Look for changes in clam densities and distributions from previous surveys. Collect the necessary data for any potential aquaculture efforts

Transcription

1

2 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 aquaculture efforts

3 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

4 1968 Grab Survey Venturi Suction Dredge Duplicated Sample technique of 1976 survey

5 Dredge utilizes water pressure from 4 water pump to vacuum all clams and sediment to a minimum depth of 12 inches Assume 100% efficiency based on pre-sampling tests Collects clams that are less than 1 centimeter in length

6 Restricted Harvest Seasonally Restricted Figure 1. Rehoboth Bay site specific clam densities and harvest classifications # clams/m 2

7 Figure 2. Indian River Bay site specific clam densities and harvest classifications

8 Nautical Miles Figure 3. Density distribution of Mercenaria mercenaria Rehoboth Bay area 3

9 Figure 4. Density distribution of Mercenaria mercenaria Indian River Bay area 3

10 Figure 5. Hard clam densities of 2011 survey using spline interpolation with a 25m x 25m grid.

11 Table 1. Comparison of clam densities between years and between bays (Wilcoxon two-sample test). 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

12 Table 2. Comparison of the distributions of clam densities between years and between bays (Kolmogorov-Smirnov two-sample test). 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< Rehoboth Bay versus Indian River Bay clam density: 2011 Not Significant P=0. 296

13 Proportion of All Observations Proportion of All Observations Proportion of All Observations Proportion of All Observations Rehoboth Bay Indian River Bay Clams/m2 Clams/m Rehoboth Bay Indian River Bay Clams/m Clams/m2 Figure 6. Distribution of clam catches in the 1976 and 2011 surveys.

14 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

15 Use available data to make educated management decisions Identify survey method which provides statistically similar data but is less costly and intensive

16 1) Humphries, E. and F.C. Daiber Shellfish Survey of 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 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 Inland Bay Clam Density Comparison Maps. Delaware Department of Natural Resources and Environmental Control. Division of Fish and Wildlife

17 The Center for the Inland Bays 2 year project totaling $20,000 EPA pass-through funds Richard Wong, Statistical Analysis, DNREC Fisheries Bart Wilson-GIS Support, The Center for the Inland Bays Field Crew-Gene Shaner and Zac Moffitt Bryan Bloch-GIS Environmental Scientist II DNREC