C. Andrew Dolloff

Response of a Brook Trout Population and Instream Habitat to a Catastrophic Flood and Debris Flow

Abstract In June 1995, a massive flood and debris flow impacted fish and habitat along the lower 1.9 km of the Staunton River, a headwater stream located in Shenandoah National Park, Virginia. In the area affected by debris flow, the stream bed was scoured and new substrate materials were deposited, trees were removed from a 30-m-wide band in the riparian area, and all fish were eliminated. In the area that was unaffected by debris flow, habitat was moderately altered by the flood and fish populations persisted at decreased densities. Basinwide fish population and habitat surveys provided data to compare (1) the pre- and postevent population densities of brook trout Salvelinus fontinalis and instream habitat conditions and (2) postevent population density, brook trout growth, and instream habitat in the debris-flow-affected and unaffected areas. By June 1998, brook trout had recolonized the entire debris-flow-affected area, and population density exceeded preevent levels. Brook trout growth was significan...

Factors Influencing Behavior and Transferability of Habitat Models for a Benthic Stream Fish

Abstract We examined the predictive power and transferability of habitat-based models by comparing associations of tangerine darter Percina aurantiaca and stream habitat at local and regional scales in North Fork Holston River (NFHR) and Little River, Virginia. Our models correctly predicted the presence or absence of tangerine darters in NFHR for 64% (local model) and 78% (regional model) of the sampled habitat-units (i.e., pools, runs, riffles). The distribution of tangerine darters apparently was influenced more by regional variables than local variables. Data from Little River and 37 historical records from Virginia were used to assess transferability of our models developed from NFHR data. In general, the models did not transfer well to Little River; all models predicted that either no (regional model) or few (local model) habitat-units in Little River would contain tangerine darter even though the species was observed in 83% of the habitat-units sampled. Conversely, the regional model correctly pred...

Fish Habitat and Fish Populations in a Southern Appalachian Watershed before and after Hurricane Hugo

Abstract Habitat features and relative abundance of all fish species were estimated in 8.4 km of a small mountain stream system before and 11 months after Hurricane Hugo crossed the southern Appalachians in September 1989. There was no change in the total amount (area) of each habitat type but the total number of habitat units decreased and average size and depth of habitat units increased. Transport and sorting of streambed sediments was evident from the increased proportion of habitat units in which cobbles and small boulders were the most common constituents. Large woody debris more than doubled from 228 to 559 pieces/km of stream channel. At the watershed scale, there were only minor changes in the fish community 11 months after the hurricane, Eleven species were found both before and after the storm, and most species were uncommon. Among common species, densities increased in riffles for darters Etheostoma spp., increased in pools for blacknose dace Rhinichthys atratulus, and were largely unaffected ...

Factors Influencing Stream Fish Recovery Following a Large-Scale Disturbance

Abstract We examined fish distribution and abundance in erosional habitat units in South Fork Roanoke River, Virginia, following a fish kill by using a reachwide sampling approach for 3 species and a representative-reach sampling approach for 10 species. Qualitative (presence–absence) and quantitative (relative abundance) estimates of distribution and abundance provided consistent measures of fish recovery for 2 of 3 species at the reachwide scale and 8 of 10 species at the representative-reach scale. Combining results across scales and estimator types showed that distributions and abundances of 5 of 11 species in the Teach affected by the kill were similar to those observed in unaffected upstream and downstream reaches 8–11 months following the perturbation. Differences in distribution and abundance between the affected Teach and unaffected reaches indicate that 4 of 11 species had not fully recovered during the same time period; results were equivocal for 2 other species. We attribute differences in rec...

Does diet influence consumer nutrient cycling? Macroinvertebrate and fish excretion in streams

Abstract Consumer nutrient cycling supplies limiting elements to autotrophic and heterotrophic organisms in aquatic systems. However, the role of consumers in supplying nutrients may change depending on their diet and their own stoichiometry. We evaluated the stoichiometry, N and P excretion, and diets of the dominant macroinvertebrates and fish at 6 stream sites to determine if the nutritional composition of food alters nutrient excretion. We used Sterners (1990) nutrient homeostasis model as a reference to gauge whether consumer nutrient excretion is influenced by diet. Body stoichiometry explained 61% of the variation in N∶P excretion by macroinvertebrates but only 11% of the variation for fish. In both cases, the relationship was driven by 2 P-rich end-members, crayfish and mottled sculpin. Results of Akaike Information Criterion (AIC) analysis showed that family alone explained 71% of the variation in N∶P excretion in macroinvertebrates and 31% of the variation in fish. Diet explained only 8% of the variation in both cases. Most consumers (9 of 11) had N∶P excretion values that were well below predictions of Sterners model. Two taxa, crayfish and sculpin, had N∶P excretion that overlapped the models predictions. Our results suggest that crayfish and sculpin may display strict homeostasis with respect to N and P and that their growth might be P-limited. Other consumers may be more flexible in their stoichiometry and not P-limited. We speculate that the extremely low excretion N∶P measured for many consumers might have been the result of semiflexible homeostasis, inaccuracies in our assessment of dietary nutrients, growth-limiting nutrients other than N or P, or lack of egestion data. Our results suggest that crayfish and sculpin may alter N and P dynamics in streams by excreting low amounts of P relative to N compared to what is generally available in the water column.

Habitat Sequencing and the Importance of Discharge in Inferences

Abstract We constructed stream maps for a low-gradient trout stream in southwestern Virginia during autumn (base flow) and spring (elevated flows) to compare spatial and temporal variation in stream habitats. Pool–riffle sequencing and total area occupied by pools and riffles changed substantially depending on the level of discharge: reduced discharge resulted in an increase in total pool surface area with more numerous but smaller pools than during spring. In contrast, total surface area of riffles decreased with decreasing discharge as did total wetted surface area. These findings suggest caution should be exercised when comparing seasonal or annual surveys, applying habitat guidelines for assessment or management, evaluating fish standing crop potential from predictive habitat models, or predicting availability of habitat or biological information at times other than when stream surveys are conducted. We demonstrate the potential dangers by intentionally applying biological sample results taken at one ...

A Comparison of Basinwide and Representative Reach Habitat Survey Techniques in Three Southern Appalachian Watersheds

Abstract We compared estimates of stream habitat at the watershed scale using the basinwide visual estimation technique (BVET) and the representative reach extrapolation technique (RRET) in three small watersheds in the Appalachian Mountains. Within each watershed, all habitat units were sampled by the BVET; in contrast, three or four 100-m reaches were sampled with the RRET. The number of pools was higher and the number of cascades was lower when estimated by the RRET than they were when estimated by the BVET, whereas the average areas of all habitat types estimated by the RRET were smaller. At the watershed scale, eight out of nine estimates of total habitat area by habitat type derived from the RRET were outside the 95% confidence intervals derived from the BVET. Depth estimates were consistently smaller with the RRET than with the BVET Large woody debris estimates with the RRET were less than with the BVET in two of three watersheds and were greater in one watershed. We observed that the degree to whi...