CHAPTER 8 Field Sampling Techniques for Crayfish Eric R. Larson1,* and Julian D. Olden2 Introduction Why do we study crayfi sh? Answers may range from their cultural or economic value (Jones et al. 2006) to ecological importance (Usio and Townsend 2004) to the high conservation need of many species (Taylor et al. 2007). Alternatively, one justifi cation for the emergence of crayfi sh as model organisms (e.g., Crandall 2000) has been their ubiquity and ease of collection relative to a rewarding range of biological insights. For example, Thomas Henry Huxley (1884) in his introduction to the study of zoology framed his book around crayfi sh in part because the “[the crayfi sh] is readily obtained.” Yet those of us who need to quantitatively sample crayfi sh recognize that “readily obtained” does not necessarily translate into representative of broader populations or communities. Huxley (1884) might be countered by observations like those of Rabeni et al. (1997), who note that no crayfi sh sampling method is without biases that may misrepresent attributes ranging from relative abundance to size and age structure of populations. Ultimately, quantitative sampling for crayfi sh presents a number of challenges to confound even the most experienced of fi eld biologists. Writing a comprehensive review of fi eld sampling methods for crayfi sh must accommodate both the diversity of crayfi sh themselves and the diversity of researchers interested in them. Crayfi sh occur in habitats ranging from large lakes to wadeable streams, to diffi cult to sample environments like caves and terrestrial burrows. These diff erent habitats demand diff erent sampling tools and approaches. Further, widely varying research objectives justify a need to sample crayfi sh, from studies of evolution or phylogeography (Trontelj et al. 2005) to bioassessments of freshwater habitats (Reynolds and Souty-Grosset 2012) to surveys of diseases like the crayfi sh plague (Holdich and Reeve 1991) or commensals like crayfi sh worms (Williams et al. 2009). Accordingly, a wide variety of fi eld sampling methodologies for crayfi sh have been developed and tested over the past century. We are unaware, however, of any comprehensive review that has attempted to make sense of how to sample for crayfi sh, or at a minimum provide a thorough bibliography to serve as a foundation for researchers seeking to work with and sample crayfi sh in the fi eld (but see Parkyn 2015 for a synthesis of the most common crayfi sh sampling techniques reported in the journal Freshwater Crayfi sh). 1 Department of Natural Resources and Environmental Sciences, University of Illinois, Urbana, IL 61801 USA. 2 School of Aquatic and Fishery Sciences, University of Washington, Seattle, WA 98195 USA. Email: [email protected] * Corresponding author: [email protected] © 2016 by Taylor & Francis Group, LLC 288 Biology and Ecology of Crayfi sh In our review, we’ve attempted to represent insights on fi eld sampling for crayfi sh from a breadth of researchers in diff erent countries and continents working on a wide range of organisms and questions. However, we should fi rst identify the experiences and accompanying biases we bring to the task of writing a review on fi eld sampling methods for crayfi sh. We are freshwater ecologists interested in animal distributions and ecological processes at landscape scales. Accordingly, our perspectives may skew toward sampling and monitoring for studying trends in crayfi sh populations over relatively large areas, whether for conservation of native species or management of invasive crayfi shes (e.g., Olden et al. 2006, 2009, 2011, Larson and Olden 2008, 2013, Larson et al. 2012). Further, we work predominantly in North America, and may be most familiar with crayfi sh literature from the United States and Canada. Consequently, we may give unintentional short shrift to biologists interested in collecting or sampling crayfi sh for other reasons, in habitats other than the streams and lakes we most typically work in, or using novel sampling tools and techniques we have not encountered. These caveats aside, our review of the literature is extensive and our hope is that we’ve provided a useful roadmap for researchers starting out on the task of quantitative fi eld sampling for crayfi sh. We also have not set out to write a book chapter on fi eld sampling in general. For that need, we direct readers to texts on sampling design and methods for the ecological sciences or freshwater fi sheries (e.g., Morrison et al. 2008, Bonar et al. 2009, Magurran and McGill 2011, Zale et al. 2013). Further, we note that many crayfi sh of conservation concern may be diffi cult to detect on the landscape, and recent research and publications on sampling for rare or cryptic species may be worth consulting (e.g., Thompson 2004, MacKenzie et al. 2006). We instead focus on two areas: a review of approaches for sampling crayfi sh in disparate habitats, and a summary of some important considerations for planning a fi eld sampling program for crayfi sh. The fi rst of these sections outlines crayfi sh sampling by habitat type: lentic or large lotic environments; wadeable streams and rivers; terrestrial environments; and caves. The second of these sections emphasizes methods to evaluate accuracy of fi eld sampling techniques for crayfi sh via sampling effi ciency; precision via power analysis; reliability of occupancy estimates by quantifying detection probability; and the use of mark-recapture methods to not only monitor crayfi sh populations but also evaluate other sampling approaches. We conclude with a brief section on the value and potential benefi ts of improving transferability and transparency of results between diff erent studies and regions by standardizing crayfi sh sampling methodologies. Sampling for crayfi sh by habitat type Crayfi sh in lentic and large lotic environments Crayfi sh are ecologically and economically important organisms in many large waterbodies globally, from tropical to temperate lakes (Harper et al. 2002, Jansen et al. 2009) and major rivers (Larson et al. 2010b). These habitats provide unique challenges for crayfi sh sampling relative to more tractable wadeable streams and rivers, where a diversity of sampling methods of diff erent merits are available (Rabeni et al. 1997). Conversely, lentic or large lotic environments typically necessitate sampling by one of three approaches: baited traps; visual searches or collection by divers or snorkelers; and throw traps. Of these, Downloaded by [University of Illinois at Urbana-Champaign] 11:56 12 May 2016 baited traps are perhaps the most commonly applied and also potentially the most problematic, with known biases favoring large adults and males over other members of the population (e.g., Brown and Brewis 1978, Capelli and Magnuson 1983). Related to baited trapping, installation and recovery of habitat structures or “bundles” has been suggested as an alternative or complementary approach that may sample under- represented members of the population or community (Parkyn et al. 2011). Dive or snorkel surveys are perhaps more accurate than trapping in representing population attributes or abundance (Lamontagne and Rasmussen 1993), but seem less commonly used owing to the required technical expertise (e.g., SCUBA certifi cation) and the time- and labor-intensive nature of this method. Moreover, environments characterized by poor light conditions and low water clarity may limit the application of underwater surveys. Surveys of some lentic environments like freshwater marshes and wetlands have also been conducted with throw traps, a less commonly applied and tested methodology (but see Dorn et al. 2005). © 2016 by Taylor & Francis Group, LLC Field Sampling Techniques for Crayfi sh 289 Figure 1. Examples of some sampling techniques for crayfi sh commonly used in lentic or large lotic environments. Baited trapping for crayfi sh with modifi ed Gee minnow traps, showing retrieval of a trap (A) and two separated trap pieces with collected signal crayfi sh Pacifastacus leniusculus (B). Visual searches for crayfi sh by snorkelers (C) with a collected crayfi sh (D). All photographs by the authors. Baited traps applied to sample for crayfi sh vary by design and dimensions between studies and countries, from the Swedish trappy commonly used in Europe (e.g., Edsman and Söderbäck 1999) to modifi ed (i.e., enlarged openings) Gee minnow traps in North America (e.g., Capelli and Magnuson 1983) to baited hoop nets used in Australia (e.g., de Graaf et al. 2010, Fulton et al. 2012). In many cases these traps are fundamentally similar. For example, Harlioĝlu (1999) gives dimensions of the Swedish trappy as an 0.5 m long mesh cylinder of 0.2 m diameter with funnels at either end with 4.5 cm diameter openings, whereas Larson and Olden (2013) give dimensions for modifi ed Gee minnow traps as an 0.42 m long mesh cylinder of 0.21 m diameter with 6.0 cm openings. Both Stuecheli (1999) and Huner and Espinoza (2004) demonstrated how choice of trap opening diameter can have implications for the number, size, and sex of crayfi sh caught. These studies found that smaller diameter openings tend to trap smaller crayfi sh and Downloaded by [University of Illinois at Urbana-Champaign] 11:56 12 May 2016 larger openings larger crayfi sh; that larger diameter openings may disproportionally favor male crayfi sh (Stuecheli 1999); and that diff erent diameter openings may select for diff erent crayfi sh species (Huner and Espinoza 2004). There has been persistent interest over time in “building a better crayfi sh trap,” with numerous alternative designs proposed (e.g., Slater 1995, Mangan et al. 2009), although many of these do not seem to have gained wide popularity or application. An exception may be the triangular or pyramid trap designs used in commercial harvest of crayfi sh (e.g., Huner and Espinoza 2004).