Dredging impacts on sea turtles in the southeastern ... - PIANC USA

<strong>Dredging</strong> and Sea Turtles:
Potential Impacts, Assessing Risk, &
Protection Methods
DENA DICKERSON
Engineer Research & Development Center
U.S. Army Corps of Engineers
Vicksburg, Mississippi

Coastal
<strong>Dredging</strong>
- Remove sediment
- Construct land

Coastal
<strong>Dredging</strong>
Cutter-suction Pipeline
Bucket or Clamshell
Trailing-suction Hopper

Coastal
Sea Turtle
Habitat
- Feeding
- Reproduction
7 species

<strong>Dredging</strong> Impacts on
Sea Turtles
Entrainment - Incidental take

Incidental Sea Turtle Take by
Trailing Suction Hopper Dredge

Kemp’s ridley
Lepidochelys kempii
US - Endangered
World – Critically
Endangered
Photo: Erin Seney

Olive ridley
Lepidochelys olivacea
US – Threatened /
Endangered
World – Vulnerable
Photo by Bill Curtsinger
National Geographic

Olive ridley – Arribada (Mass nesting)
Mexico
India

Flatback
Natator depressus
World – Data
Deficient
Photo: Sea Turtle, Inc

Hawksbill
Eretmochelys imbricata
US - Endangered
World - Critically
Endangered
Photo: Gerry O’Mara

Green
Chelonia mydas
US – Threatened/
Endangered
World - Endangered
Photo: Dena Dickerson

Loggerhead
Caretta caretta
US - Threatened
World - Endangered
Photo: Dena Dickerson

Leatherback
Dermochelys coriacea
US - Endangered
World - Critically
Endangered
Photo: Matthew Godfrey

Southeast U.S. Sea Turtles
Loggerhead
Green
Kemp’s ridley
Leatherback
Hawksbill

Dredge Observer Program
Trailing Suction Hopper Dredges
1980 - Began
1995 - Consistent methods
90+ - Sites monitored

Dredge Observer Program
Dredged Material Sampling
Inflow screening Overflow screening

Dredge Observer Program
- Sea turtles
- Marine mammals
- Shark / fish
- Bycatch

Documented
Sea Turtle Takes
Sea Turtle Incidental Takes
450
400
350
300
250
200
150
100
50
0
1995- 2008
401 Turtle Takes
(28/year)
280 63 52 6
Loggerhead Kemp's ridley Green Unidentified
Species

http://el.erdc.usace.army.mil/seaturtles/

Annual Sea Turtle Take Limits
(National Marine Fisheries Service)
North Atlantic – North of North Carolina
Varies by Project
REGIONAL Limits
Gulf South Atlantic
Loggerheads 40 35
Kemp’s ridley 20 7
Greens 14 7
Hawksbills 4 2
Leatherbacks None designated

Risk Assessment Factors for
Potential <strong>Dredging</strong> Impacts
1. <strong>Dredging</strong> Project
• Location
• Timing
• Duration
• Dredge & equipment type
• Dredge operations
2. Biological Data
• Species occurrence & behavior
• Habitat utilization at dredging site
3. Entrainment Data
- Available monitoring methods
- Effective documentation
- Data Analyses (temporal, spatial, vessel)
4. Protection Methods
• Availability
• Effectiveness

Risk Assessment Factor
1. <strong>Dredging</strong> 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 Data
Available monitoring methods
- Dredge Observer Program
- Dredged material screening
- Bridge watch, strandings
Effective documentation
Data analyses
- Spatial, temporal, vessel

0.80
0.70
0.70
Atlantic
Takes per Project
Turtle Takes per Dredge Project
Turtle Takes per Dredge Project
0.60
0.50
0.40
0.30
0.20
0.10
0.00
0.70
0.60
0.50
0.40
0.30
0.20
0.10
0.58
0.42
0.39
0.33
0.35
0.38
0.29
0.11
0.08 0.08
0.06
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Month
0.59 0.59
0.53
0.49
0.15 0.17
Gulf of Mexico
0.45
0.38
0.30
0.24
0.21
0.19
0.00
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov* Dec
Month

401 Turtle Takes
(1995 - 2008)
NA
53
NA
CA
64
CA
WG
69
WG
NWG
71
NWG
29° 00”
Gulf
Gulf of Mexico
176
NEG
18
NEG
EG
EG
18
SA
108
Atlantic
Atlantic Ocean
225

Takes per Project
(1995-2008)
NA
NA
0.77
CA
0.76
CA
WG
WG
1.82
NWG
1.11 NWG
29° 00”
Gulf
Gulf of Mexico
1.14
NEG
0.43
NEG
EG
EG
1.50
SA
0.96
Atlantic
Atlantic Ocean
0.85

Risk Assessment Factor
4. Protection Methods
a. Availability
b. Effectiveness

Available Protection Methods
(Implemented 1992)
Minimize hopper use
Bucket or Clamshell
Cutter-suction Pipeline
Trailing-suction Hopper

Available Protection Methods
(Implemented 1992)
Environmental Window
Based on Water Temp. & Nesting Timeline
Nesting
Hatching
JAN FEB
MAR APR MAY JUN JUL AUG SEP OCT NOV DEC

Available Protection Methods
(Implemented 1992)
Draghead turtle deflector
Reduce pumps in water column

Available Protection Methods
(Implemented 1992)
Capture and relocate turtles

Effectiveness of Protection Methods
(Annual Turtle Takes)
Sea Turtle Incidental Takes
Projects Monitored

Effectiveness of Protection Methods
(Annual Turtle Takes per Project)
71
Turtle Takes per Dredge Project
Protection Methods
Implemented 1992
-Dredge type
-<strong>Dredging</strong> window
-Draghead turtle deflector
-Reduce pumps in water column
-Capture and relocate turtles

Newly Available Protection Methods
Implemented 2008 – Dhamra, India
Water-injection to move turtles
Implemented 2008 - USA
Non-capture seabed sweeping

Newly Available Protection Methods
To be implement 2009 - USA
“Turtle friendly” bed-leveler

UNavailable Protection Tools
Acoustic Dispersal
Acoustic Detection
or =

Olive ridley
Lepidochelys olivacea
Photo by Bill Curtsinger
National Geographic

Dhamra Port,
India
Protection Methods
Turtle deflector
- Minimized hopper use
- Reduced pumps in water
- Moved turtles with:
- Water-injection
Water-injection
- Capture netting
Capture netting

Dhamra Port,
India
Effectiveness of
Protection Methods
- 3 Hopper dredges working
- 17 Months (Mar 08-Jul 09)
- > 200,000 Olive ridleys nesting nearby
- 8 Documented turtle takes

Global
<strong>Dredging</strong>
Impacts on
Sea Turtles