where the wild quahogs are: looking at quahog larval supply and distribution in the upper...

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.

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






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%







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%





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

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.

Passive Particles, Spatial Distributions after 10 Days

Particles Released From Providence

River Site

2006: 34% lost 2007: 20% lost


2006: 51% lost 2007: 45% lost

Particles Released From GB Spawner

Sanctuary Site


2006: 21% lost 2007: 11% lost

Particles Released From Greenwich

Cove Site


2006: 95% lost 2007: 96% lost

Particles Released From Rome Point

Site


2006: 46% lost 2007: 35% lost

Particles Released From Hog Island

Site


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

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

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?

where the wild quahogs are: looking at quahog larval supply and distribution in the upper...

Education

quahog supply

quahog stock assessments

quahog resources

upper bay

occurrence of quahog

commercial bullrake

knowledge of quahog

bullrake sampling