Journal of Student Research (2015) Volume 4, Issue 1: pp. 90-98 Research Article a. Department of Biology; Westfield State University, Westfield, MA 01085 90 Evaluation of a Modified Habitat Suitability Index Model for Eastern Brook Trout: Implications for Efficient Habitat Assessment Carl A. Favata a , David R. Christensen a , Robert Thompson a , Kelly Anne McKeown a , and Jennifer A. Hanselman a Species-specific habitat suitability models have potential for use in restoration efforts, but their efficiency still remains in question. As eastern brook trout, Salvelinus fontinalis, populations in New England have declined over the last few decades as a result of anthropogenic and natural impacts on critical habitat, habitat suitability models have become a common tool for conservation efforts. These models, however, have inherent flaws that prevent widespread and uniform use. To better adapt these models, the flaws must be properly addressed. Using a modified habitat suitability index (HSI) model developed for eastern brook trout, we explained the correlation between catch per unit effort (CPUE) of brook trout with designated HSI variables such as temperature, dominant substrate type, and percent riffle fines for nineteen reaches within the Westfield River watershed. CPUE was not significantly correlated with HSI outputs. A principal components analysis (PCA) was employed and revealed driving factors within the system. Four variables were shown to yield the highest explained variance over the first two axes: velocity, instream cover, percent pools, and thalweg depth. Evidence suggests that habitat assessment based around these core variables may lead to a more efficient and accurate assessment. Recommendations for improved methodologies include revised tolerance curves, a reworked index rating system, and revised model variables based on current field research. Alterations to existing models provide hope for more accurate assessment, and increased efficiency in conservation efforts. Keywords: brook trout; restoration; HSI model; habitat suitability; habitat assessment Introduction Species driven ecological management and restoration has become an important focus in recent years in the eastern United States (Whiteley et al., 2012). States such as Massachusetts suffer from both anthropogenic and natural disturbances that affect local fisheries. There are approximately 3,000 dams throughout Massachusetts, approximately 250 of which still serve a functional purpose (Dam removal in Massachusetts, 2007). These structures impact ecosystems in many ways; effects may include altered temperatures, stream and river restructuring, altered turbidity and dissolved oxygen levels, build-up of organic wastes above the dam, and habitat fragmentation due to connectivity issues (Letcher et al., 2007; Niles et al., 2013). When conditions are altered, tolerance thresholds of key aquatic species are often exceeded. Streams and rivers also face natural disturbances such as hurricanes, floods, and tornadoes that may drastically alter habitat in a much shorter time. Habitat restoration is often necessary to ensure that a system is suitable for the survival of particular species of interest. A key example of such a species is the eastern brook trout (EBT), Salvelinus fontinalis. In Massachusetts, native EBT populations have been greatly impacted over the last 100 years by a number of disturbances (Petty and Merriam, 2012). EBT are highly susceptible to habitat alterations such as increased temperatures, stream restructuring, low connectivity (Niles et al., 2013), and decreased flow rates (Hakala and Hartman, 2004). Throughout much of the Northeast, EBT habitat and population integrity have seen drastic declines (Conservation success index, 2012). Since EBT have narrow tolerance levels for a variety of environmental variables, they may often be considered an indicator species for cold, clean water that is suitable for a variety of important aquatic organisms (Lund et al., 2003; Waco and Taylor, 2010). To combat the decline in EBT populations, a variety of research has focused on assessment and rehabilitation of habitat (Petty and Merriam, 2012). Habitat assessment models are commonly used to accomplish this, but there currently exists no widespread uniform model (Petty and Merriam, 2012). One popular species-specific model was developed over two decades ago and is still widely used today, albeit in a variety of applications (e.g. wildlife management, habitat surveys, and wide scale land assessments). Habitat Suitability Index (HSI) models (each species- specific) were developed in the early 1980’s to better characterize habitat suitability based on target species (Habitat suitability index models, 2014). HSI models employ a set of environmental parameters related to critical and limiting biological tolerances of an organism, and provide a single index (HSI) based on a set of mathematical formulas. This index, ranging from zero to one, is directly related to a habitat’s capacity to support a given species; the closer to one the output, the larger the theoretical population that the habitat could support. HSI models are readily available for many different species of animals and plants, giving them great versatility. They also are easily adaptable to meet the unique traits of any environment, factor in many different variables, and report a single index which allows for ease of longitudinal comparisons. These traits make the HSI model an optimal candidate to meet current assessment and restoration goals for native EBT populations.