Events
Progress Report: Evaluation of Northern Pike Regulations On Big Birch Lake
24-36 Inch Protected Slot Limit
January 2011
The Little Falls Area DNR Fisheries office has continued to monitor the effects of experimental northern pike regulations on Big Birch Lake (DOW#-77-84) since their inception in the spring of 1996. A 24 inch maximum length limit was in place from 1996 to 2006 when it was modified. The current regulation consists of a 24-36 inch protected slot and a three fish limit which allows one fish over 36 inches in length. The “sunset” date for the present slot limit is scheduled for March of 2015. Since 2006 several sampling efforts have been conducted to track changes in northern pike size structure and abundance and evaluate potential fish community responses to the regulations. These sampling efforts include spring ice-out trapnet assessments in 2007, 2009, and 2010 and gillnet assessments in 2077 and 2010.
Results: Due to the fact that few male northern pike in Big Birch Lake reach a length of 24 inches and no male pike in excess of 30 inches have ever been documented, we have chosen to focus on the female segment of the population when evaluating size structure changes. The proportion of female pike exceeding 30 inches in length captured in spring trapnets has risen steadily since 2005. Roughly 2.5% of female pike exceeded 30 inches in 2005 compared to 4.1% in 2007, 6.7% in 2009, and 11.3 % in 2010. Prior to 2005 the proportion of female pike over 30 inches consistently fell within the 2% to 5% range with the exception of 2003 (22%). The 2003 sample consisted of only 188 pike of which fewer than 100 were females. In the four gillnet surveys prior to implementation of the experimental regulations the northern pike catch averaged 8.7/lift with a range of 4.1 to 14.5/lift. Four gillnet surveys have been performed since the regulation was enacted with pike averaging 9.6/lift and ranging from 5.5 to 14.1/lift.
Walleye are the primary management species in Big Birch Lake and maintaining a desirable population is an important management goal. The 2010 gillnet catch of 11.5/lift fell within the range of management goals (10-15 per lift). Walleye gillnet catch rates have averaged 10.4/lift since the establishment of pike regulations and have ranged from 5.7 to 16.8 per lift. Prior to the pike regulations walleye gillnet catches averaged 14.2/lift with a range of 8.1 to 20.2/lift.
Yellow perch abundance has varied considerably throughout the lake’s history including the regulation evaluation period. No yellow perch were sampled in gillnets in 2007, however numbers rebounded to 16.3/lift in 2010 which is within the normal range for the lake class. The highest perch catch recorded during the evaluation period was 44.9/lift in 1999. Perch catches prior to the northern pike regulations ranged from 4.6 to 40.3 per gillnet lift. Big Birch also continues to support a viable cisco population. Cisco have been present in every gillnet assessment conducted with the 2010 gillnets supplying a sample of 19 fish (1.3/gillnet).
Summary: Our netting evaluations suggest that pike in excess of 30 inches are higher in abundance and make up a larger proportion of the population than they did prior to the enactment of experimental northern pike regulations. The increased presence of larger pike has not resulted in reduced pike recruitment or a consistent reduction in overall pike abundance. Walleye abundance has been somewhat variable during the evaluation period, although it appears that maintaining a population level within the range of management goals is attainable in the presence of current pike regulations. Yellow perch continue to show dramatic fluctuations in abundance as they did prior to the regulations.
Round up of all northern pike regulated lakes near Grey Eagle.
