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In niche‐based community assembly theory, it is presumed that communities in habitats with high natural disturbance regimes are less likely to be structured by competitive mechanisms. Laurentian Great Lakes (hereafter Great Lakes) coastal wetlands can experience drastic diel fluctuations in dissolved oxygen levels, severe wave action, ice scour, and near complete freezing during the winter such that conditions are inhospitable for most organisms. The high natural disturbance levels are thought to cause high interannual turnover for aquatic macroinvertebrate communities and support the hypothesis that these communities are less likely to experience less competitive interactions and negative co‐occurrence structure. We hypothesize that non‐random co‐occurrence patterns will be rare in Great Lake coastal wetlands and non‐competitive processes (e.g., through shared or differential microhabitat affinities, pollution tolerances, or biotic homogenization) will be more common than competitively driven negative co‐occurrence patterns. Null model analysis was performed on 134 macroinvertebrate communities sampled from across the Great Lakes basin from 2000 to 2013. To disentangle the effects of alternative structuring mechanisms (i.e., shared/differential habitat affinities, shared/differential pollution tolerance, and biological homogenization/competitive exclusion), communities were parsed based on the year sampled, the vegetation type from which community samples were collected, and lastly species' functional feeding group assignment or taxonomic group. As expected, very few communities were non‐randomly structured; however, all of those that were non‐random exhibited showed more negative co‐occurrences than by chance. Upon further investigation, these communities consisted of species that are known to overwinter in wetlands, and therefore, avoid having to recolonize after each spring thaw. With expected changes in habitat conditions due to climate change, we propose that null model analyses can be used as an early warning system for community change. [ABSTRACT FROM AUTHOR] more...

Aquatic invasive species (AIS) threaten biodiversity and ecosystem services around the world, but their management has been hampered by the lack of quantifiable control targets. The introduction of Silver Carp (Hypophthalmichthys molitrix) throughout the mid‐western United States epitomizes both the impacts of AIS and the need for quantitative control targets. Silver Carp are large‐bodied planktivores that compete with native planktivores, which can cause cascading effects throughout the food web. Our study tested the threshold of abundance beyond which Silver Carp alter fish assemblage structure. We used a community size spectra (CSS) approach to evaluate fish community size structure across temporal and spatial gradients of Silver Carp abundances. We hypothesized that Silver Carp would flatten the size spectra slope because they are large‐bodied and feed at a low trophic position. Electrofishing data were obtained for the La Grange Pool of the Illinois River (1994–2021) and for six pools of the Ohio River (2015–2020). Results supported our hypothesis, showing a 98% probability that the relative biomass of Silver Carp is positively related to the CSS slope (resulting in "flattening"). This pattern was strongest in the Illinois River, where Silver Carp made up >30% of fish assemblage biomass in recent years. The pattern was weakest in the Ohio River (78% probability of a positive relationship) where Silver Carp rarely exceeded 20% of total fish biomass. Subsequent changepoint models indicated that a Silver Carp relative biomass of ~24% represents a threshold below which negative food web impacts should be minimized. Our study demonstrates a clear shift in fish community size structure following invasion by Silver Carp and suggests that pre‐invasion CSS slopes may serve as a restoration target. It also illustrates the benefits of CSS to guide Silver Carp and other AIS management. [ABSTRACT FROM AUTHOR] more...

We developed a management framework based on community size‐spectra (CSS) to establish targets to maximize desirable gamefish. We evaluated the influence of relative abundance of fish functional groups and watershed characteristics on the slope of the CSS or ecological efficiency. Both ecological efficiency and capacity were strongly influenced by relative abundance of fish functional groups and the degree of water level variation. Steeper slopes indicated overfished gamefish populations, whereas flatter slopes indicated systems dominated by undesirable invasive large‐bodied low trophic position fish. We hypothesize that a desirable fishery would have a target range of CSS slopes that provides a deterministic community‐based framework of predictable responses to environmental and food web changes that can be used to evaluate outcomes of management actions and a means to assess annual progress toward desirable conditions. [ABSTRACT FROM AUTHOR] more...

Abstract: Stable isotopes of carbon (C) and nitrogen (N) are commonly used to evaluate trophic relationships and food web structure; however, the decision to extract lipids or not may influence [...] more...

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. [ABSTRACT FROM AUTHOR] more...

Frequency distributions of log-scaled abundance and body size for aquatic biota, including fish, yield size spectra that provide gross estimates of food-web capacity (number of individuals supported by the food web indexed by the midpoint height or y-intercept) and ecological efficiency (rate of decreasing organismal abundance with increasing body size as indicated by the size-spectra slope)., Size spectra are known to respond in predictable fashion to exploitation by commercial (marine) fisheries, but there has been relatively little research of size spectra in freshwater systems and less evaluation of how community size-structure responds to the wider array of ecological perturbations prevalent in freshwater systems., We used a 29-year experimental gillnet data set to test the responses of food-web capacity and ecological efficiency (as indexed by size spectra) of a large river fish community to variations in predatory demand (population expansion of double-crested cormorant, Phalacrocorax auritus) and perturbations affecting primary production (reductions in total phosphorus and warming summer water temperature)., Fish community capacity (size-spectra elevation) and ecological efficiency (size-spectra slope) showed low interannual variation (coefficients of variation 5.6 and 15.4%, respectively). Though highly stable, food-web capacity decreased over time concurrent with declining total phosphorus concentrations and increasing cormorant abundance. Interannual variation in ecological efficiency was not related to the measured perturbations., Relative abundance of the core species that comprised 95% of the community remained relatively consistent over time. The fish community size-structure was also stable and resistant to ecological perturbation. However, we found measurable changes in the composition of secondary species, and these were associated with an increase in cormorant abundance and decrease in total phosphorus. The lack of change in core community species representation and in overall size structure suggest community-level compensatory mechanisms were operating. [ABSTRACT FROM AUTHOR] more...

Habitat utilization of native young-of-the-year (YOY) muskellunge, Esox masquinongy, was quantified by the type and density of vegetation present, water depth, and fish communities associated with their presence and abundance in nursery bays of the Upper St. Lawrence River. We completed 441 seine hauls and captured 400 YOY muskellunge in 11 bays that were sampled each July and August over a 3-year period (2002–2004). We hypothesized a change in habitat utilization related to increasing body size, as YOY muskellunge doubled in total length from July to August. Fine-leafed submerged and emergent macrophytes and prey availability (cyprinids, Notropis sp., banded killifish, Fundulus diaphanous and tessellated darter, Etheostoma olmstedi), were positively related to muskellunge use in July, while in August coverage of broad-leafed submerged macrophytes and increased overall vegetation density were the best habitat descriptor. In both months, muskellunge were associated with moderate (20–60%) vegetation coverage and density, however, captures were in areas of significantly greater vegetation coverage and density than was generally available. A negative relation of muskellunge occurrence with water depth, yellow perch, Perca flavescens, and stonewort, Chara vulgaris, was observed in both months. The negative relationship between muskellunge and depth, plus their strong linkages to nearshore submerged vegetation and forage fish that inhabit the nearshore areas, highlights the importance of protecting the ecological integrity of nearshore habitats. Our findings should assist managers in protecting native stocks, planning restoration and enhancement initiatives, and in regulating riparian and nearshore development. [ABSTRACT FROM AUTHOR] more...