The Influence of the North Atlantic Oscillation (NAO), El Nino Southern Oscillation (ENSO), and Pacific Decadal Oscillation (PDO), on Loggerhead Nesting Seasons in Broward County, FL, USA

Sea turtles spend their life in the ocean, except when females emerge to nest. Since the development rates and sex ratios of turtle embryos are determined by temperature, changes in the timing of the nesting season can affect reproductive success. Therefore, it is important to understand the factors which may cause the nesting to begin earlier or later in the year. Several previous studies have reported connections between nesting season timing and sea surface temperature. Large-scale climatic phenomena such as the North Atlantic Oscillation (NAO), El Nino Southern Oscillation (ENSO) and Pacific Decadal Oscillation (PDO) affect ocean temperatures and current patterns and therefore may be linked to sea turtle nesting season timing and duration. These climatic phenomena have been described by simple indices that can be used to determine if any such effects on sea turtle nesting populations exist. The NAO, ENSO and PDO indices were compared to 20 years of loggerhead sea turtle nesting data from Broward County, FL, USA. There were significant inverse relationships between NAO index values and the beginning and ending dates of the nesting seasons suggesting that warmer temperatures, associated with positive phases of the NAO, may have caused nesting seasons to shift slightly earlier in the year. There were significant direct relationships between all three climate indices and the parameters related to the lengths of the nesting seasons however the changes in season lengths were small.