Model
Digital Document
Publisher
Florida Atlantic University
Description
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.
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.
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