Yoichiro Kanno

Fine‐scale population structure and riverscape genetics of brook trout (Salvelinus fontinalis) distributed continuously along headwater channel networks

Linear and heterogeneous habitat makes headwater stream networks an ideal ecosystem in which to test the influence of environmental factors on spatial genetic patterns of obligatory aquatic species. We investigated fine‐scale population structure and influence of stream habitat on individual‐level genetic differentiation in brook trout (Salvelinus fontinalis) by genotyping eight microsatellite loci in 740 individuals in two headwater channel networks (7.7 and 4.4 km) in Connecticut, USA. A weak but statistically significant isolation‐by‐distance pattern was common in both sites. In the field, many tagged individuals were recaptured in the same 50‐m reaches within a single field season (summer to fall). One study site was characterized with a hierarchical population structure, where seasonal barriers (natural falls of 1.5–2.5 m in height during summer base‐flow condition) greatly reduced gene flow and perceptible spatial patterns emerged because of the presence of tributaries, each with a group of genetically distinguishable individuals. Genetic differentiation increased when pairs of individuals were separated by high stream gradient (steep channel slope) or warm stream temperature in this site, although the evidence of their influence was equivocal. In a second site, evidence for genetic clusters was weak at best, but genetic differentiation between individuals was positively correlated with number of tributary confluences. We concluded that the population‐level movement of brook trout was limited in the study headwater stream networks, resulting in the fine‐scale population structure (genetic clusters and clines) even at distances of a few kilometres, and gene flow was mitigated by ‘riverscape’ variables, particularly by physical barriers, waterway distance (i.e. isolation‐by‐distance) and the presence of tributaries.

Modeling structured population dynamics using data from unmarked individuals

The study of population dynamics requires unbiased, precise estimates of abundance and vital rates that account for the demographic structure inherent in all wildlife and plant populations. Traditionally, these estimates have only been available through approaches that rely on intensive mark-recapture data. We extended recently developed N-mixture models to demonstrate how demographic parameters and abundance can be estimated for structured populations using only stage-structured count data. Our modeling framework can be used to make reliable inferences on abundance as well as recruitment, immigration, stage-specific survival, and detection rates during sampling. We present a range of simulations to illustrate the data requirements, including the number of years and locations necessary for accurate and precise parameter estimates. We apply our modeling framework to a population of northern dusky salamanders (Desmognathus fuscus) in the mid-Atlantic region (USA) and find that the population is unexpectedly declining. Our approach represents a valuable advance in the estimation of population dynamics using multistate data from unmarked individuals and should additionally be useful in the development of integrated models that combine data from intensive (e.g., mark-recapture) and extensive (e.g., counts) data sources.

Influence of Rare Species on Electrofishing Distance When Estimating Species Richness of Stream and River Reaches

Abstract The electrofishing distance needed to estimate fish species richness at the stream or river reach scale is an important question in fisheries science. This distance is governed by the shape of the species accumulation curve, which, in turn, is influenced by a combination of factors, including the number of species, their overall abundances, habitat associations, the efficiency of the sampling method, and the occurrence of rare species. In this study we document the influence of rare species on the species accumulation curves from stream and river sites in data sets from five dispersed regions of the USA. Spatial discontinuity (i.e., a noncontinuous distribution within reaches) was observed in four of the five data sets, and the four data sets contained numerically rare species represented by one or two individuals (termed singletons and doubletons, respectively). Numerically rare species were typically proportionately rare (i.e., <1% of the total number of individuals captured), but proportionate...

Seasonal weather patterns drive population vital rates and persistence in a stream fish

Climate change affects seasonal weather patterns, but little is known about the relative importance of seasonal weather patterns on animal population vital rates. Even when such information exists, data are typically only available from intensive fieldwork (e.g., mark-recapture studies) at a limited spatial extent. Here, we investigated effects of seasonal air temperature and precipitation (fall, winter, and spring) on survival and recruitment of brook trout (Salvelinus fontinalis) at a broad spatial scale using a novel stage-structured population model. The data were a 15-year record of brook trout abundance from 72 sites distributed across a 170-km-long mountain range in Shenandoah National Park, Virginia, USA. Population vital rates responded differently to weather and site-specific conditions. Specifically, young-of-year survival was most strongly affected by spring temperature, adult survival by elevation and per-capita recruitment by winter precipitation. Low fall precipitation and high winter precipitation, the latter of which is predicted to increase under climate change for the study region, had the strongest negative effects on trout populations. Simulations show that trout abundance could be greatly reduced under constant high winter precipitation, consistent with the expected effects of gravel-scouring flows on eggs and newly hatched individuals. However, high-elevation sites would be less vulnerable to local extinction because they supported higher adult survival. Furthermore, the majority of brook trout populations are projected to persist if high winter precipitation occurs only intermittently (≤3 of 5 years) due to density-dependent recruitment. Variable drivers of vital rates should be commonly found in animal populations characterized by ontogenetic changes in habitat, and such stage-structured effects may increase population persistence to changing climate by not affecting all life stages simultaneously. Yet, our results also demonstrate that weather patterns during seemingly less consequential seasons (e.g., winter precipitation) can have major impacts on animal population dynamics.

Biogeography of Stream Fishes in Connecticut: Defining Faunal Regions and Assemblage Types

Abstract Stream fish survey data were analyzed to describe patterns of fish distributions in wadeable streams (primarily 1st–4th order) in Connecticut. Species occurrence within the United States Geological Survey 8-digit hydrologic unit code watersheds were used to aggregate similar watersheds into stream fish faunal regions. Within each identified region, multivariate analyses were used to identify major fish assemblage types and associate stream habitat with assemblage types. The analyses revealed an eastern and western faunal region defined primarily by distribution of a few native species. Native species associated with the western watersheds were: Semotilus atromaculatus (Creek Chub), Exoglossum maxillingua (Cutlips Minnow), and Cottus cognatus (Slimy Sculpin). Native fishes associated with the eastern watersheds were: Erimyzon oblongus (Creek Chubsucker), Esox niger (Chain Pickerel), and Esox americanus (Redfin Pickerel). Inclusion of non-indigenous species in the analyses resulted in a similar east–west grouping of watersheds. Five and four assemblage types were identified in the eastern and western faunal regions, respectively. Both regions harbored 3 fluvial assemblages defined longitudinally from headwater streams to larger wadeable streams and a macro-habitat generalist assemblage inhabiting streams with proportionately more pool habitat, but taxonomic membership and indicator species rankings among assemblages were not necessarily identical between the regions. A distinct assemblage dominated by Redfin Pickerel was recognized only in the eastern region. Streams in the western region were generally higher in elevation and colder in water temperature. The discovery and description of eastern and western fish faunal regions and their fish assemblage types will be useful in stratifying the biological monitoring of streams and other aquatic resource management actions in Connecticut.

Summer Thermal Thresholds of Fish Community Transitions in Connecticut Streams

AbstractThermal tolerances have been studied for individual fish species but few have investigated how stream fish assemblages respond along a temperature gradient and which thermal ranges act as a threshold, triggering discernible community change. The purpose of this study was to define summer temperature thresholds of fish community transitions in Connecticut streams. The program Threshold Indicator Taxa Analysis suggested that the coldwater class had a June–August mean water temperature 21.70°C. Significant indicator species of coldwater streams were Slimy Sculpin Cottus cognatus and Brook Trout Salvelinus fontinalis. Significant indicator species of warmwater streams were Cutlip Minnow Exoglossum maxillingua, Smallmouth Bass Micropterus dolomieu, Rock Bass Ambloplites rupestris, Brown Bullhead Ameiurus nebulosus, Redbreast Sunfish Lepomis auritus and Yellow Bullhead A. natalis. The narrow 3.41°C temperature range between the coldwa...

Maximum Daily Consumption and Specific Daily Metabolic Demand of Juvenile Flathead Catfish (Pylodictis olivaris)

ABSTRACT Maximum daily consumption and specific daily metabolic demand were determined for juvenile flathead catfish (Pylodictis olivaris) in the laboratory over a temperature range of 3–32 °C. Maximum daily consumption increased with increasing water temperature, was significantly higher at 19 °C than at colder temperatures, and remained elevated up to 32 °C. Fish rarely ate below 15 °C, most stopped feeding at 11 °C, and no fish consumed anything at 7 °C or below. Specific daily metabolic demand showed a gradual increase with increasing temperature. The quantification of consumption and metabolic demand for juvenile flathead catfish was consistent with descriptions classifying the species as adapted to warmwater conditions.

LIFE HISTORIES OF TWO POPULATIONS OF THE IMPERILED CRAYFISH ORCONECTES (PROCERICAMBARUS) WILLIAMSI (DECAPODA: CAMBARIDAE) IN SOUTHWESTERN MISSOURI, U.S.A.

The imperiled Williams’ Crayfish, Orconectes williamsi Fitzpatrick, 1966 is endemic to southwestern Missouri and northwestern Arkansas, U.S.A., an area experiencing rapid urbanization and other land use changes. Populations of O. williamsi in two small streams were studied for 26 months to describe annual reproductive cycles, and gather information about fecundity, sex ratio, size at maturity, size-class structure, and growth. We captured a monthly average of more than 120 O. williamsi from each of the two study populations. The life history of O. williamsi appeared generally similar to what has been reported for several other stream-dwelling species of Orconectes. Breeding season occurred in mid to late autumn and perhaps into early winter. Egg brooding occurred during late winter and early spring, although it was difficult to locate females carrying eggs or hatchlings. Young of year first appeared in samples during May and June. We estimated that these populations of O. williamsi contained 3 or 4 size-classes; smaller O. williamsi grew faster than larger individuals and the mean specific growth rate was about 2% per day during summer. Life history information presented herein will be important if expected future conservation efforts are required.

Recovery of Native Brook Trout Populations Following the Eradication of Nonnative Rainbow Trout in Southern Appalachian Mountains Streams

AbstractNonnative Rainbow Trout Oncorhynchus mykiss have displaced native Brook Trout Salvelinus fontinalis in many southern Appalachian Mountains streams. We monitored the population recovery of Brook Trout following Rainbow Trout eradication at 10 sites in seven allopatric Rainbow Trout streams located in Great Smoky Mountains National Park, USA. Rainbow Trout were successfully eradicated by electrofishing or Fintrol (also known as antimycin-A), and Brook Trout were reintroduced at low densities (39–156 fish/km) from streams located within the park. Within 2 years after reintroduction, the density and biomass of adult Brook Trout recovered to levels comparable to the prerestoration density and biomass of Rainbow Trout. Spawning in the first autumn after reintroduction was assumed by the presence of young-of-the-year fish in seven out of nine sites surveyed during the following summer. Brook Trout density and biomass 3–5 years after restoration did not significantly differ from those in natural allopatri...

Stream and Riparian Habitat Use by Anurans along a Forested Gradient in Western Georgia, USA

Urban development is known to alter the structure, chemistry, and biota associated with stream systems; however, little is known about the dynamics of anurans that breed in and around streams. We used automated devices to record breeding anurans for one year across a forested gradient in an effort to identify species-specific sensitivities to urbanization. Six of 13 total species found during the study were present in surveyed streams that were representative of a gradient ranging from heavily urbanized to largely forested, and maximum species richness occurred in watersheds with rapid urban development but low values of impervious surfaces such as pavement and roof tops. The best landscape-scale predictor of assemblage metrics such as species richness, total species activity, and species diversity was generally percent forest cover at the watershed scale (or in very large buffers around the sample point). We used Bayesian inference to estimate detection probability and occupancy for 11 species. While detection probability varied across sampling occasions, there was no evidence that occupancy was a function of forest loss for any species. Urban streams and riparian areas are often severely altered when compared to similar habitats in forested areas. Anuran richness and diversity from urban areas was not altered to the same extent as caudates, which have been sampled from these same streams in previous studies. Increased vagility of anurans, coupled with different breeding strategies, may help to explain this discrepancy.