Crayfish Assemblages Research Articles

Disentangling determinants of nearshore fish and crayfish assemblages in a canyon-shaped Mediterranean reservoir

The distinct origin and hydrological characteristics of reservoirs, shaped by fluctuating water levels and seasonal variations, play a crucial role in determining aquatic species assemblages across diverse limnological zones. This study aimed to analyze fish and crayfish assemblages in the nearshore area of a canyon-shaped Mediterranean reservoir, seeking to identify seasonal and spatial convergent patterns and infer the factors influencing them. Samplings were conducted at five stations along the longitudinal profile of the reservoir at depths around 7 m using gillnets and hoops nets. A seasonal pattern emerged regarding species abundance and biomass, with higher values recorded during the warmer period. Additionally, a spatial trend was observed, indicating higher species abundance in the middle part of the reservoir and lower abundance near the dam, particularly during the colder period. Water transparency, temperature, and the distance from the dam were identified as the most significant factors affecting species assemblages in terms of abundance and biomass. This research provides valuable insights into the intricate interplay between environmental factors, seasonal changes, and the assemblages of aquatic species in a Mediterranean reservoir, contributing to our understanding of its ecological dynamics.

Identifying the environmental variables that predict crayfish assemblage structure in agricultural headwater streams

Identifying the environmental variables that predict crayfish assemblage structure in agricultural headwater streams

Winners and losers over a ½ century of change in crayfish assemblages of Wyoming, USA

Next article No AccessWinners and losers over a half century of change in crayfish assemblages of Wyoming, U.S.A.Braxton Moran Newkirk, Eric R. Larson, Andrew D. Walker, and Annika W. WaltersBraxton Moran Newkirk Search for more articles by this author , Eric R. Larson Search for more articles by this author , Andrew D. Walker Search for more articles by this author , and Annika W. Walters Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by Freshwater Science Just Accepted Published on behalf of the Society for Freshwater Science Article DOIhttps://doi.org/10.1086/725318 HistoryAccepted March 29, 2023 © 2023 Society for Freshwater Science. All Rights reserved.PDF download Crossref reports no articles citing this article.

Crayfish assemblages correlate with dam‐induced effects on abiotic factors and predatory fish assemblages in Alabama streams

AbstractStream faunal assemblage structure is tied closely to hydrology and associated physiochemical properties. By altering natural flows, dams and their impoundments impact faunal assemblages over long distances. Although numerous studies have assessed the effect of dams on stream fauna, information is lacking for crayfishes. In this study, we characterized the effects of relatively large storage dams on crayfish assemblage structures. Over 2 years, we sampled three impounded and two unimpounded streams across two drainages in Alabama, United States, to identify biotic and abiotic factors correlated with crayfish assemblage metrics. Compared to impounded streams, unimpounded streams had greater habitat complexity (e.g., aquatic vegetation and woody debris), fewer predator fishes, lower minimum temperatures, and more variable discharges. These characteristics correlated with a higher density and diversity of crayfishes and smaller adults in impounded compared to unimpounded streams. Crayfish species assemblages differed between drainages, as did the biotic and abiotic factors affecting crayfish assemblages in each drainage, suggesting that these factors were species‐specific in their effects. Additionally, analysis of land uses suggested that factors other than dams may have also contributed to the observed differences in assemblage structures between impounded and unimpounded streams. For instance, in the more urbanized drainage, crayfish assemblages were more similar between up and downstream sections in all streams, regardless of impoundment. Our results indicate that large dams alter stream crayfish assemblage structure, with potentially cascading effects in trophic and organic matter dynamics both up and downstream.

Effects of impoundments on stream crayfish assemblages

Effects of impoundments on stream crayfish assemblages

Co-occurring lotic crayfishes exhibit variable long-term responses to extreme-flow events and temperature

Crayfish serve critical roles in aquatic ecosystems as engineers, omnivores, and prey. It is unclear how increasingly frequent extreme-flow events and warming air temperatures will affect crayfish populations, partly because there are few long-term crayfish monitoring datasets. Using a unique 10-y dataset, we asked 1) whether recruitment of crayfishes in summer responded to extreme-flow events and air temperature during spring brooding and summer growing periods and 2) whether responses were similar among 3 co-occurring crayfish species. Golden (Faxonius luteus [Creaser, 1933]), Ozark (Faxonius ozarkae [Williams, 1952]), and Spothand (Faxonius punctimanus [Creaser, 1933]) crayfishes were sampled in quadrats at 2 sites each in the Big Piney (1993–2000) and Jacks Fork (1992–2001) rivers (Missouri, USA; n = 3355 1-m2 quadrats). We used zero-inflated generalized linear models to relate variability in quadrat-level age-0 counts to mean daily maximum air temperatures and flow metrics (variability, magnitude, and frequency of extreme high- and low-flow events). Species ranged from a small-bodied, abundant habitat generalist (Golden Crayfish) to large-bodied, uncommon habitat specialists (Ozark and Spothand crayfishes). Golden Crayfish occurred in higher-velocity habitats (riffles, runs) and had variable recruitment that increased during years with few spring and summer high-flow events and summers with lower flows and warmer temperatures. In contrast, annual recruitment variability of Ozark and Spothand crayfishes was low and explained by positive effects of cooler summers and by different flow metrics. Spothand Crayfish recruitment decreased in years with frequent spring and summer high-flow events, whereas lower summer minimum flow was the only flow metric that explained slight increases in Ozark Crayfish recruitment. Relationships with the preceding year’s recruitment were quadratic for Ozark and Spothand crayfishes, suggesting potential density dependence at higher recruitment levels. Species-specific responses suggest that closely related crayfishes could respond idiosyncratically to changes in temperature and flow. Temperature- and flow-related disturbances may be key mechanisms mediating competition and, thus, may help maintain crayfish diversity. However, warming air temperatures and increasingly frequent extreme-flow events could disadvantage some species, thereby altering future crayfish assemblages.

Burrow Densities of Primary Burrowing Crayfishes in Relation to Prescribed Fire and Mechanical Vegetation Treatments

Fire suppression and other factors have drastically reduced wet prairie and pine savanna ecosystems on the Coastal Plain of the southeastern United States. Restoration of these open-canopy environments often targets one or several charismatic species, and semi-aquatic species such as burrowing crayfishes are often overlooked in these essentially terrestrial environments. We examined the relationship between primary burrowing crayfishes and three vegetation treatments implemented over at least the past two decades in the Mississippi Sandhill Crane National Wildlife Refuge. Vegetation in the 12 study sites had been frequently burned, frequently mechanically treated, or infrequently managed. Creaserinus spp., primarily C. oryktes, dominated the crayfish assemblage in every site. We counted crayfish burrow openings and coarsely categorized vegetation characteristics in 90, 0.56-m2 quadrats evenly distributed among six transects per site. The number of active burrow openings was negatively, exponentially related to both the percent cover of woody vegetation and the maximum height of woody vegetation in quadrats, and to the number of trees taller than 1.2 m per transect, indicating that woody plant encroachment was detrimental to the crayfishes. Results were consistent with several other studies from the eastern US, indicating that some primary burrowing crayfishes are habitat specialists adapted to open-canopy ecosystems.

Not all methods are created equal: assessment of sampling methods for crayfishes and fishes in southern Appalachian streams

We compared the effectiveness of three sampling methods (kick seining, electrofishing, and nest trapping) to collect crayfishes and fishes, simultaneously, in southern Appalachian Mountain streams (Alabama, USA). For crayfishes, kick seining collected the highest species richness and most individuals. However, by combining kick seining and electrofishing collections, we decreased the number of sites needed to accurately assess crayfish richness relative to using one method. For 9 of the 13 species collected, no differences in crayfish sizes or sex ratios were detected between electrofishing and kick seining. In the remaining four species, electrofishing collected larger crayfishes and more females than kick seining. For fishes, electrofishing was most effective at assessing fish species richness. Sampled fish richness was higher when electrofishing in streams with higher water temperatures and width-to-depth ratios, as well as lower conductivities and smaller substrates. Electrofishing was the most effective sampling method for collecting Centrarchids, whereas kick seining was most effective at collecting Cyprinids. Nest traps were the least effective sampling method. We conclude that using a combination of kick seining and electrofishing is best for assessing stream fish and crayfish assemblages, simultaneously, which can improve management, biomonitoring, and understanding of the complex relationships between these faunal groups.

Only one can remain? Environmental and spatial factors influencing habitat partitioning among invasive and native crayfishes in the Pannonian Ecoregion (Hungary)

Biological invasions have increasingly threatened indigenous species, influence metacommunity organisation and consequently, global biodiversity. World-wide expansion of non-indigenous crayfish (NICS) is associated with dramatic changes in species poor indigenous crayfish (ICS) assemblages challenging conservation planning. We analysed long-term changes of crayfish occurrences from the pre-invasion state, through the first appearance of NICS, to their intensive spread in Hungarian waters. Further, we analysed present-day crayfish metacommunity patterns for co-occurrences and influence of spatial and environmental factors. Historic data revealed a marked pre-invasion decline in indigenous noble crayfish Astacus astacus and stone crayfish Austropotamobius torrentium populations, but not in the narrow-clawed crayfish Pontastacus leptodactylus. Historic data provided no direct evidence for the impact of NICS on ICS, rather it supported that NICS often entered areas where ICS had been extinct or were not present at all. Crayfish species extremely rarely co-occurred which could indicate their strong competition and be related to utilization of empty sites by NICS. Crayfish metacommunities were predominantly spatially structured indicating the primary influence of ongoing invasion. Crayfish species also exhibited different environmental preferences mainly along the altitude and temperature gradients. We conclude that the invasion is still in the expanding phase and without an effective conservational program the future of ICS is doubtful in Hungary. Conservation policy should focus on the preservation and reintroduction of the stone and noble crayfishes in highland refugees. Expansion of NICS should be prevented in refugee areas by utilizing possibilities provided by natural and artificial barriers, and education and strict ban should be simultaneously applied to prevent further illegal releases by aquarists.

Hungary: a European hotspot of non-native crayfish biodiversity

There is a long history of crayfish introductions in Europe and numbers keep increasing. In Hungary, spiny-cheek crayfish Faxonius limosus, signal crayfish Pacifastacus leniusculus, red swamp crayfish Procambarus clarkii, marbled crayfish P. virginalis and Mexican dwarf crayfish Cambarellus patzcuarensis have become established. Here we report on monitoring at two localities with novel crayfish assemblages closely linked to releases associated with the pet trade. Florida crayfish Procambarus alleni were recorded from the Gombás brook near Vác living in syntopy with the established spiny-cheek crayfish. Dozens of Florida crayfish individuals including egg-carrying females have been detected. The short lifespan of this species and its documented presence including two overwintering in at least two years suggests possible establishment. However, the lack of juvenile records calls for further monitoring as long-term propagule pressure cannot be ruled out. We also identified a single marbled crayfish in the Danube floodplain at the end of the monitoring campaign. The second locality (Városliget thermal pond in Budapest) harbours an even more diverse crayfish assemblage. Here, we identified numerous red swamp and marbled crayfish in syntopy with dozens of monitored redclaws Cherax quadricarinatus and seven individuals of New Guinean Cherax species − C. holthuisi, C. snowden, as well as two scientifically undescribed species. These findings clearly indicate the attractiveness of urban and, especially, thermal waters for the release of even expensive aquatic pets and highlight the hitherto poorly known biodiversity of New Guinean crayfish species.

Flow alteration-ecology relationships in Ozark Highland streams: Consequences for fish, crayfish and macroinvertebrate assemblages

We examined flow alteration-ecology relationships in benthic macroinvertebrate, fish, and crayfish assemblages in Ozark Highland streams, USA, over two years with contrasting environmental conditions, a drought year (2012) and a flood year (2013). We hypothesized that: 1) there would be temporal variation in flow alteration-ecology relationships between the two years, 2) flow alteration-ecology relationships would be stronger during the drought year vs the flood year, and 3) fish assemblages would show the strongest relationships with flow alteration. We used a quantitative richest-targeted habitat (RTH) method and a qualitative multi-habitat (QMH) method to collect macroinvertebrates at 16 USGS gaged sites during both years. We used backpack electrofishing to sample fish and crayfish at 17 sites in 2012 and 11 sites in 2013. We used redundancy analysis to relate biological response metrics, including richness, diversity, density, and community-based metrics, to flow alteration. We found temporal variation in flow alteration-ecology relationships for all taxa, and that relationships differed greatly between assemblages. We found relationships were stronger for macroinvertebrates during the drought year but not for other assemblages, and that fish assemblage relationships were not stronger than the invertebrate taxa. Magnitude of average flow, frequency of high flow, magnitude of high flow, and duration of high flow were the most important categories of flow alteration metrics across taxa. Alteration of high and average flows was more important than alteration of low flows. Of 32 important flow alteration metrics across years and assemblages, 19 were significantly altered relative to expected values. Ecological responses differed substantially between drought and flood years, and this is likely to be exacerbated with predicted climate change scenarios. Differences in flow alteration-ecology relationships among taxonomic groups and temporal variation in relationships illustrate that a complex suite of variables should be considered for effective conservation of stream communities related to flow alteration.

Relationships between landscape constraints and a crayfish assemblage with consideration of competitor presence

AbstractAimCrayfish are globally diverse and one of the most important taxa in North American streams. Despite their importance, many species are of conservation concern and efforts to improve conditions are limited. Here, we address two major impediments to improving conditions: (a) our lack of knowledge of the interplay among natural landscape and human‐induced changes; and (b) a very limited understanding of how species interactions affect overall crayfish distributions.LocationOzark Highlands ecoregion, USA.MethodsWe used both existing data and field‐collected data to examine the relationships between 12 Faxonius species and physicochemical variables at multiple spatial scales. Data were analysed using a generalized linear mixed model. After fitting our environmental variables, we also considered possible relationships between species considered strong competitors and species occurrence.ResultsOur results indicated that elevation, lithology, an interaction between drainage area and anthropogenic disturbance, and the presence of strong competitors were associated with Faxonius occurrences. Faxonius occurrences were associated with assemblage‐structuring variables: lithology and elevation. More interestingly, we found several patterns of interactions between drainage area and disturbance. The most common pattern among several species was a decline in occurrence in larger drainages when disturbance was high; however, longpincered crayfish (Faxonius longidigitus) was more likely to occupy large drainages as disturbance increased. Additionally, the presence of species considered strong competitors resulted in lower occurrence probability for many species, including two of the species classified as competitors.Main conclusionsIn addition to identifying the relationships between native species and assemblage‐structuring variables, we show how the probability of species occurrences relate to interactions between disturbance and natural landscape features. Further, our results suggest competitor presence also plays a role in structuring distributions at the stream segment scale. Our findings emphasize the value of considering both competitor presence and interactions among landscape variables and disturbances in structuring crayfish assemblages.

A multigear protocol for sampling crayfish assemblages in Gulf of Mexico coastal streams

Identifying an effective protocol for sampling crayfish in streams that vary in habitat and physical/chemical characteristics has proven problematic. We evaluated an active, combined-gear (backpack electrofishing and dipnetting) sampling protocol in 20 Coastal Plain streams in Louisiana. Using generalized linear models and rarefaction curves, we evaluated environmental and gear (separate and combined) effects on crayfish catch-per-unit-effort (CPUE), orbital carapace lengths, sex ratios, frequencies of rare species, and sample richness. Although pooled data from combined gears showed greater total numbers of crayfishes, CPUE, and richness compared to either gear individually, combined gear and backpack electrofisher results differed minimally. Overall, richness was negatively related to specific conductance, indicating potential agricultural influence. Neither crayfish sex ratios, lengths, nor frequencies of rare species differed by gear; however, combining data from both gears ensured crayfish were captured in all study streams, which was not found for electrofishing or dipnetting alone. Species accumulation and rarefaction curves indicated sampling was sufficient for recording crayfish diversity at the scale of the study and that adding streams (versus sites within streams) would be most effective for watershed-scale studies. Our results suggested the combined gear protocol was effective for assessing crayfish population and assemblage characteristics in these Coastal Plain streams.

Natural gas drilling in the Marcellus Shale region: well pad densities and aquatic communities

Few studies have examined the relationship between natural gas development and surface water quality using well pad density (the number of well pads/km2) as an indicator of potential impacts to aquatic life, specifically fish, salamander, and crayfish assemblages. We tested the hypothesis that animal assemblages, assessed by densities of ecologically important species, will differ among groups of watersheds with different well pad densities. In 2011, sites were sampled in Pennsylvania between July 13 and September 14 (N = 28; 10 = no well pads, 8 = low density, 10 = moderate density). We did not detect evidence of impact on fish, salamander, and crayfish assemblages. It should be noted that this study primarily assessed infrastructure-related impacts. Watersheds under investigations in this study area included no stream withdrawals for drilling and relatively low well pad density (≤0.541 well pads/km2), which reduces the amount of roads and pipeline as well as sediment runoff reaching the stream from this and other infrastructure during development. In addition, setback and landscape limitations also kept well pads relatively far from surface waters, and these watersheds remained highly forested after development because most were in state forests. Therefore, these findings represent the least intrusive scenario for impacts to aquatic communities while extracting natural gas.

Invasion-Related Change in Crayfish Density Affects a Stream Macroinvertebrate Community

Abstract Orconectes rusticus (Rusty Crayfish) have invaded streams of the upper Susquehanna River catchment, NY, replacing native crayfish and, in some areas, increasing overall crayfish density. Crayfish are important consumers and significant agents of disturbance in aquatic communities, so the introduction and expansion of Rusty Crayfish could affect the invaded community through the change in crayfish species composition, the increase in crayfish density, or some combination of the two. Other macroinvertebrates are prey of, competitors with, or subject to disturbance by crayfish and so are likely to be affected by changes in the crayfish assemblage. I conducted experiments in stream enclosures to determine the effects of crayfish species and density on the macroinvertebrate community. Increasing crayfish density reduced macroinvertebrate density but did not significantly affect macroinvertebrate taxon richness, diversity, or community composition. At moderate densities, the effects of native O. propin...

Development of Standardized Stream‐Dwelling Crayfish Sampling Methods at Site and Drainage Scales

AbstractMethods for assessing stream fish, freshwater mussel, and insect assemblage structure, presence, and status have existed for several decades. Such methods are lacking for assessing crayfish. The current study addresses that deficiency by testing robust sampling methods to assess species richness, distribution, and density at both site and drainage scales. We tested the ability of timed search methods to capture all known species of crayfish at a site and of a kick seine to assess the mean density of crayfish (per m2) in riffles. Riparian crayfish burrows were excavated to capture additional species not captured with the other methods. Our data and methods allow for assessments of the inherent trade‐off between sampling time and resources and statistical confidence. An example sampling regime of 3.5 h of effort per site required seven 15‐min timed search samples and captured at least 80% of the crayfish species richness, with 85% confidence across all sites tested. Twelve kick‐seine samples yielded crayfish density estimates within 50% of an estimated true density at 70% confidence for all species with densities >0.5/m2. In the drainage‐scale component, we employed a sampling effort prescription derived from our site‐scale data across seven drainages in Missouri. To achieve 100% of the species richness sampled at 97.5% confidence in wadeable second‐ to fourth‐order streams, researchers will need to sample one site for every 18 river kilometers of second‐ to fourth‐order streams occurring in a drainage. We believe our methods can provide a repeatable and statistically supported tool for researchers assessing crayfish assemblages in wadeable streams across the Midwest.Received March 9, 2015; accepted October 14, 2015

Composition of native crayfish assemblages in southern Ontario rivers affected by rusty crayfish (Orconectes rusticus Girard, 1852) invasions – implications for endangered queensnake recovery

Orconectes rusticus (rusty crayfish) is an aggressive and prolific aquatic invader. Where introduced, it has caused dramatic ecosystem changes, including the replacement of native crayfishes. In Canada, it was first reported in Lake of the Woods in northwestern Ontario and a small number of south-central Ontario lakes during the 1960s. It has subsequently spread to other regions of the province. Its current expansion into southwestern Ontario rivers presents an unknown risk to the endangered queensnake (Regina septemvittata), an obligate feeder on freshly molted crayfish. We sampled 99 river sites across southern Ontario to: (i) describe crayfish assemblages within river reaches currently occupied by Queensnake; and, (ii) characterize the impact of O. rusticus on native crayfish assemblages. O. rusticus was caught at 41% of sites sampled, and was the only species at 24% of sites. The abundance, richness, and within-site distribution of native crayfishes were all significantly lower at sites with O. rusticus. Within the distribution of queensnake, crayfish assemblages were almost entirely dominated by O. propinquus, with O. rusticus being absent. However, O. rusticus was found along the lower Speed River, where only one dam separates it from Grand River queensnake populations. Given its past spread, O. rusticus will likely be introduced into areas used by queensnake and replace O. propinquus (the primary prey of queensnake). The adaptability of queensnake to prey upon non-native crayfish is unknown and requires investigation.

Associated Use Attainment Response between Multiple Aquatic Assemblage Indicators for Evaluating Catchment, Habitat, Water Quality, and Contaminants

Use attainability analysis (UAA) at a watershed scale typically relies on the assumption that indicator organisms are responding similarly to the same environmental stressor. Factors explaining variance in fish, crayfish, and macroinvertebrate assemblage structure and function were investigated with emphasis on catchment and reach scale land use, habitat, contaminants, and water quality variables. Habitat quality scores ranged from 25 to 85 (average 61.36±10.08). The substrate score, instream cover, riffle-run score, and channel score were primary factors contributing to declining habitat quality. Factor analysis found that four factors explained 69% of the contributed variance in fish assemblage, two factors accounted for 56% of variance in macroinvertebrate assemblages, and two factors explained 49% of the variance in crayfish assemblages. Overall drivers of assemblage structure were associated with broad scale issues of wastewater treatment, groundwater, and land use. Our results show that fish, macroinvertebrate, and crayfish assemblages respond to similar broad scale stimulus; however, the specific constituents responsible for the stress may vary with the magnitude of the cumulative stress, which may be expressed by each organismal group differently. Our data suggest that varying organismal groups can respond independently and stress reflected in one assemblage may not necessarily be observed in another since each organismal group is measuring different aspects of the environment.

Effects of small impoundments on downstream crayfish assemblages

Dams and impoundments, both large and small, affect downstream physicochemical characteristics and up- and downstream biotic communities. I tested whether small dams and their impoundments altered downstream crayfish assemblages in northern Mississippi. I sampled crayfish and measured physicochemical variables at 4 sites downstream of impoundments (outlet sites) and 4 sites not influenced by impoundments (undammed sites) in August, September, and November 2004. In November 2010, I sampled 7 undammed, 6 outlet, and 3 intermediate sites (influenced by beaver activity or ∼1 km downstream of an impoundment). Crayfish assemblages differed between undammed and outlet sites. Catch-per-unit-effort (CPUE) of Orconectes (Trisellescens) sp. was higher in undammed than outlet sites in both years. Procambarus (Pennides) spp. CPUE was lower in undammed than outlet sites in November 2010 and nearly so in November 2004. In 2004, Procambarus (Ortmannicus) hayi was common in autumn at outlet sites but virtually absent from undammed sites, but in 2010, P. hayi CPUE did not differ between categories. Cambarus striatus CPUE, which was low overall, did not differ between categories in 2004 but was higher in undammed sites in 2010. Seasonal differences among taxa in reproductive timing were important to understanding impoundment effects. The most consistent difference in habitat was that undammed sites had significantly higher width:depth ratios than did outlet sites. Based on the number of mapped small impoundments and a conservative estimate that each impoundment influenced crayfish assemblages over 2 km, I estimated that impoundments probably affect crayfish assemblages in >284 km of stream in the upper Little Tallahatchie River subbasin. Extrapolated to the entire Gulf Coastal Plain, impoundments may influence crayfish assemblages over thousands of stream kilometers.

Crayfish Use of Trash Versus Natural Cover in Incised, Sand-Bed Streams

Historic land use changes and subsequent river channelization created deeply incised, unstable stream channels largely devoid of natural cover throughout the Yazoo River basin, Mississippi, USA. Large trash (e.g., televisions, toilets, car parts) dumped in streams provided shelter for some aquatic fauna. To determine whether trash served as a surrogate for natural cover, I examined crayfish use of both cover types. I sampled crayfishes by kick-seining 2 × 1-m plots in three cover classes: trash, natural cover, and no cover. I captured 415 crayfishes from 136 of the 294 plots. Most crayfishes were in natural cover (253), followed by trash (154), and no-cover (8) plots. Trash use varied by crayfish genus and size. Frequencies of all size classes of Procambarus and of the smallest Cambarus were higher in natural cover than trash. Many of the smallest individuals were found in live root mats. As Cambarus and Orconectes grew, they shifted more toward trash, and the largest Orconectes size class was significantly more abundant than expected in trash. Trash served as "artificial reefs," providing cover for crayfishes and other fauna, but functioned differently than the remaining natural cover. The results confirmed that stream substrate did not provide adequate instream cover for crayfishes in the study area and suggested that high-quality natural cover for large crayfishes was in short supply, at least for some species. Land management that provides for abundant, ongoing input and retention of complex cover, such as trees and live roots, to stream channels should be beneficial for crayfish assemblages.