Richard L. Raesly

Applying thresholds to forecast potential biodiversity loss from human development.

Abstract Ecological thresholds have much potential as a tool to use for watershed management. Not all systems exhibit abrupt nonlinear responses, but the threshold concept is still useful for describing stressor responses or changes in state variables. For example, the minimum detectable negative response is an initiation-of-impact threshold that might allow for planning and management before population-scale change occurs in taxa. An extirpation threshold, which is the point where a system loses a vital component, such as a species or function, also exists. A number of taxon-specific thresholds to landuse change in watersheds have been identified in previous research. We apply these values to make watershed-level and spatially explicit forecasts regarding imperilment and loss of biodiversity in the face of watershed alterations. We show that unchecked development in the Potapsco River watershed of Maryland could result in the loss of nearly 60% of the benthic macroinvertebrate taxa by the time impervious surface cover reaches 15% of the watershed. Application of analytical thresholds to projected increases in residential development in the Middle Patuxent River watershed by 2030 indicates substantial future changes in aquatic biodiversity, with up to 50% of benthic macroinvertebrate taxa disappearing from some stream reaches and few reaches immune from projected biodiversity loss or impairment.

Relations between Physical Habitat and American Eel Abundance in Five River Basins in Maryland

Abstract Although the American eel Anguilla rostrata occurs in a variety of habitats over large geographic areas, little is known regarding the specific habitat relations that regulate eel distribution and abundance in freshwater streams. We evaluated the importance of 17 physical habitat, chemical, and biological variables in predicting eel density in five major river basins in Maryland. Because artificial structures impede eel migration in all five basins, only sites determined to be on unblocked streams or downstream of structures that significantly restrict eel passage were used in the analysis. Stepwise regression identified a model consisting of four variables—velocity–depth diversity, the log-transformed distance (km) to the Chesapeake Bay, the log-transformed density of noneel fishes, and the distance to a semipassable or impassable structure—as the best predictor of eel densities. When applied to a random subset of data not used for model development, the model correctly predicted 44.4% of eel de...

THE EFFECTS OF BEAVER-CREATED WETLANDS ON THE BENTHIC MACROINVERTEBRATE ASSEMBLAGES OF TWO APPALACHIAN STREAMS

We examined the effects of beaver impoundments on the benthic macroinvertebrate assemblages of two small Appalachian streams, Mountain Run (Somerset County, Pennsylvania) and a tributary to Herrington Creek (Garrett County, Maryland). Benthic macroinvertebrate assemblages above the impoundments were compared with assemblages within the impoundments and 1 m, 10 m, and 100 m below the impoundments. The results of our study indicate that beaver affect both within-impoundment and downstream benthic macroinvertebrate assemblages. Taxonomic and functional changes in benthic macroinvertebrate assemblages of the beaver-altered streams were a result of direct (impoundment) and indirect (changes in temperature, water chemistry, plant growth) alterations of the stream environment.

Amphibian Sampling Techniques along Maryland Coastal-Plain Streams

Abstract Amphibians and other herpetofauna may be useful in assessing the biological integrity of small streams, so determining which sampling technique maximizes encounters is important. Area-constrained surveys (ACS), used by the Maryland Biological Stream Survey, were tested against cover-board surveys, drift fences with pitfall and funnel traps, quadrat leaf-litter searches, leaf-litter bags, and electrofishing. Twenty sites within the coastal plain region of Maryland, west of the Chesapeake Bay, were sampled with each technique once a month from June 2006 through August 2006. Overall, ACS and electrofishing yielded significantly more taxa and total individuals than cover-board surveys, quadrat searches, and leaf-litter bags; drift fence captures were moderate between ACS and electrofishing and the other methods. Electrofishing and ACS collected both more taxa and more individuals more reliably through time than the other techniques used; therefore, efforts to use herpetofauna to monitor the health of small streams will benefit from incorporating these methods into a sampling protocol.

Enneacanthus chaetodon (Blackbanded Sunfish): An Imperiled Element of Maryland's Coastal Plain Ichthyofauna

Abstract In 2002 and 2006, we conducted a survey of historical collection localities for Enneacanthus chaetodon (Blackbanded Sunfish) in Maryland. Blackbanded Sunfish were detected at only one of six historical localities. This locality consisted of 17 quarry ponds, but the Blackbanded Sunfish was collected in only three of these. These ponds were characterized by low pH (<4.9), dense submerged and overhanging vegetation, and the absence or low abundance of non-native piscivores. The acidic nature of these ponds may provide refuge from predation for Blackbanded Sunfish by limiting numbers of non-native piscivores such as Micropterus salmoides (Largemouth Bass) and Pomoxis nigromaculatus (Black Crappie). As a result of the surveys described herein, the Blackbanded Sunfish state status in Maryland was elevated from Threatened to Endangered.

Rapid Colonization of the Potomac River Drainage by the Rainbow Darter (Etheostoma caeruleum) Following Introduction

Abstract Etheostoma caeruleum (Rainbow Darter) was first collected from the Potomac River drainage in 1977 and has subsequently expanded its range to include nearly all major tributaries in the system. Analysis of the chronology of Rainbow Darter collection data demonstrates the explosive nature of this range expansion. Using this chronology, we assert that Rainbow Darter is not native to the drainage and likely occurs as a result of human-induced interbasin transfer. Although the ecological impact of non-native Rainbow Darters in the Potomac is unknown, the potential exists for competition with native species. The presence of numerous instream blockages prohibiting colonization of portions of the drainage make this system well suited to study the impacts of introduced darters on native ichthyofauna.

Extirpation of the Bridle Shiner (Notropis bifrenatus) from Maryland

Abstract We report the extirpation of Notropis bifrenatus (Bridle Shiner) from Maryland. This once widespread species has not been observed in this state since 1984 despite recent and extensive collection efforts in areas of historical occurrence. Based on these results, the status of the Bridle Shiner in Maryland was changed from endangered to endangered/extirpated in 2010.

First Record of the Bigeye Shiner (Notropis boops) from West Virginia

Abstract We report a population of Bigeye Shiner Notropis boops in the South Fork Hughes River drainage of the Little Kanawha River, West Virginia. A total of 27 individuals of N. boops were collected during five sampling efforts from 1999 to 2005. These specimens represent an addition to the state fauna, a distributional record for the Little Kanawha River, and an eastern range extension for this species on the Appalachian Plateau, West Virginia. Notropis boops in the South Fork Hughes River drainage likely represents a native population.