Lake information report

Name: Minnetonka

Nearest Town: Mound Primary County: Hennepin Survey Date: 06/13/2011 Inventory Number: 27013300

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Public Access Information

Lake Characteristics

Fish Sampled for the 2011 Survey Year

Length of Selected Species (Trapnet, Gillnet) Sampled for the 2011 Survey Year

Fish Stocking Activity

Fish Stocked by Species for the Last Ten Years

Fish Consumption Guidelines

These fish consumption guidelines help people make choices about which fish to eat and how often. Following the guidelin es enables people to reduce their exposure to contaminants while still enjoying the many benefits from fish.

Pregnant Women, Women who may become pregnant and Children under age 15

General Population

DOWID - MN DNR, Divion of Waters' lake ID number.

Contaminants listed were measured at levels that trigger advice to limit consumption.

Listing of consumption guidelines do not imply the fish are legal to keep, MN DNR fishing regulations should be consulted.

Dioxin
Mercury
PCBS - Polychlorinated biphenyls
PFOS - Perfluorooctane sulfanate

Status of the Fishery (as of 06/13/2011)

The 2011 Lake Minnetonka fisheries assessment was conducted June 13th through 30th. Annual sampling began in 1997 following a 20-year period when the fish community was sampled every five years. Sampling in Lake Minnetonka is divided between aggregations of basins that differ in their habitat and water chemistry. The Northwest Bays are most fertile, primarily because they are the first recipients of the majority of surface runoff from the watershed. The Upper Lakes are intermediate in fertility, while the Lower Lakes are least fertile. Since 1997, assessments have been conducted to assess trends in growth, condition, relative abundance, reproduction, and size structure of northern pike, walleye, and yellow perch. To effectively sample the aforementioned species, 24 experimental gillnets are set at 12 historic locations (24-hr sets; 2 net sets at each location with approximately 7-9 days between net sets). Additionally, in May 2011, an electrofishing special assessment was conducted to evaluate the status of the largemouth bass population. The 2011 gillnet assessment revealed a diverse fish community (17 species) dominated (based on lbs/gillnet) by northern pike (19.4 lbs/net), walleye (12.1 lbs/net), and bluegill (9.8 lbs/net).

Water Quality Water quality trends in Lake Minnetonka indicate a positive change in average Secchi depth and anoxic depth (< 2 ppm DO) over time. Secchi depths in 2011 were generally shallower than 2010; however, the trends in Secchi depth for all three basins show a positive relationship. The same relationship is also true of historical anoxic depths. The Lower Lakes have the best water quality, followed by the Upper Lakes, then Northwest Bays.

Walleye Lake Minnetonka is stocked with 6,446 pounds of fingerling walleye in even-numbered years. This equates to 1.1 lbs/littoral acre. Starting in the fall of 2010, walleye were and will continue to be stocked into all three basins of the lake. For more than 30 years, previous management limited walleye stocking locations to the Upper Lake and Lower Lake basins. Despite extensive stocking, walleye abundance, as indicated by gillnet catch per unit effort, has remained at low levels. The 2011 catch of 3.5 fish/net is higher than 2010 (2.9/net), but below the average from 1997-2010 (4.2 fish/net). Since 1970, 20 surveys have been conducted on Lake Minnetonka; of these, 13 (including 2011) had walleye catch rates below the 25th percentile (4.0 fish/net) for Class 22 lakes. On an entire-lake basis, walleye abundance is higher than previous years; however, catch rates differed by basin. In Upper Lakes, there was a decrease from 3.3 walleye per net in 2010 to 2.8 per net in 2011. In both Lower Lakes and the Northwest Bays there was an increase in the number of walleye per net. In Lower Lakes, catch increased by 0.6 fish per net, in the Northwest Bays there was an increase of 2 walleye per net. 2010 appeared to be a low year for walleye abundance in the Northwest Bays but the 2011 catch indicated abundance similar to 2008 and 2009. The average walleye gill-net catch per net from 1997-2010 was 4.2 in the Upper Lakes, 4.9 in the Lower Lakes, and 3.2 in the Northwest Bays. A comparison of northern pike and walleye catch rates suggests an inverse relationship. For example, the second lowest walleye catch rate (1.5 fish/net) occurred in 2005, three years after the second highest northern pike catch rate (17.7 fish/net). The high northern pike catch rate in 2002 represents a large population of northern pike in Lake Minnetonka that could have preyed upon the walleye fingerlings stocked in that year. Since walleye are recruited to gillnets by age 3, this predation was evident three years later (2005) when they were large enough to be sampled. This relationship is also evident 1999 through 2001. The size of walleyes was the largest in recent history. The current assessment (2011) was the first where walleye averaged over 20 inches in length. Walleye mean weight in 2011 (3.4 lbs) exceeded the 75th percentile when compared to other Class 22 lakes, and this has been the case since at least 1992. Mean weight was highest in the Upper Lakes (4.6 lbs), followed by the Northwest Bays (4.1 lbs), and the Lower Lakes (2.4 lbs). The general trend over time has been for the largest walleyes to be located in the Northwest Bays, followed by Upper Lakes, then Lower Lakes. This is assumed to be related to the productivity of the basins and the amount of yellow perch available as prey. Historically, the physical condition of walleye in Lake Minnetonka has been good. A relative weight value of 100 indicates the fish is in the 75th percentile for weight, relative to its length (above average condition). In 2011, walleye relative weight (90) was near the average of the previous 14 years (92). There was a significant relationship with relative weight and fish length . As walleye grew older, relative weight decreased. Walleye averaged 20.3 inches in length and ranged from 7.3 to 28.5 inches. Similar to mean weight, mean length was highest in the Upper Lakes (22.7 inches), followed by Northwest Bays (22.2 inches), then Lower Lakes (18.0 inches). Historically, size structure indices have revealed Lake Minnetonka's walleye population consists of larger individuals, and this was again observed in 2011. The proportion of walleye 20 inches and larger has increased every year for the last 5 and has doubled since 2006. The proportion of 15-inch and longer fish has fluctuated over the same time period. Size structure was highest in the Northwest Bays, then Upper Lakes , followed by the Lower Lakes. Aging walleyes using otoliths allowed year-class inferences to be made. Consistent with previous assessments, walleye natural reproduction is limited. In 2011, 13 out of 81 (16.0%) walleye originated from a non-stocked year-class. This was similar to 2010, when only 15.7 % were determined to be naturally reproduced. The stocked 2004 and 2006 year-classes continue to be strong, contributing to 42% of the walleye catch. Three year-olds in the 2008 year class also had a strong presence at 21% of the catch. The largest individual captured was an age-15, 28.5-inch, 8.7-pound male. In 2009, a catch curve analysis estimated walleye total annual mortality at 27.5%. Walleye growth was similar to other lakes in the West Metro Management Area and historic walleye growth in Lake Minnetonka. Walleye reached an average length of 12.8 inches by age 3 and 19.7 inches by age 6. Comparing basins, walleye grew fastest in the Northwest Bays, followed by Upper lakes, then Lower lakes.

Northern Pike Consistent with recent assessments, northern pike were relatively high in abundance in 2011. The 2011 northern pike catch of 6.3 fish/net fell below the 75th percentile for Class 22 lakes for the third time since 1987, the first was 2009. Northern pike gill net catch has decreased every year since the historical high of 17.7/ net in 2002. Northern pike catch rates in the Lower Lakes (7.0 fish/net) exceeded catch rates in both the Northwest Bays (6.3 fish/net) and Upper Lakes (5.4 fish/net). Northern pike average size (mean weight = 3.08 lbs) remained above the 75th percentile for Class 22 lakes. Sampled northern pike averaged 23.0 inches in length, which was smaller than in 2010 (25.4 inches) but was near the average of 22.7 inches, calculated from the previous 15 surveys. Northern pike mean length was similar in all three basins (Northwest Bays = 23.4 inches; Upper Lakes = 23.9 inches; Lower Lakes = 22.2 inches). Relative weight (92) was fair and near the historic average (88). Northern pike condition was similar among all three basins. The largest individual captured was an age-9, 34.7-inch, 9.97-pound female. Size structure indices revealed a quality northern pike population consisting of a high proportion of large individuals, with the best size structure found in the Upper Lakes. Size structure for the entire lake was lower in 2011 than 2010 as evidenced by lower mean size and lower size structure indices. The northern pike population in Lake Minnetonka may offer anglers the best chance at catching northern pike over 24 inches in the West Metro management area. The pike population is not overpopulated with small "hammer handle" fish, most are between 20 and 29 inches. Growth rates were slightly lower when compared to other West Metro Management Area lakes. On average, northern pike in Lake Minnetonka reached 20 inches by age 3 or 4 and 30 inches by age 7 or 8. Nine year-classes were sampled with the oldest individual age 9. In 2009, a catch curve analysis estimated northern pike total annual mortality at 36.1%. Ages 3-8 were used to calculate the catch curve.

Yellow Perch Yellow perch relative abundance (31.7 fish/net) was high (near the 75th percentile) compared to other Class 22 lakes and the historical average (12.6 fish/net). The trend since 2000 has been for increasing yellow perch gillnet catch, with the 2011 catch setting a historical high. The 2011 catch was nearly twice that of 2010 (17.3 fish/net). Consistent with previous assessments, perch abundance was highest in the Northwest Bays (59.5/net), followed by Upper Lakes (38.0/net) then Lower Lakes (8.7/net). Gill net catch was up in all basins; however the increase was greatest in the Northwest Bays at nearly 100%. In general, it appears there is an inverse trend of increasing yellow perch abundance with decreasing northern pike abundance. Size structure indices revealed a population consisting of small individuals (mean length = 6.7 inches). Yellow perch size structure has been historically small in Lake Minnetonka. Despite a small size structure, yellow perch mean length was the highest since 2000. The perch population in the Northwest Bays has a better size structure than the other two basins, where average length (7.06 inches) and weight (0.16 lbs) are greater. Yellow perch relative weight (86) was fair in 2011, but lower than 2010 (90), and lower than the historical average of 90. Relative weight decreased significantly with length, indicating a resource bottleneck may be occurring for larger, older individuals. Seven year-classes were sampled with the oldest individual captured age 8. The 2007 and 2008 year classes were evenly represented, together forming 87% of the population. Yellow perch growth was slower on average than other lakes in the West Metro Management Area. Comparing basins, yellow perch grew fastest in the Northwest Bays, followed by Upper Lakes, then Lower Lakes. In 2009, a catch curve analysis estimated yellow perch total annual mortality at 46.5%. Ages 3-7 were used to calculate the catch curve.

Muskellunge Muskellunge were not targeted during this assessment, but their population remains strong. Fish exceeding 50 inches and approaching 40 pounds are caught in Lake Minnetonka every year. Survival of stocked fingerling muskellunge is assumed to be very low due to the high abundance of largemouth bass and northern pike. Advanced fingerlings and yearlings have been used in recent years in attempt to improve survival rates of stocked fish. A research study is currently taking place in Lake Minnetonka investigating the survival of stocked fingerling and yearling muskellunge. Stocked fish were tagged in 2008, 2009, 2011, and will be again in 2012. These fish were tagged with an external spaghetti-type tag near the dorsal fin. These tags are yellow in color and include a six-digit number. Angler reports of captured tagged muskellunge are essential to the success of this project. If you catch a tagged muskellunge please record the tag number and length of fish and report the catch via phone, email or the Tagged Fish Reporting page within the MNDNR website. Please DO NOT remove the tag. Please contact the West Metro Fisheries Office with questions. Practicing CPR (Catch, Photo, and Release) is essential to maintaining the trophy muskellunge fishery found in Lake Minnetonka.

Largemouth Bass The largemouth bass population in Lake Minnetonka has a reputation for quality fishing. A nighttime boat electrofishing assessment was performed during May 2011 targeting largemouth bass. A total of 385 largemouth bass were sampled in 11 electrofishing transects, equating to 75.4 bass per hour of on time. Catch rates were similar to the 2009 assessment when 73.2 bass per hour were sampled. These catch rates are above average for area lakes. The size structure of the largemouth bass population in Lake Minnetonka is well-balanced and the fish are in good physical condition (Relative weight = 95). It appeared the larger fish tended to be in the best condition. Largemouth bass averaged 11.8 inches and 1.04 lbs, which is lower than in 2009 when fish averaged 13.5 inches and 1.5 lbs. The largest bass sampled was 20.9 inches long and 4.9 lbs. Fish from the 1999 through 2009 year classes were present, indicating consistent reproduction and recruitment. Age-3 bass from the 2008 year class were most abundant (25% of the total), followed by the 2007 (23% of the total) and 2005 (9.4% of the total) year classes. Growth was slower than average compared with other West Metro Area lakes. Largemouth bass reached 14 inches by age 7 and 18 inches by age 11. No smallmouth bass were sampled during the spring elecrofishing assessment. Numerous bass tournaments are held on the lake every year. Bass tournament are held by permit only and fish data must be turned into the DNR. In 2011, 11 bass tournaments were held. A total of 1,136 tournament anglers caught 3,854 largemouth bass and 38 smallmouth bass. Average size was 2.5 lbs and the largest recorded was 6.9 lbs. Since bass anglers target the largest individuals in a population, it is common for angling results to yield larger size fish, on average, than electrofishing. Additionally, individual tournaments may enact their own minimum size limit, thus only measuring a minimum size of fish. The electrofishing assessment targeted all sizes of bass.

Other Fish Bluegill and black crappie are abundant in Lake Minnetonka; however, gill nets are not reliable indicators of their relative abundance. The consistent natural reproduction and high recruitment of these species will ensure quality angling opportunities. Black bullhead, bowfin (dogfish), common carp, green sunfish, golden shiner, hybrid sunfish, pumpkinseed sunfish, rock bass, smallmouth bass, white sucker, and yellow bullhead were also captured in low numbers during the 2011 assessment. Smallmouth bass and rock bass were found only in the Lower Lakes. Invasive Species Eurasian water milfoil and curly leaf pondweed are found in high abundance throughout the lake and in 2010 zebra mussels and flowering rush were found to be present for the first time. Lake Minnetonka receives heavy recreational use, so potential for the spread of invasive species into and out of the lake is high. Anglers and boaters should take the precautions necessary to prevent the further spread of all invasive species. The shoreline and watershed of Lake Minnetonka is highly developed and puts stress on the lake's aquatic habitat and ecosystem integrity. Large docks, boating platforms, and man-made beaches have the potential to destroy vital habitat for fish and wildlife. Environmentally friendly development practices, such as shoreline buffer strips of natural vegetation, are necessary to maintain the current water quality of Lake Minnetonka. Shoreline development, invasive species, and the fish diseases Viral Hemorrhagic Septicemia (VHS) and Largemouth Bass Virus should be a concern to everyone who enjoys lake recreation.

For more information on this lake, contact: Area Fisheries Supervisor 7050 E Hwy 101, Suite 100 Shakopee, MN 55379 Phone: (952) 496-4141 Internet: West Metro Fisheries E-Mail: MetroWest.Fisheries@state.mn.us	Lake maps can be obtained from: Minnesota Bookstore 660 Olive Street St. Paul, MN 55155 (651) 297-3000 or (800) 657-3757 To order, use B0122 for the map-id.
For general DNR Information, contact: DNR Information Center 500 Lafayette Road St. Paul, MN 55155-4040 TDD: (651) 296-6157 or (888) MINNDNR Internet: www.dnr.state.mn.us E-Mail: info.dnr@state.mn.us	Turn in Poachers (TIP):     Toll-free: (800) 652-9093