Upper Mississippi River Restoration Program

Upper Mississippi River Restoration Program

Long Term Resource Monitoring

 

Development of survey methods to spatially map mussel assemblages in the Upper Mississippi River System


Introduction/Background:

Resource managers need information on mussel abundance and how they are distributed in the UMRS. Nested within this question are specific information needs at many levels. At the coarsest level, pool-wide estimates of total mussel abundance across species are needed. At a finer level, abundance estimates are often needed at smaller spatial scales, or estimates of community composition are needed. Even more detailed information is often needed regarding spatial patterns at smaller scales (e.g., project sites). At a very fine level, estimates of rare species are often needed at a project site.
Previous studies conducted in 2006 and 2007 evaluated potential sampling designs that may provide estimates that meet the needs of resource managers. In 2006, a systematic survey design used in Pool 5 produced acceptable levels of relative precision for pool-wide population estimates. The pool-wide design used in Pool 5 was subsequently used for pool-wide mussel surveys in Pools 6 and 18 in 2007. However, the design used in Pool 5 was unsuccessful at attaining the desired relative precision for abundance estimates in the shallow water zone representing the area that might be impacted by the drawdown.

Two additional sampling designs were deployed in Pool 6 in 2007. We tested the use of a double sampling design to address the inability to estimate shallow-water zone mussel abundance with the pool-wide systematic sampling design that didn't use double sampling. A double sampling design utilizes a more rapid method of mussel detection that is subsequently adjusted for detection errors. The percentage of mussels not detected using the rapid method (i.e., detection probability) is obtained from paired quantitative/semi-quantitative samples. The second design, adaptive sampling) was tested in deep water to increase the number of collected mussels. Collecting more mussels can lead to better estimates for species that are less common and provide better species lists. Adaptive sampling collects more mussels by increasing sampling frequency where mussels are found.

This proposed research will continue to use experimental sampling methods and evaluate the use of such methods to provide information on mussels in the UMR. Some of these methods have already been used by resource managers, but have gone untested (e.g., no detection probabilities were estimated). Specifically, the methods tested here will focus on mussel bed determination and characterizing the mussel assemblage within selected beds.

Relevance of research to UMRS/LTRMP:

The overall objective of this proposal is to further evaluate study designs that may be suitable for obtaining mussel assemblage information at small to intermediate spatial scales. There are two distinct projects under this proposal: 1) a study to determine detection probabilities (e.g., double sampling) for mussel bed surveys in Pools 22 and 24 and 2) a study to evaluate an adaptive double sampling design in Pools 3 and 4. These studies will provide new information on double sampling surveys in deep water, and an adaptive double sampling design.

Pools 22 and 24 double sampling

This project will provide new information on double sampling. Methods differ somewhat from the previous work using double sampling in Pool 6, thus providing needed information on the use of semi-quantitative sampling methods. This is a deep water survey in the lower part of the UMR. The rapid assessment will include a less quantitative method than the design used in Pool 6, and it will focus on selected mussel beds (e.g., areas of higher overall density than pool-wide density). The estimation of detection probabilities will provide a means of assessing the validity in comparing past data from primarily quantitative surveys to recent data using rapid qualitative assessments. In particular, the abundance of several selected species that are thought to be in decline will be better estimated, thus a better assessment of their status will be a product of this survey.
Pools 3 and 4 adaptive double sampling
The proposed study will use an adaptive double sampling design to characterize a selected number of mussel beds. Development of these methods and the evaluation of these methods will lead towards more robust sample estimates. The use of an adaptive design will address the need to allocate samples efficiently when sampling populations that have high spatial heterogeneity.
All data collected during this APE project will be available to researchers developing habitat associations for mussels.

Methods:

Pools 22 and 24 double sampling
We propose to sample two mussel beds where deertoe (Truncilla truncata) mussels were previously found to be common amongst distinct large beds in Pools 22 and 24. Transects traversing the beds will be established, with transect length estimated by determining endpoints based on mussel density observed during the survey. We will deploy semi-quantitative and quantitative sampling techniques. The entire length of each transect will be surveyed by visual/tactile surface methods (semi-quantitative) on the downstream side of the established transect line. Each transect will also be surveyed by m2 quadrat samples (quantitative) placed on the upstream side of each transect line. The distance between quadrats will be selected to achieve a desired sample size for accurate estimates of detection probabilities. The quadrat will be double sampled, with visual/tactile surface samples collected prior to excavation of the sediments. The two distinct samples will be used to determine detection probabilities. Sampling will be conducted by diving. Information on sampling effort required to complete the various techniques (i.e., surface samples and excavated quadrats) will be recorded.
Pools 3 and 4 adaptive double sampling
We propose to sample two or more known mussel beds: one off-channel bed in Pool 3 and one main channel bed in Pool 4. Sampling will radiate out from the selected starting points within the bed until criteria for a mussel bed, as predefined, are not met. Methods will include qualitative sampling along transects to "trigger" semi-quantitative sampling if mussel density criteria are met. A subset of the semi-quantitative sites will be surveyed quantitatively for the purpose of obtaining detection probability values. This approach accommodates the clustered nature of mussel distributions (i.e., mussel beds) by rapidly surveying areas with few or no mussels. The use of such a design will not only begin to provide information on mussel bed characteristics, but also provide insight into the utility of such a design for surveying HREP sites and other project areas. Sampling will be conducted by diving. Information on sampling effort required to complete the various techniques (i.e., qualitative, semi-quantitative, and quantitative) will be recorded.

Additional Information: There will likely be two additional reports, but these will be products of co-investigators and will not be funded through APE funds. The additional reports would cover mussel bed characteristics in the two respective study areas (i.e., the two lower pools and one upper pool).

Name of Principal Investigator: Jim Rogala

Collaborators: Travis Moore; Matt Combe; Mike Davis; Dean Corgiat; Teresa Newton; Brian Gray

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