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IMPRINT, the Bell Museum's quarterly magazine for members, offers stories of scientific adventure and discovery, insight into today's rapid environmental changes, updates on museum programs and exhibits, and fun activities for kids. IMPRINT is published quarterly and is available as a benefit of Bell Museum membership.

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Minnesota's wild turtles are a hot commodity, sold by the thousands as pets or for food. But can they be harvested sustainably? Bell Museum graduate student Tony Gamble is trying to find out.

The Turtle Trap

by Jennifer Amie

Last June, Bell Museum graduate student Tony Gamble launched a small boat onto a central Minnesota lake. It was the first of many expeditions he will undertake through September 2002. Steering among the reeds and lily pads, Gamble set out a series of floating traps that offer an inviting perch for basking painted turtles, which crawl up on the traps to sun themselves. When they dive off the trap, the unsuspecting turtles are caught in an underwater net.


Snapper Turtle

The same type of trap is used by commercial trappers, who harvest, on average, nearly 32,000 wild painted turtles in Minnesota each year. Snapping turtles are also trapped at an average rate of 3,400 per year. Gamble is trying to determine the effects of this activity on the state's turtle populations.

"Research with snapping turtles in Michigan and Canada shows that even small harvests can have devastating effects," says Gamble. One study (Congdon et al, 1994) found that harvesting just 10 percent of a population per year could result in a 50 percent reduction in adult snapping turtles within 15 years.

Over the course of the season, Gamble will set traps on two dozen Minnesota lakes, catching, counting, marking, measuring, and releasing turtles as part of a study sponsored by the Minnesota Department of Natural Resources.

Gamble will compare the relative abundance of turtles in lakes that have been commercially harvested to the relative abundance of turtles in lakes that have not been harvested. He is also attempting to discover whether or not older turtles are depleted from lakes that have been harvested.

All turtle species live a long time, reproducing over many years. In natural populations, mortality of young turtles is very high. However, once surviving turtles outgrow the early, vulnerable egg and hatchling stages, adult mortality is very low. Turtle harvesting specifically increases adult mortality; the question is whether this increase is sufficient to put the population at risk.

The survival of older juveniles, sub-adults, and adults is crucial to maintaining a healthy population, says turtle expert Jeffrey Lang, a professor of biology at the University of North Dakota. "The turtle's long lifespan has important implications for turtle conservation," he says.

Ironically, the turtle's evolutionary strategy makes it especially vulnerable to human exploitation. "Any harvest of larger, older individuals can easily jeopardize long-term survival if adult losses outpace the recruitment of juveniles," says Lang.

Depletion of larger, older individuals may be greater among snapping turtles, which are harvested for food, than among painted turtles, which are harvested for the pet trade where a smaller size is preferred.

Trapping, in fact, is but one of many challenges turtles face. "With the increase of urban sprawl, [humans] moving onto lakeshore property, and wetlands being drained, we've seen a decline in habitat for reptiles and amphibians," says Roy Johannes, a commercial fisheries program consultant with the Minnesota Department of Natural Resources (DNR).

Although trapping may be only one factor affecting the health of Minnesota turtles, it has become a central focus in the debate over their protection. As the DNR has moved to enforce existing regulations, the debate over commercial trapping has been played out in the courtroom, in the legislature, and among industry and conservation groups.

At the heart of the debate is the issue of sustainability; on this point, all parties agree. Rex Campbell, a commercial trapper from Grey Eagle, Minn. who has harvested turtles for 25 years, says, "The last thing I want to see is the end of the resource we've all depended on for a long time. I'm not against regulating the industry, but we want to go out and harvest and still make a living at it." Johannes, of the DNR, notes that the hard part is discovering what level of trapping is sustainable. "Given the nature of reptiles and all the things that are stacked up against them, you need to take logical steps to ensure that they'll survive for all the citizens of the state," he says. "If it happens that commercial exploitation is affecting turtle populations, then we'll have to deal with it. But we have to take some conservative measures now. We're not waiting for the population to crash before we react."

In Wisconsin, where turtle trapping had been virtually unregulated, DNR officials imposed a permanent ban on commercial turtle harvesting in 1997. "Based on what I have seen over the years, I believe that turtle densities are way down," says Wisconsin DNR herpetologist Robert Hay, "and the recovery of turtle populations is very slow, especially with species like the softshell and snapping turtle. These factors affected our decision to close Wisconsin to commercial trapping."


Tony with a turtle

In Minnesota, the DNR is currently promulgating an administrative rule change that would afford greater protection to turtles while still allowing a commercial harvest. The department has also proposed legislation that would create new licenses and limit nonresidents from taking turtles.

Currently, Minnesota regulations prohibit all trapping of Minnesota's two threatened turtles, the Blanding's turtle and wood turtle.

Regulations regarding snapping turtles limit the number of traps an individual can set and dictate a minimum size for turtles taken from the wild. Snapping turtles are protected during their egg-laying season, between May 1 and June 30.

There are no state regulations limiting the season, size, or number of traps for painted turtles.

Map turtles and softshell turtles can be taken at any time and with no size limits, though these species are not the primary component of Minnesota's turtle industry. However, many predict that the market for softshell turtles will increase because of their popularity, especially in Asia, as a food source. In neighboring Wisconsin, trappers harvested 500 softshell turtles per day on the lower Wisconsin River during the two years before the activity was banned, says Hay.

"We've got softshells here in the state, and there's a strong market for them," observes Ben Hedstrom, a turtle wholesaler in Alexandria, Minn. Hedstrom is opposed to trapping softshells. "They're a unique turtle and there aren't that many of them to start with," he says.

The primary market in Minnesota is for snapping turtles, which are sold for meat, and painted turtles, which are sold as pets. Painted turtle harvesting is concentrated in the lake country of central Minnesota. Most trappers operate in Stearns, Douglas, Morrison, and Pope counties.

Sources in the turtle industry and in the DNR indicate that a group of about a dozen licensed trappers harvest the vast majority of all turtles taken in Minnesota.

A trapper can sell live snapping turtles for 50 cents to $1 per pound, while painted turtles fetch from $1 to $1.50 each, says Campbell.

Not all turtles that are caught in traps are taken from the lake. Many are thrown back because they are the wrong size or have damaged shells.

In 2000, Hedstrom purchased 20,000 painted turtles from trappers, about half the painted turtles harvested in the state that year, according to his estimate. "We've sold turtles for 50 years," Hedstrom says. "My dad did it since the 1920s."

Hedstrom has observed an increasing demand for Minnesota turtles since the Wisconsin ban on commercial trapping. "Wisconsin is closed, and it's putting pressure over here," he says.

Statistics reported to the DNR by trappers show a sharp increase in the number of painted turtles harvested in Minnesota after 1997.

In 1997, the number of painted turtles taken in Minnesota was 22,578. The following year, after the Wisconsin ban, that number jumped to 69,887. Though the numbers declined to 43,997 in 1999 (the most recent year for which statistics are compiled), they were still nearly double the 1997 harvest.

As demand for turtles grows and trappers face increasing scrutiny by regulators, the commercial turtle industry is poised to evolve. Though the outcome of that evolution is yet to be determined, its course will inevitably be shaped by the health of Minnesota's turtle populations—and their vitality is now a point of contention.

"I can go out and catch more turtles today than I did 10 years ago," says Campbell. "I don't see that it's hurting the turtle population."

Other observers offer a different point of view. Brian Mies, a conservation officer with the DNR in Kimball, Minn., says, "I've seen a major decrease in snapping turtle populations and a decrease in painted turtles on lakes that have been trapped."

Johannes reports that, "anecdotally, the DNR has received information from people over time that turtle populations have been in decline." But, he adds, "we need to get more information about turtle populations."

Although he stresses the need to act now to protect turtles, Johannes says that "we need to put things in place so that we can better track the effects of wetland loss and the commercial harvest. Any time you increase your knowledge about a species you increase your ability to make better decisions." It is to that end that the DNR is supporting Tony Gamble's research, which will gather objective information about turtle populations. Though scientists have researched the effects of trapping on turtles in similar environments, Gamble's is the first study to focus on Minnesota turtles.

His preliminary results indicate that painted turtle populations are smaller on harvested lakes, but that the demographic makeup of populations is the same among harvested and non-harvested lakes.

In spring, the turtles will emerge from their hibernation and return to the lakes, along with Gamble, who will study them for a second season. His final results will be published in a report that will be available to the public. "My goal is to bring some objectivity to the debate over commercial trapping," says Gamble. "I want the study to be used by anyone who's concerned."



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