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Identification of lake trout spawning sites has focused on cobble substrates associated with bathymetric relief (e.g., ‘contour’ or ‘slope’ along reefs), but this ‘model’ may be narrow in scope. Previous telemetry work conducted near Drummond Island, USA, Lake Huron, identified egg presence in substrates at the base of large boulders (>1 m diameter); however, the extent of this phenomenon was unknown. Telemetry data paired with multi-beam bathymetry identified a 0.63 km2 area used by lake trout characterized by low bathymetric relief and numerous (~269) large boulders (>1 m diameter) with small-diameter substrates at their bases. Diver surveys revealed egg presence at all 40 boulders surveyed, exclusively associated with clean gravel-cobble (0.6–42 cm) substrates in undercut areas beneath overhanging edges of boulders and in narrow spaces between adjacent boulders. Egg presence was not associated with boulder or substrate physical characteristics which highlighted the possible importance of interstitial currents. Successful incubation in these habitats was inferred by capture of free embryos and post-embryos the following spring using traps and an electrofishing ROV although at lower densities than at popular spawning habitats nearby (1–3 km away). Free embryos and post-embryos were also caught where eggs were not observed the previous fall including unexpectedly on top of boulders which suggested that post-hatch stages may move more than previously thought. Extensive use of boulder-associated habitats for spawning, egg incubation, and early growth suggested this undescribed habitat type may provide an unanticipated contribution to total available lake trout spawning habitat and recruitment in the Great Lakes.

Dams across the Great Lakes basin are nearing or beyond their original design life, posing both challenges and opportunities to natural resource managers. Ageing dams can be repaired to preserve function and maintain safety, removed to promote full connectivity or retrofitted with a fish passage structure to increase connectivity without reservoir loss. The success of rock ramp structures is not well documented, especially for cool‐ and warm‐water fishes in the Great Lakes basin. The success of a recently built (2009) rock ramp for increasing upstream fish passage on the Shiawassee River in Michigan, USA, was evaluated. While there was evidence of limited fish passage during the study period (2011–2016), catches of spring migratory fishes, fish eggs and larvae were significantly higher below the rock ramp than above, indicating the dam with rock ramp fish pass continues to limit upstream migration. Overall connectivity appears improved relative to a reference, dammed river, but falls short of full connectivity.

Invasive crayfishes have a strong negative effect on multiple trophic levels, including other crayfishes. However, documentation of the spread of non-native crayfish species and their impact on native crayfishes could be improved, particularly over large spatial scales in stream ecosystems. We collected crayfish and quantified habitat at 461 stream sites throughout Michigan in 2014–2016 and compared our collections to a historical account of crayfish collections published in 1975. Our objectives were to: (1) quantify the change in non-native rusty crayfish (Faxonius rusticus) and native species distributions from 1975 to 2014–2016; (2) quantify how rusty crayfish affect the habitat associations of native species in Michigan streams; and (3) determine the effectiveness of dipnets, our primary sampling method. We found all species in more watersheds compared to 1975, likely due in part to increased sampling. However, we found rusty crayfish in 22 more HUC-8 watersheds than in 1975, a larger increase than all other species. Habitat associations of native species also shift in the presence of rusty crayfish. In instances where native species co-occurred with rusty crayfish, most obligate aquatic native species were found in less-preferred habitat such as sand or macrophytes compared to cobble substrate when the species is in isolation. Our results indicate a broad range expansion by rusty crayfish over the last 40 years, suggesting that surveys of crayfish diversity and habitat occupancy should be more routine to inform management of native crayfish species.

Fish populations that exhibit movement patterns present challenges to fishery management. In the Inland Waterway in Michigan’s northern Lower Peninsula, monitoring Walleye Sander vitreus population dynamics and harvest management is difficult because of seasonal intermixing among interconnected lakes. In addition, the presence of tribal subsistence fishing and recreational angling fisheries that occur during different discrete time periods adds complexity to understanding harvest management performance. We used stochastic simulation to determine the influence of movement and harvest dynamics on the performance of harvest management targets for Walleye in our study system. After accounting for postspawn movement and harvest dynamics, our results indicated that population-specific exploitation rates on average did not exceed the target rates (u = 0.35) that are mandated in the waterway. We did, however, determine that some areas are at risk because they experienced population-specific exploitation r...

The use of nature-like fishways to increase ecosystem connectivity has increased in recent years, but their effectiveness has rarely been evaluated. A rock ramp was constructed in the Shiawassee River in 2009, and post-construction effects (2011–2012) were evaluated on the summer fish assemblage by comparing fish assemblage composition to a nearby free-flowing river and a nearby river with a dam. Patterns of fish species richness, mean catch-per-unit-effort and proportional abundance in reaches upstream and downstream of the rock ramp, dam and comparable sites in the free-flowing river were evaluated. Overall, species richness by site and proportional abundance in the rock-ramp river were more similar to the free-flowing river, while species richness by reach was more similar to the dammed river. These findings suggest that the rock ramp has improved connectivity for the summer fish assemblage, but has not fully restored conditions to the level observed in a free-flowing river.

The Laurentian Great Lakes are a source of nonnative species for smaller inland lakes throughout the region; however, the foraging ecology of predators in smaller systems invaded by nonnative species has not been well studied. We used diet and stable isotope analyses to describe the contributions of native and nonnative forage species to the diets of Walleyes Sander vitreus within an inland lake chain invaded by multiple nonnative species. Our hypothesis was that the Walleyes' diet would be associated with the relative amount of prey available in littoral or offshore–pelagic habitats and would ultimately be linked to the dominant habitat type. We found that Walleyes in the study lakes exhibited flexibility in their dietary inclusion of nonnative prey species. Similar to predators in the Laurentian Great Lakes, Walleyes in smaller inland lakes integrated littoral nonnative species into their diets. However, Walleyes unexpectedly showed limited usage of accessible nonnative pelagic forage. We sugges...

Fish often exhibit complex movement patterns, and quantification of these patterns is critical for understanding many facets of fisheries ecology and management. In this study, we estimated movement and fishing mortality rates for exploited walleye (Sander vitreus) populations in a lake-chain system in northern Michigan. We developed a state-space model to estimate lake-specific movement and fishery parameters and fit models to observed angler tag return data using Bayesian estimation and inference procedures. Informative prior distributions for lake-specific spawning-site fidelity, fishing mortality, and system-wide tag reporting rates were developed using auxiliary data to aid model-fitting. Our results indicated that postspawn movement among lakes was asymmetrical and ranged from approximately 1% to 42% per year, with the largest outmigration occurring from the Black River, which was primarily used by adult fish during the spawning season. Instantaneous fishing mortality rates differed among lakes and ranged from 0.16 to 0.27, with the highest rate coming from one of the smaller and uppermost lakes in the system. The approach developed provides a flexible framework that incorporates seasonal behavioral ecology (i.e., spawning-site fidelity) in estimation of movement for a mobile fish species that will ultimately provide information to aid research and management for spatially structured fish populations.

Bird use of diked and undiked Michigan coastal wetlands (n = 17) was studied on Lake St. Clair and Lake Huron during late July to mid-October, 2005–2007. Relative abundance and diversity were compared via aerial (n = 9) and ground (n= 155) surveys and wetland characteristics were measured. Species richness and similarity indices suggested analogous bird use, but multivariate analyses indicated significant separation in diked and undiked bird assemblages. Wood Duck (Aix sponsa), Great Blue Heron (Ardea herodias), and Wilson's Snipe (Gallinago delicata) were more abundant on diked sites, whereas dabbling ducks combined, Mallard (Anas platyrhynchos), American Black Duck (A. rubripes), gulls (Laridae), Forster's Tern (Sterna forsteri), and Greater Yellowlegs (Tringa melanoleuca) were more abundant on undiked wetlands. Wetland characteristics also differed. Diked sites were primarily cattail (Typha spp.) marshes interspersed with small open-water areas containing aquatic plants. Undiked sites had lar...

Occupancy modeling has been applied to a wide variety of taxa and sampling methods, including bird point counts. A critical assumption of basic occupancy models is that sites are occupied throughout the duration of the study, which is unlikely to be true for typical bird point-count studies. As such, we evaluated the implications of mobile animals on parameter estimates. We simulated the movement and detection of individual birds using an individual-based simulation model. We fit the basic occupancy model to data that represented a range of animal mobility, and determined the bias relative to known parameters used in the simulation. Occupancy depends on the size of the site selected, with smaller sites leading to lower occupancy for a given area and number of individuals present. At low animal density, occupancy scales approximately linearly with the area of sites, but at very high density, occupancy asymptotes at 1.0 across all site sizes. Even small amounts of movement lead to bias in estimates of occupancy and detectability, and the typical size of bird home ranges can lead to highly biased parameters. Moreover, variation in home range size over time or across habitats can lead to varying degrees of bias. Because of the potential for large bias in occupancy estimates, and their sensitivity to behaviors of birds (e.g., home range size), we recommend against applying current occupancy models to bird point-count data. © 2015 The Wildlife Society.

We incorporated explanatory factors including stream habitat type and fish density into individual-based models with dynamic connections among adjacent habitat units to infer dispersal behaviour of juvenile steelhead Oncorhynchus mykiss in a Great Lakes watershed. We used mark–recapture data and an inverse modelling approach to estimate daily probability of steelhead moving out of a habitat unit, P(move), according to four competing models. The models used included (i) a null model where all fish had equal movement probability; (ii) a habitat-dependent model where P(move) depended on the habitat type; (iii) a density-dependent model of P(move); and (iv) a model where P(move) depended on both density and habitat type. The habitat-dependent model provided the most parsimonious fit to the observed data according to Akaike's information criteria (AICc). In the null model, P(move) averaged 0.70, whereas P(move) averaged 0.75 in pools, 0.68 in riffles and 0.73 in runs in the habitat-dependent model.

Spawning habits of fall Chinook salmon in the Hanford Reach of the Columbia River have been documented with annual aerial surveys since 1948. We developed a series of models analysing these data, exploring the influence of environmental factors on the timing of redd construction. These models included a logistic regression and a dynamic modelling approach, with combinations of day of year (as a surrogate for environmental cues such as day length), water temperature and discharge as potential explanatory factors. Results of these analyses indicate that day of year was the strongest predictor of the timing of redd construction, but with significant modifying effects of water temperature and discharge. The dynamic modelling approach provides substantial advantages over a traditional logistic regression, including (1) the ability to treat data collected at non-synchronous time intervals in a consistent fashion and (2) the ability to easily implement complex functions (e.g., threshold responses) relating behaviour to environmental cues. Evaluation of the series as a whole indicates that the median date of redd construction has increased over time, from approximately day 299 in 1950 to day 307 in 2010, as has the temperature on Oct 1 (16.3 °C–18.1 °C). The degree to which these changes are caused by climate change or dam operations is uncertain, however. Copyright © 2013 John Wiley & Sons, Ltd.

Dikes were built on Great Lakes coastal wetlands to enable water level management for wetland wildlife, particularly waterfowl, but few studies have compared bird use of these areas to undiked sites. During 2005–2007, we evaluated 9 diked and 7 undiked coastal wetlands at the St. Clair Flats (Lake St. Clair) and Saginaw Bay (Lake Huron) of Michigan, USA. We compared bird use of diked and undiked wetlands via 605 10-minute point counts at randomly selected locations of emergent marsh and 287 45-minute surveys of randomly selected open water areas. We also measured wetland characteristics in 1,521 randomly selected 0.25-m2 quadrats to compare vegetation and physical conditions between diked and undiked wetlands. Diked wetlands had greater coverage and density of cattail (Typha spp.), coverage of floating-leaved plants, water depth, and organic sediment depth compared to nearby undiked sites, whereas undiked wetlands had greater coverage and density of common reed (Phragmites australis) and bulrush (Schoenoplectus spp.) than diked wetlands. Bird species richness and similarity indices indicated comparable breeding bird communities. We observed greater abundances of Canada goose (Branta canadensis), wood duck (Aix sponsa), American bittern (Botaurus lentiginosus), least bittern (Ixobrychus exilis), and common gallinule (Gallinula galeata) in diked wetlands. These species likely responded to the deep-water cattail marsh and aquatic bed dominating most diked sites. American coot (Fulica americana), Forster's tern (Sterna forsteri), ring-billed gull (Larus delawarensis), and herring gull (Larus argentatus) abundance indices were greater in undiked wetlands, likely related to nesting and foraging habitat provided by the shallower, more open wetlands and connecting lakes. Diked wetlands did not benefit the bird community to the degree expected and conditions in diked areas were indicative of deep marshes with stabilized water levels. Periodic late-summer drawdowns could encourage growth of plants we found associated with greater abundance of some priority bird species and reduction of floating vegetation negatively associated with abundance of several species. However, effective control of invasive common reed is needed to reduce risk of expansion during impoundment dewatering. © 2013 The Wildlife Society.

Monitoring to detect temporal trends in biological and habitat indices is a critical component of fisheries management. Thus, it is important that management objectives are linked to monitoring objectives. This linkage requires a definition of what constitutes a management-relevant “temporal trend.” It is also important to develop expectations for the amount of time required to detect a trend (i.e., statistical power) and for choosing an appropriate statistical model for analysis. We provide an overview of temporal trends commonly encountered in fisheries management, review published studies that evaluated statistical power of long-term trend detection, and illustrate dynamic linear models in a Bayesian context, as an additional analytical approach focused on shorter term change. We show that monitoring programs generally have low statistical power for detecting linear temporal trends and argue that often management should be focused on different definitions of trends, some of which can be better...

Beech scale (Cryptococcus fagisuga Lindinger) (Hemiptera: Eriococcidae) is an invasive forest insect established in the eastern United States and Canada. It predisposes American beech (Fagus grandifolia Ehrhart) trees to infection by Neonectria spp. Fungi causing beech bark disease. White wax secreted by the diminutive scales obscures individual insects, making it difficult to accurately quantify beech scale density. Our goals were to 1) evaluate the relationship between the area of wax and number of beech scales on bark samples, 2) determine whether digital photos of bark could accurately quantify beech scale density, and 3) compare efficiency and utility of a qualitative visual estimate and using the quantitative digital photo technique to assess beech scale populations. We visually estimated beech scale abundance and photographed designated areas on the trunk of 427 trees in 40 sites across Michigan. Photos were analyzed using a binary threshold technique to quantify the area of beech scale wa...

Partitioning total variability into its component temporal and spatial sources is a powerful way to better understand time series and elucidate trends. The data available for such analyses of fish and other populations are usually nonnegative integer counts of the number of organisms, often dominated by many low values with few observations of relatively high abundance. These characteristics are not well approximated by the Gaussian distribution. We present a detailed description of a negative binomial mixed-model framework that can be used to model count data and quantify temporal and spatial variability. We applied these models to data from four fishery-independent surveys of Walleyes Sander vitreus across the Great Lakes basin. Specifically, we fitted models to gill-net catches from Wisconsin waters of Lake Superior; Oneida Lake, New York; Saginaw Bay in Lake Huron, Michigan; and Ohio waters of Lake Erie. These long-term monitoring surveys varied in overall sampling intensity, the total catch ...

Numerous studies have linked land use/land cover (LULC) to aquatic ecosystem responses, however only a few have included the dynamics of changing LULC in their analysis. In this study, we explicitly recognize changing LULC by linking mechanistic groundwater flow and travel time models to a historical time series of LULC, creating a land-use legacy map. We then illustrate the utility of legacy maps to explore relationships between dynamic LULC and lake water chemistry. We tested two main concepts about mechanisms linking LULC and lake water chemistry: groundwater pathways are an important mechanism driving legacy effects; and, LULC over multiple spatial scales is more closely related to lake chemistry than LULC over a single spatial scale. We applied statistical models to twelve water chemistry variables, ranging from nutrients to relatively conservative ions, to better understand the roles of biogeochemical reactivity and solubility on connections between LULC and aquatic ecosystem response. Our study illustrates how different areas can have long groundwater pathways that represent different LULC than what can be seen on the landscape today. These groundwater pathways delay the arrival of nutrients and other water quality constituents, thus creating a legacy of historic land uses that eventually reaches surface water. We find that: 1) several water chemistry variables are best fit by legacy LULC while others have a stronger link to current LULC, and 2) single spatial scales of LULC analysis performed worse for most variables. Our novel combination of temporal and spatial scales was the best overall model fit for most variables, including SRP where this model explained 54% of the variation. We show that it is important to explicitly account for temporal and spatial context when linking LULC to ecosystem response.

Lake sturgeon Acipenser fulvescens once were abundant throughout the Great Lakes basin but have been reduced to less than 1% of historical levels because of habitat degradation and overexploitation. Current management plans suggest stocking as a tool to increase abundance, but stocking also has genetic implications. The objectives of this study were to determine the supplementation level that would maintain long-term population persistence with the smallest genetic impact and to determine whether different supplementation strategies would be required for different starting conditions. An individual-based model that incorporated demographics and genetics was used to explore scenarios that included three initial population sizes, two different supplementation time frames, varying sex ratios, variance in family size, and different percentages of the adult population contributing progeny for supplementation. As expected, all supplementation scenarios reduced extinction risk, increased population size...

Beech scale (Cryptococcus fagisuga Lind.) (Hemiptera; Coccidae), an invasive insect associated with beech bark disease, was discovered in 2000 in a localized area of northwest Lower Michigan and one area in the eastern Upper Peninsula. From 2005 to 2009, we surveyed 809 sites in 73 Michigan counties to determine whether American beech (Fagus grandifolia) trees were present and, if so, whether trees had been colonized by beech scale. Beech trees were present in 696 sites in forest, recreation, and residential areas. By 2009, beech scale had infested beech trees in 8 of 15 counties in the Upper Peninsula, 14 of 68 counties in the Lower Peninsula, one of three islands in Lake Michigan, and all three sampled islands in Lake Huron. Colonization of islands more than 20 km from infestations on the mainland suggest that beech scale was likely introduced by humans or birds. Rates of expansion of 12 discrete beech scale populations varied from 3.3 to 14.3 km per year.

We investigated land use and land cover (LULC) effects, i.e., effects that perpetuate beyond an expected or perceived temporal endpoint, on the chemistry of 35 lakes in the Huron River Watershed, Michigan. Temporal changes in five time steps of LULC were represented by principal components, which were entered hierarchically into a multiple regression to predict water chemistry. We compared model fit using Akaike weights, and model predictive ability using R2, for models representing LULC from a single time up to models that included LULC from all five time steps. The regressions using only the most recent LULC provided the best fit for phosphorus species, but legacy models provided a better fit for all nine other lake water characteristics. Models for all species of nitrogen, calcium, silica, and sulfate showed an intermediate legacy effect and incorporated some historic LULC. Models for conservative ions showed the longest legacy effect, incorporating all five time steps, and had the highest explanatory power of all water chemistry characteristics in our study. Legacy timescales are likely influenced by biological reactivity: highly reactive elements had relatively short legacy timescales and conservative ions had the longest legacy timescales.

Juvenile Chinook salmon Oncorhynchus tshawytscha in nearshore areas of Lake Washington, Washington, were studied to determine their depth distribution, substrate associations, and use of overhanging vegetation (OHV) and shoreline armoring. From March to May, juvenile Chinook salmon progressively shifted to deeper waters as they increased in size. At night, they were associated with small substrates, whereas no association with a particular substrate type was detected during daytime. Juveniles were commonly found in open areas or within 5 m of overwater structures (e.g., piers and docks) but were rarely found directly under such structures. The number of juveniles associated with armored shorelines was lower than expected given the availability of this habitat type. Large numbers of small juveniles often used OHV during the day; however, at night they moved away from cover and occupied open areas with no structure. Larger juveniles did not show a strong affinity to overhead cover. Our results sugg...

The removal of the numerous ageing dams in the United States has become an important stream restoration technique. The extent to which the ecological damage done to streams by dams is reversed upon removal is unknown, especially on decadal time scales. The objectives of this study were to determine if macroinvertebrate assemblages within rivers recover following the removal of a dam and to estimate the time needed for recovery. A space-for-time substitution approach was used on eight rivers in various stages of recovery following a dam removal, ranging from

Population viability analysis is a useful tool to explore the relationship between extinction risk and population size, but often does not include genetic factors. Our objectives were to determine minimum viable population size (MVP) for lake sturgeon ( Acipenser fulvescens ) and examine how inbreeding depression may affect MVP. Our individual-based model incorporated inbreeding depression in two ways: individuals with inbreeding coefficients above a threshold experienced inbreeding depression (threshold), and individuals experienced inbreeding depression at a rate related to their inbreeding coefficient (gradual). Three mechanisms relating inbreeding to fitness were explored (young-of-the-year (YOY) viability, post-YOY viability, number of progeny). The criterion we used to determine MVP was a 5% chance of extinction over 250 years. The estimated MVP without inbreeding effects was 80 individuals. For some scenarios incorporating inbreeding, MVP did not change, but for others, MVP was substantially higher, reaching values up to 1800. Results demonstrate that extinction risk and MVP can be influenced by both demographic stochasticity and inbreeding depression. This research should inform management by determining MVP and how inbreeding, which is expected to accrue in remnant populations because of generations of low abundance, may affect MVP.

Although dam removal has been increasingly used as an option in dam management and as a river restoration tool, there are few studies providing detailed quantitative assessment of the response of fish populations to dam removal. In this study, we document the response of the fish community in the Pine River, Michigan, to the gradual removal of Stronach Dam. Ten sites were sampled annually during the course of the removal (1997–2003) and for 4 years following removal (2004–2007). Before the removal of Stronach Dam, 11 fish species were found only downstream of the dam, 1 species was found only upstream of the dam, and 19 species were captured both above and below the dam. Following removal, 8 species formerly found only below the dam utilized newly available portions of the river above the dam. Most fish species (18 of the 25 evaluated) showed an increase in abundance following removal, strongly supporting the idea that dam removal reduces multiple factors limiting riverine fishes. Brown trout Sal...

Traditional methods for modeling growth of free-ranging fish are often limited by missing recapture observations that prevent individual growth estimates for a given time interval. Our purpose is to present a method for modeling growth rates of juvenile steelhead ( Oncorhynchus mykiss ) that addresses this limitation. Age-1 juvenile steelhead were individually marked with passive integrated transponder (PIT) tags, released in a Michigan, USA, watershed, and sampled monthly (May–November) with barge electrofishing. Individual growth was modeled using daily water temperature and observed fish sizes as inputs and by determining the proportion of maximum consumption parameter (P) for the bioenergetics equation that provided a minimum residual squared error. Results demonstrate that individual steelhead growth can be accurately modeled using water temperature and a temporally specific P shared by all individuals. Advantages of using this method to model fish growth include the ability to bridge data gaps where observations are lacking in individual length histories, rigorously test for differences in P across time periods, and estimate variability of P among fish within a given stream reach.

Uncertainty in population parameters can make managing fisheries difficult, especially for long-lived species such as lake sturgeon Acipenser fulvescens. Models can be used to explore population parameter uncertainty and how uncertainty affects demographic and genetic population outputs through the use of sensitivity analyses. The objective of this study was to determine which lake sturgeon population parameters have the greatest influence on demographic characteristics, including rates of extinction and percentage of populations increasing from their initial size, and population genetic characteristics, including percentage of unique alleles retained and average inbreeding coefficient. An individual-based modeling approach that represented demographic and genetic processes was used to achieve this objective. Individual lake sturgeon were tracked throughout the modeling process with unique identifiers, allowing for the determination of the degree of inbreeding and the number of unique alleles ret...

Although dam removal has been increasingly used as an option in dam management, and as a river restoration tool, few studies provide detailed quantitative assessment of the geomorphological response of rivers to dam removal. In this study, we document the response of the Pine River, Michigan, to the gradual removal of Stronach Dam. In 1996, prior to the initiation of removal, 31 permanent cross-sectional transects were established in the 10-km study area. These transects were surveyed annually during the course of the removal (1996–2003) and for the three years following removal (2004–2006). Dam removal resulted in progressive headcutting of sediments in the former impoundment, extending upstream 3.89 km of the dam. Over the course of the 10 years since dam removal was initiated, a net total of 92 000 m 3 of sediment erosion occurred. The majority of sediments stored in the former reservoir remained in place, with only 12% of the estimated reservoir sediment fill being eroded. Approximately 14% of the net erosion was deposited within the stream channel 1 km downstream of the dam location, with the remainder being transported further downstream or deposited in the floodplain. Sediment fill incision resulted in a narrower and deeper channel upstream, with higher mean water velocity and somewhat coarser substrates. Downstream deposition resulted in a wider and shallower channel, with little change in substrate size composition. Counter-intuitively, water velocity also increased downstream because of the increased slope that developed. Prior to removal, bedforms in the former impoundment were dominated by runs but are showing signs of restoration toward reference conditions. Continuing changes in river geomorphology are evident even three years following removal and are likely to occur for years to come.

To predict effects of modifying the daily bag limit (DBL) on management of Chinook salmon Oncorhynchus tshawytscha and alewives Alosa pseudoharengus, we analyzed harvest and effort data collected from both charter and noncharter anglers during 1997–2005 in Michigan waters of Lake Michigan. Overall, the percent of anglers who caught the DBL of three Chinook salmon was low for charter (10.2%) and noncharter (3.3%) angler groups. However, during 1997–2005, the percent of anglers that caught their DBL increased from 3.3% to 26.5% for charter anglers and from 0.5% to 7.8% for noncharter anglers. To predict harvest under a higher DBL, we fit a discrete negative binomial distribution to the observed daily harvest distribution under the current DBL of three fish. We then used the fitted negative binomial to predict the daily harvest distribution under a DBL of five fish. Using this approach, the potential increase in the number of fish harvested with the higher DBL was minimal, but the additional harvest...

Barriers to prevent spawning migrations of sea lampreys Petromyzon marinus remain an important component of an integrated sea lamprey management program in the Laurentian Great Lakes. Concerns about effects on nontarget fishes have led to the construction of specially designed vertical-slot trap-and-sort fishways to mitigate potential barrier effects. To improve passage at these fishways, we used passive integrated transponder technology to assess the performance of two fishways located on low-head sea lamprey barriers. Fishways on the Big Carp River (which flows into Lake Superior) and Cobourg Brook (which flows into Lake Ontario) were assessed for attraction efficiency, trap attraction and retention, and passage efficiency. Based on the results of these assessments, fishways were modified by increasing the trap volume and altering the funnel characteristics to reduce escapement from the trap and then reassessed. Attraction efficiency for all tagged fish was high (≥80%) at both sites in all year...

Recent field studies have suggested that the dynamics of West Nile virus (WNV) transmission are influenced strongly by a few key super spreader bird species that function both as primary blood hosts of the vector mosquitoes (in particular Culex pipiens) and as reservoir-competent virus hosts. It has been hypothesized that human cases result from a shift in mosquito feeding from these key bird species to humans after abundance of the key birds species decreases. To test this paradigm, we performed a mosquito blood meal analysis integrating host-feeding patterns of Cx. pipiens, the principal vector of WNV in the eastern United States north of the latitude 36 degrees N and other mosquito species with robust measures of host availability, to determine host selection in a WNV-endemic area of suburban Chicago, Illinois, during 2005-2007. Results showed that Cx. pipiens fed predominantly (83%) on birds with a high diversity of species used as hosts (25 species). American robins (Turdus migratorius) were marginally overused and several species were underused on the basis of relative abundance measures, including the common grackle (Quiscalus quiscula), house sparrow (Passer domesticus), and European starling (Sturnus vulgaris). Culex pipiens also fed substantially on mammals (19%; 7 species with humans representing 16%). West Nile virus transmission intensified in July of both years at times when American robins were heavily fed upon, and then decreased when robin abundance decreased, after which other birds species were selected as hosts. There was no shift in feeding from birds to mammals coincident with emergence of human cases. Rather, bird feeding predominated when the onset of the human cases occurred. Measures of host abundance and competence and Cx. pipiens feeding preference were combined to estimate the amplification fractions of the different bird species. Predictions were that approximately 66% of WNV-infectious Cx. pipiens became infected from feeding on just a few species of birds, including American robins (35%), blue jays (17%, Cyanocitta cristata), and house finches (15%, Carpodacus mexicanus).

One of the major challenges facing fishery scientists and managers today is determining how fish populations are influenced by habitat conditions. Many approaches have been explored to address this challenge, all of which involve modeling at one level or another. In this paper, we explore a process-oriented model approach whereby the critical population processes of birth and death rates are explicitly linked to habitat conditions. Application of this approach to five species of Great Lakes fishes including: walleye (Sander vitreus), lake trout (Salvelinus namaycush), smallmouth bass (Micropterus dolomieu), yellow perch (Perca flavescens), and rainbow trout (Onchorynchus mykiss), yielded a number of insights into the modeling process. One of the foremost insights is that processes determining movement and transport of fish are critical components of such models since these processes largely determine the habitats fish occupy. Because of the importance of fish location, an individual-based model appears to be a nearly inescapable modeling requirement. There is, however, a paucity of field-based data directly relating birth, death, and movement rates to habitat conditions experienced by individual fish. There is also a paucity of habitat information at a fine temporal and spatial scale for many important habitat variables. Finally, the general occurrence of strong ontogenetic changes in the response of different life stages to habitat conditions emphasizes the need for a modeling approach that considers all life stages in an integrated fashion.

Yellow perch in Inner Saginaw Bay, Lake Huron, can be difficult to manage because they exhibit wide variation in abundance and individual growth rates over time, therefore continuously changing their role in the ecosystem and their fishery value. Our study objective was to identify the processes (recruitment, survival and fecundity) that most likely determine observed dynamics of Saginaw Bay yellow perch so biologists can better understand how the population changes over time. We developed 23 separate models that each parameterized one or more age-specific process. The best models were identified with Akaike Information Criteria (AIC). AIC was an effective way to prioritize population processes because it selected the most important process models as those that best fit the data with the greatest parsimony. We found a perturbation in 1990 and compensatory survival rate to be the most important processes. The perturbation was a necessary component of all models, suggesting CPUE was strongly influenced by high mortality across all age classes in a single year. Some uncertainty about the role of compensatory survival rate exists as it was difficult to differentiate compensatory survival rate from constant rate models.

We examined statewide time series (1940s–2002) of mean length at ages 2, 3, and 4 for seven fish species sampled from Michigan and Wisconsin inland lakes for temporal trends. We used a components of variance approach to examine how total variation in mean length at age was partitioned into lake-to-lake, coherent temporal, ephemeral temporal, trend, and residual variation. Using these estimated variance components, we simulated the effects of different variance structures on the power to detect trends in mean length at age. Of the 42 data sets examined, only four demonstrated significant regional (statewide) trends: age 4 largemouth bass (Micropterus salmoides) from Wisconsin lakes increased about 0.7 mm·year–1 in mean length at age, and ages 2, 3, and 4 walleye (Sander vitreus) from Wisconsin lakes decreased between 0.5 and 0.9 mm·year–1 in mean length at age. The structure of variation differed substantially among data sets, and these differences strongly affected the power to detect trends. Of particular note was that even modest levels of coherent temporal variation led to substantial decreases in power for detecting trends. To maximize trend detection capabilities, fisheries management agencies should consider variance structures prior to choosing indices for monitoring and realize that trend detection capabilities are species- and region-specific.

We examined diets of fishes from gillnet and egg pump collections conducted on reefs in western Lake Erie during walleye (Sander vitreus) egg incubation periods from 1994–1999 and 2004 to assess incidence of walleye eggs in fish diets. We collected no potential egg predators in samples taken in 1994 but from 1995–1999 and in 2004 we caught 22 different species of fish on reefs in addition to spawning walleye. In most years, white perch (Morone americana) stomachs contained more walleye eggs than any other species on the reefs averaging 253 eggs per stomach. We also found lower numbers of walleye eggs in the stomachs of channel catfish (Ictalurus punctatus; 53 eggs/stomach), johnny darter (Etheostoma nigrum; 2 eggs/stomach), logperch (Percina caprodes; 10 eggs/stomach), quillback (Carpiodes cyprinus; 184 eggs/stomach), rock bass (Ambloplites rupestris; 3 eggs/stomach), round goby (Neogobius melanostomus; 4 eggs/stomach), sculpin (Cottidae; 21 eggs/stomach), silver chub (Macrhybopsis storeriana; 3 eggs/stomach), spottail shiner (Notropis hudsonius; 14 eggs/stomach), trout-perch (Percopsis omiscomaycus; 30 eggs/stomach), white sucker (Catastomus commersonii; 20 eggs/stomach), and yellow perch (Perca flavescens; 181 eggs/stomach). Similar to other studies of predation on walleye eggs, our results indicate that prolonged incubation periods increase the potential for egg loss due to predation.

Interpolation is a type of modeling that can be used to estimate habitat variables throughout a stream based on measurements distributed along the stream's length, but little guidance is available to select the best method of interpolation. Thus, we compared several methods to determine which produced the most accurate interpolation of width, depth, and current velocity, separately. We also determined whether interpolation should be performed using separate datasets for riffles, runs, and pools or unstratified datasets. We measured stream width, maximum depth, and mean current velocity in a northern Michigan watershed. We tested seven methods of interpolation including global average, linear regression, cubic spline, moving average, Lagrange polynomials, Kriging, and Loess smoother. Accuracy of different methods was determined by comparing interpolated habitat conditions to actual values measured at points along the river. This study produced two main recommendations. First, when performing interpolations, data should be stratified by meso-habitat type (riffles, runs, and pools) only when habitat variables are different for each meso-habitat type and stratification does not increase distance between points such that interpolation accuracy is reduced. If habitat variables are similar for all meso-habitat types, knowing the meso-habitat type within which a point falls does not add information that will increase interpolation accuracy. Second, the Loess smoother with a smoothing parameter from 0.2 to 0.4 generally produced the most accurate interpolated values and is the method we recommend for similar situations.

The river continuum concept is an overarching paradigm in stream ecology, but the concept makes no provision for adventitious streams (i.e., low-ordered tributaries to larger rivers). We examined the fish community and habitat of the fifth-order mainstem, two second-order adventitious tributaries to the mainstem, and three second-order headwater streams of the Pine River (Alcona County, Michigan) from May through August 2000. Fish species richness generally increased with increasing stream order and was higher in the adventitious streams than in the headwater streams. The fish species composition of adventitious streams was more similar to the mainstem than to the headwater streams but showed greater month-to-month variability than either the mainstem or headwater streams. Habitat conditions in headwater and adventitious streams were similar except adventitious streams were generally warmer. These results indicate that factors in addition to stream order, such as stream connectivity and temperatu...

Low-head barriers used in the control of parasitic sea lamprey (Petromyzon marinus) in the basin of the Laurentian Great Lakes can alter the richness and composition of nontarget fishes in tributary streams. Identification of taxa sensitive to these barriers is an important step toward mitigating these effects. Upstream–downstream distributions of fishes in 24 pairs of barrier and reference streams from throughout the basin were estimated using electrofishing surveys. For 48 common species from 34 genera and 12 taxonomic families, 8–19 species, 5–16 genera, and 2–7 families showed evidence of being sensitive to barriers, with the variation in number depending on the statistical measure applied. Barriers did not differentially affect species from certain genera or families, nor did they affect species of certain body form. Therefore, taxonomic affiliation and swimming morphology are not useful for predicting sensitivity to barriers for fishes that co-occurred with sea lampreys but were not sampled adequately by our survey. Our estimates of sensitivity will help fisheries managers make sound, defensible decisions regarding the construction, modification (for fish passage), and removal of small, in-stream barriers.

Multilevel data structures are those that have a hierarchical structure, in which response variables are measured at the lowest level of the hierarchy and modeled as a function of predictor variables measured at that level and higher levels of the hierarchy. For example, a multilevel data structure may consist of measurements taken on individual fish (lower level) that are nested within lakes or streams (higher level). Multilevel data structures are a common feature in fisheries research. We provide simulated fisheries data examples, similar in structure to other published studies, to illustrate the application of multilevel models and discuss how hypothesis testing and inferences can be incorrect if multilevel data structures are ignored. Ignoring multilevel data structures has implications for the use of commonly-used ordinary least squares (OLS) approaches to test hypotheses and to make inferences. Multilevel models are an alternate approach that circumvents problems associated with traditiona...

Lake Erie walleye Sander vitreus exhibits significant interannual variability in year-class strength. Recent research revealed the importance of larval growth and survival rates in determining walleye year-class strength in western Lake Erie, indicating that spatial and temporal overlap of larvae with good habitat conditions (e.g., abundant prey, warm waters) promoted walleye growth and survival. To assess the spatial overlap between walleye larvae and habitat parameters (water depth, temperature, water clarity, prey density) in western Lake Erie, we evaluated the spatial distribution of walleye larvae and these habitat parameters with intensive sampling at 30 to 36 sites during spring 1994–1999. We analyzed spatial relationships among pelagic walleye larvae and various habitat attributes using a geographic information system and principal components analysis. Larval walleye density was consistently highest at nearshore sites during all years and showed a high degree of spatial overlap with high ichthyoplankton density, and warm water temperatures. Larval walleye density was negatively associated with water depth and water clarity. Two principal components represented 79.6% of the total variability in site attributes. Principle components analysis supported our spatial analysis by graphically separating sites into distinct groups based on larval walleye density and habitat attributes. These analyses indicated that similar relationships between larval distribution and habitat attributes occur each year, emphasizing the importance of nearshore coastal zones as nursery areas for walleye.

The addition of habitat enhancement structures to aquatic systems is a common practice by fisheries managers hoping to increase production, spawning success, and angler catch rates of important sport fishes. However, quantitative evaluations of these efforts are few and typically do not include the extent to which natural habitat mediates the effects of habitat enhancement structures. We evaluated the effects of two types of habitat enhancement structure on four fish groups in four reservoirs of the Au Sable River, Michigan. Using a combination of sampling methods, we compared several response variables (including relative abundance, nesting, and angler catch rates) between areas with and without structures, as well as before and after structure placement, across a gradient of natural habitat conditions. The effects of half-log habitat enhancement structures were significant in some cases, but no significant effects were detected for AquaCrib structures. Smallmouth bass Micropterus dolomieu respo...