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New BYU study reverses common notion about where to find bigger fish

Don't believe every fish story you hear. A new paper by a Brigham Young University professor reverses a view long held by some scientists about where to go to catch a big one.

"If you're looking for big fish of any species, you shouldn't go north," said Mark Belk, associate professor of integrative biology, whose new study about fish sizes in North America will appear in the December issue of "The American Naturalist."

In 1847 a scientist found that warm-blooded animals tend to be bigger the farther north they are. Then, a 1960 paper showed that fish grown at colder temperatures in a lab were larger at adulthood than those grown in warmer temperatures. Scientists have since believed that fish in the wild are bigger further north, where temperatures are cooler. Average temperatures decrease by one degree Fahrenheit for every 70 miles north you go.

"I kept reading studies that said fish were bigger in northern latitudes, but I was pretty sure it didn't apply to freshwater fish," said Belk who studies native fish of the Great Basin.. "We went to the library to see what that data said and then I was more confident. I knew we could prove that the rule didn't hold for fish."

Belk, an avid angler, collected information about sizes for 18 species of fish, including white bass, walleye and cutthroat trout. He and co-author Derek Houston, a Ph.D. candidate at the University of Nevada, Las Vegas, who began working on this project four years ago as an undergraduate, concluded that almost all species were actually smaller at northern latitudes.

On average, a largemouth bass grown in Florida was bigger than one grown in similar conditions in Ontario, Canada.

"We had to look at large samples in many locations for this pattern to emerge," Belk said. "Scientists have been citing old studies, taking for granted that the results of lab tests held true for what actually happens in nature. It doesn't matter whose study you cite if the pattern isn't right to begin with."

Belk and Houston compared fish sizes at ages one, three, and five and the species' maximum body sizes. Species were used only if data were available for at least 16 locations and spanned at least 350 miles-5 degrees latitude.

"If you ask fishermen where to go for a good day's fishing the answers will vary," Belk said. "If not over fished, the best place to catch larger fish may be in warmer climates."

Writer: Burke Olsen

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