Effects of ambient temperature on dive behavior of East Pacific green turtles before and after a power plant closure

Abstract

Water temperature plays a critical role in mediating energy budgets and influencing the behavior of marine ectotherms. Previous research has demonstrated that marine ectotherms such as sea turtles conserve energy by decreasing activity levels in colder water—often at or near the latitudinal limits of their range. San Diego Bay is near the northern edge of the range for eastern Pacific green turtles and is home to a year-round foraging population. Turtles in San Diego Bay experienced a significant decrease in ambient water temperature following the closure of a fossil-fuel-based power plant and corresponding loss of the plant’s warm-water effluent. Time-depth recorders were placed on 13 turtles before (n = 5) and after (n = 8) the closure of this plant to determine how changing water temperature influenced dive duration. Deployments lasted 2-25 d, with a mean deployment of 7.5 d. Green turtle behavior in different thermal regimes revealed a strong relationship between dive duration and water temperature; dive duration was significantly longer when water temperatures were colder, especially when water was below 14.4°C. Establishing the inactivity threshold for this population is critical to future management in light of temperature variability in coastal habitats and the impacts this may have on sea turtle energetics. Understanding organismal response to relatively rapid shifts in thermal conditions is relevant to assessments of the direct and indirect anthropogenic effects on aquatic environments.