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Abstract The current state of marine mammal populations reflects increasing anthropogenic impacts on the global Ocean. Adopting a holistic approach towards marine mammal health, incorporating healthy individuals and healthy populations, these taxa present indicators of the health of the overall Ocean system. Their present deterioration at the animal, population and ecosystem level has implications for human health and the global system. In the Anthropocene, multiple planetary boundaries have already been exceeded, and quiet tipping points in the Ocean may present further uncertainties. Long and short-term monitoring of marine mammal health in the holistic sense is urgently required to assist in evaluating and reversing the impact on Ocean Health and aid in climate change mitigation.

The vertical slots of fish passes represent bottlenecks that must be passed by every fish migrating upstream. The hydraulics in fish passes are well investigated but less is known about the small scale behaviour of fish while passing the vertical slot. Understanding the species-specific swimming behaviour during the passage could allow for creation of future fish passes with hydraulics adapted to the swimming requirements of desired target species. We recorded the swimming trajectories of three fish species as point coordinates per video frame using cameras. Then, two common machine learning algorithms were used to identify species characteristic swimming patterns in the trajectories. A Random Forest model trained on 21 trajectory features revealed that water discharge, the spatial trajectory position, and the trajectory length were most distinct trajectory features among species. The model identified the species with a mean F1 score of 0.86 ± 0.08 SD for round goby [Neogobius melanostomus (Pallas, 1814)], 0.81 ± 0.12 SD for gudgeon (Gobio L.), and 0.58 ± 0.20 SD for bullhead (Cottus gobio L.). A Convolutional Neural Network achieved a mean F1 score of 0.89 ± 0.03 SD for round goby, 0.76 ± 0.05 SD for gudgeon, and 0.67 ± 0.02 SD for bullhead if exclusively trained on the point coordinates of the swimming trajectories. These results demonstrate that fish species exhibit distinct swimming patterns when passing through a vertical slot, and how these patterns can be used for species identification using machine learning algorithms. Because round goby achieved the highest F1 scores, we conclude that round goby showed the most characteristic swimming trajectories among the species tested. Future fish passage research should account for the individual swimming patterns of the fish in these bottleneck flow fields and on adapting the flow to the individual swimming patterns of the target fish. Flow conditions being supportive for swimming patterns of the desired fish could have the potential to improve the river connectivity and thereby support the aquatic biodiversity.

Abstract Anthropogenic structures can form novel ecosystem niches. Invasive species are often particularly successful in occupying these habitats and utilize them as beachheads for further spread. The invasive round goby (Neogobius melanostomus, Pallas 1814), an inherently bottom‐dwelling fish, uses vertical harbor walls as habitat, enabling them to reach boats (i.e., potential translocation vectors). To evaluate the relevance of vertical habitat use for population dynamics and translocation, we exemplary investigated a population of round gobies in a harbor ecosystem. Specifically, we investigated differences in trophic niche characteristics, individual trophic specialization, phenotypic traits, and breeding frequency in wall versus bottom‐dwelling round gobies. Habitat‐characteristic dietary signatures indicated habitat partitioning during the breeding season. Trophic niches overlapped but were clearly distinguishable between the habitats: Walls were inhabited by 1.4 times more trophic generalists than specialists, while the bottom was inhabited by 2.1 times more trophic specialists. Breeding frequency was 24 times higher on the walls than on the bottom. After the reproductive season, we found a higher similarity in trophic ecology of gobies inhabiting the two habitats, and differences in abundance, size, and condition. These results are in line with winter migrations to deeper habitats, which are common in round gobies in lentic and marine ecosystems. Our results suggest a high potential for microgeographic adaptation to either horizontal or vertical habitat use in invasive round gobies. We demonstrated that male gobies using the walls during the breeding season are larger and heavier, suggesting that wall climbing may select for more competitive individuals. Additionally, the overall abundance of round gobies likely increases with the additional use of vertical habitat space, which may lead to higher propagule pressure. The ability to exploit anthropogenic habitats, and a higher translocation probability of competitive individuals, can contribute to the invasion success of round gobies in anthropogenically influenced aquatic systems.

Abstract Background It has been proposed that non-genetic inheritance could promote species fitness. Non-genetic inheritance could allow offspring to benefit from the experience of their parents, and could advocate pre-adaptation to prevailing and potentially selective conditions. Indeed, adaptive parental effects have been modeled and observed, but the molecular mechanisms behind them are far from understood. Results In the present study, we investigated whether maternal RNA can carry information about environmental conditions experienced by the mother in a wild vertebrate. Maternal RNA directs the development of the early embryo in many non-mammalian vertebrates and invertebrates. However, it is not known whether vertebrate maternal RNA integrates information about the parental environment. We sequenced the maternal RNA contribution from a model that we expected to rely on parental effects: the invasive benthic fish species Neogobius melanostomus (Round Goby). We found that maternal RNA expression levels correlated with the water temperature experienced by the mother before oviposition, and identified temperature-responsive gene groups such as core nucleosome components or the microtubule cytoskeleton. Conclusions Our findings suggest that the maternal RNA contribution may incorporate environmental information. Maternal RNA should therefore be considered a potentially relevant pathway for non-genetic inheritance. Also, the ability of a species to integrate environmental information in the maternal RNA contribution could potentially contribute to species fitness and may also play a role in extraordinary adaptive success stories of invasive species such as the round goby.

The mycotoxin zearalenone (ZEN) is frequently contaminating animal feeds including feed used in aquaculture. In the present study, the effects of dietary exposure to ZEN on carp (Cyprinus carpio L.) were investigated. ZEN at three different concentrations (low dose: 332 µg kg−1, medium dose: 621 µg kg−1 and high dose: 797 µg kg−1 final feed, respectively) was administered to juvenile carp for four weeks. Additional groups received the mycotoxin for the same time period but were fed with the uncontaminated diet for two more weeks to examine the reversibility of the ZEN effects. No effects on growth were observed during the feeding trial, but effects on haematological parameters occurred. In addition, an influence on white blood cell counts was noted whereby granulocytes and monocytes were affected in fish treated with the medium and high dose ZEN diet. In muscle samples, marginal ZEN and α-zearalenol (α-ZEL) concentrations were detected. Furthermore, the genotoxic potential of ZEN was confirmed by analysing formation of micronuclei in erythrocytes. In contrast to previous reports on other fish species, estrogenic effects measured as vitellogenin concentrations in serum samples were not increased by dietary exposure to ZEN. This is probably due to the fact that ZEN is rapidly metabolized in carp.

Deoxynivalenol (DON) frequently contaminates animal feed, including fish feed used in aquaculture. This study intends to further investigate the effects of DON on carp (Cyprinus carpio L.) at concentrations representative for commercial fish feeds. Experimental feeding with 352, 619 or 953 μg DON kg−1 feed resulted in unaltered growth performance of fish during six weeks of experimentation, but increased lipid peroxidation was observed in liver, head kidney and spleen after feeding of fish with the highest DON concentration. These effects of DON were mostly reversible by two weeks of feeding the uncontaminated control diet. Histopathological scoring revealed increased liver damage in DON-treated fish, which persisted even after the recovery phase. At the highest DON concentration, significantly more fat, and consequently, increased energy content, was found in whole fish body homogenates. This suggests that DON affects nutrient metabolism in carp. Changes of lactate dehydrogenase (LDH) activity in kidneys and muscle and high lactate levels in serum indicate an effect of DON on anaerobic metabolism. Serum albumin was reduced by feeding the medium and a high dosage of DON, probably due to the ribotoxic action of DON. Thus, the present study provides evidence of the effects of DON on liver function and metabolism.

The control of mycotoxins is a global challenge not only in human consumption but also in nutrition of farm animals including aquatic species. Fusarium toxins, such as deoxynivalenol (DON) and zearalenone (ZEN), are common contaminants of animal feed but no study reported the occurrence of both mycotoxins in fish feed so far. Here, we report for the first time the occurrence of DON and ZEN in samples of commercial fish feed designed for nutrition of cyprinids collected from central Europe. A maximal DON concentration of 825 μg kg−1 feed was found in one feed whereas average values of 289 μg kg−1 feed were noted. ZEN was the more prevalent mycotoxin but the concentrations were lower showing an average level of 67.9 μg kg−1 feed.

Ponto-Caspian gobies are a flock of five invasive fish species that have colonized freshwaters and brackish waters in Europe and North America. One of them, the round goby Neogobius melanostomus, figures among the 100 worst invaders in Europe. Current methods to detect the presence of Ponto-Caspian gobies involve catching or sighting the fish. These approaches are labor intense and not very sensitive. Consequently, populations are usually detected only when they have reached high densities and when management or containment efforts are futile. To improve monitoring, we developed an assay based on the detection of DNA traces (environmental DNA, or eDNA) of Ponto-Caspian gobies in river water. The assay specifically detects invasive goby DNA and does not react to any native fish species. We apply the assay to environmental samples and demonstrate that parameters such as sampling depth, sampling location, extraction protocol, PCR protocol and PCR inhibition greatly impact detection. We further successfully outline the invasion front of Ponto-Caspian gobies in a large river, the High Rhine in Switzerland, and thus demonstrate the applicability of the assay to lotic environments. The eDNA assay requires less time, equipment, manpower, skills, and financial resources than the conventional monitoring methods such as electrofishing, angling or diving. Samples can be taken by untrained individuals, and the assay can be performed by any molecular biologist on a conventional PCR machine. Therefore, this assay enables environment managers to map invaded areas independently of fishermen's' reports and fish community monitorings.

Empirical measurements on fine sediment dynamics and fine sediment infiltration and accumulation have been conducted worldwide, but it is difficult to compare the results because the applied methods differ widely. We compared common methods to capture temporal and spatial dynamics of suspended sediment (SS), fine sediment infiltration and accumulation and tested them for their suitability in a small, canalized river of the Swiss Plateau. Measurement suitability was assessed by data comparison, relation to hydrological data and in the context of previously published data. SS concentration and load were assessed by optical backscatter (OBS) sensors and SS samplers. The former exhibit a better temporal resolution, but were associated with calibration problems. Due to the relatively low cost and easy mounting of SS samplers, they can provide a higher spatial distribution in the river's cross section. The latter resulted in a better correlation between sediment infiltration and SS load assessed by SS samplers than SS concentrations measured with OBS sensors. Sediment infiltration baskets and bedload traps capture the temporal and spatial distribution of fine sediment infiltration. Data obtained by both methods were positively correlated with water level and SS. In contrast, accumulation baskets do not assess the temporal behaviour of fine sediment, but the net accumulation over a certain time period. Less fine sediment accumulated in upwelling zones and within areas of higher mean water level due to scouring of fine sediments. Even though SS and sediment infiltration assessed with the bedload traps increased from up- to downstream, less fine sediment accumulated downstream. This is probably also attributable to more scouring downstream.

The Strait of Gibraltar is an important habitat for seven regularly occurring cetacean species. These waters are heavily used for fishing and therefore experience extraordinary levels of shipping traffic. Photography provides a valuable and non-invasive tool to monitor the health of cetacean populations, where external injuries may indicate specific anthropogenic impacts, such as vessel strikes or fishery interactions. We manually screened 27,866 photos taken during whale-watching operations between 2016-20 for human-induced injuries. Injuries of potential anthropogenic origin were detected in 228 cases. The severity of these injuries ranged from superficial linear marks to severe traumas that may affect survival and fitness. Severe injuries included a gunshot wound, vessel-related traumata and abrasions, signs of previous severe entanglements and deep lacerations which could stem from recreational fishery activities or propellor cuts and occasionally served as an entry point for dermal infections. In 2007, Spanish legislation introduced regulations on how to approach cetaceans by boat, but recreational fishery vessels have been commonly observed to disregard this law. We therefore urge stricter control and enforcement of existing laws and collaboration between the Spanish and Moroccan authorities to mitigate the human impact on cetaceans in this region. [ABSTRACT FROM AUTHOR]

Cetacean populations in the Strait of Gibraltar are heavily impacted by human activities. Photographs are a valuable tool to monitor the external health of cetaceans. We visually screened 27,866 pictures taken during whale watching operations in the years 2016-2020 for abnormal conditions, such as emaciation, dermal diseases and epizoic infestations. Prevalence levels could not be calculated as data were obtained opportunistically. Dermal diseases were detected in 566 sightings and occurred in all species. Bottlenose dolphins were most strongly affected (n = 192). Hypopigmented skin lesions were most common in all species (n = 291). Tattoo skin disease‐like lesions affected 16 animals (T. truncatus: n = 12; G. melas: n = 3; D. delphis: n = 1). Other observed conditions include expansive annular lesions in three juvenile pilot whales. Furthermore, we report the presence of open wounds in 28 animals (G. melas: n = 23; T. truncatus: n = 2; P. macrocephalus: n = 3). In three pilot whales, these wounds did not heal over a period of several years. Epizoic and ectoparasitic infestations include the observation of Xenobalanus spp. and Pennella balaenopterae. Multiple fin whales were sighted with very high numbers of Pennella balaenopterae, ranging up to 84 parasites per host. Emaciation was mainly detected in bottlenose dolphins (n = 36) and seemed to affect these animals more severely during specific years, potentially indicating fluctuations in prey availability. [ABSTRACT FROM AUTHOR]

Water level fluctuations in lakes lead to shoreline displacement. The seasonality of flooding or beaching of the littoral area affects nutrient cycling, redox gradients in sediments, and life cycles of aquatic organisms. Despite the ecological importance of water level fluctuations, we still lack a method that assesses water levels in the context of hydropower operations. Water levels in reservoirs are influenced by the operator of a hydropower plant, who discharges water through the turbines or stores water in the reservoir, in a fashion that maximizes profit. This rationale governs the seasonal operation scheme and hence determines the water levels within the boundaries of the reservoir's water balance. For progress towards a sustainable development of hydropower, the benefits of this form of electricity generation have to be weighed against the possible detrimental effects of the anthropogenic water level fluctuations. We developed a hydro-economic model that combines an economic optimization function with hydrological estimators of the water balance of a reservoir. Applying this model allowed us to accurately predict water level fluctuations in a reservoir. The hydro-economic model also allowed for scenario calculation of how water levels change with climate change scenarios and with a change in operating scheme of the reservoir (increase in turbine capacity). Further model development will enable the consideration of a variety of additional parameters, such as water withdrawal for irrigation, drinking water supply, or altered energy policies. This advances our ability to sustainably manage water resources that must meet both economic and environmental demands.

Worldwide increases in fluvial fine sediment are a threat to aquatic animal health. Fluvial fine sediment is always a mixture of particles whose mineralogical composition differs depending on the sediment source and catchment area geology. Nonetheless, whether particle impact in aquatic organisms differs between mineral species remains to be investigated. This study applied an in vitro approach to evaluate cytotoxicity and uptake of four common fluvial mineral particles (quartz, feldspar, mica, and kaolin; concentrations: 10, 50, 250 mg L(-1)) in the rainbow trout epithelial gill cell line RTgill-W1. Cells were exposed for 24, 48, 72, and 96 h. Cytotoxicity assays for cell membrane integrity (propidium iodide assay), oxidative stress (H2DCF-DA assay), and metabolic activity (MTT assay) were applied. These assays were complemented with cell counts and transmission electron microscopy. Regardless of mineral species, particles ≤ 2 µm in diameter were taken up by the cells, suggesting that particles of all mineral species came into contact and interacted with the cells. Not all particles, however, caused strong cytotoxicity: Among all assays the tectosilicates quartz and feldspar caused sporadic maximum changes of 0.8-1.2-fold compared to controls. In contrast, cytotoxicity of the clay particles was distinctly stronger and even differed between the two particle types: mica induced concentration-dependent increases in free radicals, with consistent 1.6-1.8-fold-changes at the 250 mg L(-1) concentration, and a dilated endoplasmic reticulum. Kaolin caused concentration-dependent increases in cell membrane damage, with consistent 1.3-1.6-fold increases at the 250 mg L(-1) concentration. All effects occurred in the presence or absence of 10% fetal bovine serum. Cell numbers per se were marginally affected. Results indicate that (i.) natural mineral particles can be cytotoxic to gill epithelial cells, (ii.) their cytotoxic potential differs between mineral species, with clay particles being more cytotoxic, and (iii.) some clays might induce effects comparable to engineered nanoparticles.

Estrogenic exposure has been reported to occur in Swiss rivers, and there is concern that reduced reproductive health, caused by disturbances of the endocrine system, may contribute to the observed decline in brown trout catch. Consequently, we aimed to determine if disturbances of the endocrine system do occur in wild brown trout (Salmo trutta) in Switzerland and, in the affirmative case, if these might affect trout population status. Our first task was to characterize the estrogenicity of Swiss midland rivers that receive effluents from sewage treatment plants (STP). Next, we performed a set of laboratory and field exposure experiments aimed at elucidating how estrogens affect sexual development and reproductive parameters as estrogen-sensitive targets in the life cycle of brown trout. Subsequently, we assessed the demographic status of brown trout populations in the field which were exposed to the cumulative impact of estrogen-active compounds and other stressors. Finally, we integrated the data into a life-cycle model to predict potential population-level consequences of the (xeno)estrogenic exposure. The estrogenicity of 18 Swiss midland rivers was characterized bioanalytically by applying the YES bioassay to water samples and by measuring plasma vitellogenin (VTG) levels in resident brown trout. Generally, estrogenic contamination of the rivers appears to occur only locally and at comparatively low levels (0.2–2 ng/l 17?-estradiol equivalents). In laboratory experiments, potential disruptive effects of estrogens on gonadal differentiation and reproduction of brown trout were investigated. The estrogen-sensitive window of brown trout gonad differentiation was found to differ from other salmonid species. Feminisation of the developing gonads occurred only after exposure to rather high estrogen concentrations. Analysis of VTG mRNA levels indicated that the yolk may accumulate environmental estrogens and act as a long-term reservoir. The experiments to study the effects of prolonged estrogen exposure on reproduction of mature brown trout showed that, while VTG was induced at low concentrations (20 ng/l estrone (E1), 2 ng/l 17?-estradiol (E2) and 400 ng/l 4-nonylphenol (NP)), effects on reproductive parameters such as fertility became evident only at the higher dose (100 ng/l estrone, 10 ng/l 17?-estradiol and 4000 ng/l 4-nonylphenol). For the field study, the river Lützelmurg (Canton Thurgau) was selected as our study site. This river is impacted by the estrogen-active effluents of one sewage treatment plant (STP). Estrogenic levels in the river were found to be highly variable over time, but showed a distinct difference between sites upstream and downstream from the STP effluent – a difference which was also reflected by the VTG levels of caged and resident brown trout. From the brown trout demographic data, it is evident that factors other than estrogen exposure, including habitat quality, strongly influence population structure. The results from the modelling supported this finding and showed that the trout population in the Lützelmurg is likely to be more sensitive to changes of survival rates in the first winter and beyond than to changes in early life stage survival or reproductive parameters. From the overall results of our project, we conclude that a significant influence of estrogenic contamination on brown trout population densities in the majority of Swiss rivers appears not to be likely.