Charles Gowan

Monitoring vertebrate populations

Preface. Basic Concepts. Sampling Designs and Related Topics. Enumeration Methods. Community Surveys. Detection of a Trend in Population Estimates. Guidelines for Planning Surveys. Fish. Amphibians and Reptiles. Birds. Mammals. Glossary of Terms. Glossary of Notation. Sampling Estimators. Common and Scientific Names of Cited Vertebrates. Subject Index.

Long-Term Demographic Responses of Trout Populations to Habitat Manipulation in Six Colorado Streams

Fish communities in high-elevation, Rocky Mountain streams consist of only one or a few trout species, so these streams are ideal for quantifying how physical habitat manipulation influences population biology. Managers often alter habitat structure in hopes of increasing the number or size of fish in a population, but this practice has not been rigorously evaluated, and the mechanisms involved are not well understood. We measured fish abundance and habitat conditions in each half of 500-m study reaches in six streams for 2 yr before and 6 yr after installing 10 low log weirs in a randomly designated half (treatment section). Mean depth, pool volume, total cover, and the proportion of fine sub- strate particles in the stream bed increased in treatment sections within 1 to 2 years, whereas habitat in adjacent controls remained unchanged. Abundance and biomass of adult fish, but not juveniles, increased in treatments relative to controls in all streams. Recaptures of trout that were individually tagged and others that were batch marked revealed that immigration was primarily responsible for increased adult abundance and biomass, whereas no biolog- ically significant differences occurred for recruitment, survival, or growth. Few (<5%) immigrants to treatment sections came from adjacent controls, indicating that the increased adult abundance did not result simply from fish redistributing within the study reach, but was caused instead by immigration from beyond the reach boundaries. Immigration to control sections was frequent as well, leading us to conclude that fish movement was common, contrary to most literature on stream trout. We also detected a high degree of concordance in fish abundance fluctuations within and among streams, suggesting that regional factors influenced fish populations over large spatial scales. Our research shows that log weirs increase trout abundance, but only if other management activities assure that fish dispersal remains unimpeded within the drainage.

Why do foraging stream salmonids move during summer

We hypothesize that foraging stream salmonids move during summer because (1) they monitor habitat conditions at a reach scale (100s of m), and (2) dominant fish move when conditions in their present foraging location become sub-optimal relative to conditions at other locations in the reach. To test these ideas, we quantified temporal variation in foraging habitat quality between late spring and early fall in a reach of a small Rocky Mountain brook charr, Salvelinus fontinalis, stream, predicted optimal-foraging fish distributions within the reach, and experimentally manipulated access to foraging sites and measured fish responses. Our results show that high-quality foraging sites were located at certain places in the reach during one period, but at different places during others, consistent with the hypothesis that fish movement is required if dominant fish are to occupy high-quality foraging sites throughout summer. The optimal foraging model was able to predict foraging locations within study pools, but not the exact location of individual fish within the pools or the reach. However, empirical evidence suggests that fish were distributed in order to maximize energy intake at the reach scale. Finally, dominant fish excluded from their preferred foraging location either left the pools (three of six cases), or began to occupy focal points of the next largest fish which, in turn, exited the pool (two of six cases). If habitat selection was occurring only within habitat units, then large fish, when excluded from their preferred locations, would select the next best locations within the pool. Taken together, these results suggest that charr use summertime movements to both monitor habitat conditions at a large spatial scale, and to gain access to optimal foraging locations even as conditions change temporally.

Designing mark-recapture studies to reduce effects of distance weighting on movement distance distributions of stream fishes

Abstract Mark–recapture studies generate biased, or distance-weighted, movement data because short distances are sampled more frequently than long distances. Using models and field data, we determined how study design affects distance weighting and the movement distributions of stream fishes. We first modeled distance weighting as a function of recapture section length in an unbranching stream. The addition of an unsampled tributary to one of these models substantially increased distance weighting by decreasing the percentage of upstream distances that were sampled. Similarly, the presence of multiple tributaries in the field study resulted in severe bias. However, increasing recapture section length strongly affected distance weighting in both the model and the field study, producing a zone where the number of fish moving could be estimated with little bias. Subsampled data from the field study indicated that longer median (three of three species) and maximum distances (two of three species) can be detec...

Comparison of Visible Implant Tags and Floy Anchor Tags on Hatchery Rainbow Trout

Abstract Survival, effect on growth rate, tag readability and loss, and severity of injury were compared for 140–240-mm hatchery rainbow trout Oncorhynchus mykiss implanted with visible implant (VI) tags and Floy FD-68B fine-fabric anchor tags. Survival on six sampling dates over 120 d was always higher for fish tagged with VI tags than for fish tagged with Floy tags (e.g., 79 versus 68% at 120 d). Significantly more fish lost VI tags than Floy tags during the first 20 d of the experiment, but the difference was not significant by the end of the experiment (18 versus 11% offish remaining at 120 d). Most VI tags were lost either during the first 10 d or between 30 and 60 d, whereas Floy tags were lost gradually after 20 d. Overall, more rainbow trout with VI tags than with Floy tags were present at the end of the experiment (64 versus 59%), because the higher loss rate for VI tags was outweighed by the higher mortality of Floy-tagged fish. Rainbow trout with VI tags grew significantly faster than those wit...

Spinal Injury Rates in Three Wild Trout Populations in Colorado after Eight Years of Backpack Electrofishing

Abstract We examined long-term effects of annual intensive backpack electrofishing on rates of spinal injury and population abundance of three salmonid and one catostomid species in three small northern Colorado streams and compared rates of externally evident injuries to actual injuries determined by X ray. After 6–8 years of annual three-pass removal electrofishing, injury rates for brook trout Salvelinus fontinalis in treatment sections of two streams averaged 10.4% and 12.3%, but were 0% in previously unshocked controls. In a third stream containing all species in sympatry, longnose suckers Catostomus catostomus sustained the highest average injury rates (9.6%), followed by brown trout Salmo trutta (6.9%), rainbow trout Oncorhynchus mykiss (4.0%), and brook trout (3.5%). These rates were based on external evaluation and probably greatly underestimated actual rates of healed injuries because 44% of X-rayed fish with no externally evident spinal injury showed previous injury. Despite the high incidence ...

Distribution, abundance and conservation of the highly endemic Coral Pink Sand Dunes tiger beetle, Cicindela albissima Rumpp

The Coral Pink Sand Dunes tiger beetle, Cicindela albissima Rumpp, occurs only within a small area of the Coral Pink Sand Dunes in southwestern Utah. Even within this dune field, most of the population is limited to a small core area about 2 × 0.5 km2 in size (adjacent areas sometimes contain beetles, but these appear to be demographic sinks). The core habitat is a transition zone of transverse dunes located between more dynamic dunes to the south (crests of these move upwards of 3 m/y) and more stabilised ones to the north. A candidate species since 1994, the beetle was recently proposed for listing as a threatened species by the US Fish and Wildlife Service. A conservation agreement in 1997 established two off-highway-vehicle-free conservation areas, one of these supporting most of the population within the core habitat (A) and the other a potential site for establishing a second viable population (B). Annual population estimates of adults from 1999 to 2013 fluctuated significantly from a low of 558 to high of 2944. Despite a progressive increase in recent years, our studies including two population viability analyses confirmed the species remains at risk of extinction because of its localised distribution, fluctuating abundance apparently limited by reduced rainfall and the failure to establish a second population in Conservation Area B. The fate of the species is tied to the five inter-dunal swale rows that support most of the adults and larvae. Consequently, there are few options for conservation of the species. Proposed listing of C. albissima as a threatened species was recently withdrawn by the US Fish and Wildlife Service in lieu of a revised conservation agreement which modestly expands protection in Conservation Area A.

Chapter 5 – Detection of a Trend in Population Estimates

This chapter discusses some types of trends that might occur in population size. To be effective in detecting a trend, it is important to have some ideas about what types of trends might occur in a time series of population sizes. It describes the sources of variation that make the detection of a trend difficult because of the resulting stochasticity of the observations and also examines some statistical approaches to detecting a trend. This chapter examines some statistical approaches to detecting a trend. In addition to the most common approach that is based on regression, , it explores randomization of the data with regression and a non-parametric procedure based on ranks that are robust to violations of assumptions that are necessary for regression methods to be valid. The main objective of most biological monitoring surveys is to detect changes or a trend in the population size, survival, or recruitment of certain species. The purpose may be to link the observed decline in habitat with population size, such as reduction in the amount and patch size of sagebrush habitat with a decline in sage grouse population size. Conversely, monitoring may be performed to document that changes in grazing practices result in an increase in cutthroat trout populations.

Chapter 1 – Basic Concepts

This chapter discusses basic concepts and terminology associated with monitoring spatial distribution, abundance, and density of species in a given area during some period of time. The occurrence and spatial arrangement of a species within a defined area at a particular time are called its spatial distribution. The most basic distributional information may be obtained from previous records of trapped, harvested, sighted, or other form of documented occurrence of a given species. Validly assessing spatial distribution, abundance, or density requires either a survey or a census. A survey is a partial count of animals or objects within a defined area during some time interval, whereas a census refers to a complete count within a particular area and time period. These two terms are not synonymous, although they often are used incorrectly as such. Spatial distribution, abundance, and density are parameters, that is, they are fixed but unknown quantities within a defined area and time period. Obviously, the number and spatial distribution of animals will change over time and space; therefore, these parameters are “fixed” only over a short time within a defined space.

Effects of off‐highway vehicles on sandy habitat critical to survival of a rare beetle

Recreational activity, including use of off‐highway vehicles, threatens a variety of rare taxa that depend on undisturbed marine beaches, freshwater shorelines, aeolian dunes and other sandy habitats. The endemic Coral Pink Sand Dunes (CPSD) tiger beetle (Cicindela albissima Rumpp) occupies a 300 × 1500 m area within a larger dune field in southwestern Utah. Our objectives were to determine the habitat required by larvae, explain why habitat is so restricted, and to quantify how off‐highway vehicles (OHVs) affected habitat. Macrohabitat characteristics (subsurface moisture, sediment grain size, compaction, vegetation cover) were not different in areas containing high beetle densities compared to those with low. Within the core area containing most beetles, larvae were found primarily in microhabitats with cohesive sand close to the surface. Compaction and moisture provide the cohesive sand required for larvae to maintain burrows during development. Compacted sand, soil moisture and vegetation supporting larval prey were largely absent in heavy OHV‐use areas. Larvae were less abundant within OHV tracks compared to non‐track areas. Apparent survival of larvae experimentally translocated to OHV tracks was lower than that of larvae translocated to non‐OHV areas. Our results show that beetles are restricted to an area where cohesive sand occurs near the surface, interspersed with sufficient vegetation to produce prey. These conditions are localised to an area where dunes migrate at a rate sustaining these conditions. Restricting OHV use from all areas where natural processes create cohesive sand covered with adequate vegetation will minimise extinction probability for the beetle.