Loggerhead turtles record a passing hurricane

Date:
September 1, 2020
Source:
NOAA Northeast Fisheries Science Center
Summary:
Caught in an Atlantic hurricane, satellite-tagged loggerhead
turtles changed their dive behavior and movement patterns as the
storm passed.

The tags also recorded changes in the environment.



FULL STORY ==========================================================================
In early June 2011, NOAA Fisheries researchers and colleagues placed
satellite tags on 26 loggerhead sea turtles in the Mid-Atlantic
Bight. The tagging was part of ongoing studies of loggerhead movements and behavior. The Mid-Atlantic Bight, off the U.S. East Coast, is the coastal region from Cape Hatteras, North Carolina to southern Massachusetts. A
little more than 2 months later, on August 28, Hurricane Irene passed
through the area, putting 18 of the tagged turtles in its direct path. The researchers were able to track changes in the turtles' behavior coinciding
with the hurricane, and found that they reacted in various ways.


========================================================================== "Hurricanes are some of the most intense weather events loggerheads in
the mid- Atlantic experience, and we thought it was worth investigating
how turtles in our dataset may be influenced by these dramatic
environmental changes," said Leah Crowe, a contract field biologist
at the NOAA Northeast Fisheries Science Center's laboratory in Woods
Hole, Massachusetts, and lead author of the study published recently in Movement Ecology. "It was a perfect storm situation in terms of location, timing, and oceanographic conditions. We found that the turtles responded
to the changes in their habitat in different ways." Satellite tags
attached to a turtle's carapace, or shell, transmitted the turtles'
location and dive behavior. They also recorded sea-surface temperatures
and temperature-depth profiles for approximately 13 months. This enabled
the researchers to investigate the movements of 18 juvenile and adult-
sized loggerhead turtles and associated oceanographic conditions as the hurricane moved through the region.

Most of the turtles moved northward during the hurricane,
aligning themselves with the surface currents -- perhaps to conserve
energy. Researchers observed longer dive durations after the hurricane
for turtles that stayed in their pre- storm foraging areas. Some dives
lasted an hour or more, compared with less than 30 minutes for a typical
dive before the storm.

The turtles that left their foraging areas after the hurricane passed
moved south earlier than would be expected, based on their normal
seasonal movements.

This change was also more than a month earlier than the typical seasonal cooling in the water column, which is also when the foraging season for loggerhead turtles ends in the Mid-Atlantic Bight.

"Loggerheads experience environmental changes in the entire water
column from the surface to the bottom, including during extreme weather events," said Crowe. "This study was an opportunistic look at turtle
behavior during a hurricane. Their behavior makes loggerheads good
observers of oceanographic conditions where they forage." The study was conducted by researchers at the Northeast Fisheries Science Center and colleagues at the nearby Coonamessett Farm Foundation in East Falmouth, Massachusetts. The team has tagged more than 200 loggerheads in the Mid-Atlantic Bight since 2009.



==========================================================================
This work has created a continuous time-series of data on loggerhead
sea turtles. With 10 years of data, researchers can now get a deeper understanding of how turtles behave and what environmental factors
drive them. They can also look back at the data and ask new questions,
as they did in this study.

Waters in the Mid-Atlantic Bight are highly stratified, or layered, by temperature in the summer. At the surface, water is warm. A cold layer,
also called a cold pool, forms beneath this warm layer and is present
from May to October. The presence of the cold pool overlaps with the
Atlantic hurricane season, which runs from June through November. It
also overlaps with the presence of foraging loggerheads that are in the
area between May and September.

Hurricane modeling is especially difficult in the Mid-Atlantic Bight
because of the cold pool. In this study, it was unclear which aspect of
the environmental changes prompted behavioral changes. Previous studies
have found that loggerhead behavior appears to be sensitive to changes
in water temperatures throughout the water column. Hurricanes cause
the water layers to mix, which creates cooler surface temperatures. The
mixing also disrupts the thermocline - - the boundary layer between warm surface waters and colder, deeper waters.

Ocean temperature data recorded by the turtles' satellite tags are
consistent with observations from weather buoys and autonomous gliders operating in the region. Depending on how many tags are deployed, data
from tagged turtles can cover a more extensive area within a season than
other oceanographic data sources.

More measurements of water temperatures throughout the water column in
the region could help improve oceanographic models. Researchers say data
from the turtle tags are an underused resource that has the potential
to improve weather models, including hurricane models.



==========================================================================
Many of the natural and human-induced impacts on sea turtle behavior,
or the environments that sea turtles live in, are still unknown.

Previous studies indicate that sounds from dredge operations, seismic activity,offshore wind farm development, and marine recreation may
also impact sea turtle distribution and dive behavior. Turtles might
be impacted directly or through habitat alterations. While studies have
looked at how tropical storms and hurricanes affect some marine species,
there are few examples of examining sea turtle interactions with large
storms.

In this study, turtle behavior did not return to pre-storm behavior
within 2 weeks after the storm.

"The long-term cumulative effects of a changing climate and the increase
in intensity of hurricanes and other storms is something that needs to
be looked at. Changes in sea turtle movements and behavior can affect
abundance estimates and management decisions," Crowe said. "This study
reminds us that turtles live in a dynamic environment, and we cannot
assume their behavior will be consistent throughout space and time."
The study was supported by funds from the Atlantic Marine Assessment
Program for Protected Species and the New England/Greater Atlantic
Region's Research Set-Aside Program.


========================================================================== Story Source: Materials provided by
NOAA_Northeast_Fisheries_Science_Center. Note: Content may be edited
for style and length.


========================================================================== Journal Reference:
1. Leah M. Crowe, Joshua M. Hatch, Samir H. Patel, Ronald J. Smolowitz,
Heather L. Haas. Riders on the storm: loggerhead sea turtles
detect and respond to a major hurricane in the Northwest Atlantic
Ocean. Movement Ecology, 2020; 8 (1) DOI: 10.1186/s40462-020-00218-6 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200901112201.htm

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