Where the Wild Quahogs Are: Looking at Quahog Larval Supply and Distribution in the Upper Narragansett Bay presented at April 14th, 2014 Rhode Island Shellfish Management Plan Stakeholder meeting by Dale Leavitt, Matt Griffin, Scott Rutherford (RWU), and Chris Kincaid and Dave Ullman (URI).

1. 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

2. 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

3. 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?

4. 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

5. 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.

6. 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.

7. 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

8. 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?

9. 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

10. Land-based calibration

11. Accuracy of dGPS to measure linear
distance?

12. Measuring linear distance on the water

13. Bullrake transects with dGPS at stale

14. 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.

15. 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
Amountoferrorinmeasuringtransectlength(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

16. 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.

17. 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%

18. 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

19. Size class distribution
0
2
4
6
8
10
12
14
40
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
100
102
104
106
108
110
Numberofindividuals
Length Intervals (mm)
Littleneck Cherrystone ChowderSub-legal

20. – 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

21. Bullrake Stock
Assessment
• Stratified random
sampling protocol
– Sampling within
strata
• Run one 100’
transect per strata
– Annually

22. DEM Dredge Survey Sites - 2013

23. 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

24. 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.

25. 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)

26. 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

27. 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

28. 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
MeanConditionIndex
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
MeanConditionIndex
Open
Sanctuary
Closed
2012
2013

29. 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

30. 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.

31. 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.

32. 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).

33. 2006 2007
Environmental Forcing During Simulated Years

34. Obs. Surface
Model Surface
Obs. Bottom
Model Bottom
Salinity
Temperature
ROMS Model-Data Comparison: T/S at Conimicut

35. 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.

36. 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.

37. 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.

38. Passive Particles, Spatial Distributions after 10 Days
Particles Released
From Providence
River Site
2006: 34% lost 2007: 20% lost

39. Passive Particles, Spatial Distributions after 10 Days
2006: 51% lost 2007: 45% lost
Particles Released
From GB Spawner
Sanctuary Site

40. Passive Particles, Spatial Distributions after 10 Days
2006: 21% lost 2007: 11% lost
Particles Released
From Greenwich
Cove Site

41. Passive Particles, Spatial Distributions after 10 Days
2006: 95% lost 2007: 96% lost
Particles Released
From Rome Point
Site

42. Passive Particles, Spatial Distributions after 10 Days
2006: 46% lost 2007: 35% lost
Particles Released
From Hog Island
Site

43. Passive Particles, Spatial Distributions after 10 Days
2006: 43% lost 2007: 34% lost
Particles Released
From Rocky Point
Site

44. 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

45. Passive versus Active Particles, Spatial Distributions after 10 Days
2007, Passive: 20% lost 2007, Active: 53% lost
Particles Released
From Providence
River Site

46. 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.

48. Hog Island 5/31—6/4, 2012 Spawner Sanctuary 6/18—6/24, 2012

49. 9% lost
Providence River Model Providence River Drifters

50. 34% lost
Rocky Point Model Rocky Point Drifters

51. Spawner Sanctuary Model Spawner Sanctuary Drifters
45% lost

52. 96% lost
Rome Point Model Rome Point Drifters

53. 35% lost
Hog Island Model Hog Island Drifters
46% lost
(2006)

54. 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

55. 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.

56. 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.

57. Questions?