Endangered waters
By John Myers
Duluth News Tribune – 05/09/2007
Duluth, Minn. – Maybe its prophetic that Minnesota is changing its new conservation license plates to show a jumping largemouth bass.
As two million anglers prepare for Minnesotas walleye season, which opens Saturday, some fisheries experts warn that the states most popular fish may be harder to find in future years. That could mean the next generation of Minnesota anglers will be more excited about the Memorial Day
weekend bass opener than the traditional mid-May walleye opener.
Scientists say that within a few decades some Minnesota lakes probably will be too warm for walleye to thrive. And even northern Minnesota lakes might get too warm in summer to hold key walleye food such as cisco.
Walleye are the backbone of the resort, fishing and bait industry and represent a century of family fishing traditions.
Were g oing to have fewer lakes with walleyes in them, and fewer walleyes in other lakes, said Don Pereira, fisheries research and policy manager for the Minnesota Department of Natural Resources. We need to start getting the public thinking about accepting other game species, like bass.
Dealing with lakes getting warmer
Average temperatures in Minnesota already up a degree in the past century are expected to increase another 3 degrees by 2050 and keep rising.
Even if we act fast to do something, thats where well be. And were talking by midcentury, not 100 years from now, Pereira told a conference organized by the DNR this past winter. After that, it all depends on what humanity does with carbon emissions.
Thats the projection of hundreds of scientists who study the issue. The warming appears to be caused by a doubling of carbon in the atmosphere over the past 150 years that is trapping more heat near the earth. A globa l panel of scientists says the carbon problem is caused by human activities, namely burning fossil fuels.
Minnesota scientists say the states summers will be more like Kansas by centurys end, and winters more like Illinois. The fish in Kansas? Few walleyes, and lots of bass and bullheads.
Scientists already have warned that a warming climate could mean trouble for fish and wildlife at the southern edge of their natural range, such as moose and lake trout. As more lakes hold more and bigger bass and sunfish, which thrive in warmer water, experts say, lake trout will retreat to just a few lakes in far northern Minnesota within decades, and the remaining lake trout are expected to take refuge in deeper water.
Warmer water may lead to faster growth
Its the states cold winters, and relatively cold waters, that keep walleyes from growing faster and bigger here. The world record 22-pound, 11-ounce walleye came from Arkansas, afte r all. Minnesota walleye havent hit 18 pounds.
Pereira said some northern Minnesota lakes will warm up into the walleyes optimal temperature range as the states climate warms. Higher temperatures will mean many more days for walleyes to grow, and they should get bigger more quickly.
But when scientists look closer, the picture gets murkier.
Walleye do best in water that is between 59 and 77 degrees Fahrenheit. Anything warmer than that, even for short periods, and walleyes become stressed. At 82 degrees they stop eating. At 88 degrees they die. The biggest, most prolific breeding fish die first.
Water temperatures in Lake Pepin, a famous walleye lake along the Mississippi River near Lake City in Goodhue County, Minn., are projected to rise into the walleyes danger zone. Pereira said that not enough of Lake Pepin will remain below 77 degrees during hot summer months to support enough walleyes to keep the population thriving.
If the projectio ns are on target, Lake Pepin couldnt hold many walleyes, Pereira said, noting that mild summer temperatures already have caused Pepins big walleyes to grow slower, likely due to stress. And during springs after recent hot summers, those stressed walleyes have produced fewer young.
Finding relationship with oxygen, food
In some lakes, walleyes can move to deeper water if theres enough oxygen and quality food down deep. But scientists say that during the summer, deeper water will have less oxygen, causing dead zones near the bottom.
Most of Minnesotas top 10 walleye lakes the biggest, most popular, most productive walleye lakes in the state dont have a deep, cold-water refuge for fish to move into when water warms near the surface. Walleyes havent needed that refuge in the past, but may in a warmer future.
Lakes that mix deeper-water lakes like Rainy, Cass and Vermilion, and the Boundary Waters could see bette r walleye production in the future, Pereira said. But the variable is what will happen with tullibee/cisco. (Walleyes) wont grow faster if they dont have the food.
Pereira said Minnesota anglers in 50 years will need to know how to catch more largemouth bass and sunfish. But hes not suggesting that Minnesota change its official state fish. Not yet.
Were still going to have some walleye lakes, and likely some good walleye lakes up north, Pereira said. But lakes that are marginal now will no longer be able to support walleyes. And were going to have to make some decisions on whether it makes sense to keep trying to force them to produce walleyes or shift to a more suitable, warmer water species.
Temperatures on the rise
Average temperatures in Minnesota are expected to rise 3 degrees
by 2050, which may affect the walleye population.
– Walleye do best in water between 59 and 77 degrees. For example, Lake Pepin in southeastern Minnesota is not expected to remain below 77 degrees during the hot summer months.
– Walleye stop eating when the water is 82 degrees.
– Walleye die at 88 degrees.
If you go
– When: Saturday
– Resident license: Individual $18, husband/wife $26, 24-hour $9.50
– Nonresident license: Individual $35, family $45, 72-hour $21, 7-day $25,
24-hour $9.50, 14-day couple $36
The Forum and Duluth (Minn.) News Tribune are both owned by Forum Communications Co.
