Seasonal shifts in the movement and distribution of green sea turtles Chelonia mydas in response to anthropogenically altered water temperatures

Anthropogenically altered water temperatures (AAWT) have the potential to affect the movement and distribution of marine ectothermic species. Green sea turtles (GSTs) Chelonia mydas are an ectothermic species observed inhabiting 2 sites with AAWT at the northern point of their geographical range in the eastern Pacific. An acoustic receiver array was deployed with temperature loggers at the San Gabriel River, Long Beach, CA, where 2 power plants discharge warm water into the river, and at the 7th St. Basin, Seal Beach, CA, a dredged shallow basin with warmer water compared to surrounding coastal habitats during the summer months. Juvenile GSTs (n = 22, straight carapace length = 45.2 to 96.8 cm) were tagged with acoustic transmitters. Turtles in the basin migrated into the river during winter months when temperatures dropped below 15°C. During the winter, turtles were most frequently detected at the river receiver stations adjacent to and downstream of the power plants. This suggests that GSTs use the warm effluent as a thermal refuge, avoiding colder areas upstream of the power plants and near the river mouth. In the summer, turtles were most frequently detected at receiver stations upstream of the power plants, potentially exploiting areas of the river with higher primary productivity. AAWT sustain the northernmost aggregation of GSTs in the eastern Pacific year round; however, based on GST thermal tolerance, this population is expected to change their movement patterns when the power plants discontinue discharging warm water by 2029.