Spatial Patterns of Fish Communities in Lake Michigan Tributaries

Understanding spatial patterns in freshwater fish communities is critical for the successful management of natural resources as well as a vital component for understanding aquatic ecosystems. Spatial patterns of species similarity of freshwater fish assemblages can be affected by dispersal processes and environmental conditions. We hypothesized that as distance increased between study systems, species similarity would decrease. We sampled 15 drowned river mouths (DRMs) connected to Lake Michigan by conducting 10-minute electrofishing transects (n = 5-6 per DRM) parallel to the shoreline in each DRM to characterize littoral fish assemblages. At each transect, we also characterized environmental conditions (e.g., specific conductivity or number of houses/buildings along shoreline). We captured 3,080 individual fish representing 45 species across the 15 DRMs, with catch among DRMs ranging from 115 to 358 individuals per system and species richness ranging from 11 to 26 species per system. The most abundant species in the catch were yellow perch Perca flavescens (13.9%), pumpkinseed Lepomis gibbosus (10.9%), and bluegill Lepomis macrochirus (9.8%). We found a weak positive correlation between species similarity and distance between each pair of DRMs (R2 = 0.03), which did not support our hypothesis that species similarity would decrease with distance, even though we found evidence of spatial autocorrelation of environmental variables. A potential explanation for our findings is related to gear selectivity associated with boat electrofishing. We suggest that sampling fish with additional gear or approaches is necessary to more rigorously test for the spatial pattern of species similarity among DRMs

Reducing effects of dispersal on the bias of 2-sample mark-recapture estimators of stream fish abundance

The 2-sample mark-recapture method with Chapman’s estimator is often used by inland fishery managers to estimate the reach-scale abundance of stream fish. An important assumption of this method is that no dispersal into or out of the study reach occurs between the two samples. Violations of this assumption are probably common in practice, but their effect on bias (systematic error) of abundance estimates is poorly understood, especially in small populations. Estimation methods permitting dispersal exist but, for logistical reasons, often are infeasible for routine assessments in streams. The purpose of this paper is to extend available results regarding effects of dispersal on the bias of Chapman’s estimator as applied to reach-scale studies of stream fish abundance. We examine for the first time the joint effects of dispersal and sampling variation on the bias of this estimator. To reduce the bias effects of dispersal, we propose a modified sampling scheme in which the original study reach is expanded, a central subreach is sampled during the mark session (sample 1), and the entire reach is sampled during the recapture session (sample 2). This modified sampling scheme can substantially reduce bias effects of dispersal without requiring unique marking of individual fish or additional site visits. Analytical and simulation results show that sampling variation tends to create negative bias with respect to study-reach abundance, while dispersal tends to create positive bias; the net effect can be positive, negative, or zero, depending on the true abundance, capture probabilities, and amount and nature of dispersal. In most cases, simply expanding the study reach is an effective way to reduce dispersal-related bias of Chapman’s estimator, but expanding the study reach and employing the modified sampling scheme we propose is a better alternative for accurately estimating abundance with the same level of sampling effort

Scientists’ Warning to Humanity: Rapid degradation of the world\u27s large lakes

Large lakes of the world are habitats for diverse species, including endemic taxa, and are valuable resources that provide humanity with many ecosystem services. They are also sentinels of global and local change, and recent studies in limnology and paleolimnology have demonstrated disturbing evidence of their collective degradation in terms of depletion of resources (water and food), rapid warming and loss of ice, destruction of habitats and ecosystems, loss of species, and accelerating pollution. Large lakes are particularly exposed to anthropogenic and climatic stressors. The Second Warning to Humanity provides a framework to assess the dangers now threatening the world\u27s large lake ecosystems and to evaluate pathways of sustainable development that are more respectful of their ongoing provision of services. Here we review current and emerging threats to the large lakes of the world, including iconic examples of lake management failures and successes, from which we identify priorities and approaches for future conservation efforts. The review underscores the extent of lake resource degradation, which is a result of cumulative perturbation through time by long-term human impacts combined with other emerging stressors. Decades of degradation of large lakes have resulted in major challenges for restoration and management and a legacy of ecological and economic costs for future generations. Large lakes will require more intense conservation efforts in a warmer, increasingly populated world to achieve sustainable, high-quality waters. This Warning to Humanity is also an opportunity to highlight the value of a long-term lake observatory network to monitor and report on environmental changes in large lake ecosystems

Effects of shoreline and watershed development on eastern Lake Michigan drowned river mouth ecology

Lake Michigan’s drowned river mouths (DRM) are hydrologically unique systems with riverine and large-lake influences that create biologically diverse ecosystems. Serving as focal points for human development due to the ecosystem services they provide, DRMs have experienced a history of industrialization, urbanization, and are now moving towards an era of rehabilitation. Today, DRM shorelines have been hardened, their riparian zones have been severely altered, and their watersheds exist on a latitudinal gradient of less to greater anthropogenic stress (agriculture and development). The main goal of this study was to understand the current ecological state of DRMs related to anthropogenic development across multiple spatial scales. I hypothesized (1) that there is a latitudinal gradient in indicators of water quality in DRM lakes of eastern Lake Michigan, which is the result of natural land cover and anthropogenic land use, and (2) that natural shorelines support more fish species less tolerant to environmental degradation than residential and hardened shorelines in DRM lakes. To assess the impacts of development on DRM fish communities, I sampled the littoral fish community of 6 DRMs at shorelines hardened with riprap or seawall, residential shorelines with lawns and homes, and natural shorelines with intact riparian vegetation. Within DRMs, I did not find that shoreline structure was a significant driver of fish assemblages. However, I found a general gradient in DRMs from north to south with more fish species tolerant to degraded conditions in southern DRMs, corresponding to watersheds with more development and agriculture in southern DRMs than those with more forested land cover in northern DRMs. I also sampled 12 DRMs for water quality and found that chlorophyll-a and total phosphorus (TP) concentrations increase in southern DRMs, which corresponds to increased agriculture and development. My research suggests that the impacts of land use at the watershed scale were a strong driver of fish assemblages and water quality among the DRMs in eastern Lake Michigan, which will be useful to managers and researchers concerned with coastal habitats in Lake Michigan

Environmental Variation, Fish Community Composition, and Brown Trout Survival in the Pigeon River, Ottawa County, Michigan

The Pigeon River, a small coolwater stream in western Michigan, has a history of hydrologic, stream habitat, and water quality degradation that led to the loss of its trout population by the late 1980s. After regulatory and watershed management efforts to reduce point- and nonpoint source pollution in the 1990s, the Michigan Department of Natural Resources reinstituted brown trout (Salmo trutta) stocking in 2003. As part of these efforts, we monitored water quality in the Pigeon River each fall between 1996 and 2008, and conducted stream surveys in 2006 and 2007 to evaluate the fish community and outcome of trout stocking. Water quality tended to improve and stabilize through time, although point- and nonpoint source pollution still contributed to water quality problems. Hydrologic instability, caused by wetland drainage, agricultural land use, and irrigation withdrawals from the lower mainstream, created periods of environmental stress. As a result, the fish community of the Pigeon River was dominated by common tolerant warmwater species, typical of agricultural watersheds in southern Michigan. Nonetheless, brown trout surviving from initial stockings in 2003 and 2004 had attained lengths of between 18 and 24 inches by 2007, suggesting the thermal regime, water quality, stream habitat, and forage base of macroinvertebrates and small fish were suitable to maintain a stocked brown trout population. Continued efforts to improve water quality, protect instream habitat, reduce high stormflows, and maintain adequate summer baseflows are needed to fully restore environmental conditions for the native fish community and stocked brown trout in the Pigeon River

Disturbance regime and limits on benefits of refuge use for fishes in a fluctuating hydroscape

Refuge habitats increase survival rate and recovery time of populations experiencing environmental disturbance, but limits on the ability of refuges to buffer communities are poorly understood. We hypothesized that importance of refuges in preventing population declines and alteration in community structure has a non-linear relationship with severity of disturbance. In the Florida Everglades, alligator ponds are used as refuge habitat by fishes during seasonal drying of marsh habitats. Using an 11-year record of hydrological conditions and fish abundance in 10 marshes and 34 alligator ponds from two regions of the Everglades, we sought to characterize patterns of refuge use and temporal dynamics of fish abundance and community structure across changing intensity, duration, and frequency of drought disturbance. Abundance in alligator ponds was positively related to refuge size, distance from alternative refugia (e.g. canals), and abundance in surrounding marsh prior to hydrologic disturbance. Variables negatively related to abundance in alligator ponds included water level in surrounding marsh and abundance of disturbance-tolerant species. Refuge community structure did not differ between regions because the same subset of species in both regions used alligator ponds during droughts. When time between disturbances was short, fish abundance declined in marshes, and in the region with the most spatially extensive pattern of disturbance, community structure was altered in both marshes and alligator ponds because of an increased proportion of species more resistant to disturbance. These changes in community structure were associated with increases in both duration and frequency of hydrologic disturbance. Use of refuge habitat had a modal relationship with severity of disturbance regime. Spatial patterns of response suggest that decline in refuge use was because of decreased effectiveness of refuge habitat in reducing mortality and providing sufficient time for recovery for fish communities experiencing reduced time between disturbance events

Empirical distribution of Chapman’s estimator in simulations with the standard sampling scheme.

<p>Study-reach length is 90 (arbitrary units), study-reach abundance <i>n</i> = 300, sample-1 capture probability <i>q</i> = 0.1, 0.3, 0.5, 0.7, sample-2 capture probability <i>q</i>′ = <i>q</i>, and maximum movement distance <i>δ</i> = 0, 30, 60, 90. Dispersal is balanced, so the average change in abundance between samples is approximately zero. Symbols and lines are defined as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0200733#pone.0200733.g003" target="_blank">Fig 3</a>.</p

Empirical distribution of Chapman’s estimator in simulations with the modified sampling scheme.

<p>Study-reach length is 90 (arbitrary units), study-reach abundance <i>n</i> = 300, sample-2 capture probability <i>q</i>′ = 0.1, 0.3, 0.5, 0.7, sample-1 capture probability <i>q</i> = 1 − (1 − <i>q</i>′)³, and maximum movement distance <i>δ</i> = 0, 30, 60, 90. Sample-1 capture probabilities ensure sampling effort (duration of sampling) is the same as in sample 2. Dispersal is balanced. Other symbols and lines are defined as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0200733#pone.0200733.g003" target="_blank">Fig 3</a>.</p

Comparison of standard and modified sampling schemes applied to a stream reach subject to dispersal.

<p>The study reach is shown in tints of blue, parts of the population domain outside the study reach in yellow. Black dots: fish marked and released in sample 1 (unmarked fish not shown). Top row: Standard scheme applied to a short study reach. Middle row: Standard scheme applied to an expanded study reach. Bottom row: Modified scheme applied to an expanded study reach, with zones U, C, and D indicated (darker blue: samples 1 and 2 are taken; lighter blue: only sample 2 is taken). Left panels show locations of marked fish upon completion of sample 1. Center panels show dispersal of marked fish in progress. Right panels show locations of marked fish when sample 2 is taken.</p