De Gruyter
Seasonal migration patterns of bottlenose dolphins -- what we
know for sure?
With the changing of the seasons comes the urge to migrate for
many animals of the world, whether they be furred, feathered, or even finned.
One finned animal in particular, the common bottlenose dolphin, undertakes
seasonal migrations each spring and fall, but how the dolphins know when to
migrate has not always been clear.
It was usually assumed that their southern
migration begins when the ocean waters drop in temperature.
However, until now
there was little evidence to support this and it was largely unknown what
factors influence the initiation of dolphin migration.
A new study from the
online journal Animal Migration, has discovered some of the factors
that influence these seasonal migrations.
In the article, Masters student Anna Taylor, from the University of Georgia (USA), and colleagues studied the common bottlenose dolphin, which migrates seasonally along the southeastern United States Atlantic coast.
While this species of dolphin is
widely studied, surprisingly little is known about what influences the timing
of these migrations.
The scientists needed to track the comings and goings of
dolphins at their study sites on the Georgia and South Carolina coasts, and
they did so using photographic identification of individual dolphin fins.
This
technique is used with many studies of Cetaceans (whales, dolphins and
porpoises), which all have dorsal fins. As the animals age, their dorsal (back)
fins become worn and chipped, which allows individuals to be uniquely
identified, much like fingerprints.
By teaming up with the National Oceanic and Atmospheric
Administration (NOAA) and the Georgia Dolphin Ecology Program (GDEP), the
researchers conducted boat-based surveys, where they photographed all dolphins
(or their fins) they came across.
They then used photo analysis software to
analyze each dolphin's fin shape and pattern, which told them when and where
each dolphin (nearly 1000 uniquely-identified individuals) went over the course
of their study.
Then, by combining the dolphin movement data with information
on various aspects of water quality, the authors discovered that seasonal
movements, or migrations, were best explained by water temperature; while
seasonal abundance was best explained by water salinity.
The authors pointed out that this information can inform
conservation strategies for common bottlenose dolphins, and help managers
predict when a migration event is likely to occur.
According to the Georgia
Aquarium in Atlanta, Georgia, one of the main threats facing this species is
from "entanglement in recreational and commercial fishing gear";
therefore, understanding when dolphins are in the area might mitigate the
chances that these dolphins are injured.