jeff mercer, "following the quahog through time and space," baird symposium
DESCRIPTION
Jeff Mercer, Principal Biologist, R.I. Department of Environmental Management Topic: Maximizing HarvestTRANSCRIPT
Following the QuahogThrough Time and Space
Jeff MercerRI DEM, Principal Biologist
November 14, 2013
39.1 Million Clams6.96 Million Pounds $5.15 million Dollars534 Fishermen
Quahogs by The Numbers
2012 Landings1. Squid $19 Million2. Lobster $12 Million3. Sea Scallop $9 Million4. Summer Flounder $7 Million5. Quahog $5 Million
CHERRY3%
CHOWDER10%
LITTLE NECK64%
TOP NECK23%
Why Quahogs?
Oviatt et al (2003)
Shellfish Catch from 1865 (Goode and Associates, 1887)
Why Quahogs?
Why Quahogs?
30,000,000 lbs
Why Quahogs?
Why Quahogs?
Why Quahogs?
• ~50% of nitrogen in quahog derived from sewerage
Why Quahogs?(Oczkowski et al, 2008)
• ~50% of nitrogen in quahog derived from sewerage
•More tolerant to hypoxia than predators = Predation refuge
Why Quahogs?
(Altieri, 2008)
(Oczkowski et al, 2008)
• ~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
Why Quahogs?
Density 8‐20 X Greater than Avg
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
Impact of Pollution Closures
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1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Land
ings (M
T) & Licen
ses (#)
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# of Licenses Meat Weight (MT)
* NMFS Landings Data
Impact of Pollution Closures
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Land
ings (M
T) & Licen
ses (#)
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# of Licenses Meat Weight (MT)
* NMFS Landings Data
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# of
Qua
hogs
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ions
)
Year
Landings
Size Structured Stock Assessment Model
Gibson, 2010
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# of
Qua
hogs
(mill
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Abundance Landings
Size Structured Stock Assessment Model
Gibson, 2010
Size Structured Stock Assessment Model
1984
19851986
198719881989
1990 1991
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19981999 200020012002
20032004
200520062007
20082009
2010 20112012
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0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70
Abu
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F Rate (t-1)
Size Structured Stock Assessment Model
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19851986
198719881989
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20032004
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2010 20112012
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0.00 0.10 0.20 0.30 0.40 0.50 0.60 0.70
Abu
ndan
ce in
Mill
ions
(t)
F Rate (t-1)
Size Structured Stock Assessment Model
1984
19851986
198719881989
1990 1991
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19981999 200020012002
20032004
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2010 20112012
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Abu
ndan
ce in
Mill
ions
(t)
F Rate (t-1)
Polynomial
Logarithmic
Stock‐Recruitment ModelsGreat South Bay, NY
How Many Quahogs do We Need?
Kraeuter et al, 2005
Density Dependence
0.75 Adults/m2 = Recruitment Failure
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# of
Qua
hogs
(mill
ions
)
Year
AbundanceLandingsRecruitment Failure
0.75 Adults/m2 X 125km2 Fishable Area
How Many Quahogs do We Need?
How Many Quahogs do We Need?
Kraeuter et al, 2005
How Many Quahogs do We Need?
Kraeuter et al, 2005
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Land
ings
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ions
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AbundanceLandingsReduced Recruitment
How Many Quahogs do We Need?
1.5 Adults/m2 X 125km2 Fishable Area
West Passage
Conditional B
Conditional A
Greenwich
East Passage
ma
ma
ma
ma
Uneven Spatial Distributions of Quahogs
West Passage25.9%
Conditional A23.6%
Conditional B20.9%
Greenwich Bay14.4%
East Passage11.9%
Management Areas0.9%
Coastal Ponds0.8%
Not Identified0.7%
Sakonnet0.6%
Mt Hope Bay0.3%
Block Island0.0%
• No info on Closed Waters• Tagging Areas are Large
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
Spatial Distributionof Quahogs
• Not corrected for dredge efficiency
• High densities correspond to productive fishing grounds
• Shallow areas poorly assessed
• Closed Areas highest densities
• ~100 million eggs/m2
• Larval Duration 8‐12 days• Large potential reproductive output
Larval Export from Closed Areas
• ~100 million eggs/m2
• Larval Duration 8‐12 days• Large potential reproductive output
Larval Export from Closed Areas
Too Dense?
Marroquin‐Mora & Rice (2008)
CI = dry soft tissue wt X 1000/ (total wt ‐ shell wt)
Crowding may lead to poor condition and low reproductive output
•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?
Where are the Larvae?
Average Larval Densities at Surface
• 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
LTRANSTracking Larvae from Source to Settlement
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
Larval CountsUpperBayLost 38.2%
Larval CountsProhibited Lost 28.6%
Larval CountsOpenLost 43.8%
Greenwich Cove Transplants
High Banks
PotowomutSanctuary
Greenwich Cove
Greenwich Cove Prohibited
High Banks Management Area Approved
Dispersal From Donor & Transplant Sites
Potowomut Spawner Sanctuary Approved‐Closed
High Banks Management Area Approved
Comparison of Transplant Sites
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 GriffinRWU/URI
Soft Shell Clams‐ A Cautionary Tale
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2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
Shell W
eight (lbs X 1000)
Year
Soft Shell Clams‐ A Cautionary Tale
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2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
Shell W
eight (lbs X 1000)
Year
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
Candace Oviatt Tatiana RynearsonMark GibsonDennis Erkan & everyone who assisted with DEM Dredge survey
Funding Sources:The Nature Conservancy Global Marine Initiative
Student Research AwardURI GSO Alumni ScholarshipRhode Island DEM
Acknowledgements
Dave UllmanChris KincaidChristelle Balt
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2003 2004 2005 2006 2007 2008 2009 2010 2011 2012
# of Licen
ses
Year
MPURP PEL CFL SFO65 STUD
MPURP Active PEL Active CFL Active SFO65 Active STUD Active
Number of Active Licenses for Quahogs‐ Grouped by License Type
Licenses and Landings
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1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010
Une
mploymen
t Rate (%
)
Land
ings (M
T) & Licen
ses (#)
Year
# of Licenses Meat Weight (MT) Unemployment Rate
* NMFS Landings Data
Habitat Area
Habitat Area
ProtectedFished
PF
49% of Studies Fisheries Yield Higher with Traditional
Management
51% of Studies Fisheries Yield Higher with
MPAs
Adapted from Gaylord, et al., 2005
Habitat Area
Habitat Area
ProtectedFished
PF