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reclassification of growing areas if possible Look for changes in - - PowerPoint PPT Presentation
reclassification of growing areas if possible Look for changes in - - PowerPoint PPT Presentation
Identify areas of high clam densities to focus efforts of reclassification of growing areas if possible Look for changes in clam densities and distributions from previous surveys Collect the necessary data for any potential
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Unfunded Federal mandate which strictly controls the
harvest of bi-valve molluscan shellfish( clams, oysters, mussels, etc.) through State Shellfish Programs
State Shellfish Programs establish harvest areas
following strict regulations
State Shellfish Programs are audited by U.S. Food and
Drug Administration annually
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1968 Grab Survey1 1976 Venturi Suction Dredge2 2011 Duplicated Sample technique of 1976 survey
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Dredge utilizes water pressure from 4” water pump to
“vacuum” all clams and sediment to a minimum depth
- f 12 inches
Assume 100% efficiency based on pre-sampling tests Collects clams that are less than 1 centimeter in length
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Restricted Harvest Seasonally Restricted # clams/m2
Figure 1. Rehoboth Bay site specific clam densities and harvest classifications
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Figure 2. Indian River Bay site specific clam densities and harvest classifications
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2 1 Nautical Miles
1975-76 2010
Figure 3. Density distribution of Mercenaria mercenaria Rehoboth Bay area 3
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1975-76 2010
Figure 4. Density distribution of Mercenaria mercenaria Indian River Bay area3
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Figure 5. Hard clam densities of 2011 survey using spline interpolation with a 25m x 25m grid.
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Statistical Test Result P-value Rehoboth Bay clam density: 1976 versus 2011 Not Significant P=0.45 Indian River Bay clam density: 1976 versus 2011 Not Significant P=0.36 Rehoboth Bay versus Indian River Bay clam density: 1976 Significant P<0.001 Rehoboth Bay versus Indian River Bay clam density: 2011 Significant P=0.049
Table 1. Comparison of clam densities between years and between bays (Wilcoxon two-sample test).
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Statistical Test Result P-value Rehoboth Bay clam density: 1976 versus 2011 Not Significant P=0.31 Indian River Bay clam density: 1976 versus 2011 Not Significant P=0.34 Rehoboth Bay versus Indian River Bay clam density: 1976 Significant P<0.0001 Rehoboth Bay versus Indian River Bay clam density: 2011 Not Significant P=0. 296
Table 2. Comparison of the distributions of clam densities between years and between bays (Kolmogorov-Smirnov two-sample test).
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0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 Proportion of All Observations Clams/m2
Indian River Bay 2011
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 Proportion of All Observations Clams/m2
Indian River Bay 1976
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 Proportion of All Observations Clams/m2
Rehoboth Bay 1976
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 Proportion of All Observations Clams/m2
Rehoboth Bay 2010
Figure 6. Distribution of clam catches in the 1976 and 2011 surveys.
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General survey conducted at 10 stations using a bull
rake and hand rake to determine if any bi-valve shellfish were present
Only 9 clams were found at all 10 sites Sites were selected to represent all areas of the bay Majority of clams were found near Southern portion of
the bay
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Use available data to make educated management
decisions
Identify survey method which provides statistically
similar data but is less costly and intensive
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1) Humphries, E. and F.C. Daiber. 1967. Shellfish Survey
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Indian River Bay and Rehoboth Bay, Delaware. Technical Report. Northeast Marine Health Sciences Laboratory. Public Health Service. Narragansett, Rhode Island. 2) Cole, R.W. and L.W. Spence. 1976. Shellfish Survey of Rehoboth Bay and Indian River Bay. Technical
- Report. Delaware Department of Natural Resources
and Environmental Control. Division of Fish and Wildlife. 3) Lynch, Rebecca. 2012. Inland Bay Clam Density Comparison Maps. Delaware Department of Natural Resources and Environmental Control. Division of Fish and Wildlife
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