Development of Techniques for Assessment of Population Characteristics of the Federally Endangered Diamond Darter

Development of techniques for assessment of population characteristics of the federally endangered Diamond Darter Austin A. Rizzo Population monitoring is an essential component of endangered species recovery programs. One species for which monitoring is needed is the federally endangered Diamond Darter Crystallaria cincotta. This species was placed on the Endangered Species List in 2013 because of its small range and population size, and because of continued anthropogenic threats to the species’ habitat. The Diamond Darter is believed to occur only within the lower 50 rkm of the Elk River in West Virginia. Museum specimens indicate the Diamond Darter was once distributed throughout the Ohio River Basin, but it is now likely extirpated from the Muskingum River, the Ohio River, the Green River, and the Cumberland River drainages. Because of the Diamond Darter’s small size, cryptic coloration, nocturnal behavior, and seemingly patchy distribution, along with limitations associated with current sampling methods, the species may appear to be rarer than it actually is. This may have also contributed to its late discovery as a species in 2008. As a result of several of the above-mentioned factors, the Diamond Darter is a much understudied fish with very little known about life history, population size, or current distribution. One problem with monitoring populations of rare and elusive species is detection. Failure to account for detection probability can be a major source of bias in presence-absence and count survey data, potentially resulting in false determination of species absence and underestimation of abundance, respectively. Additionally, if these variables are not accurately estimated, their relationship to associated habitat and environmental variables may also be inaccurate. Ultimately, not accounting for detection probability may lead to misinformed management decisions, which can prove costly for an endangered species. For this study, I sought to develop techniques that would allow for the assessment of population characteristics for this rare, elusive species. In my first chapter, I evaluated the precision and accuracy of photogrammetric length measurements relative to direct board measurements of Greenside Darters Etheostoma blennioides and Variegate Darters Etheostoma variatum. Agreement between board and photogrammetric measurements were high for these species, supporting photogrammetry as a useful method for obtaining length measurements of benthic stream fishes. Consequently, I applied photogrammetry in a field study of the Diamond Darter and assessed length frequency of 199 individuals throughout the sampling season. Based on these data I was able to identify a single cohort using glide habitat and estimate growth rate throughout the summer. My second chapter focused on determining if there were any seasonal and diel patterns in Diamond Darter detectability during population surveys. In addition to temporal factors, I also assessed five sampling covariates that might influence individual detection. N-mixture models were used to estimate site abundances and relationships between covariates and individual detectability. The best supported model included water temperature as a quadratic function influencing individual detectability, with temperatures around 22 C resulting in the highest detection probability. Detection probability when surveying at the optimal temperature was approximately 6% and 7.5% greater than when surveying at 16 C and 29 C, respectively. Two variables, time of night and day of year, were not strong predictors of Diamond Darter detectability. The results of this study will allow researchers and agencies to maximize detection probability when surveying populations, resulting in greater monitoring efficiency and likely more precise abundance estimates. In my third chapter, I assessed the impacts on an extreme flood event on Diamond Darter populations. To accomplish this, relative abundances for one cohort of this species were estimated using pre-flood and post-flood surveys at 15 sites. Our results indicate the short-term response of Diamond Darter relative abundances to this extreme event were negligible, indicating individuals are able to withstand high velocities and resist displacement or mortality. In addition, site-level abundances were estimated at three sentinel sites during 2015 and 2016 using a multinomial N-mixture model that accounted for variation in detectability resulting from water temperature. Mean estimated abundance varied among the three sites and between the two years. Our results suggest there is substantial variation in year-class strength between the two cohorts we sampled. Using detection probabilities generated from our highest supported model, we conducted simulation modeling to determine the number of replicate surveys needed to 7 replications. It is recommended that survey efforts at established sentinel sites be continued on an annual basis in order to help determine factors influencing year-class strength.