Battle Lake is a 199 acre lake located east of Effie, MN in the Bigfork River watershed. The lake has a maximum depth of 15 feet and is part of a navigable chain of lakes including Pickerel and Deer Lakes. The lake has limited development, and the primary access is through a shallow channel from Pickerel Lake. Battle Lake is managed primarily for bluegill, while northern pike and walleye are considered secondary species. All three lakes in the chain have a conservation regulation (10 fish daily bag limit) for sunfish and a slot length limit (17-26 inch protected) for walleye.
The bluegill trap-net catch rate in 2010 was 9.1/net, above the management plan goal of 3.0/net but within the expected range for similar lakes. The two highest historical catch rates for bluegill have occurred in the two most recent assessments. A trend of increased bluegill abundance has been noted in many area lakes in recent years. Bluegill size structure in Battle Lake has declined over the same period. Sampled bluegill in 2010 ranged from 3.0 to 8.4 inches, with a mean length of 6.2 inches. This compares to mean lengths of 6.8 inches in 2004 and 8.4 inches in 1998. Bluegill were not aged in this assessment, but results from the two most recent spring trap-net assessments (2005, 2009) showed growth similar to the lake class average. Additional spring assessments are planned to further evaluate the effectiveness of the conservation regulation.
The gill-net catch for northern pike was 12.3/net, above the expected range and the highest on record for Battle Lake. Catch rates in most recent assessments have exceeded the lake class median and management plan goal of 7.0/net. Sampled pike in 2010 ranged from 13.0 to 27.7 inches with a mean length of 21.0 inches. Ages 1 through 5 were represented in the sample. Mean length-at-age was similar to the statewide average for ages 1 and 2, and above the statewide average for ages 3 through 5. Northern pike reached 23.7 inches in four years.
The walleye gill-net catch was 1.3/net, below the lake class expected range but similar to previous assessments. Net catches for walleye have only exceeded the management plan goal of 2.0/net in two of the nine assessments since 1960. Sampled walleye ranged from 16.3 to 22.2 inches, with a mean length of 19.0 inches. Ages 5, 7 and 9 were represented in the sample, all which correspond to years of fry stocking. Mean back-calculated length at age was similar to the statewide average for all ages. Walleye reached 16.7 inches in five years.
The 2010 black crappie gill-net catch was a historical high at 7.2/net. The two highest catch rates for crappie have occurred in the last two surveys. Gill-net and trap-net catches were generally below 1.0/net in most previous assessments. The 2010 trap-net catch remained near the long-term average at 0.4/net. Black crappie size structure was moderate. Crappie from gill nets ranged from 4.6 to 10.9 inches, with a mean length of 8.9 inches. Recruitment appeared consistent, with ages 2 through 7 represented in the sample. Mean length-at-age was similar to the statewide average. Black crappie took five years to reach 9.3 inches.
The gill-net catch for yellow perch was below the expected range at 2.7/net. The two lowest net catches for yellow perch have occurred in the two most recent assessments, and are likely related to the higher abundance of northern pike. Although catches in past surveys have been as high as 51.3/net, historical catch rates have generally been less than 10.0/net. Size structure of yellow perch was poor, with only one perch over 8 inches in the sample.
Other species sampled in test nets included brown bullhead, largemouth bass, rock bass, pumpkinseed, hybrid sunfish and white sucker. Near-shore IBI (Index of Biotic Integrity) sampling with a small-mesh seine and back-pack electrofishing was conducted in 2010 in an attempt to capture smaller fishes not normally encountered with standard sampling gear. Additional species captured in near-shore sampling included bluntnose minnow, blacknose shiner, golden shiner, and Johnny darter.