Estimation of vital rates to assess the relative health of mussel resources in the Upper Mississippi River System: Data

The Minnesota Department of Natural Resources (MNDNR) has been quantitatively sampling a mussel bed in West Newton Chute (a side channel in Navigation Pool 5 of the Upper Mississippi River, UMR) annually since 2008. Briefly, ~200 systematically-placed 0.25 m2 quads are sampled annually; divers excavate substrates to a depth of ~15 cm and place material into a 6 mm mesh bag. Mussels are identified to species, aged via external annuli, measured for shell length, and sexed. From 2008-2016, this mussel bed contained 12-16 live species, had densities that ranged from 4-10/m2, and juveniles (≤ 5 years old) comprised 3-18% of the assemblage. Because this assemblage was well characterized, it represented an excellent location to estimate vital rates (i.e., survival and growth) in mussels. Our objectives were to estimate patterns in survival and growth across four species of mussels and over time within a mussel bed, and to assess if these patterns changed across patches with varying mussel densities. 
The counts of live mussels in quadrats sampled by the MNDNR during surveys from 2008-2011 was compiled and interpolated using an inverse distance weighted (IDW) algorithm in ArcGIS. The IDW surface of mussel density was classified by quartiles and the highest quartile was delineated as the core areas of the bed and the lowest quartile was delineated as the peripheral areas of the bed. This resulted in four polygons—two with relatively high mussel densities (core, labelled A1-A5 and B1-B5) and two with relatively low mussel densities (periphery, labelled C1-C5 and D1-D5). Five study plots (5 m x 5 m) were randomly selected within each polygon. Plot C5 was inaccessible, so we used plot C5a. Plots were aligned with the direction of river flow and demarcated into four quarters by driving nine pieces of PVC pipe into the substrate in a 3 x 3 array.
To obtain mussels to PIT tag, we haphazardly searched West Newton Chute in August 2012 and obtained 578 mussels, including both common (Amblema plicata, Obliquaria reflexa) and less common (Cyclonaias pustulosa, Pleurobema sintoxia) species. Shells were scrubbed to remove existing zebra mussels. A 20- or 23-mm PIT tag was attached near the umbo of each mussel with cyanoacrylate glue to enable recovery of individual mussels in subsequent years. One end of a 36-cm piece of buoyant fishing line (color coded by species) was glued near the posterior edge of each shell to facilitate recovery. We randomly allocated 9-10 A. plicata and O. reflexa and 4-5 C. pustulosa and P. sintoxia into each plot. Mussels were placed into a randomly chosen quarter of each plot. The age, shell length, and PIT tag identification number of each mussel was recorded prior to placement within a plot. 
We returned to WNC to recover tagged mussels in August 2013, August 2014, July 2015, and July 2016. Once each plot was found, a diver placed a 2.5 m x 2.5 m PVC frame over each plot quarter to facilitate a thorough search. The diver systematically searched each plot quarter using an 18-cm loop antenna that was connected, via a 15.2 m cord, to a PIT-tag reader located in an attending boat. Surface to diver communication was used to notify the diver when a marked mussel had been found. During recovery efforts, divers searched within each plot and then searched the periphery of each plot (~1-2 m outside each plot) for any marked mussels that might have moved out of the plot. All recovered mussels were identified by PIT tag, recorded as alive or dead, measured for age and shell length, and any attached zebra mussels were removed and counted.  If the PIT tag was damaged or missing, we replaced it with a new one and recorded the new PIT tag ID number.

Tags: biota, growth, native-mussels, survival, usgs-5d583085e4b01d82ce8ec16e, vital-rates
Organization: Department of the Interior