644 CHUNG AND STRAWN 



~40°C discharge-canal water, reduces canal temperatures to 35°C or 

 less between the cooling towers and Galveston Bay. 



Experiments were conducted over a 16-month period, June 1974 

 through September 1975. All-glass 38-liter tanks filled with water 

 from the intake canal were aerated to provide circulation and were 

 thermally controlled within 0.1°C of predetermined levels. Survival 

 from June to September was determined at temperatures increasing 

 from 32 to 41°C in 1°C increments. Test temperatures above 35°C 

 represented those between the plant and the cooling towers, and 

 temperatures of 35° C or lower represented those between the 

 cooling towers and Galveston Bay. Average test temperatures were 

 lower from October to May when discharge-canal temperatures were 

 lower. A 1.5-mm mesh screen was used to confine small animals to 

 the front of the tank for easier observation. We measured survival for 

 180-min exposure periods, which we felt were representative of 

 exposure at the plant. Drift-bottle studies indicated that surface 

 water passed from the plant discharge to the first cooling-tower 

 intake in ~30 min. Temperature, taken by a hand thermometer, and 

 salinity, measured by a refractometer (American Optical Instrument 

 Company), in the intake and discharge canals at the water surface 

 were taken in conjunction with each experiment. All organisms 

 tested were captured from the intal<:e canal by dip net, cast net, lift 

 net, hoop net, and various traps on a daily basis during the hot 

 season (June— September) and once a month from October to May. 

 During the hot season, otter trawl and log and revolving screens were 

 also used occasionally. Hook and line and seine were used once a 

 week during the hot season and once a month during the remainder 

 of the year. After capture, animals were placed in a 45-liter ice chest 

 to minimize temperature change, aerated, and transported from the 

 intake canal to the laboratory in less than 5 min. In the laboratory 

 they were divided among experimental tanks according to species 

 and previous results at various temperatures. The number of animals 

 of one species in a tank never exceeded 30 and rarely exceeded 10, 

 except for small common species; availability was usually limited to 

 1 or 2 for most species (Chung, 1977). Species were mixed in the test 

 tanks, except highly predaceous species, such as the blue crab 

 {Callinectes sapidiis), which was tested separately. Care was taken to 

 avoid overcrowding and to use only animals that appeared to be in 

 good health. Preliminary tests indicated that animals very sensitive to 

 handling, such as the bay anchovy (Anchoa mitchilli) and silversides 

 {Membras martinica and Menidia beryllina), survived well beyond 

 180 min at intake-canal temperatures. For a given capture tempera- 

 ture, 100% of a sample frequently survived at reduced test 

 temperatures; these, thus, served as controls. This was true even 



