CRITICAL THERMAL MAXIMA OF THREE PLATTE RIVER FISH SPECIES RELATIVE TO WATER TEMPERATURE REGIMES
Brett P. Fessell, Edward J. Peters, Richard S. Holland, Department of Forestry, Fisheries, and Wildlife, University of Nebraska, Lincoln, NE
Temperature is considered to be a controlling factor and has pervasive influences on the biology, physiology, and ecology of fishes. Direct effects of elevated temperatures may stem from decreased metabolic activity in nervous tissue resulting in asphyxiation; however indirect effects on reproduction, ability to resist disease, and maintain performance in the presence of competition and predation may be more influential on the ultimate success of fishes occupying harsh environments (Brett 1956). Harsh environments typically exhibit extreme fluctuations in temperature, discharge, and turbidity and can have significant effects on fish populations therein (Matthews 1987). Exact mechanisms which allow fluctuating temperatures to play a pivotal role in regulating fish populations remain unclear. Fish either evolve physiologically to tolerate high temperatures or avoid temperatures less conducive to physiological performance through behavioral modifications (Hutchinson 1976; Reynolds and Casterlin 1976; Hutchinson and Maness 1979; Neill 1979; and Matthews 1987; Rutledge and Beitinger 1989). Huey and Stevenson (1979) argue that thermal tolerance measurements have limited ecological significance, and they feel behavioral regulation of optimum body temperature may provide more relevant information for extrapolation to ecological influences. However it is difficult to measure and interpret behavioral responses of fish under laboratory conditions and complications are magnified in the field. Information obtained from thermal tolerance studies appears to be reliable for measuring physiological stress and adaptation of fishes giving researchers the ability to set observable limits of tolerance by measuring physiological performance thresholds (Kowalski et al. 1978; and Paladino et al. 1980).
Critical Thermal Maximum (CTM) has been used extensively as a tool to measure thermal tolerance of ectotherms, primarily in laboratory experiments, since it was defined by Cowells and Bogert (1944), modified for statistical analysis by Lowe and Vance (1955), and standardized by Hutchinson (1961). Critical thermal maximum is defined as the "arithmetic mean of collected thermal points at which locomotor activity becomes disorganized to the point at which the organism loses its ability to escape conditions that will promptly lead to its death" (Cowells and Bogert 1944). This is typically characterized by the inability to right oneself and the onset of muscular spasms. Direct field measurements of CTM have been virtually ignored in the literature, therefore it is difficult to effectively correlate laboratory data with field data. Most previous work has examined CTM's of fish acclimated to stable temperatures in the laboratory where little attempt is made to directly correlate laboratory and field data (Reynolds 1977; Magnuson et al. 1979; and Deacon et al. 1987). Both field and laboratory studies were conducted in this project, however only the field component is reported here.
Rivers of the Great Plains often exhibit declines in summer flow as a result of drought and dewatering for agricultural, domestic, and industrial purposes. Consequently, fish communities may be adversely affected through modification of abiotic factors such as temperature or dissolved oxygen (Matthews 1988). The wide, shallow braided channels of the Platte River are typical of Great Plains Rivers. These characterisitcs make the Platte susceptible to drought and diversion of water for power and irrigation districts contributing further to the depletion of summer flows critical for fish populations during this stressful period. Instream temperatures are susceptible to the effects of insolation and have been known to exceed 39o C under such conditions. Fish kills have been reported along several reaches of the Platte River periodically since the summer of 1988 (Dinan 1992). However temperature could not be conclusively implicated in the fish kills reported. The focus of this research was to determine whether temperature can in fact be implicated in fish kills reported. Using the information obtained from this work we hope to predict periods where fish populations may be susceptible to temperature related mortalities. Finally, thermal tolerance estimates of 16 common species in the Platte River will be presented.
FRESHWATER MUSSEL SURVEY OF THE PLATTE RIVER AND ASSOCIATED IRRIGATION AND HYDROPOWER CANALS AND LAKES
Mark M. Peyton and Jeremiah L. Maher, Central Nebraska Public Power and Irrigation District, Holdrege, Nebraska
In response to concerns expressed over the effects of hydropower and irrigation on the presence of freshwater mussels in the Platte River, the Central Nebraska Public Power and Irrigation District (Central) initiated a survey in 1991 for freshwater mussels in the upper Platte River and associated irrigation and power canals and lakes within this stretch of river.
From 1991 through 1994, 19 sites consisting of 30 kilometers of river and 20 kilometers of canals were surveyed, as well as ten canal lakes. The results of those surveys are presented here.
SUMMARY OF LEAST TERN AND PIPING PLOVER NESTING ACTIVITIES AT SITES IN THE UPPER PLATTE RIVER VALLEY MANAGED BY THE CENTRAL NEBRASKA PUBLIC POWER AND IRRIGATION DISTRICT
Mark M. Peyton and Jeremiah L. Maher, Central Nebraska Public Power and Irrigation District, Holdrege, Nebraska
In 1992 as a voluntary amendment to its interim license the Central Nebraska Public Power and Irrigation District (Central) began management of nesting areas of the endangered least tern (Sterna antillarum) and threatened piping plover (Charadrius melodus) in the upper Platte River valley.
In 1994 Central personnel surveyed the Platte River valley from Lexington to North Platte. Four areas were identified and monitored at least twice weekly throughout the season.
RECENT USE OF BEACHES AT LAKE MCCONAUGHY BY PIPING PLOVERS (CHARADRIUS MELODUS): A REVIEW
Mark M. Peyton and Jeremiah L. Maher, Central Nebraska Public Power and Irrigation District, Holdrege, Nebraska
The presence of piping plovers (Charadrius melodus) along the shore of Lake McConaughy was first documented in 1978 (Rosche, 1994), with the first record of nesting reported in 1985 (Johnsgard, 1990). In recent years the numbers of birds observed at the lake has increased significantly. The sandy beaches surrounding the lake have become one of the most important nesting areas for this species within Nebraska with 50 nests being recorded in 1994 and a total of 199 since 1992. Potential conflict arises because of high recreational activity at the lake. Observation of this subpopulation of birds has shown the birds to be remarkably tolerant of human activity. Experimental management practices using minimal protection measures appear to be successful.
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Last updated by Darren A. Jack on 6/11/97