Upper Mississippi River Restoration Program Long Term Resource Monitoring

Introduction/Background:

Resource managers are currently using water level drawdowns to rehabilitate habitats for vegetation and other desirable species in the Upper Mississippi River (UMR). Drawdowns may have unintended effects on native mussel populations. Over the past few summers, scientists from UMESC and river resource agencies have conducted systematic pool-wide surveys of mussels in three navigation pools (Pools 5, 6, and 18) to determine pool-wide population estimates (Rogala et al. 2007, Rogala and Newton 2008a). Collectively, these surveys suggest that there is a considerable mussel population in these pools, but that a small, but significant fraction resides in shallow water-the area presumed to be most affected by a drawdown (Rogala and Newton 2008b). We estimated mortality of mussels associated with the drawdown, but in the absence of more definitive data, we assumed that mortality in the drawdown zone was 100%. However, it is likely that some fraction of these mussels are able to migrate out of the drawdown zone and reach deeper water-especially in sloped areas. Some mussels may also survive by burrowing into the substrate to estivate. The proposed research aims to estimate the fraction of mussels that are able to move, either vertically or horizontally, to avoid short-term mortality during a water level drawdown.

Movement behavior is an important adaptation of unionids to flow conditions in rivers and enables them to respond to regular disturbances that occur as a result of changing flow conditions and water levels. Unionids move for several reasons. First, mussels may move (vertically and horizontally) seasonally into aggregations to enhance reproduction (Amyot and Downing 1998, Watters et al. 2001). Second, vertical movement may help mussels to escape predation as buried mussels are less prone to predation. Third, vertical burial in sediments may help unionids to control zebra mussel infestation (Schwalb and Pusch 2007). Natural rates of mussel movement in rivers are largely unknown. Three mussel species in the River Spree in Germany moved an average of 11 ± 15 cm/wk (range, 0-226) in the horizontal plane from May to October and roughly 70% of the mussels were found completely buried in sediment (Schwalb and Pusch 2007).

The Schwalb and Pusch (2007) study was limited in spatial scale-movement of mussels was restricted within corrals. Recent technological advances may allow us to follow movement of mussels over larger spatial scales. Kurth et al. (2007) evaluated the effectiveness of passively integrated transponder tags (PIT tags) in mussels. They successfully recaptured 78% of tagged mussels and found that 93% of the recaptured mussels retained their PIT tags after 21 months. Mortality of tagged mussels was 1.3%. In particular, the recapture rate of mussels in the Sebasticock River, Maine, with PIT tags and visual confirmation were 2-fold greater than those of visual searches alone. Thus, PIT tags permit repeated, non-destructive sampling of individuals with little disturbance, last indefinitely, and appear to have negligible effects on short-term survival of mussels.

Movement of mussels may be influenced by differences in shell geometry among species because shell form has been shown to be closely related to locomotor function (Watters 1994). Unionids have been categorized into subfamilies that differ greatly in behavior and life history. Thus, we may expect species-specific differences in movement behavior associated with water level drawdowns. Amblemine mussels close their valves tightly and are probably better at conserving water than Lampsiline mussels. Prior research suggests that Lampsilines are more active than Amblemines (Haag et al. 1993, Waller et al. 1999). Thus, we hypothesize that Lampsilines are more likely to move horizontally across the sediment surface to reach deep water, whereas Amblemines are more likely to burrow vertically into sediments and "wait" for the water to return. In a study of mortality of unionids associated with water level drawdown in Pool 5 of the UMR, Amblemine mussels had higher survival rates than Lampsiline mussels (WDNR et al. 2006).

Movement of mussels may also be influenced by physicochemical variables. Movement of mussels in the River Spree was influenced by discharge, water temperature, day length, and water level (Schwalb and Pusch 2007). It has been hypothesized that the lower limit of a mussel's vertical distribution may be limited by low dissolved oxygen concentrations in deeper sediment (Schwalb and Pusch 2007) and perhaps by sediment temperatures. Slope may also be important in predicting survival of mussels as water levels recede during a drawdown. Research by the WI DNR during the Pool 5 drawdown suggested that survival of mussels on sloped sites was potentially greater than on un-sloped sites (WDNR et al. 2006). Highly sloped surfaces might cue directional movement and provide easier access to deeper water than unsloped surfaces.

Relevance of research to UMRS/LTRMP:

In the past few years, we have developed a scientifically rigorous sampling design to obtain pool-wide population estimates of unionid mussels. Although the systematic pool-wide mussel abundance data have assisted resource managers in understanding where mussels are located, and in what abundances, within specific UMRS pools, concern about the potential for deleterious effects on native mussels continues to jeopardize HREP activities such as water level drawdown. Lacking definitive data, we have assumed a 100% mortality of mussels in the drawdown zone. The proposed research aims to evaluate the movement of mussels out of the drawdown zone and survival of mussels that estivate in river sediments during the drawdown period. Thus, the proposed research is relevant to the UMRS and the LTRMP because it addresses the unintended consequences of a key resource management tool on populations of an important faunal group in the UMRS.

Methods:

The proposed work will contribute to the overall collaborative effort of understanding the unintended consequences of water level drawdowns on native mussel populations in the UMRS. Our objective is to characterize and compare the movement of two common mussel species across low and high slope areas in Pool 6 during the summer of 2009. We will use data from a shallow water survey in Pool 6 (Rogala and Newton 2008) to choose 3 high slope and 3 low slope areas in shallow water sandy areas off the main navigation channel (the current plan calls to draw down the pool by 0.5 foot). We will also have 6 control areas-3 with low slope and 3 with high slope-in a portion of Pool 6 that is not overtly influenced by the drawdown. The corners of each of the 12 areas will be marked with stakes. Each area will be roughly 2 meters in width and length.

We will randomly place about 5-15 Amblemine mussels (e.g., Amblema plicata, Quadrula pustulosa, or Fusconaia flava) and 5-15 Lampsiline mussels (e.g., Lampsilis cardium, Lampsilis siliquoidea, or Obliquaria reflexa) in the 0-1 ft contour within each area before the drawdown begins. This way, most mussels have a relatively high probability of being exposed during the drawdown without all individual being placed near the shoreline. We will attempt to collect mussels from the general vicinity of each area to reduce the placement of mussels into different habitats. All mussels will be marked using an identification mark (number etched into shell and/or bee tag) and a fraction of mussels will be marked using PIT tags and I-buttons to record sediment temperature. In addition, we will affix a known length of buoyant fishing line to each shell to estimate the vertical position of each mussel in the substrate at each time period. We will try and locate mussels at least twice a month from June through October-a time period that encompasses the drawdown. We anticipate the field effort will take about 3 days per week from June to October. For each mussel we recover, we will record (1) its horizontal position by triangulation with the stakes demarking the area, (2) its vertical position with the fishing line, (3) a crude estimate of the slope of the sediment surface in the immediate vicinity of the mussel, (4) water temperature at the sediment-water interface, and (5) water depth.

Statistical analyses will include comparisons of survival, and horizontal and vertical migration rates of mussels between high slope and low slope areas and between species. Directionality and dispersion of movement will be assessed by Monte Carlo tests on random walks (Hooge et al.2001). The experimental design includes the main effects of treatment (low slope, high slope), species (Amblemine, Lampsiline) and time. Co-variates include sediment temperature, water temperature, water depth, and discharge.

In the event that the drawdown is cancelled, we would continue with the proposed research because it provides baseline information and methodologies to estimate the natural movement of mussels in shallow water zones of the UMR.

References:

Amyot, J.P. and J.A. Downing. 1998. Locomotion in Elliptio complanata (Mollusca:Unionidae): a reproductive function? Freshwater Biology 39:351-358.

Haag, W.R., D.J. Berg, D.W. Garton, and J.L. Farris. 1993. Reduced survival and fitness in native bivalves in response to fouling by the introduced zebra mussel (Dreissena polymorpha) in western Lake Erie. Canadian Journal of Fisheries and Aquatic Sciences 50:13-19.

Hooge, P., W. Eichenlaub, and E. Soloman. 2001. Using GIS to analyze animal movements in the marine environment. p. 37-51 In G. Kruse, N. Bez and others (eds.) Spatial Processes and Management of Marine Populations. Alaska Sea Grant College Program, Anchorage, Alaska.

Kurth, J., C. Loftin, J. Zydlewski, and J. Rhymer. 2007. PIT tags increase effectiveness of freshwater mussel recaptures. Journal of the North American Benthological Society 26:253-260.

Rogala, J.T. and T.J. Newton. 2008a. Poolwide population estimates of native mussels in Pool 18, Upper Mississippi River. Final report to the U.S. Army Corps of Engineers, Rock Island, IL. 2 pp.

Rogala, J.T. and T.J. Newton. 2008b. Shallow water surveys of native freshwater mussels in Pool 6 of the Upper Mississippi River: Population estimates and sampling design evaluation. Final report to the U.S. Fish and Wildlife Service, Winona, MN. 8 pp.

Rogala, J.T., T.J. Newton, and B.R. Gray. 2007. Documentation of mussel survey methodology deployed in Pool 5 with applications for future pool-wide estimates in the Upper Mississippi River. Final report to the U.S. Army Corps of Engineers, Rock Island, IL. 12 pp.

Schwalb, A.N. and M.T. Pusch. 2007. Horizontal and vertical movements of unionid mussels in a lowland river. Journal of the North American Benthological Society 26:261-272.

Waller, D.L., S. Gutreuter, and J.J. Rach. 1999. Behavioral responses to disturbance in freshwater mussels with implications for conservation and management. Journal of the North American Benthological Sociewty 18:381-390.

Watters, G.T. 1994. Form and function of unionoidean shell sculpture and shape (Bivalvia). American Malacological Bulletin 11:1-20.

Watters, G.T., S.H. O'Dee, and S. Chordas III. 2001. Patterns of vertical migration in freshwater mussels (Bivalvia: Unionoida). Journal of Freshwater Ecology 16:541-549.

WDNR et al. (Wisconsin Department of Natural Resources, Minnesota Department of Natural Resources, and the U.S. Army Corp of Engineers). 2006. Preliminary report on the effects
Movement of unionids during a planned water level drawdown in Pool 6 of the Upper Mississippi River 26 of the 2005 Pool 5, Mississippi River drawdown on shallow-water unionids. Wisconsin Department of Natural Resources, La Crosse, WI. 24 pp.

Principal Investigator: Teresa J Newton

Collaborators: Steve Zigler, Mike Davis, and Gary Wege