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Timed Search Technique Used to Evlauate Freshwater Mussel (Bivalvia: Unionidae) Species Richness in Headwater Streams: Is a Single One-Hour Visit Enough?
Journal of Freshwater Ecology
Abstract
Freshwater mussels were sampled in the upper Mackinaw River basin, Illinois, for five years to determine if a single, one-hour visit was enough to adequately characterize the species richness at a headwater stream site when using the timed search technique. Eight sites were each handpicked for one person-hour every year, and species richness was calculated to determine if it varied by year for five years. During 39 person-hours, 2,692 live individuals of 14 species were collected. Species accumulation curves and Spearman's correlation analysis suggested that a single, one-hour visit was not adequate when using the timed search technique to determine species richness in headwater streams of the Mackinaw River basin and might not be sufficient in other basins.
... Sites included the most recent known locations of E. triquetra in the state, along with those sites where valves had been found during previous surveys (data taken from INHS Mollusk Collection, Champaign). The aforementioned surveys utilized timed-searches, which is a quick, cost effective method used for obtaining information on species richness (Strayer and Smith, 2003;Tiemann et al., 2009 and references therein); however, none of the previous surveys used quadrats. Area searches (e.g., quadrats) are better suited than timed-searches for determining densities and length frequencies of freshwater mussels (Strayer and Smith, 2003;Tiemann et al., 2009 and references therein), thus 1-m 2 quadrats were used in this study. ...
... The aforementioned surveys utilized timed-searches, which is a quick, cost effective method used for obtaining information on species richness (Strayer and Smith, 2003;Tiemann et al., 2009 and references therein); however, none of the previous surveys used quadrats. Area searches (e.g., quadrats) are better suited than timed-searches for determining densities and length frequencies of freshwater mussels (Strayer and Smith, 2003;Tiemann et al., 2009 and references therein), thus 1-m 2 quadrats were used in this study. At each site, at least five transects were uniformly spaced 5-m apart, perpendicular to the river channel along a sandy-gravel riffle / run, and up to five points were evenly established 0.5-m apart along the length of each transect. ...
Within Illinois, the state-endangered snuffbox mussel Epioblasma triquetra (Rafinesque) is currently found only in a small stretch of the Embarras River in Douglas and Coles counties and is considered one of the rarest freshwater mussels in the state. To assess the current population status of E. triquetra in Illinois, I estimated density, length frequency, and sex ratio of the Embarras River population. I also examined the status of the snuffbox mussel's host fish, the logperch Percina caprodes (Rafinesque), to determine if the fish was present in this area. Seven sites in the Embarras River were sampled for freshwater mussels and fishes during the summers of 2007 and 2008 using common sampling protocols. Only five adult (>55 mm) E. triquetra males were collected from two sites, suggesting this species is functionally extirpated in Illinois. Although P. caprodes was collected at five sites including the two that housed E. triquetra, it occurred at low densities. It seems unlikely that E. triquetra can recover naturally in Illinois, and carefully planned translocation or augmentation methods might be required to restore the species.
... Metcalfe-Smith et al. (2000) reported that 1.5-manhour (mh) searches generally failed to catch all species in Ontario streams. Tiemann et al. (2009) found that 1-mh searches were insufficient at most reaches of a small river in Illinois. These studies suggest that inadequate sampling might be common in time-based mussel surveys. ...
... First, 16-mh searches at each sampling site provided a solid basis for estimating species diversity accurately, something essential for evaluating sampling adequacy. In comparison, previous studies were based on sampling efforts ,5 mh/site (e.g., Metcalfe-Smith et al. 2000, Tiemann et al. 2009). We also accounted for imperfect species detectability by using Chao-1 to estimate the total number of species present at a site. ...
Freshwater mussels are one of the most imperiled groups of animals in North America. Effective resource management and conservation efforts require reliable estimates of species diversity and their distributions. However, sampling protocols for qualitative mussel surveys have not been well established and tested. Furthermore, the sampling effort required for a given data-quality goal (90% of species captured) often varies substantially among sites, and application of a standard effort probably would introduce bias into assemblage comparisons. We tested the sampling adequacy of time-based hand searches. We conducted 16-man-hour (mh) searches at each of 18 wadeable stream sites in Illinois that differed widely in environmental factors and historical species diversity and collected 27 to 942 individuals and 5 to 18 species per site. We accounted for imperfect species detectability by using the Chao-1 richness estimator and measured sampling adequacy as the % of the estimated number of species sampled. Four-mh searches, a frequently used effort, captured 15 to 100% of all species with an average of 61%, and yielded estimates of richness that were not significantly correlated with the estimated total richness (Pearson's r = 0.39, p > 0.05). Ten-mh searches captured >70% of all species at >70% of sites and resulted in a significant correlation between observed and estimated richness (Pearson's r >= 0.78, p < 0.01). A Random Forests (RF) model based on watershed and habitat characteristics (e.g., stream size and dominant substrate types) accounted for 45% of the variance in sampling adequacy of 4-mh searches. Sampling adequacy decreased with increasing stream size and substrate size but increased with % forest in the riparian zone and logs in the stream. A 2(nd) RF model was developed to predict the number of man-hours required to capture 70 +/- 3% of all species, and it accounted for 37% of the variance. Our findings should serve as a guide for setting standard sampling efforts for mussel surveys in Illinois and probably other midwestern states and should provide a baseline for setting site-specific efforts. Our modeling approach is of general applicability for addressing sampling-adequacy issues in studies of any assemblage.
... All collected mussels were placed in mesh bags until survey completion, at which time identifiable mussels were returned to the stream, and unidentified taxa were placed on ice and returned to the lab for identification [57,61,62]. These data allowed for calculation of catch per unit effort and relative abundance for each species, as well as assemblage richness and evenness at each study site ( [63]; but acknowledging concerns in [64]). ...
Although rivers support significant unionid mussel (Unionida: Unionidae) diversity, Gulf of Mexico tributary rivers have been subject to changes in water quality and habitat due to altered watershed land use. We quantified mussel species richness and relative abundance and environmental factors in small tributary streams of the Pearl River, Mississippi-Louisiana. Freshwater mussel and habitat surveys were conducted at 27 stream sampling sites over two summers (9 sites revisited), and coverage of seven land use categories and seven geological categories above each reach were calculated. Mussels were patchily distributed (53% of sites sampled yielded mussels) and typically not abundant (only 26% of sites yielded >10 mussels). Surveys revealed nine species, with total abundance ranging from 0–66 mussels and richness ranging from 0–5 species per site. Assemblages were driven by an upper to lower watershed gradient of decreasing CPUE and richness, with microhabitat and water quality, land cover, and geology locally modifying this gradient. Environmental variables did not seem of sufficient magnitude to account for the patchy distributions and low abundances of mussels at most study sites, and we hypothesize that high discharge events related to tropical storm passage may have exerted an overriding influence on mussel assemblages in these streams through direct mortality and/or altered availability of suitable glochidial hosts.
... Some research has been conducted regarding the requirements for the various sampling methods. For example, 1 hour has been deemed insufficient in species-rich (14 species) headwater sites (Tiemann, Cummings, & Mayer, 2009). As for the area search methods, the bank-to-bank method has been suggested to be slightly more efficient (Dickson, 2000) than the quadrat method (for description of the sampling methods, see Strayer & Smith, 2003). ...
Riverine mussel investigations involve laborious fieldwork, yet acquiring adequate sample sizes is of high importance. This paper presents the calculated minimum sample size required for the bank‐to‐bank transect method in species‐poor rivers. Data were collected from 50 transect dives from four Finnish rivers, and individual‐based rarefaction calculations were used to detect the minimum sample size at which the number of new species plateaus (i.e., species richness curve reaches an asymptote). The results indicate that a minimum of 100 mussels per transect is necessary for general semiquantitative investigations using bank‐to‐bank transect surveys. Because riverine systems typically exhibit high variation in habitats, expert evaluation should always be used to determine the number and location of transects. The effort must be increased if very rare species need to be collected.
... some gravel and cobble substrates in the main channel. Our search method was a 3.5-hr timed search (Tiemann et al., 2009, Huang et al., 2011 and we left all mussels instream until processing. ...
... Efforts were made to cover all available habitat types present at a site including riffles, pools, slack water, and areas of differing substrates. We imple-mented a 4-hour timed search method (Tiemann et al., 2009;Huang et al., 2011) and left all mussels instream until processing. ...
... Efforts were made to cover all available habitat types at a site including riffles, pools, slack water, and areas of differing substrates. A two-hour timed search method was implemented at most sites since these were small, degraded headwater streams and previous surveys recorded diminished species richness within the basin (Tiemann et al., 2009; Huang et al., 2011; Price et al., 2012). We held live mussels in mesh bags in the stream until processing. ...
... A minimum of one-person hour was spent at each site. Despite current studies suggesting that one hour is not enough time to discover rare freshwater mussel species (Metcalf-Smith et al. 2000, Tiemann et al. 2009), timed searches are effective for detecting the majority of freshwater mussel species present at a site (Miller and Payne 1993, Strayer et al. 1997, Vaughn et al. 1997, Strayer 1999, Strayer and Smith 2003. The objective of our survey was to detect the presence of freshwater mussel species at a site, and therefore timed searches are considered an appropriate method. ...
Freshwater mussels are increasingly recognized as important components of aquatic ecosystems but paradoxically are one of the most critically imperiled faunal groups in North America. In California the conservation status of all three native genera had not been comprehensively evaluated in over 30 years. We determined the current distribution of freshwater mussels in California by resurveying historical sites of known occurrences and evaluating the relative change between historical and contemporary surveys. A total of 450 historical records were compiled and represented 116 unique, locatable sites. Nearly 70% of the historical sites were resurveyed, and freshwater mussels were found at 47% of the resurveyed sites. Of the three mussel genera (Anodonta, Gonidea and Margaritifera) known from California, Anodonta was historically the most commonly observed genus, but was only found at 33% of the resurveyed sites. Although Margaritifera and Gonidea were historically found at fewer sites than Anodonta, they were extant at 65% and 55% of the resurveyed sites, respectively. Mussel losses were especially apparent in southern California, with mussels extirpated from 13 of 14 resurveyed sites. The absence of mussels from many historical sites, especially in southern California, parallels the on-going decline of freshwater mussel populations nationally.
... A minimum of one-person hour was spent at each site. Despite current studies suggesting that one hour is not enough time to discover rare freshwater mussel species (Metcalf-Smith et al. 2000, Tiemann et al. 2009), timed searches are effective for detecting the majority of freshwater mussel species present at a site (Miller and Payne 1993, Strayer et al. 1997, Vaughn et al. 1997, Strayer 1999, Strayer and Smith 2003. The objective of our survey was to detect the presence of freshwater mussel species at a site, and therefore timed searches are considered an appropriate method. ...
We compared population characteristics of adult Chinook salmon (Oncorhynchus tshawytscha) during 2003–2006 in the lower Stanislaus River, Stanislaus County, California, by counting and measuring live fish moving past a resistance board weir and dead fish counted and measured by the California Department of Fish and Wildlife (CDFW) during annual carcass surveys. The comparison of annual escapement was extended
to 2007–2009 by including unpublished data. Although annual salmon passage counts at the weir were significantly correlated with estimates of carcass survey escapement, size estimates of live fish passing the weir were smaller on average than dead fish measured during carcass surveys. Sex ratios also differed for fish counted at the weir compared to those counted during carcass surveys. In general, females outnumbered males in both datasets, except in 2004 when more males than females were counted at the weir. Ratios of clipped to unclipped adipose fins differed significantly between fish from the weir and from the carcass surveys during 2005–2006, but not during 2004. These results suggest that population characteristics of adult salmon returning to the Stanislaus River may be better represented by the relatively high numbers of live fish examined during their concentrated passage through the weir than by the lower numbers of widely dispersed dead fish examined during carcass surveys.
... Although not indicated in this study's data, we have recently encountered these species through stream assessments in large river and tidal-fresh habitats as part of other studies while using the same informal visual search. Nonetheless, we realize the current methods may be insufficient to detect and characterize the true mussel richness in some habitats where species with cryptic life history traits reside (Metcalfe-Smith et al., 2001;Tiemann et al., 2009). However, a cursory comparison of our mussel richness data to that collected by the Maryland Natural Heritage Program using timed-snorkel surveys has shown good agreement between most small to medium sized streams and watersheds. ...
Gaps in our knowledge of freshwater mussel life history, distribution, and ecology remain even though their study has increased considerably over the past few decades. These studies have traditionally taken place within a population, river, or larger drainage unit, but rarely across a broad landscape, such as a state. Given the imperiled status of a majority of unionid species alternative opportunities to collect valuable data cannot be overlooked. We present results from a statewide biological monitoring program (Maryland Biological Stream Survey) that has incorporated a visual survey for mussels, several example analyses using mussel-bioassessment data, and discuss the utility and limitations of incorporating freshwater mussels into stream assessments. Since 2007, we encountered 11 of the 16 mussel species extant in Maryland during assessments of wadeable streams by using an informal visual survey and recording incidental observations. On several occasions, we have discovered new populations of imperiled mussels or extended a species distribution. The biological and physiochemical data collected at sites coincident with freshwater mussels have allowed us to hypothesize factors potentially limiting species distribution, such as fish-host dynamics, habitat quality, nutrient concentration, and catchment land use. We feel that the addition of a survey effort into a biological monitoring program, invaluable data can be collected that can assist resource managers, malacologists, and researchers answer a variety of questions. Further investigation into the cost-benefits of an appropriate level of sampling effort is needed as this could vary markedly among molluscan faunal regions and by objectives.
Qualitative sampling is recommended over quantitative sampling when the objective of a mussel survey is to find rare or endangered species. Although advice on how to conduct quadrat surveys is available, there is little information on the influence of sampling effort on the effectiveness of timed searches. We conducted timed searches for mussels at 28 sites on 5 rivers in southwestern Ontario using 4.5 person-hours (p-h) of sampling effort/site. The survey period was divided into 3 equal time intervals, and the number of species and individual mussels collected within each interval were recorded. Increasing the sampling effort dramatically improved the detection of rare species. Sampling for 1.5 p-h, which is the level of effort commonly used in timed search surveys, would have resulted in <½ of the rare species being found and would have underestimated species richness by an average of 37%. Seventy percent of encounters with 3 federally endangered species took place during the 2nd and 3rd time intervals. Increasing the sampling effort from 1.5 to 4.5 p-h/site resulted in all but 2 of the 28 species being found at more sites. Even 4.5 p-h of effort may be insufficient for detecting all species at all sites or estimating species richness for a river. Researchers who rely on qualitative surveys to determine the presence of rare and endangered mussel species should consider the amount of time they spend at their sites because sampling effort can significantly affect their ability to detect these species.
Two-phase sampling provides a statistical framework for combining data from qualitative and quantitative sampling methods. It is a useful approach when the survey objective is a drainage-wide estimate of mussel density and the cost of qualitative sampling is small relative to the cost of quantitative sampling. This survey design has several advantages including: 1) no need for a priori classification of stream reaches into sampling strata, 2) allocation of sampling effort so that more time is spent sampling where mussels are at higher density and less time is spent sampling where mussels are not present, 3) the ability to evaluate the relationship between qualitative and quantitative estimates of density and 4) efficient allocation of effort so that more stream reaches can be surveyed compared to quantitative-only sampling designs with similar effort. The survey design consists of sampling as many sites as possible during a qualitative 1(st) phase and sampling far fewer sites during a quantitative 2(nd) phase. In 1995, we used a 2-phase sampling design to estimate the distribution and abundance of freshwater mussels in riffle habitat in the Cacapon River, West Virginia. Our estimate of river-wide surface density of freshwater mussels in riffles was 0.59/m(2) (SE = 0.14). We used resampling simulation based on our data and determined that the most effective 2(nd)-phase sampling strategy was to sample a low to moderate proportion of low-density sites and a high proportion of high-density sites.
We studied aggregation in 76 populations of freshwater mussels from relatively homogeneous surroundings in a wide range of habitats. Chi-square tests for spatial aggregation found only 53% of mussel populations significantly (p < 0.05) aggregated. The variance of replicate mussel samples (s2) varied with the mean number collected (m) as 1.49m1.17, but conformed to the general variance relation found for other aquatic taxa (m1.5) at m > 1. The number of replicate samples (n) required to estimate mussel abundance with a given level of precision (D = SE/m) is approximately m-0.5 D-2. Sampling mussels with large quadrats requires between 5 and 25 samples for 20% precision. Sampling designs to determine significant impacts (alpha = beta = 0.05) require 7-50 samples of each population to detect doubling or halving of the population density, or three to nine to detect order-of-magnitude changes. Large sampling units are recommended to ensure acceptable sampling precision and accurate chi-square analyses of spatial aggregation and to permit ecologists to detect significant impacts on freshwater mussel populations.
Quantitative and qualitative sampling methods were used to study community characteristics, density, recruitment rates and population demography of abundant species of freshwater mussels (Family: Unionidae), at Ohio River Miles 444.2-445.6 in July 1989 and September 1990. Mean unionid densities (±SD) based on 100, 0.25-sq m total substratum samples at four sites ranged from 4.4 ± 6.8 to 52.4 ± 13.9 individuals/sq m. Mean densities of Corbicula fluminea ranged from 66.8 ± 67.7 to 1352.8 ± 96.1 individuals/sq m. Shannon-Weaver species diversity log2.3026 (2.32 to 2.50) and evenness (0.76 to 0.90) at these sites indicated an equitable distribution of species within the community. Individuals of two abundant species, Quadrula pustulosa pustulosa and Pleurobema cordatum, were represented by most size classes, indicating generally sustained recruitment with some annual variation. Both sampling methods provided similar estimates of community composition, species richness, diversity and evenness. A comparison of these results with those from a previous survey at this bed indicates no major changes in biotic conditions between 1984 and 1989-1990.
We sampled the mussel assemblages at 4 locations in the St. Croix River, Minnesota and Wisconsin, to examine sampling bias between quantitative (sediment excavation) and qualitative (timed searches) methods. Both methods provided similar species richness, diversity, and evenness values among locations examined. At all locations, each sampling method resulted in similar relationships between the number of mussels collected and the number of species found. However, assemblage composition and the mean length of individuals collected differed significantly between methods. Quantitative samples included smaller mussels than qualitative samples; individuals <20 mm long (approximately) were excluded from qualitative collections. Examination of length-frequency histograms for individual species revealed that the degree of bias differed among locations. This bias occurred even with large sample size (n > 1000 individuals) and was probably related to differences in substrate composition among locations.
Nine sites in the Neosho River (Kansas) were surveyed for unionid mussels during summer 1994 to compare the effectiveness of quadrat sampling vs. timed snorkel searches for evaluating relative abundance, species richness and diversity, size distribution and evidence of recruitment. At each site, timed snorkel searches were conducted in a 100-m stretch, 10-m wide, of wadable habitat. Mussels were returned to their original location following identification and sizing. Next, 40 1 m2 quadrats were sampled from the same stretch. Finally, 15 qualitative substrate samples (approximately 1 m2) were sieved in an attempt to detect recruitment. A total of 786 mussels were caught during 12 h, 11 min of snorkel searches compared to 896 mussels from 360 1-m2 quadrats. Quadrula metanevra was the most abundant species collected by either qualitative or quantitative methods. Differences in assessments of species diversity and relative abundance between methods were not significant; however, timed searches revealed significantly fewer species, and were less effective in detecting cryptic species than were quadrat samples. Little evidence of recent recruitment was detected in any of the methods. Quantitative methods are recommended for assessments of density, biomass, size demographics and local scale phenomena, whereas qualitative searches are more efficient when targeting large species or examining broad distributional patterns. However, some form of substrate sieving is necessary to detect small mussels.
Species richness is a fundamental measurement of community and regional diversity, and it underlies many ecological models and conservation strategies. In spite of its importance, ecologists have not always appreciated the effects of abundance and sampling effort on richness measures and comparisons. We survey a series of common pitfalls in quantifying and comparing taxon richness. These pitfalls can be largely avoided by using accumulation and rarefaction curves, which may be based on either individuals or samples. These taxon sampling curves contain the basic information for valid richness comparisons, including category–subcategory ratios (species-to-genus and species-to-individual ratios). Rarefaction methods – both sample-based and individual-based – allow for meaningful standardization and comparison of datasets. Standardizing data sets by area or sampling effort may produce very different results compared to standardizing by number of individuals collected, and it is not always clear which measure of diversity is more appropriate. Asymptotic richness estimators provide lower-bound estimates for taxon-rich groups such as tropical arthropods, in which observed richness rarely reaches an asymptote, despite intensive sampling. Recent examples of diversity studies of tropical trees, stream invertebrates, and herbaceous plants emphasize the importance of carefully quantifying species richness using taxon sampling curves.