Christopher J. Chizinski

Mixed-source reintroductions lead to outbreeding depression in second-generation descendents of a native North American fish.

Reintroductions are commonly employed to preserve intraspecific biodiversity in fragmented landscapes. However, reintroduced populations are frequently smaller and more geographically isolated than native populations. Mixing genetically, divergent sources are often proposed to attenuate potentially low genetic diversity in reintroduced populations that may result from small effective population sizes. However, a possible negative tradeoff for mixing sources is outbreeding depression in hybrid offspring. We examined the consequences of mixed‐source reintroductions on several fitness surrogates at nine slimy sculpin (Cottus cognatus) reintroduction sites in south‐east Minnesota. We inferred the relative fitness of each crosstype in the reintroduced populations by comparing their growth rate, length, weight, body condition and persistence in reintroduced populations. Pure strain descendents from a single source population persisted in a greater proportion than expected in the reintroduced populations, whereas all other crosstypes occurred in a lesser proportion. Length, weight and growth rate were lower for second‐generation intra‐population hybrid descendents than for pure strain and first‐generation hybrids. In the predominant pure strain, young‐of the‐year size was significantly greater than any other crosstype. Our results suggested that differences in fitness surrogates among crosstypes were consistent with disrupted co‐adapted gene complexes associated with beneficial adaptations in these reintroduced populations. Future reintroductions may be improved by evaluating the potential for local adaptation in source populations or by avoiding the use of mixed sources by default when information on local adaptations or other genetic characteristics is lacking.

Variation in native micro-predator abundance explains recruitment of a mobile invasive fish, the common carp, in a naturally unstable environment

Why certain species of fish become invasive is poorly understood and a key obstacle to restoring many of the world’s ecosystems. In this study we tested whether variation in biotic resistance exerted by native predators might explain the reproductive success of the common carp, a large and fecund invasive species that typically spawns in outlying and unstable shallow habitat. An initial three-year study of the relative abundance of young-of-year (YOY) carp in interconnected lakes in the Upper Mississippi River Basin discovered that YOY carp are only found in shallow waters that experience winter hypoxia (winterkill) and have low densities of the native egg-predators that otherwise dominate these locales. A follow-up experiment tested if native fish predation on carp eggs could explain this distribution. It found that while carp eggs survived in winterkill lakes, they only survived in non-winterkill lakes when protected by a mesh that excluded fish. Large numbers of carp eggs were found in the stomachs of native fish inhabiting lakes that did not winterkill. We conclude that common carp, and likely many other highly mobile and fecund invasive fish, have evolved life histories to avoid egg predators and can become invasive when they are absent.

The Influence of a Rapid Drawdown and Prolonged Dewatering on Fishing Effort, Catch, and Harvest in a Nebraska Reservoir

Red Willow Reservoir, Nebraska, experienced a rapid reduction (drawdown) in surface area, from 580 to 240 ha (59%), and prolonged maintenance at a low-water level from November 2009 until June 2012 (although the reservoir did not begin to refill until 2013 due to drought conditions). We documented changes in fishing effort, catch, and harvest at Red Willow Reservoir from two years pre-drawdown to three years post-drawdown. Fishing effort shifted from a majority of boat anglers to roughly equal representation by boat and bank anglers because of the low-water level. Effort also shifted from anglers seeking specific species to anglers simultaneously seeking all species (anything) during first-year post-drawdown, and then reverted back to anglers seeking specific species during the second and third years post-drawdown. Angler catch of fishes declined substantially post-drawdown. This case study highlights the complicated dynamics that exist among angler participation, reservoir quality, and sport-fish community. Understanding these dynamics is important in the management of fisheries, particularly when fishery managers must manage a reservoir subjected to an extreme change.

Variability in Age Estimation Results in Ambiguity and False Understanding of Population Persistence

AbstractMortality, growth, and recruitment are the primary dynamic rate functions that regulate fish populations. Age data obtained from calcified structures can provide direct and indirect information needed for calculations of these metrics; therefore, knowledge of the fish population age structure is often coveted information. Unfortunately, potential sources of error exist in the form of subjectivity in interpretation of growth increments, inconsistent deposition of growth increments, and lack of validation in age-estimation processes. However, many sources of error are either not known or simply ignored, particularly for long-lived fishes. Therefore, we included a level of uncertainty in our age estimates of a periodic life history strategist, the Shovelnose Sturgeon Scaphirhynchus platorynchus, by incorporating variability in reader assignment of age. We used a bootstrapping procedure to generate a matrix of new age distributions and demonstrated how calculations of mortality varied as a result of r...

Different Migratory Strategies of Invasive Common Carp and Native Northern Pike in the American Midwest Suggest an Opportunity for Selective Management Strategies

AbstractInundated floodplains, backwaters, and wetlands are important spawning habitats for many freshwater fish. In Midwestern North America and areas of northern Europe, the Common Carp Cyprinus carpio and Northern Pike Esox lucius inhabit many of the same watersheds and perform migrations to interconnected wetlands during the spring to spawn. In this study, the movement patterns of adult Northern Pike and Common Carp from lakes into adjoining wetlands were assessed in Minnesota to determine how and when these species moved, and if Common Carp might be blocked or trapped without disrupting the Northern Pike. Adult Northern Pike migrated over an extended several-week period starting early each March, when temperatures were greater than 4oC and when the fish were fully sexually mature (i.e., females were ovulated and running with eggs, and males were spermiating). In contrast, adult Common Carp migrated over relatively short time periods that lasted just a few days between April and June, and whose specif...

Measuring park visitation vulnerability to climate extremes in U.S. Rockies National Parks tourism

ABSTRACT Changes in temperature and precipitation can affect tourist experiences. This study examines how summer park visitation has changed in response to temperature and precipitation extremes. The study goals were two-fold. The first is to introduce a framework and the second is to test it in a pilot region with four mountainous National Parks. The framework is designed to compare the vulnerability of seasonal park visitation to shifts in a combined indicator of temperature and precipitation. It uniquely considers needed measurements, and the data required to conduct an analysis. The second goal is to test it in four destinations in the U.S. Northern Rockies, including Glacier, Yellowstone, Grand Teton, and Rocky Mountain National Parks. The preliminary test reveals outlier cases of visitation under wet and dry extremes. The analysis connects time series climate and visitation data for the peak summer season from 1991–2012. Outlier analysis illustrates more change in extremely dry conditions, with four out of the six dry-year outliers resulting in a visitation decline. Whether this decline in park tourism is attributable to climate features, economic factors, or conscious management decisions, these drops have significant economic impacts: estimates of changes in visitor spending during dry years are between roughly 9 and 90 million USD. These differences may be connected to the popular activities in each park, and the extent they are dependent on weather conditions. This framework can be used to test the relationship between climate and tourism visitation in other regions, in various seasons and time frames. The work may inform the tourist sector in adjusting and planning for a range of conditions. We discuss opportunities and conclude with additional needs for understanding the mechanisms behind risk in mountain park tourism under climate extremes.

Reservoir Area of Influence and Implications for Fisheries Management

AbstractUnderstanding the spatial area that a reservoir draws anglers from, defined as the reservoirs area of influence, and the potential overlap of that area of influence between reservoirs is important for fishery managers. Our objective was to define the area of influence for reservoirs of the Salt Valley regional fishery in southeastern Nebraska using kernel density estimation. We used angler survey data obtained from in-person interviews at 17 reservoirs during 2009–2012. The area of influence, defined by the 95% kernel density, for reservoirs within the Salt Valley regional fishery varied, indicating that anglers use reservoirs differently across the regional fishery. Areas of influence reveal angler preferences in a regional context, indicating preferred reservoirs with a greater area of influence. Further, differences in areas of influences across time and among reservoirs can be used as an assessment following management changes on an individual reservoir or within a regional fishery. Kernel de...

Masked expression of life-history traits in a highly variable environment

Differing life-history strategies may act as a constraint on reproductive expression that ultimately limits the ability of individual species to respond to changes in the magnitude or frequency of environmental variation, and potentially underlies the variation often inherent in phenotypic and evolved responses to anthropogenic change. Alternatively, if there are environmental cues that predict reproductive potential, differential expression of life-history strategies may represent differences in the adaptive capacity to optimize current reproductive value given variation in environmental conditions. We compared several aspects of walleye Sander vitreus spawning ecology at two reservoirs that differ in environmental variability (i.e., annual water-level fluctuation) to identify the capacity of phenotypic expression and the corresponding association with age. Despite significant differences in female body and liver masses between reservoirs that differ in environmental variability, we found no difference in reproductive investment measured by egg size and fecundity. Walleye in a highly variable environment appear to exhibit reproductive traits more typical of a short-lived life-history strategy, which may be resultant from the interaction of environmental and anthropogenic pressures. This finding emphasizes the need to identify the degree to which life-history expression represents physiological constraints versus ecological optimization, particularly as anthropogenic change continues to alter environmental conditions.

Variation in angler distribution and catch rates of stocked rainbow trout in a small reservoir

We investigated the spatial and temporal relationship of catch rates and angler party location for two days following a publicly announced put-and-take stocking of rainbow trout (Oncorhynchus mykiss). Catch rates declined with time since stocking and distance from stocking. We hypothesized that opportunity for high catch rates would cause anglers to fish near the stocking location and disperse with time, however distance between angler parties and stocking was highly variable at any given time. Spatially explicit differences in catch rates can affect fishing quality. Further research could investigate the variation between angler distribution and fish distribution within a waterbody.

Synchrony — An emergent property of recreational fisheries

1Nebraska Cooperative Fish and Wildlife Research Unit, School of Natural Resources, University of Nebraska, Lincoln, Nebraska 2School of Natural Resources, University of Nebraska, Lincoln, Nebraska 3Nebraska Game and Parks Commission, Lincoln, Nebraska 4U.S. Geological Survey—Nebraska Cooperative Fish and Wildlife Research Unit, and School of Natural Resources, University of Nebraska, Lincoln, Nebraska