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|Title:||Factors affecting fish production and fishing quality in new reservoirs, with guidance on timber clearing, basin preparation, and filling|
|Authors:||U.S. Fish and Wildlife Service.|
Environmental and Water Quality Operational Studies (U.S.)
Ploskey, Gene R.
|Publisher:||Environmental Laboratory (U.S.)|
Engineer Research and Development Center (U.S.)
Abstract: Fishing pressure on U.S. reservoirs is increasing rapidly and may double in the next 20 years. To meet increasing fishing demands, effective practical plans must be implemented to maximize and prolong the high sport-fish production that characterizes new impoundments. This report reviews literature on fishery resource development and fish production in new reservoirs and provides guidance on filling and site preparation techniques that should enhance fish production and angling quality. During filling, reservoirs are extremely productive because virtually all allochthonous nutrients, detritus, and drowned terrestrial animals, as well as autochthonous production (primary and secondary), are retained in the basin. After a new impoundment is filled, fish production and harvest are high for the first 5 to 10 years but progressively decline as the reservoir ages. Strong year classes of fish may be produced in years of increased precipitation which increases inflow of nutrients and detritus from the drainage basin and raises the lake level to inundate woody vegetation, forest litter, and/or herbaceous plants. Declines in reservoir fisheries primarily result from the losses of nutrients and detritus to outflow and sediments and from the use of detritus by invertebrates and fish. Concerns during filling include timing of inundation and control of water levels. Because most riverine fishes have evolved reproductive strategies cued to spring floods, filling that resembles natural spring flooding is often the most successful in increasing fish production. Waters that have recently risen to inundate terrestrial vegetation when water temperatures are about 11°C (warmwater fish communities) or 5°C (coolwater fish communities) should greatly enhance spawning success and survival of young-of-year fishes by providing suitable spawning sites, food, and cover. Stage filling (filling to well defined successive pool level s) can be an effective tool to increase fish production, but it is seldom practical except in large storage reservoirs that are built in areas where consumptive needs do not exceed the amount of water that can be supplied at successive stages. Concerns for reservoir clearing depend on trade-offs among factors such as mosquito control, water quality, recreation, and fish production. Herbaceous plants and forest litter provide an enormous source of food for many microorganisms, zooplankton, benthos, and for some fish. In addition, herbs provide cover for young fish and spawning sites for adults. Woody vegetation provides cover for prey and young sport fish, and the amount of cover influences feeding efficiency and therefore the energy flow through predatory sport fish. Submerged timber, artificial shelters and other structures also concentrate sport fish to improve harvest. On the basis of biological observations, practical methods of clearing reservoirs are presented, but the effectiveness of various methods has not been evaluated, because of insufficient quantitative data. Nevertheless, on the basis of available literature, it is clear that the best clearing plans are those in which all herbaceous plants and forest litter are retained and where timber is retained in selected sites (coves, embayments, along old creek channels, in blocks, or in clusters). However, hazards to navigation and recreational usage should be kept in mind when considering leaving timber in place. A procedure for retaining blocks of timber along steeper shorelines is described. Construction of artificial structures presently cannot be justified monetarily for most new reservoirs in forest regions, where selective retention of timber may provide adequate, maintenance-free structure for no direct cost. In prairie regions, however, artificial structures may be justified and could greatly improve sportfishing.
|Appears in Collections:||Technical Report|