|dc.description.abstract||An agreement in 1993 between the Wisconsin Department
of Transportation and Wisconsin Department of Natural
Resources called for mitigation of 0.54 acres (0.22 ha) of
lost centrarchid spawning habitat in Irogami Lake, Waushara
County, Wisconsin, due to future relocation of State Trunk
Highway 21. An ecological study was conducted to determine
recommendations for restoring the lost habitat, as well as
to assess the pre-construction characteristics of the
bluegill Lepomis macrochirus and largemouth bass Micropterus
salmoides populations and species composition of aquatic
invertebrates and plants in the construction area. Data
were collected from April through August in 1993 and 1994.
Physical habitat characteristics of bluegill spawning
colonies in all areas of the lake were documented.
Substrate, bottom gradient, water depth, distance from
shore, and relation of nests to cover are the
characteristics on which the mitigation plan was based.
Fish were caught with fyke nets, boat-mounted electrofishing
gear, and seines. Scale samples were collected from
bluegills and largemouth bass for age determination.
Bluegills built colonies in areas with mean (range) bottom
gradient of 6% (1.1-13.2%), depth of 89 cm (65-119 cm) and
distance from shore of 19.1 m (1.5-86.9 m). Spawning
substrate particle size ranged from fine (< 0.5 mm) to
cobble (64-256 mm). About half of the colonies (56%) were
greater than 5 m from cover. Length increments of bluegills
of ages 1-7 were not significantly different from state (P =
0.17) and regional (P = 0.36) increments. Length increments
of largemouth bass were significantly smaller than average
state (P = 0.05) and regional (P = 0.02) increments.
Mortality rates, based on fyke net catches, of bluegills of
ages 2-7 were Z = 0.314 and A= 27%, and of ages 7-8 were Z
= 2.1 and A= 88%. Mortality rates, based on electrofishing
catches, of largemouth bass of ages 4-7 were Z = 0.27 and A
= 24%, and of ages 7-8 were z = 1.9 and A= 85%.
Recommendations for recreating spawning habitat include:
placing the spawning bed along the new highway; rip-rapping
of the lake shore in that area; laying a 15.2-cm blanket of
substrate consisting of 80% (by weight) of gravel 6.3-19 mm
diameter with an allowance of no more than 10% gravel of 19
-200 mm diameter, and 20% consisting of fine gravel and
coarse sand containing no more than 5% of particles less
than 0.5 mm diameter, on the preexisting bottom slope;
maintaining 0.46-1.2 m of water on top of the substrate; and
adding a 2:1 slope to the outer edge of the new spawning
bed. The new spawning bed would cover 0.6 acres (0.25 ha)
of lake bottom.||en_US