Sean C. Sterrett

Movement and habitat use of two aquatic turtles (Graptemys geographica and Trachemys scripta) in an urban landscape

Our study focuses on the spatial ecology and seasonal habitat use of two aquatic turtles in order to understand the manner in which upland habitat use by humans shapes the aquatic activity, movement, and habitat selection of these species in an urban setting. We used radiotelemetry to follow 15 female Graptemys geographica (common map turtle) and each of ten male and female Trachemys scripta (red-eared slider) living in a man-made canal within a highly urbanized region of Indianapolis, IN, USA. During the active season (between May and September) of 2002, we located 33 of the 35 individuals a total of 934 times and determined the total range of activity, mean movement, and daily movement for each individuals. We also analyzed turtle locations relative to the upland habitat types (commercial, residential, river, road, woodlot, and open) surrounding the canal and determined that the turtles spent a disproportionate amount of time in woodland and commercial habitats and avoided the road-associated portions of the canal. We also located 21 of the turtles during hibernation (February 2003), and determined that an even greater proportion of individuals hibernated in woodland-bordered portions of the canal. Our results clearly indicate that turtle habitat selection is influenced by human activities; sound conservation and management of turtle populations in urban habitats will require the incorporation of spatial ecology and habitat use data.

Effects of disturbance at two spatial scales on macroinvertebrate and fish metrics of stream health

We analyzed macroinvertebrate and fish assemblage data collected from the upper southeastern coastal plain of the USA to (1) assess the relative sensitivities of bioassessment metrics to in-stream habitat quality, catchment scale land disturbance, and the presence of a reservoir in the catchment and (2) determine whether fish differ from macroinvertebrates in their responses to these variables. Fish and macroinvertebrates responded differently to anthropogenic disturbance: macroinvertebrates were affected most strongly by in-stream habitat quality and fish by the presence of a reservoir in the catchment. Neither taxonomic group were significantly affected by the catchment scale disturbance, probably because the proportions of disturbed land in the study areas were low. Fish may be particularly sensitive to the presence of reservoirs because of their need to cover relatively large distances to complete life cycles and maintain viable populations and because of their sensitivity to the effects of invasive reservoir species, particularly predator fishes. Although not an important predictor in itself, disturbance at the watershed scale was significantly and positively related to in-stream habitat quality, indicating that watershed disturbance had an important indirect effect on aquatic organisms. Direct and indirect ordination showed that the metric data were more strongly related to the disturbance variables than the taxonomic data from which the metrics were derived, possibly because the metrics were less sensitive than the taxon-specific abundances to nondisturbance-related factors. Other factors that may have contributed to this result include greater statistical tractability of the metric data and the relatively high sensitivity of the collective properties represented by the metrics to disturbance-related environmental changes.

Movement and habitat use of the snapping turtle in an urban landscape

In order to effectively manage urban habitats, it is important to incorporate the spatial ecology and habitat use of the species utilizing them. Our previous studies have shown that the distribution of upland habitats surrounding a highly urbanized wetland habitat, the Central Canal (Indianapolis, IN, USA) influences the distribution of map turtles (Graptemys geographica) and red-eared sliders (Trachemys scripta) during both the active season and hibernation. In this study we detail the movements and habitat use of another prominent member of the Central Canal turtle assemblage, the common snapping turtle, Chelydra serpentina. We find the same major upland habitat associations for C. serpentina as for G. geographica and T. scripta, despite major differences in their activity (e.g., C. serpentina do not regularly engage in aerial basking). These results reinforce the importance of recognizing the connection between aquatic and surrounding terrestrial habitats, especially in urban ecosystems.

Effects of Turbidity on the Foraging Success of the Eastern Painted Turtle

Abstract The effect of increased turbidity levels on aquatic organisms is an increasing concern for aquatic biologists. Recent studies show reduced foraging efficiency of drift-feeding fish species, which are highly visual predators, with increasing water turbidity. Similar to fish, many aquatic turtle species are highly visual aquatic predators that may be negatively affected by increasing water turbidity. We used Eastern Painted Turtles (Chrysemys picta) to test the hypothesis that increasing water turbidity would decrease prey capture efficiency. We classically conditioned eight C. picta to search for a food item when presented with a novel stimulus, and then measured the time it took each turtle to find a prey item under a range of 26 turbidity levels (≤40 nephelometric turbidity units, NTUs) presented in a random order. All turtles were successfully trained within 29 days to search for the food item when presented with the stimulus. Turbidity had no effect on the probability of successful prey capture. Turtles located the prey item in 97% of trials regardless of turbidity level. Turbidity had a minor effect on time to prey capture, increasing from an average of 30 seconds at a turbidity level of 2 NTUs to 55 seconds at 40 NTUs. Overall, turbidity level explained approximately 2% of the variation in the time it took a turtle to locate a prey item. These results contrast sharply with a nearly identical study, which showed that turbidity explained 70% and 90% of the variation in drift-feeding fish reactive distance and prey capture success respectively, and that a turbidity of only 9–10 NTUs reduced fish foraging performance by 50%. We suggest that resilience to turbidity effects on foraging proficiency among generalist species may be important to understanding their persistence in more degraded aquatic environments compared to more specialized species.

Factors Influencing Stream Fish Species Composition and Functional Properties at Multiple Spatial Scales in the Sand Hills of the Southeastern United States

AbstractAn understanding of how fish communities differ among river basin, watershed, and stream reach spatial scales and the factors that influence these differences can help in the design of effective conservation programs and the development of reference models that appropriately represent biota under relatively undisturbed conditions. We assessed the heterogeneity among fish assemblages in first- to fourth-order stream sites from four river basins (Savannah, Chattahoochee, Cape Fear, and Pee Dee rivers) within the Sand Hills ecoregion of the southeastern USA and compared it with the heterogeneity associated with watershed and stream reach spatial scales. Fifty-five species of fish representing 15 families were collected by electrofishing, with the most speciose families being Cyprinidae, Centrarchidae, Percidae, Ictaluridae, and Catostomidae. Constrained ordination identified clearly demarcated species assemblages among river basins as well as subbasin environmental variables that affected fish specie...

Spatial Ecology of Female Barbour's Map Turtles (Graptemys barbouri) in Ichawaynochaway Creek, Georgia

Abstract Quantifying patterns of habitat use by riverine species is logistically challenging, yet instream habitat characteristics are likely important in explaining the distribution of species. We integrated radiotelemetry and sonar habitat mapping to quantify instream habitat use by female Barbours Map Turtles (Graptemys barbouri) in Ichawaynochaway Creek, a tributary to the Flint River. We used logistic regression and a Bayesian information-theoretic approach to evaluate habitat use relative to habitat availability based on random locations. Over the two-year study period, turtles used an average of 839±199 m of creek length and exhibited site fidelity (mean 50% kernel density  =  0.23±0.05 ha). Substrate was generally more predictive of habitat use of female G. barbouri compared to large woody debris and water depth. Turtles generally used deeper habitats close to rocky-boulder and rocky-fine substrate with greater amounts of large woody debris. Estimates of home range size and habitat use found in this study improve our understanding of the spatial ecology of G. barbouri and provide a baseline for their habitat use in a relatively undisturbed section of stream. It is imperative to understand the spatial ecology of species, such as map turtles, that are particularly vulnerable to indirect effects of habitat modifications caused by impoundments, sedimentation, pollution, and snagging.

A Stream Multimetric Macroinvertebrate Index (MMI) for the Sand Hills Ecoregion of the Southeastern Plains, USA

A macroinvertebrate multimetric index is an effective tool for assessing the biological integrity of streams. However, data collected under a single protocol may not be available for an entire region. We sampled macroinvertebrates from the full extent of the Sand Hills ecoregion Level IV of the Southeastern Plains with a standard protocol during the summers of 2010–2012. We evaluated the performance of 94 metrics through a series of screening criteria and built 48 macroinvertebrate multimetric indexs with combinations of the best performing metrics, representing richness, habit, functional feeding guild, sensitivity, and community composition. A series of narrative-response tests for each macroinvertebrate multimetric index was used to find the best performing macroinvertebrate multimetric index which we called the Sand Hills macroinvertebrate multimetric index. The Sand Hills macroinvertebrate multimetric index consisted of the measures Biotic Index, % Shredder taxa, Clinger taxa2/total taxa, Plecoptera and Trichoptera richness, and Tanytarsini taxa2/Chironomidae taxa. Comparison of the Sand Hills macroinvertebrate multimetric index with existing assessment tools calculated with our data indicated that the Sand Hills macroinvertebrate multimetric index performs at a high level with regard to identifying degraded sites and in its response to stress gradients.