THE INFLUENCE OF SPRING AND FALL TEMPERATURES ON THE AVOIDANCE RESPONSE OF JUVENILE ATLANTIC MENHADEN, BREVOORTIA TYRANNUS, EXPOSED TO SIMULTANEOUS CHLORINE‐δT CONDITIONS1

Abstract

ABSTRACT: The avoidance response of groups of juvenile Atlantic menhaden, Brevoortia tyrannus, was evaluated by exposing test species to a range of simultaneous total residual chlorine (TRC) (0.00, 0.05, 0.10, and 0.15 mg/L) and elevated temperature (0, 2, 4, and 6°C) conditions simulating power plant discharges. This species was tested at both 15 and 20°C to determine possible effects of acclimation temperature on the avoidance response. These temperatures were selected to represent spring or fall thermal conditions when most East Coast power plant facilities initiate power plant chlorination in the spring or terminate the use of this biocide in the fall. An unbalanced 3‐factor factorial design was used to develop response surface avoidance models at 15 and 20°C. The model developed at 15°C showed: (1) an increase in avoidance occurred at all δT conditions as TRC increased from 0.00 to 0.05 mg/L; (2) a greater degree of avoidance occured at TRC concentrations above 0.05 mg/L at all δT conditions; and (3) TRC was the most important term inflencing avoidance. The model for Atlantic menhaden at 20°C showed: 1) avoidance increased with increasing TRC concentration at each δT condition; (2) avoidance did not necessarily increase with increasing δT's at each TRC concentration; (3) greatest avoidance occured at 0°C δT and 0.15 mg/L TRC; and (4) TRC was the most important term influencing avoidance. There was a significant difference (p < 0.00001) between avoidance models at 15 and 20°C. However, when extreme conditions of 0.15 mg/L TRC and 0–6°δT were compared, the degree of avoidance responses (percent time in control area) was similar.