Record heat may be contributing to fish kills in Minnesota lakes

July 16, 2012

by Chris Schultz

From the DNR

Record-setting heat may be contributing to fish kills in lakes across the state, according to the Minnesota Department of Natural Resources (DNR).

“Natural summer fish kills are not unusual,” according to Brian Schultz, DNR assistant regional fisheries manager. “In the past several days, however, we’re getting increased reports of dead and dying fish in many lakes from around the state.”
Unusually warm weather has raised water temperatures of many shallow lakes.

Schultz has received reports from DNR field staff of surface water temperatures in some lakes reaching 90 degrees, with temps at the bottom only a few degrees cooler where maximum depths are less than 10 feet.

“Those are some high readings and northern pike are especially vulnerable when the water gets this warm,” Schultz said. “They are a cool water species and just can’t adjust to the high temperatures when sustained for more than a few days.” Warm water temps can also impact other species such as walleye, yellow perch and bluegills.

Should the high heat continue, there may be die-offs of both northern cisco (tulibee) and lake whitefish in central and northern Minnesota lakes.

Oxygen depletion can be another factor contributing to fish kills of a broader range of fish species.

Heavy rains earlier in the summer caused unusually high runoff from fertilized lawns, athletic fields, golf courses and farm fields, starting a chain reaction of high nutrient loads in some lakes.

The runoff carries nutrients into the lakes, which combined with hot weather, can accelerate the growth of algae.

Hot, dry, sunny and calm weather can cause algae growths to suddenly explode, according to Craig Soupir, DNR fisheries habitat specialist.

“Aquatic plants remain relatively stable over time, but algae have the ability to rapidly increase or decrease under various conditions,” Soupir said.

Algae produces oxygen during the daylight hours, but it uses oxygen at night. This can create drastic daily changes in lake oxygen levels.

These daily changes can result in complete saturation of oxygen during peak sunlight and a near complete loss of oxygen during the night.

“All of this can add up to stressful conditions for fish,” Soupir said, “and even summer kill events.”

Fish don’t seem to sense when oxygen depletion occurs and may suffocate in isolated bays, even when another area of the lake contains higher levels of oxygen.

Disease may also be a contributing factor to some fish kills.

Schultz explained that when lake temperatures rapidly change, fish can become more susceptible to bacteria and viruses that naturally occur in the water. Columnaris is one of the most common diseases.

The bacterium is always present in fish populations but seems to affect fish when water temperatures are warming rapidly and fish are undergoing some stress due to spawning.

Fish may die or be seen weakly swimming along shores.

Species affected are usually sunfish, crappies and bullheads and occasionally, largemouth bass and northern pike.

“It is difficult to pin a summer kill on just one cause,” Schultz said, “and although it is a natural occurrence, it can be disturbing.”

Fish kills are usually not serious in the long run. Most lakes contain thousands of fish per acre and the fish kills represents a very small percent of that total.

Some positive effects from partial fish kills is that it creates an open niche in the fish population, allowing the remaining fish species to grow faster with less competition.

Minnesota lakes are resilient. The DNR has documented these conditions many times over and lake conditions and fish populations do return to managed expectations, either naturally or with the help of stocking if necessary.

If strange behavior is seen in fish, contact the local DNR fisheries office immediately.

“If we can sample fish before they die, we may be able to learn what’s going on in the lake,” Schultz said. “Once the fish are dead it can be difficult to determine what happened.”

Visit http://www.dnr.state.mn.us/areas/fisheries/index.html for a complete list of DNR fisheries offices in the state.

People can also call the DNR Information Center at (651) 296-6157 or toll-free 888-646-6367.

Watertown firearms training coming up

Registration for Watertown firearms training will be Saturday, July 28 from 10 a.m. to noon at the Watertown Rod and Gun Club.

Class dates are Aug. 3, 6, 7, 9, and 10 from 6 to 9 p.m., with a field day Saturday, Aug. 11 at 8 a.m.

For additional information, contact Cory at (612) 218-3228 or WatertownFST@yahoo.com.

DNR partners with Minnesota Zoo to preserve bison
From the DNR

The Minnesota Department of Natural Resources (DNR) has joined with the Minnesota Zoo in an effort to conserve the North American plains bison.

The DNR will work with the Minnesota Zoo to cooperatively manage a genetically-pure bison herd at Minnesota state parks and at a zoo exhibition.

A herd of 100+ bison currently reside at Blue Mounds State Park in southwestern Minnesota, a project that started in 1961 with three bison from Nebraska. The zoo exhibits bison on its Northern Trail.

During the recovery of this species from near extinction in the early 1900s, cattle interbred with bison in many locations.

Recent scientific advances estimate that less than 1 percent of the world’s remaining American bison are free of cattle hybridization – posing a serious threat to the long-term conservation of pure wild bison across the nation.

The new effort will help protect the genetic diversity of this native Minnesota species and educate Minnesotans about the bison’s conservation story and the important roles bison (and other large herbivores) play in our prairie ecosystem.

“American bison were the first wildlife species that zoos actively worked to help save, with a small herd originating from the Bronx Zoo being returned to the wild in 1907 to help restore the species in the Western Plains,” said Minnesota Zoo Director/CEO Lee Ehmke. “A strategic priority of the Minnesota Zoo is to increase awareness and to actively participate in the restoration of the prairie ecosystems that once occupied vast areas of Minnesota. Helping to expand the population and range of a keystone species like the bison, in collaboration with our colleagues at the DNR, is exactly the sort of conservation action our Zoo is committed to engage in.”

Courtland Nelson, director of the DNR Parks and Trails Division, said, “We are very excited to work with Minnesota Zoo staff to help preserve and expand the number of plains bison in Minnesota being managed for species conservation and ecological restoration. By signing this memorandum of agreement today, we will be helping Minnesota play a greater role in preserving one of the icons of the North American conservation movement, and providing additional opportunities for visitors to see and learn more about these magnificent animals and the prairie ecosystems they inhabit.”

The project will begin this fall.

About bison

Massive and thick-coated, bison – the largest land animals in North America – were once the icons of North America’s Great Plains.

They were the most abundant, with an estimated 30 to 60 million animals, before European settlement.

Bison were hunted to near extinction in the 1800s, with populations down to less than 600 before protective measures were put into place.

Currently, there are approximately 19,000 total plains bison in 54 conservation herds (herds managed in the public interest by governments and environmental organizations); the species is considered near-threatened and conservation-dependent.

About Blue Mounds State Park

Since 1961, Blue Mounds State Park, located in southwestern Minnesota, has been home to Minnesota’s only wild bison.
About 100 bison range across more than 500 acres of prairie and outcrops of Sioux quartzite within the 1,600 acre park.

The bison can be observed by visitors year-round.

About the Minnesota Zoo

The Minnesota Zoo is located in Apple Valley, just minutes south of Mall of America.

For more information, call (952) 431-9500 or visit www.mnzoo.org.

The Minnesota Zoo is an accredited member of the Association of Zoos and Aquariums and an institutional member of the World Association of Zoos and Aquariums.

DNR announces wolf season details
From the DNR

The Minnesota Department of Natural Resource (DNR) has finalized rules for Minnesota’s first regulated wolf hunting and trapping season this fall and winter.

There are several changes to what the DNR originally proposed in May as a result of input received since the proposal was announced.

“We changed the closing date for the late season from Jan. 6, 2013, to Jan. 31,” said Steve Merchant, DNR wildlife program manager. “We also tightened the wolf harvest registration requirement so we can more quickly close a zone based on harvest results.”

Another notable change is that the wolf range will be divided into three zones for the purposes of harvest targets, registration and season closure.

The northeast zone and the east-central zone closely parallel the 1854 and 1837 treaty ceded territory boundaries.

These zones will allow the state to allocate and manage wolf harvest in consultation with Indian bands that have court-affirmed off-reservation hunting rights.

The northwest zone will be the other area open to wolf hunting.

Only that portion of Minnesota where rifles are legal for deer hunting will be open for taking wolves.

When harvest targets are reached in any zone, that zone will be closed and hunters will be able to continue to hunt in any other open zone.

The state’s first regulated wolf hunt will begin Saturday, Nov. 3. The target harvest is 400.

The early wolf season will last up to nine days in the 200-series deer permit areas and up to 16 days in the 100-series deer permit areas.

The late season, which also allows trapping for those with a wolf trapping license, will begin Nov. 24 statewide.

Target harvests are 265 in the northwest zone, 117 in the northeast zone and 18 in the east-central zone.

The state’s inaugural wolf season will be conducted under a conservative approach that is consistent with the goal of ensuring the long-term survival of wolves, and addressing wolf and human conflicts.

The state’s wolf population is estimated at 3,000.

This year’s wolf season follows the transition of wolves from federal protection under the Endangered Species Act to state management this past January.

The 2012 Legislature also passed and Gov. Dayton signed a bill providing additional direction and authorities for conducting a wolf season.

Merchant said the public comment period that ended June 20 was helpful, providing additional insights that helped determine the final decisions.

The DNR received 7,351 online survey responses.

The survey was designed to solicit input on specific management options for the hunting and trapping season.

“Of those who approved of the season, 82 percent of survey respondents said they supported the DNR’s proposed season structure and implementation of a limited fall hunt,” said Merchant. “That suggested our proposal was generally in line with hunter and trapper expectations.”

Other survey results included strong backing (75 percent) from those who supported wolf hunting for having both early and late wolf hunts.

The DNR also asked hunters and trappers for their preference on notification and closure for ending the hunt when the target harvest quota is reached.

Respondents overwhelmingly preferred that notification of closure be published by early morning, and that hunters and trappers be allowed to finish out the day’s hunt.

The season will close at the end of the first full day for which closure notification is posted and sent to license holders.

Additional information about wolf management and the upcoming season is available online at www.mndnr.gov/wolves.

Details of the season

Consistent with state law, the state’s first regulated wolf season will start with the beginning of firearms deer hunting on Saturday, Nov. 3.

The season will be split into two parts: an early wolf hunting season coinciding with firearms deer hunting; and a late wolf hunting and trapping season after the firearms deer season for those with a specific interest in wolf hunting and trapping.

A total of 6,000 licenses will be offered, with 3,600 available in the early season and 2,400 in the late season.

Late season licenses will be further split between hunting and trapping, with a minimum of 600 reserved for trappers.

The target harvest will be 400 wolves for both seasons combined, and will initially be allocated equally between the early and the late seasons.

The early hunting only season will be open only in the northern portions of Minnesota where rifles are allowed for deer hunting.

It will start on Saturday, Nov. 3, the opening day of firearms deer hunting.

It will close either at the end of the respective firearms seasons in the two northern deer zones (Nov. 18 in Series 100 deer permit areas or Nov. 11 in Series 200 deer permit areas), or when a registered target harvest by zone is reached.

The late hunting and trapping season will begin Saturday, Nov. 24. It will close Jan. 31, 2013, or when a registered total target harvest by zone or total harvest of 400 in both seasons combined is reached, whichever comes sooner.

The late season will be open only where rifles are allowed for deer hunting.

The use of bait and electronic calls will be allowed.

Wolf hunting licenses will be $30 for residents and $250 for nonresidents.

Nonresidents will be limited to 5 percent of total hunting licenses.

Wolf trapping licenses will be $30 (limited to residents only).

A lottery will be held to select license recipients.

Proof of a current or previous hunting license will be required to apply for a wolf license.

The application fee will be $4. A wolf season regulation booklet is being developed.

Season structure

• The early wolf hunting season (legal firearms or archery) will be concurrent with the deer season and open only in that portion of the state where rifles can be used to hunt deer.

• The early season dates are Nov. 3-18 in 100 Series deer permit areas (northeastern and east-central Minnesota) and Nov. 3-11 in the rifle zone portion of 200 Series deer permit areas (central and northwestern Minnesota).

The early season will close before those dates if the target harvest by wolf zone is reached sooner.

• No trapping will be allowed in the early season.

• The late hunting and trapping season will open Nov. 24 statewide. It will close Jan. 31 or when the total target harvest by wolf zone is reached, whichever is sooner.

• Licensed wolf hunters will be responsible for checking each day to assure that the season is still open.

• Landowners and tribal authorities may close land under their control to wolf harvest at their discretion.

• The bag limit is one wolf per licensee.


• A person cannot purchase both a wolf hunting and a wolf trapping license. A person with a hunting license may take a wolf only by firearms or archery; a person with a trapping license may take a wolf only by trap or snare.

• 3,600 licenses will be available for the early season and are only valid for the early season.

• 2,400 licenses will be available for the late season (at least 600 trapping) and are only valid for the late season.

• The number of hunting licenses offered to nonresidents will be capped at 5 percent for both the early and late seasons.

• Licenses must be purchased prior to the opening day of the respective seasons.

Application process

• Application materials will be available online in mid-August with a $4 application fee.

• A person must have proof of a current or previous hunting license to apply.

• Trappers born after Dec. 31, 1989, need a trapper education certificate or proof of a previous trapping license to purchase a wolf trapping license.

• The application deadline will be Sept. 6; online winner notification will be no later than Oct. 14.

• Licenses will be available for purchase no later than Oct. 15.

• Groups of up to four individuals many apply as a single group and may assist another licensed wolf hunter, but may not shoot or tag for each other.

• Applicants can apply for only one of three license types: early wolf hunting, late wolf hunting, or late wolf trapping.

• All animals must be registered by 10 p.m. of the day of harvest (can be done electronically at ELS agent, online or by phone).

• Harvest registration information/reporting will be available online and via a toll-free phone number.

• Harvest registration must identify the zone in which the wolf was taken.

• Carcasses must be presented for collection of biological data.

Season closure and notification

• The season for each wolf zone will close at the end of legal shooting hours on the day for which hunters and trappers are notified that the closure will occur.

• Notification will be available via a toll-free phone number and DNR web site indicating whether the season is open or closed in each wolf zone.

CO weekly reports
From the DNR

• CO Brian Mies Annandale station checked anglers.
CO Mies conducted boat and water work crews.
CO Mies also assisted with AIS work crews.

• CO Jackie Glaser (Mound) worked boat and water safety details on Lake Minnetonka with district officers.
The holiday week brought thousands of boats onto Lake Minnetonka.
Six individuals were arrested for BUI, numerous juveniles were found drinking alcohol, one individual was arrested on a warrant, and others were cited for safety violations.
She also attended a boat and water meeting and worked public accesses for Invasive Species.

• CO Steve Walter (Waconia) handled beaver and muskrat damage complaints.
ATV and off road vehicle areas were patrolled.
Several DNR related calls were returned.

• CO Wayne Hatlestad (Litchfield) checked angling, boating, and PWC activity.
Additional time was spent checking and educating boaters on AIS laws.
Hatlestad also checked turtle trapping activity and assisted other law enforcement agencies.

• CO Brett Oberg (Hutchinson) worked an extremely hot, but overall safe 4th of July.
Boating activity seemed down, most likely due to the extreme temperatures.
Boating enforcement involved fail to have fire extinguishers, no type IV PFDs, and PWC violations.
AIS and angling enforcement was also worked.
Enforcement action was taken for over limit of crappies and transporting lake water.
CO Oberg also worked the Outdoor Wall of Shame at the Winthrop Farm Fest and answered several questions about AIS, hunting and angling laws.