Methods for Shellfish Population Density and Demographics in Living Shoreline Treatments

Transcription

1 PARTNERSHIP FOR THE DELAWARE ESTUARY Science Group Methods for Shellfish Population Density and Demographics in Living Shoreline Treatments Date Prepared: 09/12/2017 Prepared By: Joshua Moody Suggested Citation: Moody, J Methods for Shellfish Population Density and Demographics in Living Shoreline Treatments. Partnership for the Delaware Estuary. PDE Method No pp. PDE Method (v1, 09/12/2017) Page 1

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3 Shellfish Population Density and Demographics in Living Shoreline Treatments Partnership for the Delaware Estuary (PDE) Method Joshua Moody Description This method describes two procedures for field-based surveys to determine shellfish population densities and population demographics in living shoreline treatments. It does not include methods for determining the same metrics on living shoreline wave attenuation structures; for those methods please contact Joshua Moody. The method has been organized into the following sections: 1. Methods for determining shellfish population densities: 1.1. Quadrat based sampling 1.2. Full survey of an AOI 2. Methods for determining shellfish population demographics Summary of Approach Shellfish population densities can be measured using two approaches: a quadrat-based subsampling method, or a full survey of an Area of Interest (AOI). A quadrat-based sub-sampling method describes counts of shellfish conducted within the bounds of a 1m 2 (or other sized) quadrat, placed at a specific location. This does not describe methodologies to determine the placement or number of quadrats needed to estimate the population density in a given area, as those methods are site-specific and dependent on the size of the AOI and the variability of the population within the area. As shellfish populations typical exhibit a patchy distribution, it recommended that measurements are taken in triplicate, at minimum, within each delineated strata (e.g. high marsh, low marsh edge, within the boundaries of a bio-based living shoreline treatment, etc ). To conduct the sampling, the quadrat is placed flush with the surface at its proper location (e.g. permanently marked sampling plot, randomly chosen location, etc ), so that any vegetation contained within the boundaries is not obstructing the view of the substrate. Two meter sticks are oriented to partition the inside area of the quadrat into four 0.25m 2 sections. Each section is investigated visually and by running gloved hands into the substrate to a depth of approximately 5cm (if possible) to account for subsurface individuals. All individuals are counted and summed to total the shellfish density per m 2. A full survey of an AOI involves the complete count of all shellfish within an AOI. This methodology is typically only used within smaller living shoreline treatments where the temporal requirement of such a methodology is minimal. To conduct this methodology, rope or twine is used to partition the AOI in smaller subsections, and visual and tactile counts as described above are conducted within the sub-areas. The sub-counts are then summed for a total shellfish count of the AOI. PDE Method (v1, 09/12/2017) Page 3

4 Shellfish population demographics can be conducted in tandem with either of the above methods for determining shellfish population density. Demographics are assessed by measuring a subsample of individuals, determined by a balance between the number of measurements needed and temporal/financial resource availability, within each sampling unit (i.e. each 1m 2 quadrat, or subsect of an AOI). The percentage of individuals within each 10mm size class bin (e.g. 1-10mm; 11-20mm; 21-30mm; etc ) is applied to the total population count per sampling unit. Equipment Procedure Data sheets Pens/pencils Gloves Shellfish population density: Either: 1m 2 quadrat and two meter sticks or a spool of rope/twine Shellfish population demographics: Either digital calipers or a clear 6 ruler 46.1 Methods for determining shellfish population densities: Quadrat-based sampling Place quadrat flush with surface at proper location Move all vegetation to minimize the obstruction of the substrate Orient the meter sticks so that they partition the internal area of the quadrat in to four equal 0.25m 2 areas Start at one corner of the quadrat, and moving towards the center, sweep hands across the surface to a depth of ~5cm (where possible) in order to make contact with all individual shellfish with the subsection of the 1m 2 quadrat Count all individual with which you make tactile or visual contact Write count per subsection on the data sheet Full survey of an AOI Use rope/twine to partition AOI into subareas Start at one corner of a subarea, and moving towards its center, sweep hands across the surface to a depth of ~5cm (where possible) in order to make contact with all individual shellfish with the subsection of the 1m 2 quadrat Count all individual with which you make tactile or visual contact Write count per subsection on the data sheet PDE Method (v1, 09/12/2017) Page 4

5 46.2 Methods for determining shellfish population demographics Starting at the waterward-most corner of either the quadrat or subarea of the AOI, remove the first shellfish that you make contact with. If shellfish are unable to be removed (i.e. oysters cemented in place), conduct the measurements without removal Using digital calipers: Place the ends of the calipers so that they capture the distance between the anterior (near hinge and umbo) to posterior areas of the animal; this is likely the longest distance across the animal Measure animal to nearest millimeter Write length on data sheet Using clear plastic 6 ruler Place the ruler so that so that the zero unit is aligned with the anterior end of the animal (near hinge and umbo) and so that the rule is oriented towards the posterior end; this is likely the longest distance across the animal Measure animal to nearest millimeter Write length on data sheet PDE Method (v1, 09/12/2017) Page 5

6 PDE Living Shoreline Field Data Collection Sheet Site: Staff: Date: Treatment: Transect: 1. Shellfish Population Density and Demographics: Choose all that are applicable to the monitoring plan Quadrat Survey: Total counts of shellfish in monioring plots. "Plot a" at waterward extent Ribbed Mussels Oysters Full Survey: Total number of mussels in treatment Describe Treatment Including Full Dimensions: Totals: Ribbed Mussels Oysters Demographics: Measure up to 25 randomly chosen shellfish to the nearest mm Partnership for the Delaware Estuary

7 PDE Living Shoreline Field Data Collection Sheet 2. Vegetation Robustness A) General Plot Characteristics: Dominant Species Conduct A, B, and C record dominant species (up to 4) and their percent covers in each plot Percent Cover B) Vertical Vegetation Obstruction: Settings Take light meter readings (n=5 top and bottom); make sure units are appropriate and consistent Top 1 Top 2 Top 3 Top 4 Top 5 Bottom 1 Bottom 2 Bottom 3 Bottom 4 Bottom 5 C) Horizontal Vegetation Obstruction Measure general height of vegetation in plot and take horizontal readings at each level below that height General Vegetation Height Measured in Plot Center (cm): Record Number of Bars Observed at each Height 25cm 50cm 75cm 3. Bearing Capacity Record the initial sinking depth with hammer on shaft and compaction depth after 5 blows Initial Blow 1 Blow 2 Blow 3 Blow 4 Blow Partnership for the Delaware Estuary