Jeff Mercer, Principal Biologist, R.I. Department of Environmental Management Topic: Maximizing Harvest

1. Following the Quahog
Through Time and Space
Jeff Mercer
RI DEM, Principal Biologist
November 14, 2013

2. Quahogs by The
Numbers
39.1 Million
6.96 Million
$5.15 million
534
Clams
Pounds
Dollars
Fishermen
CHERRY
3%
2012 Landings
1.
2.
3.
4.
5.
Squid
Lobster
Sea Scallop
Summer Flounder
Quahog
$19 Million
$12 Million
$9 Million
$7 Million
$5 Million
CHOWDER
10%
TOP NECK
23%
LITTLE NECK
64%

3. Why Quahogs?
Shellfish Catch from 1865
(Goode and Associates, 1887)
Oviatt et al (2003)

4. Why Quahogs?

5. Why Quahogs?
30,000,000 lbs

6. Why Quahogs?

7. Why Quahogs?

8. Why Quahogs?

9. Why Quahogs?
• ~50% of nitrogen in quahog
derived from sewerage
(Oczkowski et al, 2008)

10. Why Quahogs?
(Oczkowski et al, 2008)
• ~50% of nitrogen in quahog
derived from sewerage
•More tolerant to hypoxia than
predators = Predation refuge
(Altieri, 2008)

11. Why Quahogs?
• ~50% of nitrogen in quahog
derived from sewerage
•More tolerant to hypoxia than
predators = Predation refuge
•Closure areas due to pollution
de facto marine reserves
Density 8‐20 X Greater than Avg

12. Spatial Management
of Shellfish In RI
•
•
•
•
Prohibited = 122.6 km2
Conditional = 56 km2
Seasonal = 4.1 km2
Approved = 215.1 km2
• Management = 67.8km2
• Est. Fishable Area ~ 125km2

13. Impact of Pollution Closures
3000
# of Licenses
Meat Weight (MT)
Landings (MT) & Licenses (#)
2500
2000
1500
1000
500
0
1945
1950
1955
1960
1965
1970
1975
1980
Year
1985
1990
1995
2000
2005
2010
* NMFS Landings Data

14. Impact of Pollution Closures
3000
# of Licenses
Meat Weight (MT)
Landings (MT) & Licenses (#)
2500
2000
1500
1000
500
0
1945
1950
1955
1960
1965
1970
1975
1980
Year
1985
1990
1995
2000
2005
2010
* NMFS Landings Data

15. Size Structured Stock Assessment Model
160
Landings
140
# of Quahogs (millions)
120
100
80
60
40
20
0
Year
Gibson, 2010

16. Size Structured Stock Assessment Model
600
Abundance
Landings
# of Quahogs (millions)
500
400
300
200
100
0
Year
Gibson, 2010

17. Size Structured Stock Assessment Model
600
1984
Abundance in Millions (t)
500
1985
1986
400
1987
1988
1989
300
1991
1990
1992
1994
2010 2011
2008
2002 2001
2006
2012 2005 1997
2007 2009
1999 2003 1998 2000 1996
2004
200
1993
1995
100
0
0.00
0.10
0.20
0.30
0.40
F Rate (t-1)
0.50
0.60
0.70

18. Size Structured Stock Assessment Model
600
1984
Abundance in Millions (t)
500
1985
1986
400
1987
1988
1989
300
1991
1990
1992
1994
2010 2011
2008
2002 2001
2006
2012 2005 1997
2007 2009
1999 2003 1998 2000 1996
2004
200
1993
1995
100
0
0.00
0.10
0.20
0.30
0.40
F Rate (t-1)
0.50
0.60
0.70

19. Size Structured Stock Assessment Model
600
1984
Abundance in Millions (t)
500
1985
1986
400
1987
1988
1989
300
1991
1990
1992
1994
2010 2011
2008
2002 2001
2006
2012 2005 1997
2007 2009
1999 2003 1998 2000 1996
2004
200
1993
1995
100
0
0.00
0.10
0.20
0.30
0.40
F Rate (t-1)
0.50
0.60
0.70

20. How Many
Quahogs do
We Need?
Logarithmic
Stock‐Recruitment Models
Great South Bay, NY
Polynomial
Density Dependence
0.75 Adults/m2 =
Recruitment Failure
Kraeuter et al, 2005

21. How Many Quahogs do We Need?
600
Abundance
Landings
Recruitment Failure
# of Quahogs (millions)
500
400
0.75 Adults/m2 X 125km2 Fishable Area
300
200
100
0
Year

22. How Many Quahogs do We Need?
Kraeuter et al, 2005

23. How Many Quahogs do We Need?
Kraeuter et al, 2005

24. How Many Quahogs do We Need?
600
Abundance
Landings
Reduced Recruitment
Landings (millions)
500
1.5 Adults/m2 X 125km2 Fishable Area
400
300
200
100
0
Year

25. Uneven Spatial Distributions of Quahogs
ma
Coastal Ponds
0.8%
Conditional A
Greenwich
Not Identified
0.7%
Management
Areas
0.9%
Conditional B
Sakonnet
0.6%
Mt Hope Bay
0.3%
Block Island
0.0%
ma
ma
East Passage
East Passage
11.9%
West Passage
West Passage
25.9%
Greenwich Bay
14.4%
ma
Conditional B
20.9%
Conditional A
23.6%
• No info on Closed Waters
• Tagging Areas are Large

26. RI DEM Quahog
Dredge Survey
1993‐2013
• Use hydraulic dredge
to sample adult
populations
• Stratified Random
Sampling Design
• 2368 tows of 30 m
• 26,000+ clams

27. Spatial Distribution
of Quahogs
• Not corrected for
dredge efficiency
• High densities
correspond to
productive fishing
grounds
• Shallow areas poorly
assessed
• Closed Areas highest
densities

28. Larval Export from Closed Areas
• ~100 million eggs/m2
• Larval Duration 8‐12 days
• Large potential
reproductive output

29. Larval Export from Closed Areas
• ~100 million eggs/m2
• Larval Duration 8‐12 days
• Large potential
reproductive output
Too Dense?
Crowding may lead to
poor condition and low
reproductive output
Marroquin‐Mora
& Rice (2008)
CI = dry soft tissue wt X 1000/
(total wt ‐ shell wt)

30. Where are the
Larvae?
•Sampled 60 sites,
once/week for 6 weeks
•Used qPCR to enumerate
larvae
•Providence River, Warren
River, Western Greenwich
Bay have highest densities
•2 major spawning events;
mid‐June and early to mid
July
•Only a snapshot in time –
Where will they end up?
Average Larval
Densities at Surface

31. Tracking Larvae
from Source to
Settlement
• Larvae released
randomly over 30 day
period
• Released in top 2
meters
• Passive for 11 days
• Swim towards bottom
for 24 hours –
randomness added
• Site Specific Settlement
– OFF
LTRANS

32. Source – Sink
Dynamics
• Assess larval dispersal
throughout the Bay
• Release larvae in
proportion to adult
densities
• Working towards
developing a matrix
model including:
– Adult population
demographics
– Fecundity index
– Spatially varying
mortality rates
– Connectivity matrix

33. Larval Counts
UpperBay
Lost 38.2%

34. Larval Counts
Larval Counts
Open
Prohibited
Lost 43.8%
Lost 28.6%

35. Greenwich Cove
Transplants

36. Greenwich
Cove
Potowomut
Sanctuary
High
Banks

37. Dispersal From Donor & Transplant Sites
Greenwich Cove
Prohibited
High Banks Management Area
Approved

38. Comparison of Transplant Sites
Potowomut Spawner Sanctuary
Approved‐Closed
High Banks Management Area
Approved

39. Reproductive Condition of Quahogs: Efficacy of Transplants
Preliminary Results (2012)
 Significantly lower mean CI in closed sites (p=0.0001)
 Lag in CI of quahogs in closed sites (Spring and Fall)
 Mark‐Recapture experiment (ongoing)
‐ Tag 1600 quahogs from G.C.
‐ Transplant to Potowomut S.S.
Matt Griffin
RWU/URI

40. Soft Shell Clams‐ A Cautionary Tale
1400
Shell Weight (lbs X 1000)
1200
1000
800
600
400
200
0
2003
2004
2005
2006
2007
2008
Year
2009
2010
2011
2012
2013

41. Soft Shell Clams‐ A Cautionary Tale
1400
Shell Weight (lbs X 1000)
1200
1000
800
600
400
200
0
2003
2004
2005
2006
2007
2008
Year
2009
2010
2011
2012
2013

42. Summary & Recommendations
•
Fishing rates and quahog populations in fished waters have been
relatively stable since 2004
•
Areas prohibited to fishing act as sanctuaries where biomass
accumulates‐ May contribute as much as half of the effective
reproductive potential of the Bay
•
Need to carefully assess impact of opening additional areas to harvest
to the bay‐wide population
•
Need more monitoring of populations in closed areas – density and
reproductive health
•
Continue development of spatially explicit population model that will
allow for better assessment of management strategies
•
Need better understanding of post–set processes and mortality

43. Acknowledgements
Dave Ullman
Candace Oviatt
Chris Kincaid
Tatiana Rynearson
Christelle Balt
Mark Gibson
Dennis Erkan & everyone who assisted
with DEM Dredge survey
Funding Sources:
The Nature Conservancy Global Marine Initiative
Student Research Award
URI GSO Alumni Scholarship
Rhode Island DEM

44. Number of Active Licenses for Quahogs‐ Grouped by License Type
1400
MPURP
PEL
CFL
SFO65
STUD
MPURP Active
PEL Active
CFL Active
SFO65 Active
STUD Active
1200
# of Licenses
1000
800
600
400
200
0
2003
2004
2005
2006
2007
2008
Year
2009
2010
2011
2012

45. Licenses and Landings
3000
# of Licenses
Meat Weight (MT)
12
Unemployment Rate
10
2000
8
1500
6
1000
4
500
2
0
1945
Unemployment Rate (%)
Landings (MT) & Licenses (#)
2500
0
1950
1955
1960
1965
1970
1975
1980
Year
1985
1990
1995
2000
2005
2010
* NMFS Landings Data

46. Fished
Protected
Habitat Area51% of Studies
49% of Studies
Fisheries Yield
Fisheries Yield
Higher with
Higher with
MPAs
Traditional
Management
F
P
Habitat Area

47. Fished
Protected
Habitat Area
F
P
Habitat Area
Adapted from Gaylord, et al., 2005