Hartley Lake is a 281-acre lake located 15 miles northwest of Nashwauk, MN. The west fork of the Prairie River flows through the lake and water levels are controlled by a small low-head dam. Hartley Lake has a maximum depth of 49 ft and moderate water clarity with a Secchi disk reading of 6 ft. A public access is located on the east shore by the outlet. Primary fish species include northern pike, panfish and walleye.
The northern pike gill net catch rate was 5.7/net and was higher than any previous assessment and within the expected range for similar lakes. Catch rates in past assessments have varied from 0.2 to 4.7/net. Catch rates appear to be increasing as the two highest catch rates were also the two most recent assessments. Size structure was generally poor with few fish greater than 24 inches and only one fish greater than 30 inches. Growth was similar to the statewide average with fish averaging 25 inches at age five.
Walleye were stocked in 2005, 2007, and 2009 at a higher than standard rate to improve the walleye population. Despite recent stocking, no walleye were sampled in this assessment and past assessments have sampled few or no walleye. Anglers report catching walleye, however the gill net catch indicates the population is low. In the spring of 2011, the outlet dam was modified with a series of rock weirs to allow fish from the Prairie River to migrate into Hartley Lake and other lakes upstream. It is hoped that this project will improve walleye and other fish populations in the watershed.
The bluegill catch rate was 13.0/trap net and was the lowest recorded catch rate, but was within the expected range for similar lakes. Catch rates in past assessments have varied from 13.3 to 73.8/net. Size structure was generally poor with some fish exceeding 7 inches, however no fish greater than 8 inches were sampled.
Catch rates for black crappie were 7.3/gill net and 1.2/trap net. The catch rate in gill nets was much higher than the expected range for similar lakes. Catch rates have been highly variable from 0 to 13.4/ for gill nets and 1.4 to 9.5 for trap nets. Size structure was poor with few fish exceeding 9 inches and no fish larger than 10 inches. Although scales were not collected for age and growth in this assessment, previous surveys have documented slow growth and poor size structure dating back to the first survey in 1954.
Yellow perch gill net catch was 10.2/gill net and was towards the upper end of the expected range. Catch rates in past assessments have been highly variable varying from 5.0 to 185.2/net. Size structure was poor with no fish exceeding 7 inches. Yellow perch size structure has consistently been poor in past assessments and yellow perch are more important as prey than a species of interest to anglers.
Largemouth bass are difficult to sample in gill nets and trap nets and few fish were sampled in this assessment. Although few fish were sampled, size structure was good with fish up to 19 inches sampled.
Other species sampled by gill nets and trap nets include brown bullhead, golden shiner, tullibee, rock bass, pumpkinseed sunfish and white sucker. Additional nearshore sampling using backpack electrofishing and seining sampled Johnny darter, Iowa darter, bluntnose minnow, fathead minnow, mottled sculpin, blackchin shiner and other young-of-the-year gamefish species previously sampled in gill nets and trap nets.
Lakeshore owners may affect fish populations not only through harvesting fish, but also through land use practices. It is important to leave a 30 to 50 ft buffer strip of native vegetation along the shoreline to prevent erosion and provide habitat for fish and wildlife. Nonfunctioning septic systems can also lead to water quality problems. Good water quality and fish populations are the direct result of good land use practices. Anglers can also help to improve the size structure of the fish community by harvesting fewer smaller fish and releasing medium and larger fish.