Robert J. DiStefano

The stygobitic Caney Mountain cave crayfish, Orconectes stygocaneyi, is among the rarest crayfish species in North America. It is known only from Mud Cave, a small linear cave on the 3,200 ha Caney Mountain Conservation Area in Ozark County, Missouri. The species is listed as “Endangered” by the state of Missouri and “Threatened” by the American Fisheries Society. Previous studies documented its population range and limited life history notes; but little is known about Mud Cave’s habitat. We conducted a one-year study to document the cave’s water-chemistry, quality, and interior wetted pool volume, and how this habitat varies monthly, to establish a baseline for future study.

The Little St. Francis River and its tributaries drain metals-contaminated areas of the Madison County Mines National Priority List Superfund site (MCM) which was designated in 2003 to facilitate remediation of metals contamination within the MCM. One concern for natural resource trustees in the MCM is the potential effects of elevated metals concentrations on the federally threatened St. Francis River crayfish, Faxonius quadruncus, which has a geographic range that is limited to the St. Francis River watershed. A survey of riffle-dwelling crayfish, in-situ cage study, and laboratory toxicity tests were conducted to assess the effects of mining-derived metals on F. quadruncus and other crayfish species in the MCM. Crayfish densities were significantly greater at sites upstream of metals releases from historical mining (henceforth mining releases) compared to densities at sites downstream of mining releases, and metals concentrations in whole-body crayfish, surface water, sediments, macroinvertebrates, fish, and plant material were greater at sites downstream of mining releases compared to sites upstream of mining releases. Crayfish densities were also negatively correlated with consensus-based adverse effects indices, expressed as surface-water toxic units and sediment probable effects quotients. Decreased growth and increased mortality during cage and laboratory studies were likely due to exposure to, and subsequently uptake of, elevated concentrations of metals. Crayfish in all studies were found to bioaccumulate metals, which supports their utility as bioindicators of metals contamination. Study results show that elevated metals concentrations associated with mining releases in the MCM continue to adversely affect biota, including the federally threatened F. quadruncus.

Comprehensive surveys are critical to conserve and monitor crayfish communities, imperiled species, and detect crayfish invasions. The Missouri portion of the North Fork White River drainage (MONFWR) was never comprehensively surveyed, but adjacent drainage surveys suggested it could harbor species of conservation concern (SOCC). We surveyed the MONFWR to determine crayfish species richness, distributions of potential SOCC, and potential invasive species. We included recent sampling of the Arkansas portion of the drainage for a more holistic assessment of the entire drainage. We examined potential changes in crayfish communities after three decades at 22 previously sampled MONFWR locations. We also collected the first habitat association data for the endemic, Faxonius longidigitus. We detected eight taxa; none that were not known from the drainage. Faxonius neglectus chaenodactylus and Cambarus hubbsi were SOCC; F. n. chaenodactylus was common and abundant in the MONFWR; C. hubbsi was detected at only one site in Arkansas. Faxonius neglectus neglectus and Faxonius virilis were each detected only once and are likely introduced. Intermittent streams harbored diversity and abundance rivaling perennial segments. We observed no notable temporal differences between 22 historical and current samples. Faxonius longidigitus, detected at few sites in low numbers, was associated with deeper waters and larger substrates.

Invasive crayfish (family Cambaridae) displace native crayfish species and alter aquatic habitat, community structure, and ecosystem function. We evaluated whether chemical control can be a reliable control agent for crayfish to ensure that shipments from fish hatcheries did not result in new infestations of invasive crayfish. A series of acute (≤1 h) toxicity tests were conducted to evaluate the toxicity of cypermethrin and pyrethrin to crayfish, freshwater mussels, and fish; chemical concentrations in test organisms; effectiveness of carbon-block filters to remove cypermethrin from test waters; and the cost of chemical control relative to extra handling of fish. Cypermethrin dosed at 75 μg/L for 15 min resulted in 100% mortality of adult white river crawfish Procambarus acutus and virile crayfish Faxonius virilis but did not cause >20% mortality in adult pondmussel Ligumia subrostrata, juvenile fatmucket Lampsilis siliquoidea, fingerling Bluegill Lepomis macrochirus, hybrid sunfish (Bluegill × Green Sunfish L. cyanellus), hybrid Striped Bass (White Bass Morone chrysops × Striped Bass M. saxatilis), yearling Paddlefish Polyodon spathula, or ready-to-eat Bluegill, hybrid sunfish, and Channel Catfish Ictalurus punctatus. Behavioral effects, such as loss of equilibrium or head shaking, were generally limited to 1 h postexposure. Mean concentrations of cypermethrin increased in fish fillets (4–26 μg/g) and whole fish (5–1,770 μg/g); therefore, regulations limiting harvest for up to 7 d following stocking may be required. A carbon-block filtration system was effective in reducing (<90%) cypermethrin concentrations and thus reducing potential effects to nontarget species in receiving waters. Extra handling of fish was more cost-effective for all fish tested except for Paddlefish, where the cost of chemical control was half that for extra handling. For all other fish tested, chemical control was 4–10 times more expensive than extra handling. Special use permits or chemical registration are needed before chemical control for crayfish could be routinely used at fish hatcheries.

The increasing worldwide popularity of the aquatic pet trade causes widespread transport and introduction of alien species, including crayfish (Astacidea), into fisheries. Thirty crayfish species have invaded North America, affecting native species and changing ecosystems. Growing numbers of crayfish introductions are linked to the pet trade, and this pathway increasingly requires attention from natural resource managers. The Missouri Department of Conservation implemented regulations in 2014 to restrict pet store crayfish sales. We surveyed all Missouri pet stores in 2019 to estimate regulation compliance. Undercover enforcement agents visited stores and assessed crayfish sales by inspecting livestock and interviewing owners/employees. Simultaneously, we conducted a comparative survey of Ohio stores, where minimal regulations exist. Crayfish, including three alien species, were illegally sold at 15.5% of Missouri stores. In Ohio, 63% of stores sold crayfish, including three alien species. The Missouri regulations appear effective for managing and reducing pet store sales of potentially invasive crayfish.

Crayfish are key organisms in freshwater ecosystems across the United States (USA) and Canada, yet are among their most highly imperiled taxonomic groups. In 1996, a committee of prominent USA crayfish biologists warned of a crayfish imperilment plight and neglect of the fauna by natural resources agencies. It is unclear whether crayfish conservation has been prioritized by those agencies in the intervening decades. Our objective was to evaluate the status of crayfish conservation and management in 50 USA and 13 Canadian fish and wildlife agencies through a telephone survey. Fifty-one percent of agencies employed biologists to conduct crayfish work, mostly in the southern USA, and focused on threats (e.g., invasive species) or species’ distributions and conservation status. Of the 32 agencies working on crayfish, 59% considered them a priority, but 53% acknowledged insufficient funding. The most commonly cited information needs were threats, species compositions (native and introduced), distributions, conservation status assessments, and ecology. We report an encouraging but limited increase in agencies working on crayfish over the past two decades.

The Caney Mountain cave crayfish (Orconectes stygocaneyi) is one of North America’s rarest crayfish, endemic to one cave in southern Missouri, USA. The species is listed as “critically imperiled” by Missouri, and “threatened” by the American Fisheries Society. Previously, only 15 crayfish have been observed in Mud Cave, and only two have been collected (for original species description). We aimed to collect the first natural history data on the species and search adjacent caves and springs for additional populations. Twelve visual searches and supplemental trapping over four years, in all seasons, yielded 69 O. stygocaneyi (including 11 young-of-year) observations and capture of 22 crayfish, including one ovigerous female. Visual searches of nearby caves and springs yielded no O. stygocaneyi records. However, multiple surveys of those caves and springs, using environmental DNA detected the species in one additional cave adjacent to Mud Cave, but only during spring high flow events when the caves may be ephemerally connected. Orconectes stygocaneyi’s distribution is among the most restricted of any North American crayfish, and further evaluation of its conservation status designations might be warranted. Long term conservation of O. stygocaeyi would benefit from management practices promoting sustained, unimpacted surface runoff within Mud Cave’s recharge area.

The saddleback crayfish, Faxonius medius (Faxon, 1884), is endemic to a single drainage in eastern Missouri, USA, that is affected by heavy metals mining, and adjacent to a rapidly-expanding urban area. We studied populations of F. medius in two small streams for 18 months to describe the annual reproductive cycle and gather information about fecundity, sex ratio, size at maturity, and size-class structure. We also obtained information about the species’ density at supplemental sites. The species, though rare in a geographic context, is locally abundant; we captured a monthly average of more than 75 F. medius from each of the two study populations. Densities of F. medius were high relative to several sympatric species of Faxonius Cope, 1872 and Cambarus Erichson, 1846. The species exhibited traits of an r-strategist life history; it was relatively short-lived and early to maturity. Its fecundity and egg size were comparable to Ozark congeners. Breeding season occurred in autumn, perhaps extending into early winter. Egg brooding occurred primarily in April. Young-of-year first appeared in samples in June. We estimated that these populations contained 2 to 3 size-classes, and most individuals became sexually mature in their first year of life. Life history information presented herein will be important for future conservation efforts.

Knowledge of crayfish species’ life history traits is vital to their conservation and management. Fecundity is one trait that is a likely indicator of extinction risk and potential invasiveness. Fecundity-related data are lacking for the imperiled St. Francis River crayfish (Faxonius quadruncus) that is declining in the presence of the invasive woodland crayfish (Faxonius hylas). We sampled ovigerous females in three populations each of F. quadruncus and invasive F. hylas in Missouri (USA) Ozarks streams during April 2014 to compare fecundity and egg size between the two species. Differences in fecundity-related traits existed among populations of F. quadruncus, but no differences existed between the species. Results for both species were well within the ranges reported for other Faxonius species, but likely reflect small sample sizes rather than the entirety of each species. We also investigated the utility of field versus laboratory fecundity measures and found that field egg counts on live females varied among observers and also underestimated laboratory counts by an average of 22%. We provide a linear equation that can serve as a correction adjustment for field pleopodal fecundity estimates on live females to avoid specimen sacrifice during future monitoring of these species.