HISTORY AND STATUS OF FISHERY
Lake Benton is a 2,857-acre lake that is classified as a DNR class 41 lake located in Lincoln County nine miles east of the Minnesota-South Dakota border and adjacent to the city of Lake Benton at County Highway 14 and US Highway 75. A class 41 lake is shallow and relatively large with good areas of sand and gravel lake bottom. The surrounding land area that drains to Lake Benton is row-crop dominated with roughly 90 percent of the watershed planted in corn and soybeans. Part of the 10% that is not in row crops is the immediate shoreline surrounding Lake Benton. The immediate shoreline land area is composed mostly of grasslands (80%), and undeveloped forest or woodland (20%); however, some urban development is present in the Lake Benton city limits. The watershed-to-lake ratio is 9 upland acres for every 1 lake acre, which indicates a fairly small contributing watershed in relation to the lake size. In general, the smaller the ratio the more realistic it is to positively influence the water quality of the lake by improving land-use practices in the upland areas of the watershed. In the case of Lake Benton, surrounding land practices that may improve water quality in the lake may include no till farming, cover crops planted in September, increased buffer strips on waterways, and reduced or targeted fertilizer application. More than 120 cabins or homes were present on Lake Benton in 2013 and no additional changes were noted in 2015. There are a total of six inlets and one major outlet (Coon Creek).
Lake Benton has a maximum depth of 9 feet, average summer water clarity of 2.5 feet, and at times supports vegetation to 8 feet deep. Recently underwater and above water vegetation in the lake was sparse and was composed of native species with no obvious presence of curly leaf pondweed at the time of the 2015 fish survey. Curly leaf pondweed in Lake Benton was at one time very prolific and covered nearly 100% of the surface water. After chemical (Floridone) treatments from 2005 to 2009 the lake has been returned to undetectable levels of curly leaf pondweed growth in 2015. The lake bottom composition of Lake Benton was mostly gravel, sand, and rubble covered with detritus. The water level of Lake Benton was at normal stage during the summer of 2015 relative to historic observed water levels.
The fishery of Lake Benton is primarily managed for Walleye and secondarily for Black Crappie, Bluegill, Northern Pike, and Yellow Perch. A population assessment was conducted the week of July 27th, 2015 with 4 gill nets and 15 trap nets to assess the managed fish species.
One hundred and seven Walleye were sampled during the 2015 population assessment. Ninety-two were caught in 4 gill nets and 15 were caught in 15 trap nets for catch rates of 23.0 per gill net and 1.0 per trap net. Fish appeared to be healthy when caught and analysis of length and weight information for each fish verified this. The gill net catch rate was equivalent to the 59 year historical catch rate average of 22.9 per gill net. Additionally, the 2015 gill net catch rate exceeded the expected range of 3.2 to 15.3 per gill net and was equal to the upper expected range value for Windom Area class 41 lakes (23.3 per gill net).
Walleye stocking was changed after the 2005 survey to increase stocking of Walleye fry from every other year to 2 out of every 3 years at a rate of 1,000 fry per acre. Since that change, the catch rate of Walleye in gill nets has remained near or above 15.0 per gill net. In fact, the catch rate since 2010 has remained above 20.0 per gill net over 4 surveys (2010, 2011, 2013, and 2015). The historical catch rate prior to 2010 never exceeded 20 per gill net over two or more surveys in a row. The Walleye population appears to be stable and at a high level never seen before in Lake Benton.
The additional year of stocking coupled with natural reproduction of Walleye is also becoming more regular in Lake Benton. Natural reproduction of Walleye has been verified in each non-stocked year since 2006. Non-stocked years occurred in 2008, 2011, and 2014. Scale samples of the naturally reproduced Walleye contain genetic material and were sent to Dr. Loren Miller (MN DNR researcher and geneticist) at the University of Minnesota. Genetic analysis indicated that the 2008 and 2011 year classes of fish are more closely related to a recently verified southern MN strain of Walleye (Lower Mississippi River Strain, aka Lake Sarah Strain or Canon River Strain) than they are to DNR stocked Walleye (Diamond Lake Strain from Spicer Area Fisheries). This indicates that natural reproduction of a potentially "native" or historically stocked Walleye strain with some kind of survival advantage may be occurring. The 2014 naturally produced group of Walleye has not been analyzed yet, but scale samples will be tested during 2016 to determine their genetic ancestry.
The change in stocking strategy of Walleye coupled with more favorable conditions for natural reproduction since 2006 have led to increased catch rates of Walleye in Lake Benton in DNR surveys. However, the average length of the Lake Benton Walleye has decreased since 2010. Regardless of the decline, healthy Walleye populations can exist with a smaller size structure. The smaller size of Walleye sampled could be due to sampling inefficiencies during the most recent survey when weather was very windy or it could be a result of successful stocking and natural reproduction in recent years leading to larger amounts of smaller fish. Another population assessment will be conducted in 2017 and the Walleye population will be reevaluated. In the meantime, Walleye fry stocking was conducted in the spring of 2015 and will continue in the spring of 2016. A more balanced size structure is anticipated in the near future because 63% of the Walleye sampled in 2015 were between 12 and 15 inches and growth from now until the Summer of 2016 should result in Walleye exceeding 15 inches.
One hundred and four Yellow Perch were caught in gill nets and trap nets on Lake Benton during 2015. The trap net catch rate of 0.3 per net was within the expected catch rate range of 0.3 to 2.6 per trap net. The gill net catch rate of 25.0 per net exceeded the expected catch rate range of 3.0 to 22.5 per gill net. The Yellow Perch population in Lake Benton is cyclical in nature and commonly fluctuates between periods of low and periods of high catch rates. Lake Benton is mostly devoid of ideal spawning habitat for Yellow Perch except for a few downed trees and some lake bottom areas that can favor spawning. Therefore, when conditions are not exactly right for spawning the result is typically a mediocre or failed reproduction. The 2015 net catch was composed of larger Yellow Perch and didn't have any individuals smaller than 6 inches indicating a potential year class failure or increased predation on smaller Yellow Perch or sampling inefficiencies during high winds. But the Yellow Perch that were caught in the sample indicated a population that has a large size structure with fish in the 8 to 10 inch range. In addition, the health of the Yellow Perch appears to be good. Overall, the Yellow Perch population is dominated by larger fish that are in good condition. This should translate to an ability to fish for an abundant Yellow Perch population during 2016 and 2017.
Six Northern Pike were captured in trap nets and gill nets in 2015. The trap net catch rate was 0.1 per net which is less than the Windom Fisheries Management Area expected catch rate range of 0.2 to 1.0 per trap net. The gill net catch rate in 2015 was 1.0 per gill net, less than the statewide expected catch rate range for class 41 lakes (1.2 to 7.8 per gill net) but within the southwest MN catch rate range for class 41 lakes (0 to 1.3 per gill net). The low catch rates were not unexpected due to a lack of spawning habitat for Northern Pike to sustain their population through natural reproduction. Additionally, the last time Northern Pike were stocked was 2006 so the population is aging and decreasing. However, the size structure and the overall health of the Northern Pike population is good. The next stocking of Northern Pike fingerling is scheduled for June 2016 so the population should receive a boost provided MN DNR rearing ponds produce adequate numbers of Northern Pike in 2016. This boost will sustain the low density population of predators that are essential to maintaining a balance in the entire fish community of Lake Benton.
Twelve Black Crappie were caught in gill nets and trap nets combined in 2015. The gill net catch rate was 0.8 per gill net and 0.6 per trap net. Both catch rates for gill nets and trap nets were less than the statewide expected catch rate ranges. All Black Crappie caught were less than 8 inches but the health of each fish was noted as excellent. The low abundance population appears to have been dominated by small fish in 2015 but growth can be fast for crappie. No stocking is advised as Crappie populations are up and down naturally and will increase and decrease in catchability and numbers based on slight changes in habitat or environmental variables (temperature, water quality, water clarity, etc.). The Black Crappie population at the moment appears to be sustaining a small population that should translate to a catchable population by late 2016.
Eight Bluegill were sampled in gill nets and trap nets combined. The gill net catch rate was 0.3 per net and the trap net catch rate was 0.5 per trap net. The trap net catch rate is below the statewide low expected catch rate value of 1.1 per trap net. The Bluegill in Lake Benton are most likely larger than 6 inches based on the sample in 2015. Bluegill adults are stocked periodically by the local fish and game club and they appear to be contributing to a low density fish population with most fish between 8 and 10 inches.
Other species sampled in 2015 include Black Bullhead, Common Carp, and White Sucker.
The Black Bullhead catch rates were within the statewide expected catch rate ranges at 24.8 per gill net and 8.7 per trap net. Historically, they are below the long-term catch rate averages and are at lower than expected abundances, and have been since 2007. Most Black Bullhead were between 8 and 10 inches.
Common Carp catch rates are 0.8 per gill net and 1.4 per trap net, both within their respective expected statewide catch rate ranges. As for Black Bullhead, the Common Carp catch rates are lower than their long-term averages for Lake Benton. Sizes of Common Carp were all over the board but most were adults larger than 16 inches.
The White Sucker gill net catch rate was the highest on record at 50.0 per gill net. The trap net catch rate of White Sucker (1.0 per trap net) was within the expected statewide catch rate range. Most White Sucker were between 11 and 17 inches and should provide a potentially high available forage base for large Walleye and Northern Pike helping the gamefish to have an ability to grow to very large sizes.
While Lake Benton supports a limited diversity of fish, it is a destination for Walleye anglers in southwestern Minnesota. When the bite is on, anglers should have the opportunity to catch their limit of Walleye in the 13 to 15 inch range with some fish larger than 16 inches as a bonus. To have a chance to catch the big one you need to wet a line, get out there and give it a try in 2016!
Prepared by Nate Hodgins