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Role of oyster age vs. oyster size in determining sex ratios on
restored oyster reefs in Chesapeake Bay
M. Lisa Kellogg, Marcy E. Chen, Victor S. Kennedy, C. Paul Miller, Sara E. Rowland, Richard T. Paynter, Kennedy C. Paynter,
Nancy J. Ward, Dawn Goldsmith, Mark W. Sherman, Jacob D. Goodwin, Christopher P. McIntyre, Steven Allen and Kennedy T. Paynter
Oyster Reef Restoration in Maryland:– Oyster Recovery Partnership coordinates oyster
reef restoration efforts in MD portion of Chesapeake Bay
• MDNR, MD Watermen’s Association, ACOE, UMD and various NGOs (e.g. CBF)
– In recent years, sanctuaries and managed reserves have been planted annually in Maryland
• Sanctuaries focus on ecological restoration
• Managed reserves focus on fishery rehabilitation
• Almost all spat are produced from wild stock at HPL
• Planted as spat on shell
• Planted in discrete year classes (i.e. same location rarely planted in subsequent years)
Sex Ratios in Oyster Populations:– Oysters are protandric
• Generally male when they first mature
• Proportion of females increases with increasing age/size
– Previous studies found a greater proportion of females associated with:
• Increasing distances between individuals (Burkenroad 1931)
• Single oysters vs. clumps (Smith 1949)
• Settlement on shell vs. settlement on adult oysters (Menzel 1951)
Questions:
1) What are the sex ratios of oysters on planted reefs in MD?
2) Do they exhibit the same patterns as previously studied populations?
3) What can sex ratio patterns on plantings tell us about possible factors influencing sex ratio patterns of oysters in general?
4) What are the implications for oyster reef restoration efforts?
Questions:
1) What are the sex ratios of oysters on planted reefs in MD?
2) Do they exhibit the same patterns as previously studied populations?
3) What do sex ratio patterns on plantings tell us about possible factors influencing sex ratio patterns of oysters in general?
4) What are the implications for oyster reef restoration efforts?
Oyster Reef Restoration in Maryland:
– Unique opportunity to examine the relationship between sex ratio and oyster age and/or size in the field
• All oysters sampled have similar history
– Spat on shell from HPL Hatchery
– Known planting dates
• Monitoring records show that there has been no significant natural recruitment
– Estimates of oyster age are not confounded
– No need to use oyster size as a proxy for oyster age
Sampling Sites:
Magothy River
• Chest Neck Point - 2001
Chester River• 13 sites
Choptank River• 12 sites
Chester River:• Boathouse
– 2005
• Emory Hollow
– 2001, 2002, 2004
• Devil’s Playground
– 2005
• Strong Bay
– 2003 (2), 2004, 2005
• Blunts
– 2002, 2003, 2005 (2)
Emory Hollow
Boathouse
Strong Bay
Blunts
Devil’s Playground
Choptank River:• Howell Point
– 2001
• Green Marsh
– 2003
• Shoal Creek
– 2001, 2004, 2005
• Bolingbroke Sand
– 2002, 2003, 2005
• The Black Buoy
– 2004, 2005
• Dixon
– 2005
• Mill Dam
– 2005
Mill Dam Dixon
The Black Buoy
Bolingbroke Sand
Shoal Creek
Green Marsh
Howell Point
Field Sampling:
– Quadrat grabs by divers
• 30 cm x 30 cm quadrat = 0.09 m2
• All shell material in quadrat collected
– Goal:
• Minimum of 50 oysters/site
• Minimum of 3 quadrats/site
– Actual:
• 39 – 291 oysters collected/site
• 3 – 22 quadrats collected/site
• 2214 oysters collected in total
Sample Processing:
– All oysters collected were individually labeled
– Data collected:
• Shell height (mm) of all oysters
• Distances between the ventral shell margins of all oysters in each clump
• Sex of all oysters determined by microscopic examination of gonad smears
Resulting Data:
– Individual oyster sex
– Individual shell heights
– Planting year
– # of oysters/quadrat
– # of oysters/clump
– # of single oysters
– Distance to nearest neighbor
– Distance to nearest neighbor of opposite sex
Resulting Data:
– Individual oyster sex
– Individual shell heights
– Planting year
– # of oysters/quadrat
– # of oysters/clump
– # of single oysters
– Distance to nearest neighbor
– Distance to nearest neighbor of opposite sex
“Natural” Oyster Bars
Kennedy Samples from NOBs in 1977 and 1978
0
10
20
30
40
50
60
70
80
90
100
0 50 100 150 200
Size Class (mm)
% Female
All Oysters – All Sites
y = 0.6647x - 7.2064
R2 = 0.7696
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
0.0 20.0 40.0 60.0 80.0 100.0 120.0
Average Length (mm)
% Female
All Oysters – All Sites
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
100.0
1 2 3 4 5
Years Since Planting
% Female
1 Year After Planting
Planting Year = 2005
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
0 20 40 60 80 100 120 140 160
Size Class (mm)
% Female
2 Years After Planting
Planting Year = 2004
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
0 20 40 60 80 100 120 140 160
Size Class (mm)
% Female
3 Years After Planting
Planting Year = 2003
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
0 20 40 60 80 100 120 140 160
Size Class (mm)
% Female
4 Years After Planting
Planting Year = 2002
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
0 20 40 60 80 100 120 140 160
Size Class (mm)
% Female
5 Years After Planting
Planting Year = 2001
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
0 20 40 60 80 100 120 140 160
Size Class (mm)
% Female
“Natural” Oyster Bars
Kennedy Samples from NOBs in 1977 and 1978
0.00
10.00
20.00
30.00
40.00
50.00
60.00
70.00
80.00
90.00
100.00
0 50 100 150 200
Size Class (mm)
% Female
Low n for Largest Size Classes
0
50
100
150
200
250
300
350
400
450
1-10 11-20 21-30 31-40 41-50 51-60 61-70 71-80 81-9091-100101-110111-120121-130131-140141-150151-160161-170171-180
Size Classes (mm)
Frequency
Future Directions:
– Detailed analysis of all current data
• Determine influence of other measured factors (e.g. # of oysters/quad, average distance to nearest neighbor, etc.)
• Include more info on planting history (e.g. density at time of planting, growth rates, mortality rates, disease history)
• Formulate testable hypotheses about factors driving observed patterns
– Additional data collection in 2007:
• Target bars with older plantings to increase the sample sizes in the larger size classes
• Sampling of “natural” oyster bars in vicinity of plantings
Acknowledgements:
Oyster Recovery
Partnership
Charlie Frentz, Director
“Mutt” Meritt and Hatchery Crew
