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Migratory Behavior of Hatchling Sea Turtles: Evidence for Population-Specific Divergence in the Loggerhead (Caretta caretta L.)

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Date Issued:
2007
Summary:
Migratory bird and insect populations show differences in orientation direction, timing, and distances moved depending upon where they reside in relation to their migratory goals. These differences presumably occur because of selection for behavioral responses that promote the most efficient migratory strategies among members of each population. The purpose of this study was to determine whether migratory behavior in loggerhead hatchlings differs between populations that exit nesting beaches on the East and West coast of Florida. When the turtles emerge from the nests, they initially show a swimming "frenzy" that serves to distance individuals from shallow coastal waters, displacing them toward oceanic currents that are used to transport the turtles to the North Atlantic Gyre. On the East coast of Florida, turtles swim eastward toward the Florida Current (western portion of the Gulf Stream) located relatively close to the shoreline (on average, 2 km offshore at Miami to 33 km offshore at Melbourne Beach). On the West coast of Florida, turtles swim westward toward the Loop Current in the Gulf of Mexico, which is located farther offshore (150 km offshore at St. Petersburg to over 200 km offshore at the Everglades National Park). In a previous study, we demonstrated that for East coast loggerheads, the frenzy consists of continuous swimming for - 24 h, followed over the next 5 days by postfrenzy (diurnal, with little nocturnal) swimming activity. No comparable data exist that characterize the frenzy period of loggerheads from the West coast ofFlorida. We used identical methods to quantify the migratory activity of hatchlings from the West coast of Florida. Hatchlings were captured as they emerged from nests located between Venice and Sarasota, Florida. They were then tethered in water-filled pools under laboratory conditions, where temperature and photoperiod could be controlled to duplicate conditions used when studying the East coast turtles. Activity was continuously recorded over the next six days. The data were analyzed to determine the proportion of time the turtles spent swimming every day, and the proportion of that swimming activity that occurred during the light and dark period of each day. Turtl~s from each coast showed no statistical difference in the proportion oftime spent swimming each day. However, after day 1, West coast hatchlings showed statistically lower levels of swimming activity during the day and statistically higher levels of swimming activity at night than did turtles from the East coast. We hypothesize that these differences may reflect a more diffuse period of active "searching" for appropriate oceanic currents by the West coast turtles, under conditions where greater predation pressures might select for more movement under conditions of darkness. Such a response may be appropriate when migratory goals are located at greater distances, and when turtles must migrate farther from the coast to reach deeper, and presumably less predator-rich, waters.
Title: Migratory Behavior of Hatchling Sea Turtles: Evidence for Population-Specific Divergence in the Loggerhead (Caretta caretta L.).
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Name(s): Madrak, Sheila Veronica, author
Salmon, Michael, Thesis advisor
Florida Atlantic University, Degree grantor
Type of Resource: text
Genre: Electronic Thesis Or Dissertation
Date Created: 2007
Date Issued: 2007
Publisher: Florida Atlantic University
Place of Publication: Boca Raton, Fla.
Physical Form: application/pdf
Extent: 44 p.
Language(s): English
Summary: Migratory bird and insect populations show differences in orientation direction, timing, and distances moved depending upon where they reside in relation to their migratory goals. These differences presumably occur because of selection for behavioral responses that promote the most efficient migratory strategies among members of each population. The purpose of this study was to determine whether migratory behavior in loggerhead hatchlings differs between populations that exit nesting beaches on the East and West coast of Florida. When the turtles emerge from the nests, they initially show a swimming "frenzy" that serves to distance individuals from shallow coastal waters, displacing them toward oceanic currents that are used to transport the turtles to the North Atlantic Gyre. On the East coast of Florida, turtles swim eastward toward the Florida Current (western portion of the Gulf Stream) located relatively close to the shoreline (on average, 2 km offshore at Miami to 33 km offshore at Melbourne Beach). On the West coast of Florida, turtles swim westward toward the Loop Current in the Gulf of Mexico, which is located farther offshore (150 km offshore at St. Petersburg to over 200 km offshore at the Everglades National Park). In a previous study, we demonstrated that for East coast loggerheads, the frenzy consists of continuous swimming for - 24 h, followed over the next 5 days by postfrenzy (diurnal, with little nocturnal) swimming activity. No comparable data exist that characterize the frenzy period of loggerheads from the West coast ofFlorida. We used identical methods to quantify the migratory activity of hatchlings from the West coast of Florida. Hatchlings were captured as they emerged from nests located between Venice and Sarasota, Florida. They were then tethered in water-filled pools under laboratory conditions, where temperature and photoperiod could be controlled to duplicate conditions used when studying the East coast turtles. Activity was continuously recorded over the next six days. The data were analyzed to determine the proportion of time the turtles spent swimming every day, and the proportion of that swimming activity that occurred during the light and dark period of each day. Turtl~s from each coast showed no statistical difference in the proportion oftime spent swimming each day. However, after day 1, West coast hatchlings showed statistically lower levels of swimming activity during the day and statistically higher levels of swimming activity at night than did turtles from the East coast. We hypothesize that these differences may reflect a more diffuse period of active "searching" for appropriate oceanic currents by the West coast turtles, under conditions where greater predation pressures might select for more movement under conditions of darkness. Such a response may be appropriate when migratory goals are located at greater distances, and when turtles must migrate farther from the coast to reach deeper, and presumably less predator-rich, waters.
Identifier: FA00000792 (IID)
Degree granted: Thesis (M.S.)--Florida Atlantic University, 2007.
Subject(s): Animal migration--Florida
Sea turtles--Migration--Florida
Predation (Biology)
Animal orientation--Florida
Held by: Florida Atlantic University Libraries
Sublocation: Digital Library
Persistent Link to This Record: http://purl.flvc.org/fau/fd/FA00000792
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Host Institution: FAU
Is Part of Series: Florida Atlantic University Digital Library Collections.