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Where the Wild Quahogs Are: Looking at Quahog Larval Supply and Distribution in the Upper Narragansett Bay
Dale Leavitt, Matt Griffin & Scott Rutherford – RWU
Chris Kincaid & Dave Ullman – URI
An Assessment of Quahog Larval Supply and Distribution in the Upper Narragansett Bay with a Focus on Spawning Sanctuaries
and Alternative Area Management Strategies
Dale Leavitt, Matt Griffin & Scott Rutherford – RWU
Chris Kincaid & Dave Ullman – URI
The Big Picture
• Often thought that the quahog supply in NarBay originated in the Providence River and upper bay.
• Research effort originated with discussions among CFRF, RISA, RWU and DEM Marine Fisheries (2010)
• With increased fishing pressure in Areas A & B (resulting from, NBC’s CSO Project) and Greenwich Bay – how would that affect quahog resources?
Southern New England Collaborative Research Initiative (SNECRI)
• NOAA funding became available through
• CFRF Directors dedicated funding to assist in expanding our knowledge of quahog dynamics in the bay
• In 2011, the project was started to address some of the questions proposed in discussions with DEM Marine Fisheries
An assessment of quahog larval supply and distribution in the upper Narragansett Bay with a focus on spawning sanctuaries
and alternative area management strategies.
• Develop a cooperative assessment of quahog standing stock and reproductive condition in the upper NarBay with commercial fishermen – Conduct side-by-side quahog stock assessments comparing the
efficacy of the RI DEM’s standard method (hydraulic dredge) with the commercial bullrake and diver quadrat sampling
• Through the application of the ROMS Hydrodynamic Model for NBay, simulate specific quahog larval release points (spawning areas) based on stock assessments and predict sites of juvenile recruitment resulting from these releases
• Using the results of the model, validate predicted larval settlement sites through a combined effort of surface drifter deployments and monitoring for the occurrence of quahog larvae
• Apply the prediction of quahog larval sources and sinks to the development of a state-wide shellfish management plan currently under discussion among RI-DEM, CRMC, CRC, and others.
An assessment of quahog larval supply and distribution in the upper Narragansett Bay with a focus on spawning sanctuaries
and alternative area management strategies.
• Develop a cooperative assessment of quahog standing stock and reproductive condition in the upper NarBay with commercial fishermen – Conduct side-by-side quahog stock assessments comparing the
efficacy of the RI DEM’s standard method (hydraulic dredge) with the commercial bullrake and diver quadrat sampling
• Through the application of the ROMS Hydrodynamic Model for NBay, simulate specific quahog larval release points (spawning areas) based on stock assessments and predict sites of juvenile recruitment resulting from these releases
• Using the results of the model, validate predicted larval settlement sites through a combined effort of surface drifter deployments and monitoring for the occurrence of quahog larvae
• Apply the prediction of quahog larval sources and sinks to the development of a state-wide shellfish management plan currently under discussion among RI-DEM, CRMC, CRC, and others.
Develop a cooperative assessment of quahog standing stock in the upper Narragansett Bay with commercial fishermen.
– Develop improved stock assessment protocols • The ultimate goal is to have RI quahoggers conduct their own
stock assessment, in collaboration with DEM Marine Fisheries
– Step 1 • Bullrake sampling
– Want to compare the effectiveness of a bullrake to other stock assessment methods
– Diver sampling is highest standard
• How? – Measure exact area that a bullrake samples
» Need to know width and length of sample track
– Count the number of quahogs and measure their size
Area sampled with a bullrake?
• Width – 15”
• Tooth length – 1.5” to 3”
• Length of sample track? – That’s a problem!
• With the rake at the end of a rigid pole, can we measure the distance the handle travels as a proxy for the distance the rake travels?
Bullrake calibration with dGPS
• Global Positioning Service (GPS) – Routinely good to locate within 10 meters (~30 feet) – Usually okay for navigation but…
• Differential GPS – Utilizes a base station to increase
accuracy – Can be accurate to within 10 cm (4 in)
• Attach dGPS to a bullrake
– Can track the movement of the rake across the bottom
Land-based calibration
Accuracy of dGPS to measure linear distance?
Measuring linear distance on the water
Bullrake transects with dGPS at stale
Transect Method
Diver
Measured
transect
length (m)
Estimated
transect
length using
dGPS (m)
Difference
between
measured
and dGPS
%
Difference
between
measured
and dGPS
2-1 continuous 14.17 19.48 5.31 37.5%
2-2 continuous 15.54 14.52 -1.02 -6.6%
2-3 continuous 18.59 24.81 6.22 33.5%
2-4 continuous 15.54 14.61 -0.93 -6.0%
3-1 start/stop 8.69 7.03 -1.66 -19.1%
4-1 start/stop 13.41 15.75 2.34 17.4%
4-2 start/stop 13.26 15.50 2.24 16.9%
4-3 start/stop 12.68 12.62 -0.06 -0.5%
5-1 start/stop 29.57 30.32 0.75 2.5%
5-2 start/stop 29.26 29.16 -0.10 -0.3%
5-3 start/stop 28.96 29.66 0.70 2.4%
5-4 start/stop 27.58 28.25 0.67 2.4%
5-5 start/stop 15.41 15.79 0.38 2.5%
6-1 start/stop 21.03 20.40 -0.63 -3.0%
6-2 start/stop 20.42 19.63 -0.79 -3.9%
6-3 start/stop 28.96 28.51 -0.45 -1.6%
average 0.07 0.1%
stdev 0.64 2.7%
Diver-measured bullrake transect length compared
to that observed using post-processed dGPS
data.
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0 10 20 30 40 50 60
Am
ount
of e
rror
in m
easu
ring
tra
nsec
t le
ngth
(m
)
Angle of deflection from transect line (degrees)
4 m stale with 24 m transect
8 m stale with 24 m transect
14 m stale with 24 m transect
4 m stale with 30 m transect
8 m stale with 30 m transect
14 m stale with 30 m transect
Error due to stale angle off from transect direction
Transect Method
Diver
Measured
transect
length (m)
Estimated
transect
length using
dGPS (m)
Difference
between
measured
and dGPS
%
Difference
between
measured
and dGPS
2-1 continuous 14.17 19.48 5.31 37.5%
2-2 continuous 15.54 14.52 -1.02 -6.6%
2-3 continuous 18.59 24.81 6.22 33.5%
2-4 continuous 15.54 14.61 -0.93 -6.0%
3-1 start/stop 8.69 7.03 -1.66 -19.1%
4-1 start/stop 13.41 15.75 2.34 17.4%
4-2 start/stop 13.26 15.50 2.24 16.9%
4-3 start/stop 12.68 12.62 -0.06 -0.5%
5-1 start/stop 29.57 30.32 0.75 2.5%
5-2 start/stop 29.26 29.16 -0.10 -0.3%
5-3 start/stop 28.96 29.66 0.70 2.4%
5-4 start/stop 27.58 28.25 0.67 2.4%
5-5 start/stop 15.41 15.79 0.38 2.5%
6-1 start/stop 21.03 20.40 -0.63 -3.0%
6-2 start/stop 20.42 19.63 -0.79 -3.9%
6-3 start/stop 28.96 28.51 -0.45 -1.6%
average 0.07 0.1%
stdev 0.64 2.7%
Diver-measured bullrake transect length compared
to that observed using post-processed dGPS
data.
Bullrake Catch Efficiency
Transect Quahogger Location substrate
Quahogs
caught
Quahogs
missed
catch
efficiency Comments
1 A off Allen's Harbor sand 19 3 86.4%
2 A off Allen's Harbor sand 21 7 75.0%
3 A off Allen's Harbor sand 24 11 68.6%
4 A off Allen's Harbor sand 52 3 94.5%
5 A off Allen's Harbor sand 46 2 95.8%
6 A off Allen's Harbor sand 39 2 95.1%
7 A off Allen's Harbor sand 46 3 93.9%
8 B Oakland Beach sand 24 14 63.2% inexperienced divers
9 C Rocky Point sand 129 14 90.2%
10 C Rocky Point sand 115 12 90.6%
11 C Rocky Point sand 80 15 84.2% bottom hardened up
12 C Chepwenoxit mud 20 2 90.9%
13 C Chepwenoxit mud 50 2 96.2%
14 C Chepwenoxit mud 57 1 98.3%
15 C Chepwenoxit mud 129 8 94.2%
16 C Chepwenoxit mud 97 9 91.5%
17 D Sally's Rock mud 27 3 90.0%
18 D Sally's Rock mud 9 4 69.2% rake jumped on rock
19 D Sally's Rock mud 14 3 82.4% shell on tooth
20 D Rocky Point sand 48 1 98.0%
21 D Rocky Point sand 71 4 94.7%
sand avg 89.3% average 90.8%
mud avg 93.5% stdev 7.9%
Transect Locations Fisherman
Substrate
Type
Area
sampled
w/ bullrake
(m2)
density
measured by
bullrake
(quahogs/m2)
catch
efficiency
total density
(adjusted for
avg efficiency)
(quahogs/m2)
avg density
measured by
diver quadrat
(quahogs/m2)
Bullrake
density - Diver
density
(quahogs/m2)
2-1 Allen's Hbr A sand-mud 6.66 7.81 94.5% 8.35 8.00 0.35
2-2 Allen's Hbr A 7.30 6.30 95.8% 6.73 7.00 -0.27
2-3 Allen's Hbr A 8.74 4.46 95.1% 4.77 4.00 0.77
2-4 Allen's Hbr A 7.30 6.30 93.9% 6.73 6.33 0.40
4-1 Rocky Point C sand 8.40 15.35 90.2% 16.41 8.00 8.41
4-2 Rocky Point C 8.27 13.91 90.6% 14.87 13.00 1.87
5-1 Chepwenoxit C soft mud 16.94 1.18 90.9% 1.26 6.00 -4.74
5-2 Chepwenoxit C 16.30 3.07 96.2% 3.28 3.50 -0.22
5-3 Chepwenoxit C 16.53 3.52 98.3% 3.76 5.00 -1.24
5-4 Chepwenoxit C 16.57 7.97 94.2% 8.52 6.00 2.52
5-5 Chepwenoxit C 15.79 6.29 91.5% 6.72 8.50 -1.78
6-1 Sally's Rock D soft mud 9.33 2.90 90.0% 3.10 3.33 -0.23
7-2 Rocky Point D sand 7.16 8.74 94.7% 9.34 7.50 1.84
overall average 93.5% 7.22 6.63 0.59
standard deviation 2.6% 4.45 2.58 2.99
93.6% 9.60 7.69 1.91
2.2% 4.39 2.72 2.97
93.5% 4.44 5.39 -0.95
3.3% 2.67 1.92 2.38
on sand
SD
on mud
SD
Quahog density measured by diver compared to that measured by bullrake
Size class distribution
0
2
4
6
8
10
12
144
0
42
44
46
48
50
52
54
56
58
60
62
64
66
68
70
72
74
76
78
80
82
84
86
88
90
92
94
96
98
10
0
10
2
10
4
10
6
10
8
11
0
Nu
mb
er
of
ind
ivid
ual
s
Length Intervals (mm)
Littleneck Cherrystone ChowderSub-legal
– Step 2 • Conduct side-by-side quahog stock assessments between DEM
hydraulic dredge and bullrakers
Develop a cooperative assessment of quahog standing stock and reproductive condition in the upper NarBay with commercial fishermen
Bullrake Stock Assessment
• Stratified random sampling protocol
– Sampling within strata
• Run one 100’ transect per strata
– Annually
DEM Dredge Survey Sites - 2013
RI-DEM Tow
ID
Dredge
adjusted for
57.7%
efficiency
Bullrake
adjusted for
90%
efficiency StDev Substrate type
2389 15.36 9.37 2.22 hard bottom
2393 0.80 0.12 0.11 hard bottom
2424 20.19 13.73 6.87 very hard bottom
2429 3.29 8.05 4.60 moderate hard bottom
2445 0.43 0.77 0.70 soft mud
2448 6.40 6.63 3.99 soft sticky mud
2453 0.80 0.43 0.33 soft sticky mud
2484 0.47 3.21 2.13 soft sticky mud w/ shell
2485 5.13 11.80 6.41 hard w/ shells
2496 4.54 10.37 1.74 moderate hard bottom
GB adjacent 1.11 1.99 1.07 soft mud w/ shell
average 5.32 6.04
stdev 6.59 4.95
Bullrake – DEM Dredge comparison
Discussion with RIDEM – Marine Fisheries • Looks like a bullrake is a viable stock assessment tool.
– If the dredge catch efficiency is factored in – then the two techniques appear to measure quahog density similarly.
– Can we improve on the technique?
• What more do we need to do to confirm this observation? – How many samples are required?
• Is there a role for quahoggers to assist in stock assessment? – How many samples would be needed to “calibrate” a
quahogger?
• If it works, how do we make it happen? – Starting during summer 2014 – quahoggers may be used to
sample shallow coves where dredge can not sample.
Quahog Reproduction • Some attempts to
manage areas for quahog reproduction – Areas with high numbers
of quahogs that allow for intensive reproduction • Spawning Sanctuaries • Closed areas
• May be problematic – Quahogs in protected
areas may not be spawning!!!! Marroquin-Mora & Rice (2008)
Reproductive effort study • Selected 8 sites for
long-term sampling
• Sample 2x per month
• Assess for gonad condition, i.e. reproductive status
Site Lat Lon Density Fishing Status
*Bissel Cove 41 32.520 71 25.164 Low Open
*Greenwich Cove 41 40.160 71 26.529 High Closed
*Spawner Sanctuary 41 40.050 71 23.630 Med Closed
*Rocky Pt. 41 41.940 71 21.111 Med Open
*Providence River 41 45.650 71 22.030 High Closed
Conditional Area B 41 40.475 71 20.370 Low Conditional
Prudence Island 41 38.055 71 19.622 Med/High Open
*Hog Island 41 38.136 71 16.689 Low Open
Reproductive Condition of Quahogs: Efficacy of Transplants
• 2012 – Condition Index & Gonad
Index at 8 sites • Sample every 3 weeks • Open, closed & sanctuary
– Mark/Recapture experiment • Tag 1,600 quahogs from
Greenwich Cove • Transplant to Spawning
Sanctuary
• 2013 – Repeat 2012 (April –
November) – Mark-Recapture experiment
• Sample every 3 weeks (April – November)
• Condition Index & Gonad Index
Reproductive Condition of Quahogs
Preliminary Results
Significantly lower mean CI in closed sites
2012 and 2013 fall gonad recovery different
60
70
80
90
100
110
120
130
140
150
10-Apr-12 30-May-12 19-Jul-12 7-Sep-12 27-Oct-12
Me
an
Co
nd
itio
n I
nd
ex
Open
Sanctuary
Closed
60
70
80
90
100
110
120
130
140
150
10-Apr-13 30-May-13 19-Jul-13 7-Sep-13 27-Oct-13
Me
an C
on
dit
ion
In
de
xOpen
Sanctuary
Closed
2012
2013
Recruitment • Based on our stock
surveys and consultation with quahoggers, we know where there are high concentrations of reproductive quahogs
• However, what happens to the quahog larvae following gamete release?
Providence River
Rocky Point
DEM Spawning Sanctuary
Hog Island
Greenwich Cove
Bissel Cove
An assessment of quahog larval supply and distribution in the upper Narragansett Bay with a focus on spawning sanctuaries
and alternative area management strategies.
• Develop a cooperative assessment of quahog standing stock and reproductive condition in the upper NarBay with commercial fishermen – Conduct side-by-side quahog stock assessments comparing the
efficacy of the RI DEM’s standard method (hydraulic dredge) with the commercial bullrake and diver quadrat sampling
• Through the application of the ROMS Hydrodynamic Model for NBay, simulate specific quahog larval release points (spawning areas) based on stock assessments and predict sites of juvenile recruitment resulting from these releases
• Using the results of the model, validate predicted larval settlement sites through a combined effort of surface drifter deployments and monitoring for the occurrence of quahog larvae
• Apply the prediction of quahog larval sources and sinks to the development of a state-wide shellfish management plan currently under discussion among RI-DEM, CRMC, CRC, and others.
Objectives of this portion of talk: • Describe results of particle tracking
simulations in Narragansett Bay for the purpose of evaluating the dispersal of planktonic quahog larvae.
• Demonstrate the important effect of larval behavior (vertical swimming) on dispersal in the Bay.
Model Domains: •Low resolution •Nested high resolution
Realistically-Forced Circulation Model
Nested (ROMS) configuration: • Low resolution model extending
onto continental shelf provides boundary conditions for high-resolution Bay model.
• Curvilinear grid with resolution of 50-100m in upper Bay.
• Sigma vertical coordinate (15 levels).
• Forced with measured river inflows and surface fluxes and tides from ADCIRC (NOAA).
• Simulate 45 day period (May 15-June 30, 2007).
2006 2007
Environmental Forcing During Simulated Years
Obs. Surface Model Surface Obs. Bottom Model Bottom
Salinity
Temperature
ROMS Model-Data Comparison: T/S at Conimicut
Larval Tracking Model Larval dispersal modeled with Lagrangian TRANSport model (LTRANS) developed by E. North and collaborators (U. Maryland):
• 4th order Runga-Kutta advection using ROMS velocities. • Random displacement model, based on ROMS vertical
diffusivity simulates effect of vertical turbulence. • Zero horizontal diffusion in our application. • Particles reaching open boundary assumed lost to the
system. • Perform simulations without larval behavior (passive
particles) and with vertical swimming. Clusters of 65 particles released every 2 hours over a 1 month period at 6 potential sanctuary sites:
• Get trajectory simulations under wide range of forcing conditions (e.g. wind, tide, mixing) characteristic of the ~1 month spawning period of hard clams.
Example trajectory simulations: • Clusters of 65 particles
released every hour for 6 hours.
• Particles tracked over 24 hours (starting at time of 1st release).
Illustrates the variability in particle trajectories depending on the time (relative to the tidal cycle) of release.
Example trajectory simulations: • Clusters of 65 particles
released every hour for 6 hours.
• Particles tracked over 24 hours (starting at time of 1st release).
Illustrates the variability in particle trajectories depending on the time (relative to the tidal cycle) of release.
Passive Particles, Spatial Distributions after 10 Days
Particles Released From Providence
River Site
2006: 34% lost 2007: 20% lost
Passive Particles, Spatial Distributions after 10 Days
2006: 51% lost 2007: 45% lost
Particles Released From GB Spawner
Sanctuary Site
Passive Particles, Spatial Distributions after 10 Days
2006: 21% lost 2007: 11% lost
Particles Released From Greenwich
Cove Site
Passive Particles, Spatial Distributions after 10 Days
2006: 95% lost 2007: 96% lost
Particles Released From Rome Point
Site
Passive Particles, Spatial Distributions after 10 Days
2006: 46% lost 2007: 35% lost
Particles Released From Hog Island
Site
Passive Particles, Spatial Distributions after 10 Days
2006: 43% lost 2007: 34% lost
Particles Released From Rocky Point
Site
Larval Behavior Hard clam larvae:
• Planktonic stage lasts 1-2 weeks (T dependent). • Swim upward early in planktonic period, downward later.
(LTRANS superimposes a degree of randomness on this pattern.)
Model swimming behavior:
upward
downward
Passive versus Active Particles, Spatial Distributions after 10 Days
2007, Passive: 20% lost 2007, Active: 53% lost
Particles Released From Providence
River Site
An assessment of quahog larval supply and distribution in the upper Narragansett Bay with a focus on spawning sanctuaries
and alternative area management strategies.
• Develop a cooperative assessment of quahog standing stock and reproductive condition in the upper NarBay with commercial fishermen – Conduct side-by-side quahog stock assessments comparing the
efficacy of the RI DEM’s standard method (hydraulic dredge) with the commercial bullrake and diver quadrat sampling
• Through the application of the ROMS Hydrodynamic Model for NBay, simulate specific quahog larval release points (spawning areas) based on stock assessments and predict sites of juvenile recruitment resulting from these releases
• Using the results of the model, validate predicted larval settlement sites through a combined effort of surface drifter deployments and monitoring for the occurrence of quahog larvae
• Apply the prediction of quahog larval sources and sinks to the development of a state-wide shellfish management plan currently under discussion among RI-DEM, CRMC, CRC, and others.
Hog Island 5/31—6/4, 2012 Spawner Sanctuary 6/18—6/24, 2012
9% lost
Providence River Model Providence River Drifters
34% lost
Rocky Point Model Rocky Point Drifters
Spawner Sanctuary Model Spawner Sanctuary Drifters
45% lost
96% lost
Rome Point Model Rome Point Drifters
35% lost
Hog Island Model Hog Island Drifters
46% lost (2006)
Looking for the larvae
Name Lat Long
Anticipated
larval
supply
Greenwich Cove 41.661637 -71.442319 High
Chepiwanoxet 41.676307 -71.442443 High
Sandy Point 41.664646 -71.405473 Low
Spawning Sanctuary 41.669821 -71.389343 Low
Sugar Mountain 41.655645 -71.370999 High
Warwick Neck 41.663884 -71.368550 High
Hope Island 41.377688 -71.377688 Low
An assessment of quahog larval supply and distribution in the upper Narragansett Bay with a focus on spawning sanctuaries
and alternative area management strategies.
• Develop a cooperative assessment of quahog standing stock and reproductive condition in the upper NarBay with commercial fishermen – Conduct side-by-side quahog stock assessments comparing the
efficacy of the RI DEM’s standard method (hydraulic dredge) with the commercial bullrake and diver quadrat sampling
• Through the application of the ROMS Hydrodynamic Model for NBay, simulate specific quahog larval release points (spawning areas) based on stock assessments and predict sites of juvenile recruitment resulting from these releases
• Using the results of the model, validate predicted larval settlement sites through a combined effort of surface drifter deployments and monitoring for the occurrence of quahog larvae
• Apply the prediction of quahog larval sources and sinks to the development of a state-wide shellfish management plan currently under discussion among RI-DEM, CRMC, CRC, and others.
What next?
• Will continue to work with the quahog fishing fleet and RIDEM Marine Fisheries to integrate bullraking into their stock assessment process.
• RI Sea Grant has funded continuation of the ROMS modeling effort where we will add more years to the data set to look at annual variability.
• Will more closely analyze the reproductive cycle in the quahogs collected in 2012/2013.
• Will integrate the results from this study into our baseline knowledge for use in the Shellfish Management Plan.
Questions?