ABSTRACT
This chapter constitutes a reversal, to some degree, by many fisheries ecologists regarding the mechanisms which control fish population dynamics. Alteration of water levels to attempt to manipulate fish populations and communities has been used extensively by fish management agencies on many of the nation's hydroelectric reservoirs, flood control reservoirs, recreational fishing lakes, farm ponds, and irrigation reservoirs. Certain species of fish, especially largemouth bass, do best when water level increases occur immediately before, during, and for a short time following the spawning and nursery period. Low water levels at improper periods may have detrimental effects on fish populations. Water level fluctuations may also alter temperature regimes in littoral zones, thus influencing fish spawning periods and rates of food production. Natural changes in water level fluctuations in Great Lakes coastal marshes are generally not as abrupt as those in a reservoir but still impact fish productivity by altering habitat quantity and quality.
