lowe, a marine biology professor at Long Beach State University. "They go to the library, they go online, they do their homework. They tell me, 'I'm really worried about fish populations.' "

Al Kroeger, a Sacramentan who spent Saturday taking a friend's son on his first fishing trip, said he's constantly on the lookout for the best strategies to boost fish survival.

"I enjoy it so much, I want to pass it on to future generations," Kroeger said.

Many researchers say that passion among anglers is why more information about the effects of catch and release is especially important.

Among the cautionary tales is the one that Illinois scientist Philipp tells about largemouth and smallmouth bass. In both species, males make a nest and tend the fertilized eggs and young, hatched fry for several weeks. If the male is pulled from the water, predators can destroy half the offspring in five minutes and 90 percent in just 10.

A bass caught and released while it is caring for young often cannot return to its nest in time or abandons the few offspring left. That means it is removed from the gene pool for that breeding season. The bass fathers whose fry survive tend to be smaller, more docile fish that are less likely to strike at an angler's hook, Philipp has found in comparative studies of fished and less-fished lakes.

"We are putting selective pressure on every bass fishery around and selecting for the least aggressive fish," he said. "It probably means they're not as good defenders of their babies … which can't be good for the population."

Most other fish are not as well studied, so we don't know which ones might lose their ability to spawn or produce less viable eggs because they've been caught and released, he said.

"Any fishing during the reproductive period of a fish is probably a bad idea," Philipp said.

About the writer:

• Call The Bee's Carrie Peyton Dahlberg, (916) 321-1086.