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Genetic Evidence Confirms, "There's No Place Like Home"

Loren Miller conducting research

Loren Miller, conducting research on a North Shore stream this summer.

The Wizard of Oz's Dorothy and northern pike have something in common: a primal desire to return home. In a large lake, northern pike (Esox lucius) routinely disperse over 4 miles (7 km) and have been caught over 15.5 miles (26 km) from their hatching site. (Oh, Toto, we're not in Kansas anymore!)

Ichthyologists, those people who study fish, have known for over 15 years that each spring these voracious predators leave their territories to return to the spawning-sites they used in previous years.

Increasingly-sensitive genetic techniques coupled with traditional field research have recently raised this understanding a step further. Minnesota Sea Grant researcher Loren Miller, associate professor with the College of Natural Resources, and his colleagues found in their study of Lake Kabetogama in northern Minnesota that northern pike in large lakes usually spawn at the site of their birth. (There's no place like home.)

"The fact that these fish return to their natal grounds has implications for fisheries management," said Miller. "The notion that there might be different stocks and a potential for biological differences between them makes each spawning site more valuable.

"Beyond that, if reproductive success depends on returning to a particular spawning site, the loss of that site would damage the reproductive output of an entire spawning population." Northern pike spawn in vegetated habitat that is vulnerable to drainage and shoreline development.

Natal-site fidelity during spawning is well-known in salmon. Now, researchers are finding that other species of fish also prefer to spawn where they were born.

"This may be a behavioral feature of several fish species in relatively large waterbodies," said Miller. "Walleye in Lake Erie, like the pike we studied in Lake Kabetogama, run up streams to spawn and have a population structure that suggests they are returning to their natal sites."

Researchers are also finding that smallmouth bass and yellow perch in large lakes probably return to their natal sites to spawn. They are doing this using traditional techniques for estimating population size such as tagging the fish or clipping their fins, and with newer techniques such as genetic analyses and models based on egg mass counts at spawning sites.

Size matters. Lake Kabetogama in Voyageurs National Park, MN, is fairly large, with a surface area of 26,062 acres (10,425 ha), a maximum length of 15 miles (25.2 km) and a maximum width of 4 miles (7 km). The two tributaries where Miller and his colleagues tagged fish were 8.8 miles (14.8 km) apart. Although a few individuals from both tributaries dispersed into areas surrounding their non-natal spawning site, more than 95 percent spawned in the tributary where they hatched. In smaller lakes, researchers found that northern pike move freely among spawning areas separated by up to 1.8 miles (3 km).

The state fish of Minnesota is the walleye, but the northern pike is the most widespread large game fish. To thrive, pike need relatively clean water, adequate forage, and abundant shoreline marshes and wetlands for spawning. Many spawning areas, however, are being lost to drainage, dredging, and shoreline development. For northern pike, which can grow to over 40 inches (1 m), weigh 19 pounds (8.6 kg), and live for over a decade, individual spawning grounds, especially on large lakes, can create genetically-diverse populations. Sometimes, even for a fish, there's no place like home.

Miller's results were recently published in Transactions of the American Fisheries Society. To find out more, order a reprint of the article, Spawning-Site and Natal-Site Fidelity by Northern Pike in a Large Lake: Mark-Recapture and Genetic Evidence, from Sea Grant (JR 453 on the products order form).

By Sharon Moen
August 2001

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