methods to minimize dredging impacts on sea turtles · 2017-11-21 · 693 documented sea turtles...
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Methods to Minimize Dredging Impacts on Sea Turtles
DENA DICKERSONERDC, Environmental Lab
U.S. Army Corps of Engineers Vicksburg, Mississippi
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Coastal Sea Turtle Habitat
7 species worldwide
Feeding
Juvenile development
Reproduction
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Southeastern US Sea Turtles
Kemp’s ridley Loggerhead
Leatherback Olive ridley
Green
Hawksbill
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Dredging Impacts to Sea Turtles
• Entrain adults, subadults, juveniles
• Disrupt nesting activities
• Destroy nests and nesting habitat
On Shore Impacts In Water Impacts
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Hopper Trailing Suction
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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
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Southeastern US
77+ sites monitored44 sites with turtle takes
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Photo: Dena Dickerson
LoggerheadCaretta caretta
US - ThreatenedWorld - Endangered
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GreenChelonia mydas
Endangered US – Threatened/
World - Endangered
Photo: Dena Dickerson
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Photo: Erin Seney
Kemp’s ridleyLepidochelys kempii
US - EndangeredWorld – Critically
Endangered
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Olive ridleyLepidochelys olivacea
Photo: Bill Curtsinger
US – Threatened /
World – Vulnerable
Endangered
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Olive ridley – Arribada (Mass nesting)
Mexico
India
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HawksbillEretmochelys imbricata
US - EndangeredWorld - Critically
Endangered
Photo: Dena Dickerson
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Photo: Matthew Godfrey
LeatherbackDermochelys coriacea
US - EndangeredWorld - Critically
Endangered
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FlatbackNatator depressus
Photo: Sea Turtle, Inc
World – DataDeficient
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Risk Assessment Factors forPotential Dredging Impacts
1. Dredging Project2. Biological Data3. Entrainment Data4. Protection Methods
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1. Dredging Project• Location• Timing• Duration• Dredge type• Dredge operations
Bucket or Clamshell
Cutter-suction Pipeline Trailing-suction Hopper
Risk Assessment Factor
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2. Biological Data• Species occurrence and behavior• Habitat utilization at dredging site
Risk Assessment Factor
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3. Entrainment DataData collection
Dredge Observer Programs
Data archivingUSACE Database Warehouse
Data analysesSpatial, temporal, vessel
Risk Assessment Factor
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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
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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
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4. Protection Methodsa. Availabilityb. Effectiveness
Risk Assessment Factor
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Bucket or Clamshell
Cutter-suction Pipeline
Trailing-suction Hopper
Available Protection Methods
(Implemented 1992)
Minimize hopper use
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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
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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
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Available Protection Methods(Implemented 1992)
Draghead turtle deflector
Reduce pumps in water column
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Available Protection Methods(Implemented 1992)
Capture and relocate turtles
(Implemented 2008)
Non-capture Trawling
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Effectiveness of Protection Methods(Annual Turtle Takes)
Proj
ects
Mon
itore
d
Sea
Turt
le In
cide
ntal
Tak
es
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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)
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Newly Available Protection MethodsImplemented 2008 – Dhamra, India
Water-injection to move turtles
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Newly Available Protection MethodsTo be Implemented - USA
“Turtle friendly” bed-leveler
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Acoustic Detection
or = ?
UNavailable Protection ToolsAcoustic Dispersal
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Global Dredging
Impacts on Sea Turtles??