For more than 30 years the U.S. Army Engineer
Research and Development Center (ERDC) has been
leading research and technology development to
minimize the risk of entrainment of sea turtles (and other
protected species) during dredging projects.
“Entrainment of sea turtles (direct uptake by the suction
field generated at the draghead) during hopper dredging
has been a potential issue during hopper dredging projects
in the Southeastern U.S. since 1980,” said Environmental
Laboratory Research Biologist Dena Dickerson, who is a
leading researcher in these efforts as ERDC’s foremost turtle
Developing efficient and effective protection systems
for the seven species of sea turtles, which have existed since
the time of the dinosaurs, continues as an ERDC research
priority. With a streamlined shell design for swimming,
these turtles differ from their land cousins, having no ability
to retract heads and legs into their shells.
Dickerson and Research Hydraulic Engineer Tim Welp
with the Coastal Hydraulics Laboratory have teamed up
within the USACE Dredging Operations Environmental
Research (DOER) Program to evaluate a new technique
to protect sea turtles during hopper dredging. The field
testing team also included Biological Science
Environmental Manager Stephen Willis, San
Francisco District, and Doug Novy, Great Lakes
Dredge and Dock Inc.
The sea turtle protection equipment tested was
an array of chains forming a curtain that extends
from the dredging drag arm approximately 25
feet ahead of the draghead. These “tickler” chains
were designed after similar chain equipment used
by the fishing industry and for aquatic biological
sampling. For these applications, tickler chains
are hung from fishing nets and dragged along the
sediment to induce organisms to move up off the
sediment and into the nets.
“We hung the tickler chains off the [Portland
District dredge] Essayons’ drag arm and dragged
them along the seafloor ahead of the draghead to stimulate
any turtles on or near the seafloor to move away from the
draghead to prevent entrainment,” Dickerson said.
If shown to be effective in sea turtle protection, these
tickler chains could potentially be used during some
hopper dredging projects where the currently used
protection equipment, such as draghead deflectors, cannot
be used; in tandem with draghead deflectors to provide
increased protection and allow for expanded dredging
windows; or in lieu of draghead deflectors.
“The lighter-weight tickler chains would potentially
provide more efficient, safer and productive dredging than
the currently used draghead deflector,” Dickerson said.
The field testing team conducted evaluations of this
new equipment March 24-25 aboard the Essayons at
Barber’s Point in Oahu, Hawaii.
“Beginning in March, hopper dredging projects in
Hawaii were required to implement the same sea turtle
management and mitigation techniques required on Atlantic
and Gulf of Mexico dredging projects,” Dickerson said.
“ERDC assisted Honolulu District and Pacific Islands
National Marine Fisheries Service in five channels
throughout Hawaii, establishing appropriate sea turtle and
marine mammal protection equipment and protocols there.
We are now monitoring programs for hopper dredging
done during March and April.”
The Honolulu District contacted ERDC for assistance
through the Dredging Operations Technical Support
program, known as DOTS, because of its prior assistance
to the district for protected species consultation work with
NOAA related to the Hawaii dredging projects.
“The new approach to sea turtle protection required
field validation, performed in Hawaii through the DOER
program, since these mitigation techniques would be
directly applicable to all U.S. coastal hopper dredging
projects as well as international hopper dredging within sea
turtle habitat,” Dickerson said.
The partnership between ERDC, the Honolulu and
Portland districts, and the National Marine Fisheries Service
(NMFS) provided a valuable opportunity to test innovative equipment designed to provide additional
protection to sea turtles and improve
“The DOER study evaluated the chains’
performance (fouling, entanglement)
during actual dredging activities using three
types of underwater camera systems for
equipment monitoring, including a high frequency
acoustic camera (3.0 MHz high
resolution/high definition imaging sonar)
mounted on a pan/tilt rotator assembly,
a high definition camera with lights, and
GoPro cameras in underwater housings.
“All were mounted
on the dragpipe near
the draghead of the
dredge. The study also
evaluated the ability
to utilize underwater
camera systems to
turbidity really limited
data quality of the high
definition and GoPro
camera systems, images
collected with the
acoustic camera were
so good that we were
able to discriminate
individual links in the
half-inch diameter chain
and also ‘see’ sediment
interactions with the
draghead and chains
that, to my knowledge, has not been done
before,” Welp said.
“This study demonstrated that the
chains could be deployed as designed on an
operating dredge without entanglement or
restriction to dredging activities,” Dickerson
The chains’ effectiveness in reducing
entrainment of sea turtles is still being
evaluated through data collected by
endangered species monitors on the
dredge. The study also demonstrated
for the first time that high-frequency
acoustic cameras could be successfully
used to monitor dredging equipment and
operations, as well as sea life.
Dickerson emphasized that study
results will have direct application for all
hopper dredging projects with potential
entrainment issues of protected resources.
“This is a new tool for the U.S. dredging
industry to provide more flexibility
in the management options for sea
turtle protection and
potentially other species.
“Issues related to
of sea turtles and other
sea life during dredging
projects is a primary
concern for USACE, the
dredging industry and
Over the past 30 years,
have been invested in
to minimize impacts to
protected resources, such
as sea turtles, during
is a prime example
of how ERDC’s
researchers can develop
innovative solutions to
from dredging projects.
“One of ERDC’s key talents is that we are
a multi-discipline organization. That allows
for across-laboratory and across-USACE teamwork — and, in this study, additional
partnering with NMFS and the dredging
industry — to address complex problems
facing our nation,” Dickerson said.