role of oyster age vs. oyster size in determining sex ratios on restored oyster reefs in chesapeake...

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