An inexpensive and rapid technique for mapping instream habitat of navigable rivers is needed by natural resource professionals. Unlike more expensive side scan sonar devices, the Humminbird® Side Imaging system employs a boat‐mounted transducer enabling the survey of shallow, rocky streams. This device can be used to obtain high resolution, georeferenced images of underwater habitat. We developed a technique employing geographic information systems (GIS) to transform raw sonar images to fit the configuration of a stream channel. The end product is a GIS layer that can be interpreted to map instream habitat. We demonstrated this approach by mapping substrate and large woody debris in a southwest Georgia stream, and evaluated the technique through a comprehensive accuracy assessment. An overall classification accuracy of 77% was observed for substrate mapping and sonar estimates of large woody debris were correlated (r2 = 0.79) with actual wood abundance. Sonar mapping generated estimates of reach and substrate area comparable to a traditional field approach, and reduced the time investment by 90%. Applications for high resolution habitat maps are widespread and numerous; the ability to produce these maps at low cost is now within the grasp of researchers and managers alike.

An efficient, low-cost approach for mapping habitat features in navigable streams is needed to support the research and management of aquatic ecosystems at the landscape level. We developed a method that uses high-resolution (455 kHz) side-scan sonar imagery obtained with the inexpensive (~$2000) Humminbird W Side Imaging system and ArcGIS to produce sonar image maps (SIMs) used to interpret and map habitat features such as substrates and large woody debris, in addition to continuously recording depth along the survey route. This method was recently demonstrated and evaluated in several small streams in southwestern Georgia (30-50 m width, 40 km mapped). To evaluate the feasibility of this method for mapping substrate and depth in larger rivers and over greater spatial extents, we conducted a sonar survey and generated SIMs for 124 km of the lower Flint River (85-140 m width). We interpreted the SIMs to digitize and classify substrate and bank boundaries. To assess classification accuracy, we visually inspected substrate at randomly assigned reference locations. A comparison of reference and map data revealed an overall classification accuracy of 84%. These results were consistent with previous findings and indicate that low-cost side-scan sonar is also an effective mapping tool for larger rivers. The sonar survey did, however, result in more missing and unsure substrate data and a lower map accuracy for fine-textured substrates than previously achieved when mapping smaller streams. We found a strong, positive relationship (r 2 = 0.89) between the sonar range and the proportion of unsure substrate in the map, suggesting that a multi-pass, parallel-transect sonar survey could be used to maintain high-image resolution when stream widths exceed 100 m and/or obstructions, such as islands, are encountered. Applications for sonar-based habitat maps are widespread and numerous. The ability to produce these maps efficiently at low-cost is within the grasp of researchers and managers alike.

Large woody debris provides essential habitat in sand‐bed streams of the southeastern United States. In many Coastal Plain streams, pre‐cut timber, lost more than a century ago during river transport, contributes to the extant large woody debris pool. The extraction of these logs, otherwise known as deadhead logging, threatens habitat integrity in these systems. Little is known of the distribution, abundance, and ecological value of deadhead logs, thus hindering attempts to manage and protect this resource. Moreover, the use of traditional field‐based methods to inventory wood is slow and costly in large turbid streams. Our objectives were to assess wood at several sites in southwest Georgia using traditional methods, then use these data to evaluate the efficacy of quantifying wood using side scan sonar imagery. Deadhead logs were widely distributed and constituted a substantial proportion (> 50% volume and surface area) of the total large woody debris found at study sites. Given these findings, the wholesale removal of deadhead logs could largely impact the ecological integrity of such streams. Analyses revealed strong correlations (r2 = 0.82—0.98) between sonar wood estimates and actual counts suggesting that side scan sonar can be used as a rapid, inexpensive method to quantify wood throughout navigable systems.

Riparian zones are critical for protecting water quality and wildlife, but are often impacted by human activities. Ongoing threats and uncertainty about the effectiveness of buffer regulations emphasize the importance of monitoring riparian buffers through time. We developed a method to rapidly categorize buffer width and landuse attributes using 2007 leaf-on aerial photography and applied it to a 65 km section of the Toccoa River in north Georgia. We repeated our protocol using 1999 leaf-off aerial photographs to assess the utility of our approach for monitoring. Almost half (45%) of the length of the Toccoa River was bordered by buffers less than 50 ft wide in 2007, with agricultural and built-up lands having the smallest buffers. The percentage of river length in each buffer width category changed little between 1999 and 2007, but we did detect a 5% decrease in agricultural land use, a corresponding increase in built-up land use, and an additional 149 buildings within 100 ft of the river. Field verification indicated that our method overestimated buffer widths and forested land use and underestimated built-up land use and the number of buildings within 100 ft of the river. Our methodology can be used to rapidly assess the status of riparian buffers. Including supplemental data (e.g., leaf-off imagery, road layers) will allow detection of the fine-scale impacts underestimated in our study. Our results on the Toccoa River reflect historic impacts, exemptions and variances to regulations, and the ongoing threat of vacation home development. We recommend additional monitoring, improvements in policy, and efforts to increase voluntary protection and restoration of stream buffers.

The goldline darter (Percina aurolineata) is threatened by recent increases in urbanisation in the Coosawattee River watershed, but no studies have addressed their current status. Similarly, limited data on habitat use make it difficult to understand factors that may impact this species. We compared occurrence data before (1996)(1997)(1998)(1999)(2000) and after (2009-2011) a period of rapid development and population growth within the watershed. Single-season occupancy models were built to account for imperfect species detection and to identify habitat covariates. MaxEnt was used to identify important stream reaches for conservation and to understand landscape scale factors correlated with the distribution of goldline darters. Our results indicate a high proportion of sites occupied upstream of Carters Lake during the historic and recent time periods, with no evidence of decline. However, occurrences of goldline darters for sites in Talking Rock Creek and the lower Coosawattee River were sparse in the historic period and absent during the recent period. The probability of detecting goldline darters is low and was positively associated with the occurrence of small substrate. Species distribution models were strongly influenced by watershed area and elevation and indicated a high probability of suitable habitat within the Coosawattee River and large tributaries upstream of Carters Lake. While goldline darter occupancy is currently stable upstream of Carters Lake, continued urbanisation is a threat to long-term persistence. We recommend additional monitoring and describe a protocol that allows for precise estimates of species occupancy while minimising the risk of sampling-related mortality.