Monitoring the Milwaukee Harbor breakwater : an Engineering With Nature® (EWN®) demonstration project

The US Army Corps of Engineers (USACE) maintains breakwaters in Milwaukee Harbor. USACE’s Engineering With Nature® (EWN®) breakwater demonstration project created rocky aquatic habitat with cobbles (10–20 cm) covering boulders (6–8 metric tons) along a 152 m section. A prolific population of Hemimysis anomala, an introduced Pontocaspian mysid and important food source for local pelagic fishes, was significantly (p < .05) more abundant on cobbles versus boulders. Food-habits data of alewife (Alosa pseudoharengus) and rainbow smelt (Osmerus mordax) provided evidence that H. anomala were a common prey item. Night surveys and gill netting confirmed O. mordax preferred foraging on the cobbles (p < .05) and consumed more H. anomala than at the reference site (p < .05). H. anomala comprised a significant portion of the diets of young-of-the-year (YOY) yellow perch (Perca flavescens), YOY largemouth bass (Micropterus salmoides), and juvenile rock bass (Ambloplites rupestris) caught on the breakwater. The natural features’ construction on the breakwater increased the available habitat for this benthopelagic macroinvertebrate and created a novel ecosystem benefiting forage fish and a nursery habitat benefiting nearshore game fish juveniles. These data will encourage the application of EWN concepts during structural repairs at other built navigation infrastructure.

Spread of seafish invasions in the northen sea of okhotsk as a factor of human infection

The results of the analysis are presented in the comparative aspect of the long-term - 1989 - 2021. - dynamics of infection of commercial fish with parasites common to humans and animals, and determination of their role in the spread of invasions among the population of the region. During this period, in marine fish – herring Clupea pallasii Valenciennes, 1847 (Clupeiformes: Clupeidae), saffron cod Eleginus gracilis, flounder Acanthopsetta nadeshnyi and smelt Osmerus mordax dentex Steindachner, 1870 – 5 types of helminthes potentially dangerous for humans have been identified, which can cause such dangerous diseases like anisacidosis, diphyllobothriasis and corynosomiasis. All fish species show high rates of invasion. Herring is infested by 97.4%, saffron cod - 55.2%, flounder - 67.5%, smelt - 58.4%. Ichthyopathological examinations isolated Anisakis simplex, Pseudoterranova decipiens, Pyramicocephalus phocarum, Diphyllobothrium sobolevi, Corynosoma strumosum. Individuals with combined invasion were registered: saffron cod Anisakis simplex, Pyramicocephalus phocarum, Corynosoma strumosum; smelt Anisakis simplex (Pseudoterranova decipiens), Diphyllobothrium sobolevi, Corynosoma strumosum. The most dangerous for humans are flounder and smelt due to the localization of helminths in the muscles.

Hypoxia’s impact on pelagic fish populations in Lake Erie: a tale of two planktivores

Whether bottom hypoxia has long-lasting consequences for pelagic fish populations remains speculative for most ecosystems. We explored hypoxia’s influence on two pelagic zooplanktivores in Lake Erie that have different thermal preferences: cold-water rainbow smelt (Osmerus mordax) and warm-water emerald shiners (Notropis atherinoides). To assess acute effects, we combined predictive bioenergetics-based modeling with field collections made across the hypoxic season in central Lake Erie during 2005 and 2007. To assess chronic effects, we related fishery-independent and fishery-dependent catches with hypoxia severity and top predator (walleye, Sander vitreus) abundance during 1986–2014. As our modeling predicted, hypoxia altered rainbow smelt movement and distributions, leading to avoidance of cold, hypoxic bottom waters. In response, diets shifted from benthic to pelagic organisms, and consumption and energetic condition declined. These changes were lacking in emerald shiners. Our long-term analyses showed rainbow smelt abundance and hypoxia to be negatively related and suggested that hypoxia avoidance increases susceptibility to commercial fishing and walleye predation. Collectively, our findings indicate that hypoxia can negatively affect pelagic fish populations over the long term, especially those requiring cold water.

Life-history variability and conservation status of landlocked Atlantic salmon: an overview

Nonanadromous Atlantic salmon (Salmo salar) exhibit a combination of variation in life history, habitat, and species co-existence matched by few vertebrates. Distributed in eastern North America and northern Europe, habitat ranges from hundreds of metres of river to Europe’s largest lakes. As juveniles, those with access to a lake usually migrate to feed and grow prior to reproduction. Prey such as smelt (Osmerus mordax, Osmerus eperlanus) and vendace (Coregonus albula) facilitate large body size (50–85 cm at maturity) and persistence in high-diversity (>20 fish species) environments; small-bodied salmon (10–30 cm at maturity), relying on insects as prey, coexist with few (fewer than five) other fishes. At maturity, weight varies more than 400-fold (17 to 7200 g) among populations, fecundity more than 150-fold (33 to 5600), and longevity almost fivefold (3 to 14 years). Landlocked salmon are managed to support sustainable fishing, achieve conservation and restoration targets, and mitigate threats; successes are evident but multiple challenges persist. Extraordinary variability in life history coupled with extensive breadth of habitat and species co-existence render landlocked Atlantic salmon singularly impressive from a biodiversity perspective.

Advances in Understanding Landscape Influences on Freshwater Habitats and Biological Assemblages

<i>Abstract.</i>—Lakes, like islands, have been model systems for testing important concepts in landscape ecology. Lake assemblage and community composition, generally, and the occurrence of invaders, specifically, are controlled by a range of factors across scales. Here, I use the example of Rainbow Smelt <i>Osmerus mordax </i>invasions in inland lakes to illustrate common problems in both predictive and explanatory models of invasive species distributions across landscapes. Using variables related to dispersal and regional- and lake-scale environment, I fitted a series of boosted regression tree models to examine the factors that explain Rainbow Smelt invasion success. These models illustrate the potential effects of extrapolation and nonequilibrium conditions, the role of human activities, and the difficulty of understanding the importance of biotic interactions in the spread of invasives. Understanding the factors controlling invasions should inform management and conservation of inland lake ecosystems. For this to be effective, a mechanistic framework is needed to untie correlations in potential driving factors. Emerging data sets with fine spatial grain and broad spatial extent will support the transition from correlative models to mechanistic understanding of aquatic invasions.

Long-term assessment of ichthyoplankton in a large North American river system reveals changes in fish community dynamics

Larval fishes are sensitive to abiotic conditions and provide a direct measure of spawning success. The St. Clair – Detroit River System, a Laurentian Great Lakes connecting channel with a history of environmental degradation, has undergone improvements in habitat and water quality since the 1970s. We compared 2006–2015 ichthyoplankton community data with those collected prior to remediation efforts (1977–1978) to identify patterns in spatial and temporal variability. Both assemblages exhibited a predictable phenology, with taxa from the subfamily Coregoninae dominant in early spring followed by families Osmeridae, Percidae, and Moronidae (May–June) and Cyprinidae and Clupeidae (June–August). While higher densities of larval fish were found in the Detroit River, greater taxa richness and Shannon diversity were observed in the St. Clair River. System wide, 14 new taxa were observed in the 2000s study period. In addition, relative densities of two nonnative species, alewife (Alosa pseudoharengus) and rainbow smelt (Osmerus mordax), declined since the 1970s. Increased larval fish richness and decreased densities of nonnative taxa in the 2000s are consistent with improvements to environmental conditions.