Field data and laboratory feeding experiments support the hypothesis that predation can be an important factor in the adaptive significance of vertical migration among zooplankton. In both Gatun Lake in Panama and Fuller Pond in Connecticut the diel vertical migration patterns of prey populations assume distributions which result in lessened predation by the dominant lake planktivores. It is concluded that such patterns of vertical migration will result when prey populations are under intense, selective pressures from visually dependent predators.

No abstract

Th is report was prepared as an account of work sponsored by the Un1ted Stat es Government. Neither the United States nor the Energy Research and Development Administration / United States Nuclear Regulatory Commission , nor any of the1r employees , nor any of their contractors. subcontractors , or their employees. mak es any warranty , express or implied, or assumes any legal liability or respon sibil i ty for the accuracy, completeness or usefulness of any information, apparatus, product or process disclosed, or represents that its use would not infringe privately owned nghts .

In analyzing the surrogate sites certain assumptions were made, one being that the technology used in the large NECs was the same as that in 4-and 10-unit plants. This caused certain effects, such as eutrophication and silting, to be much greater at a 40-unit plant than at a 4-unit plant.

An experimental program to evaluate the effects of entrainment on aquatic organisms is being conducted at ORNL. The damage to fish eggs and larvae during entrainment through condenser cooling water systems is one of the major environmental impacts of electric power plants. St~dies at operating P?wer plants have indicated that mortality rates can be excessive. These r~tes may vary among species and between plants. In order to assess the mortality associated with each component of the cooling system, a power plant simulator has been designed and is now under construction. The design of the apparatus is such that the internal hydraulics of an operating power plant condenser cooling system will be effectively reproduced. Experiments will be conducted using fresh water and marine fish species according to the experimental designs described herein. Rearing and holding facilities have been designed and assembled to assure a supply of specimens ~nd allow assessment of delayed mortality. The identification •of the factors which cau~e mortality during entrainment will provide a rational foundation for redesign of the components in cooling systems to minimize environmental impacts.