S.W. Raborn, L.E. Miranda, and M.T. Driscoll, Mississippi
Cooperative Fish and Wildlife Research Unit, P.O. Box 9691, Mississippi State, Mississippi
39762; Voice 601-325-3217; FAX 601-325-8726; E-Mail smiranda@cfr.msstate.edu or sraborn@cfr.msstate.edu
Keywords: striped bass, prey inadequacy, feeding competition,
supply-demand, fish production, bioenergetics, reservoirs
Prey deficiency is generally considered the single most important
limitation on gamefish production in southeastern reservoirs; thus, competition for
limited forage is likely. We compared prey supply to predator consumptive demand to assess
the degree of feeding competition among major game fishes in Norris Reservoir. Prey supply
was defined as the biomass plus production of clupeids and lepomids. Predator demand was
estimated with bioenergetics models and was partitioned into size-specific demands based
on actual prey sizes eaten. The overall mean supply-demand ratio weighted by the
importance of prey to the gamefish community was 3.5. Also, we modeled increases and
decreases in both supply and demand, to simulate natural fluctuations in prey supply and
predator demand. Given fluctuations in both supply and demand from 0.25 to 2 times that of
the mean estimates, we observed the supply-demand ratio to range between 0.4 and 28.2. It
is difficult at best to associate a supply-demand ratio to competition without additional
information on the minimum ratio necessary to sustain predator demand, but given the
potential range of supply-demand ratios, it is evident that intensity of competition
varies annually. The mean supply-demand ratio, 3.5, may be interpreted as an approximation
of what is needed to maintain historical average gamefish biomass and production in Norris
Reservoir.
