RIVER RESEARCH AND APPLICATIONS River. Res. Applic. (2010) Published online in Wiley InterScience (www.interscience.wiley.com) DOI: 10.1002/rra.1367 SITE LENGTH FOR BIOLOGICAL ASSESSMENT OF BOATABLE RIVERSy J. E. FLOTEMERSCH,a* J. B. STRIBLING,b R. M. HUGHES,c L. REYNOLDS,d M. J. PAUL b and C. WOLTER e a U.S. Environmental Protection Agency, Office of Research and Development, 26 W. Martin Luther King Drive, Cincinnati, OH 45268, USA b Tetra Tech, Inc., Center for Ecological Sciences, 400 Red Brook Blvd., Suite 200, Owings Mills, MD 21117, USA c Department of Fisheries and Wildlife, Oregon State University, 200 SW 35th St., Corvallis, OR 97333, USA d U.S. Environmental Protection Agency, Region 3, 1060 Chapline St. Ste. 303, Wheeling, WV 26003, USA e Leibniz-Institute of Freshwater Ecology and Inland Fisheries, Mu¨ggelseedamm 310, 12587 Berlin, Germany ABSTRACT There is increasing international interest by water resource management agencies worldwide in developing the capacity for quantitative bioassessments of boatable rivers. This interest stems from legal mandates requiring assessments, plus growing recognition of the threats to such systems from multiple and co-varying stressors (e.g. chemical pollutants, physical habitat alterations, altered flow regimes, channel modifications and alien species). The elevated cost and inefficiencies of jurisdictionally- and taxonomically- segregated assessments is widely recognized, as is the desire to obtain comparable data that can be easily shared among political jurisdictions and ecological regions. The objectives, sampling methods, indicators, site-scale sampling designs and geographic extent of the resources being sampled differ among programmes, thereby limiting such data exchanges. Our objective in this paper is to review major biological assessment design alternatives for boatable rivers, with special attention given to the sample site length from which data are collected. We suggest that sufficient site length determinations should be based on the survey objectives, the relative heterogeneity of the habitat template, and the quality of data necessary for meeting programmatic data quality objectives. Future sampling effort studies should be designed to allow separate samples of several short sub-sites at many diverse sites to generate multiple data points for each site. Data from those multiple sub-sites should be analysed using randomization-based data evaluation methods. We hope that our recommendations will be useful to the maximum number of institutions, including those with limited funds and a purely local focus, as well as those responsible for sampling at continental geographic extents. Copyright # 2010 John Wiley & Sons, Ltd. key words: reach length; non-wadeable; electrofishing distance; bioassessment; sampling effort; fish; benthic macroinvertebrates; algae Received 17 February 2009; Revised 22 December 2009; Accepted 7 January 2010 INTRODUCTION logistically nor economically feasible to monitor them directly. For example, episodic pollutants cause mortality or Biological assemblages are the central focus of biomonitoring morbidity that is reflected by changes in assemblage structure programmes, because they provide a direct measure of long after the event (e.g. Dixit et al., 1999) and historical land biological condition relative to biological integrity—a stated uses continue having legacy effects on biota (Harding et al., objective of the Clean Water Act of 1972 (USGPO, 1989) and 1998). Similarly, impassable barriers (Adams, 2000; Jackson the Water Framework Directive of the European Union (2000/ and Marmulla, 2001; SEARIN, 2004) and sediment inputs 60/EG, Abl. L 327 of 22.12.2000). In addition, biological associated with spatially variable erosion (Waters, 1995) may assemblage assessments contribute to narrative water quality have biological impacts on multiple assemblages detected far standards that are an important part of U.S. state water laws, from the sources of the stressors or pressures. and similarly, are essential for enforcement of the U.S. There are four primary survey constraints (objectives, Endangered Species Act (16 U.S.C. 1531–1544), Canada’s funding, timeline and institutional) and three secondary Species at Risk Act (SARA; http://laws.justice.gc.ca/en/s- constraints (survey design, indicators and logistics) that 15.3/text.html) and the EU Habitats Directive (92/43/EEC, dictate sampling effort requirements (Hughes and Peck, Abl. L 43 of 21.05.1992). Biota integrate the effects of 2008). For biological monitoring programmes focused on multiple stressors in space and time, thus acting as streams and rivers, where indicators of water body condition environmental sentinels. They provide a way of detecting are based on assemblage-level data (e.g. fish, benthic the effects of stressors that may be so variable that it is neither macroinvertebrates and algae), the site-scale sampling design is typically defined by a combination of site length or extent *Correspondence to: J. E. Flotemersch, U.S. Environmental Protection and the sampling effort exerted therein, particularly for fish, Agency, Office of Research and Development, 26 W. Martin Luther King but increasingly for macroinvertebrates and periphyton. In Drive, Cincinnati, OH 45268, USA. E-mail: fl[email protected] yThe contributions of Joseph Flotemersch and Louise Reynolds were wadeable streams, extent essentially equals site area because prepared as part of their official duties as US Government employees. all habitats are generally accessible to sampling, although Copyright # 2010 John Wiley & Sons, Ltd. J. E. FLOTEMERSCH ET AL. often only specifichabitattypesaresampled(e.g.pools,riffles, et al. (2009) recommended standardization of fish sampling shorelines; Hughes and Peck, 2008). Site lengths for sampling protocols to increase the effectiveness of long-term, routine fish in wadeable streams typically range from 100 m to sampling and analysis for decision-making in water resource 40 mean wetted channel widths (MWCW; Hughes and Peck, management. There is no reason these recommendations should 2008). In studies of non-wadeable habitats, site lengths for fish not extend to other commonly samples assemblages as well. sampling vary from 500 m fixed length (e.g. Gammon, 1976; European electrofishing standards have been developed (CEN, Blocksom et al., 2009) to 100 MWCW (Hughes et al., 2002). 2003), but they were based on expert opinion rather than Site lengths for sampling benthic macroinvertebrates and empirical studies. Lack of standardization confounds efforts at algae are commonly the same as those selected for fish at a broad scale assessments that are based on multiple data sources given site. Likewise, within-site sampling effort may vary by (Hughes et al., 2000; Hughes and Peck, 2008), and weak the types of gears employed (Curry et al., 2009; Guy et al., standards lack precision, accuracy and statistical power. 2009), the crew size, and the habitat types sampled (e.g. In this paper, we review several approaches that were used shoreline only, all available, all that can be effectively for determining sample site length, as well as technical sampled). While realizing the importance of all site-scale issues related to defining appropriate sample site extent for design elements, this paper will focus primarily on the large river bioassessments. To a large extent, the review question of site length in boatable rivers. primarily relies on fish literature, as relatively few studies There is no single site length that addresses all research and have been published that examine the question of appro- applied questions; instead, the appropriate site length for stated priate site length for other biotic indicators. However, much objectives will be a compromise between the overall survey of the rationale discussed is taken from basic principles of design, the intensity of data collection for a particular sampling ecology, hydrology and geomorphology, and thus, should be event, and the sampling gear used. Additionally, with increasing applicable to other areas of stream and river research as well. channel size, the open-water column becomes important habitat, with some species only occurring as it becomes SAMPLING SITE LENGTH available (Wolter and Bischoff, 2001; De Leeuw et al., 2007) or as deep pools develop (Herzog et al., 2005). For example, In a hierarchical context, Frissell et al. (1986) defined the effective sampling for fish species occurring in open-water areas word ‘reach’ as a length of a small stream between breaks in frequently requires sampling approaches other than electro- channel slope, local side-slopes, valley floor width, riparian fishing. Such sampling may involve adjustments to the site vegetation and bank material. They further added that the length, as well as the inclusion of alternate gears, such as gill reach is sometimes the least physically discrete unit in the nets, fyke nets, push nets or trawls; however, the use of multiple hierarchy, but an exceedingly useful scale for describing gears must be balanced with data quality requirements and medium- and long-term effects of human activities on current and projected resource availability. Effective sampling streams. In small wadeable streams, reaches are typically of benthic macroinvertebrate species occurring in open-water 10–100 m long, but in boatable rivers, reaches are typically areas may require the use of drift nets, bottom grab samplers or hundreds to thousands of metres long. The next larger units, tow nets. Increased sampling effort and