|SREL Reprint #0932|
Thermal Effluent as a Sporadic Cornucoplia:
Effects on Fish and Zooplankton
Janssen and John P. Giesy
We report effects of a thermal effluent on fish and
zooplankton in an impoundment in South Carolina. The effects are not directly due to heated effluent but are
indirect effects on the trophic dynamics of the system and depend on the
physical structure of the system, season, and geography.
As effluent from a nuclear reactor cooling pond (Pond C) enters the
larger Par Pond it sporadically carries with it zooplankton and/or dead fish.
Pond C produces high zooplankton densities in two situations:
(1) high and hot effluent flow during cold winter weather; and (2) low
(cool) effluent flow during warmer seasons.
High zooplankton densities attract blueback herring, Alosa aestivalis,
which attract largemouth bass, Micropterus salmoides.
Dying and dead bluegills, Lepomis macrochirus from Pond C
(heat killed) are eaten by Par Pond bass which swim into effluent temperatures
as high as 46C to take these easy prey. Blueback
herring and largemouth bass distribution are affected by the presence of food
rather than by temperature. Par
Pond blueback herring appear to be available to bass mainly when herring are
near the effluent from Pond C and when they spawn in spring in the littoral
zone. Because blueback herring in
Par Pond live only one year and because their presence in bass habitat is
seasonal there is a strong seasonal component to bass food abundance. A previously reported annual oscillation in bass condition
(K), with a peak in winter, occurs throughout Par Pond but is extreme in the
vicinity of the effluent. The
strong seasonality of food abundance for bass at the effluent correlates the
winter peak in bass condition.
Thermal effects, Thermoregulation, Predation, Stress, Bluegill,
Largemouth bass, Blueback Herring
SREL Reprint #0932
Janssen, J. and J.P. Giesy. 1984. A thermal effluent as a sporadic
cornucopia: effects on fish and zooplankton. Environmental Biology of Fishes