Orientation

Little is known about the visual capabilities of marine turtles. The ability to discriminate between colors has not been adequately demonstrated on the basis of behavioral criteria. I used a three-part methodology to determine if color discrimination occurred. FIrst, I exposed naèive, light-adapted hatchlings to either a blue, green or yellow light. I manipulated light intensity to obtain a behavioral phototaxis threshold to each color, which provided a range of intensities we knew turtles could detect. Second, I used food to train older turtles to swim toward one light color, and then to discriminate between the rewarded light and another light color ; lights were presented at intensities equally above the phototaxis threshold. Lastly, I varied light intensity so that brightness could not be used as a discrimination cue. Six turtles completed this task and showed a clear ability to select a rewarded over a non-rewarded color, regardless of stimulus intensity. Turtles most rapidly learned to associate shorter wavelengths (blue) with food. My results clearly show loggerheads have color vision. Further investigation is required to determine how marine turtles exploit this capability.

In Florida, loggerhead sea turtle (Caretta caretta) nesting populations are in decline, and human presence on beaches during nesting season can create an array of problems for the sea turtles. Volunteers and workers from the Loggerhead Marinelife Center collected nesting data from 2001 to 2005 along a 9.7 km stretch of Jupiter and Juno Beach, in Palm Beach County, Florida. Using these data, I found that human presence appears to have a negative impact on false crawl rates. The rate of false crawl was significantly higher on weekends than on weekdays(χ2 = 6.3, p < 0.05), and in areas with continuous public access than in areas with no public access(χ2 = 69.0, p < 0.0001). However, there was no significant difference in the number of nests laid on weekends versus weekdays(χ2 = 0.6, p > 0.05), although there are still other, less obvious negative effects caused by false crawling, and even nesting, while humans are in the vicinity. Even though it is impractical to try to keep people off the beach at night, it is important to increase awareness of the negative impacts that human presence may have on sea turtle nesting in order to help reverse the decline in the population of loggerhead sea turtles.