EFFECTS OF WATER DRAWDOWN ON THE FAUNA IN SMALL COLD WATER RESERVOIRS¹

Abstract

Two small cold water reservoirs with stable water levels were compared with two reservoirs scheduled for complete drawdown to determine the effects of drawdown on invertebrate abundance and fiih abundance and density. An extensive literature review supplemented the results with other applicable information. No conclusive evidence of effects of drawdown on invertebrates or fish was found. Characteristics of a reservoir and its drainage basin which obscure or lessen drawdown effects are discussed. Analysis and observation of drawdown procedures showed that duration and scheduling of drawdown periods are important in determining whether drawdown will be harmful to fauna in a given reservoir. (KEY TERMS: drawdown effects; drawdown patterns; small cold water reservoirs; invertebrates; trout; suckers; reservoir ecology.) LITERATURE CITEDAass, P., 1960. The effects of impoundment on inland fisheries.

LIMNOLOGICAL PROPERTIES OF A ROCKY MOUNTAIN HEADWATER RESERVOIR1

“…In early June they decreased to 12 d. Subsequently, they gradually increased to 44 d by mid-October and were maintained between 38 to 42 d until mid-December 1976. Through the entire period from mid-March to mid-December, storage times averaged 40 d. These results and those from McAfee (1980) indicate that, while retention times in Rocky Mountain headwater reservoirs can be brief during some periods, average water exchange rates for these systems can be similar to those for larger, lower elevation reservoirs (cf., Hrbacek and Straskaba, 1966;Rada, 1974;Whalen, et al, 1982). Euphotic zone depths in Hyalite Reservoir averaged 12 m, ranging from 17 m on August 16 to 10 m on August 30.…”

RECREATIONAL ENHANCEMENT OF HIGH COUNTRY WATER SUPPLY RESERVOIRS1

“…Most of the reservoirs of the Colorado Front Range can support cold water fisheries (McAfee, 1976). However, management practices resulting in extreme drawdown and refill of a reservoir can adversely affect the potential for fishery development.…”

Ecological impacts of winter water level drawdowns on lake littoral zones: a review

“…For example, Delong and Mundahl (1995) found significant reductions in invertebrate densities in littoral zones after a 4.6 m drawdown; however, in the same lake 16 years later, Swanson (2010) found no significant density reductions at 0.6 and 1.5 m depths shortly after a 0.9 m winter drawdown. Under these amplitudes, other environmental factors (e.g., lake morphometry, local-habitat features, water quality) may better explain variation of assemblage level character (McAfee 1980;White et al 2011). Despite the level of drawdown amplitude, invertebrate densities can remain similar across winter drawdown lakes at exposed and unexposed depths (Aroviita and Hämäläinen 2008).…”

“…Winter drawdowns can also affect littoral spawning species if eggs are exposed to desiccation (Gaboury and Patalas 1984;Mills et al 2002) and low DO concentrations (Sutela et al 2002). McAfee (1980) recorded significantly lower abundances of Salvelinus fontinalis (brook trout) in winter drawdown lakes potentially due to temporal overlap of water level lowering and their spawning period. Drawdowns and subsequent refills can also benefit recruitment for some fish species.…”

“…For example, Dupont (1994) showed higher catch rates for habitat generalists (e.g., Catostomus macrocheilus) and species that utilize the pelagic zone in a winter drawdown reservoir relative to a natural system. Feeding generalists (e.g., Catostomus commersonii) also maintain high abundances in winter drawdown lakes (McAfee 1980), suggesting resilience to an impoverished littoral macroinvertebrate food supply (Haxton and Findlay 2009). Piscivores with pelagic juvenile stages (e.g., Sander vitreus, S. canadensis) are more abundant in annual winter drawdown lakes, compared to unregulated lakes.…”