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Methods to Minimize Dredging Impacts on Sea Turtles
DENA DICKERSONERDC, Environmental Lab
U.S. Army Corps of Engineers Vicksburg, Mississippi
Coastal Sea Turtle Habitat
7 species worldwide
Feeding
Juvenile development
Reproduction
Southeastern US Sea Turtles
Kemp’s ridley Loggerhead
Leatherback Olive ridley
Green
Hawksbill
Dredging Impacts to Sea Turtles
• Entrain adults, subadults, juveniles
• Disrupt nesting activities
• Destroy nests and nesting habitat
On Shore Impacts In Water Impacts
Hopper Trailing Suction
693 Documented Sea Turtles Takes by Dredges
(1980-2011) (31.5-yrs)
Kemp’s ridleyLoggerhead Green
3 Sea Turtle Species (61 Unknown)
471 87 74
Southeastern US
77+ sites monitored44 sites with turtle takes
Photo: Dena Dickerson
LoggerheadCaretta caretta
US - ThreatenedWorld - Endangered
GreenChelonia mydas
Endangered US – Threatened/
World - Endangered
Photo: Dena Dickerson
Photo: Erin Seney
Kemp’s ridleyLepidochelys kempii
US - EndangeredWorld – Critically
Endangered
Olive ridleyLepidochelys olivacea
Photo: Bill Curtsinger
US – Threatened /
World – Vulnerable
Endangered
Olive ridley – Arribada (Mass nesting)
Mexico
India
HawksbillEretmochelys imbricata
US - EndangeredWorld - Critically
Endangered
Photo: Dena Dickerson
Photo: Matthew Godfrey
LeatherbackDermochelys coriacea
US - EndangeredWorld - Critically
Endangered
FlatbackNatator depressus
Photo: Sea Turtle, Inc
World – DataDeficient
Risk Assessment Factors forPotential Dredging Impacts
1. Dredging Project2. Biological Data3. Entrainment Data4. Protection Methods
1. Dredging Project• Location• Timing• Duration• Dredge type• Dredge operations
Bucket or Clamshell
Cutter-suction Pipeline Trailing-suction Hopper
Risk Assessment Factor
2. Biological Data• Species occurrence and behavior• Habitat utilization at dredging site
Risk Assessment Factor
3. Entrainment DataData collection
Dredge Observer Programs
Data archivingUSACE Database Warehouse
Data analysesSpatial, temporal, vessel
Risk Assessment Factor
NA
CA
SA
Atlantic OceanWG
NWGNEG
EG29° 00”
Gulf of Mexico
401 Turtle Takes(1995 - 2008)
WG
69
NWG
71
NEG
18
EG
18
SA
108
CA
64
NA
53
Gulf
176
Atlantic
225
NA
CA
SA
Atlantic OceanWG
NWGNEG
EG29° 00”
Gulf of Mexico
Takes per Project (1995-2008)
WG
1.82
NWG
1.11
NEG
0.43
EG
1.50
SA
0.96
CA
0.76
NA
0.77
Gulf
1.14
Atlantic
0.85
4. Protection Methodsa. Availabilityb. Effectiveness
Risk Assessment Factor
Bucket or Clamshell
Cutter-suction Pipeline
Trailing-suction Hopper
Available Protection Methods
(Implemented 1992)
Minimize hopper use
JAN FEB MAR APR MAY JUN JUL AUG SEP OCT NOV DEC
Nesting
Hatching
Based on Water Temp. & Nesting Timeline
Available Protection Methods(Implemented 1992)
Environmental Window
0.11
0.29
0.70
0.390.42
0.08 0.08 0.06
0.33
0.58
0.350.38
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Month
Turt
le T
akes
per
Dre
dge
Proj
ect
Atlantic
0.15 0.17
0.49
0.59 0.59
0.53
0.21
0.38
0.19
0.45
0.300.24
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov* Dec
Month
Turt
le T
akes
per
Dre
dge
Proj
ect Gulf of Mexico
Take
s pe
r P
roje
ct
Month
Available Protection Methods(Implemented 1992)
Draghead turtle deflector
Reduce pumps in water column
Available Protection Methods(Implemented 1992)
Capture and relocate turtles
(Implemented 2008)
Non-capture Trawling
Effectiveness of Protection Methods(Annual Turtle Takes)
Proj
ects
Mon
itore
d
Sea
Turt
le In
cide
ntal
Tak
es
Protection MethodsImplemented 1992-Dredge type-Dredging window-Draghead turtle deflector-Reduce pumps in water column-Capture and relocate turtles
71
Turt
le T
akes
per
Dre
dge
Proj
ect
Effectiveness of Protection Methods(Annual Turtle Takes per Project)
Newly Available Protection MethodsImplemented 2008 – Dhamra, India
Water-injection to move turtles
Newly Available Protection MethodsTo be Implemented - USA
“Turtle friendly” bed-leveler
Acoustic Detection
or = ?
UNavailable Protection ToolsAcoustic Dispersal
Global Dredging
Impacts on Sea Turtles??
