Defining habitat preferences of pelagic loggerhead sea turtles (Caretta caretta) in the North Atlantic through analysis of behavior and bycatch

• Main Author: McCarthy, Abigail L.
• Other Authors: Heppell, Selina S., Strub, P. Ted, Krueger, William, Boehlert, George, Fisheries and Wildlife, Oregon State University. Graduate School
• Format: Master Thesis
• Language: English; unknown
• Published: Oregon State University
• Subjects: Loggerhead turtles > Habitat > North Atlantic Ocean > Remote sensing; Loggerhead turtles > Behavior > North Atlantic Ocean; Sea turtles > Habitat > North Atlantic Ocean > Remote sensing; Sea turtles > Behavior > North Atlantic Ocean; North Atlantic
• Online Access: https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/0r967674h

For many species of marine turtle the characteristics that define pelagic habitat have yet to be fully identified. A better understanding of these habitat characteristics is critical to reduce high seas fisheries interactions with turtles, especially as the status of many turtle populations has placed them on the threatened or endangered species list. The combination of high-resolution satellite-tracking data with remotely sensed oceanographic data makes it possible to identify habitat for loggerhead turtles by analyzing the behavior of individual animals. Bycatch of loggerhead turtles in longline fisheries can also be examined using the same high-resolution oceanographic data to determine if there are identifiable habitat differences in high- and low- bycatch areas. I analyzed the tracks of ten loggerhead turtles tagged in the spring and fall of 1998 near Madeira, Portugal in relation to the marine environment they occupied. To determine the relationship between an individual turtle and its environment, some measure of behavior was necessary. I calculated the straightness index (SI), the ratio of the displacement of the animal to the total distance traveled, for individual weekly segments of the ten tracks as a measure of individual behavior. I then extracted information about the chlorophyll, sea-surface temperature (SST), bathymetry, and geostrophic current of the ocean in a 20km buffer surrounding the tracks, and examined the relationship between the straightness index and those characteristics using logistic regression. Chlorophyll a value, bathymetry, and movement of the turtle with geostrophic currents were consistently related to the straightness index of the tracks of all ten animals (two-sided p-value from Wald's test: 0.005, 0.0017, and 0.0018, respectively). Tracks were less straight in high chlorophyll regions and in shallower ocean areas, and animals were more likely to be moving with prevailing geostrophic currents during straighter track segments. These results confirm comparable analyses of ...