The Influence of Habitat Modifications on the Fish Community in the Weaver Bottoms Backwater of Mississippi River Navigational Pool 5
File(s)
Date
1996-05Author
Metz, Michael T.
Publisher
University of Wisconsin-Stevens Point, College of Natural Resources
Metadata
Show full item recordAbstract
The influence of secondary channel modification and artificial island and levee
construction on the fish community was investigated in Weaver Bottoms, a 1,620 hectare
backwater lake of Mississippi River Navigational Pool 5. Experimental gill nets, trap nets,
and electrofishing were used to sample the fish community at 11 treatment stations within,
and 6 reference stations outside the backwater during July and September 1984-1994.
Analyses of pre-project (1984-1986) and post-project (1988-1994) data generally indicate
that the rehabilitation project did not affect species diversity nor did it increase or decrease
overall relative abundance of fishes in Weaver Bottoms. No change in species richness
relative to project modification was evident. Overall, species richness was significantly
greater at stations located within the modified backwater compared to reference stations
(Wilcoxon rank sum, p < 0.05) but differences may have been due to the greater number of
treatment stations rather than differences between treatment and reference stations. Trends
in species diversity (Shannon-Wiener Index) were similar at treatment and reference stations
and changes in diversity appeared to be related to variation in year-class strength of
predominant species. Similarly, no significant change (MANCOV AR, P < 0.05) in relative
abundance occurred for most species (e.g., black crappies, bluegills, common carp, and
northern pike) because of habitat modification. However, for many of these species (e.g.,
black crappie, bluegill, common carp, gizzard shad, largmouth bass, and shorthead redhorse)
relative abundance or relative biomass differed significantly among years at both modified and
reference sites (MANCOV AR, P < 0.05), suggesting that some changes resulted from
system-wide influences. Some of the changes in relative abundance or relative biomass were
related to variation in year-class strength that occurred system-wide. For example, strong
black crappie, bluegill, and common carp year classes appeared in 1986 and 1987, and
persisted for several years. Length frequency distributions for most of the predominant
species were also significantly different (Chi-square, p < 0.001) between pre-project and post-project
periods at both treatment and reference stations. For some species (e.g., black
crappie, bluegill, common carp) changes in length frequency distributions appeared to
influenced by strong year classes persisting in subsequent years, but for other species ( e.g.,
northern pike) changes in length frequencies were not clearly associated with strong or weak
year classes. Habitat modification did appear to increase relative abundance of smallmouth
bass in select areas. Smallmouth bass catch-per-effort increased significantly (MANCOV AR,
P < 0.05) at stations in secondary channels entering the backwater following partial closure
and placement of rock rip-rap, and these areas appeared to be used by all size/age classes of
smallmouth bass recruitable to electrofishing gear. Therefore, this analysis indicates that
project modifications produced few measurable changes in the fish community and suggests
that systemic factors affecting year-class strength and persistence may have had the greatest
influence on the fish community in Weaver Bottoms.