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 Background
The fisheries component of the LTRM element
is charged, in part, with monitoring and reporting trends in the status
of selected fish populations and fish communities of the UMRS (U.S. Fish
and Wildlife Service 1993). Fish are the primary biotic object of recreational and commercial use
on the UMRS. During 1982, UMRS fisheries provided more than 8.5 million
activity days of sportfishing that generated more than $150 million in
direct expenditures (Fremling et al. 1989). Commercial fisheries of the
UMRS were valued at more than $2.4 million in 1987 (Upper Mississippi
River Conservation Committee 1989). Adverse trends in fisheries of the
UMRS would have detrimental effects on recreation and the regional economy.
Therefore, it is important to detect any adverse trends as they occur
so that remedial actions can be considered.
Monitoring of and research on fish are also important because fish often
affect other ecosystem elements. Although documentation of the effects
of fish on other biota is derived primarily from lakes and reservoirs
(Northcote 1988) and traditional thought maintains that the dynamics of
river biota are influenced primarily by abiotic factors, recent evidence
shows that the dynamics of fish assemblages in temperate rivers are regulated
in part by biotic factors (Welcomme et al. 1989). Fish may exert influences
on other biota in riverine ecosystems and may, therefore, be of broad
ecological importance. For example, evidence shows that common carp (Cyprinus
carpio), an abundant species in the UMRS, may depress or even eliminate
macrophytes either through uprooting or disturbance of substrate (Cahn
1929; Macrae 1979). Effects of fish on benthic macroinvertebrates are
well known (Northcote 1988). Therefore, trends in abundance of fish may
be crucial in explaining trends in abundance of other riverine biota.
Resource monitoring is an important component of long-term ecological
research on processes governing large-scale ecosystems. It is nearly impossible
to perform experimental manipulations of the UMRS on large spatial scales
and to incorporate replication. Long-term data from standardized sampling
programs that span natural or anthropogenic disturbances are the only
means for gaining an understanding of large-scale processes governing
large river systems (Sparks et al. 1990). Further, the LTRM fisheries
component will provide support for the formulation and investigation of
research hypotheses concerning smaller scales using focused experimentation.
Therefore, the combination of routine monitoring coupled with more intensive
investigation of consequences of disturbances and experimentation at reduced
spatial and temporal scales is the only available means for better understanding
the UMRS and for identifying viable management alternatives.
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