Proximity to Riparian Wetlands Increases Mercury Burden in Fish in the Upper St. Lawrence River

Mercury deposited in the Upper St. Lawrence River watershed by atmospheric deposition accumulated in riparian wetlands and is at risk of remobilization due to water level fluctuations. To examine if riparian wetlands are a source of mercury to fish, 174 yellow perch (Perca flavescens) and 145 round gobies (Neogobius melanostomus) were collected in 2019 from eight wetland and seven non-wetland habitats throughout the Upper St. Lawrence River. Mercury levels were significantly (p < 0.01) higher in fish collected from wetlands than those collected from non-wetland habitats for both yellow perch and round goby. Perch had mercury concentrations of 74.5 ± 35.4 ng/g dry wt in wetlands compared to 59.9 ± 23.0 ng/g dry wt in non-wetlands. Goby had mercury concentrations of 55.4 ± 13.8 ng/g dry wt in wetlands and non-wetland concentrations of 41.0 ± 14.0 ng/g dry wt. Riparian wetlands are areas of elevated mercury methylation and mobilization in the Upper St. Lawrence River and consequences to predators should be considered from the perspective of both wildlife preservation as well as fish consumption advisories for public health concerns.

Sex biased effect of acute heat shock on the antioxidant system of non-native round goby Neogobius melanostomus

Monitoring oxidative stress biomarkers has become a powerful and common tool to estimate organismal condition and response to endogenous and environmental factors. In the present study, we used round goby (Neogobius melanostomus) from non-native European populations, as a model species to test sex differences in oxidative stress biomarkers. Considering sex differences in reproductive investment, we hypothesized that males would display lower resistance to abiotic stress. Fish were exposed to a heat shock (temperature elevated by 10°C) for 1h, 6h, and 12h and catalase activity (CAT), reduced glutathione (GSH), total antioxidant capacity (TAC) and lipid peroxidation (LPO) were measured in liver and muscle tissues. Liver of males was significantly more responsive compared to liver of females in all tested parameters. GSH was found to be the most responsive to heat stress exposure in both sexes. The results supported our hypothesis that male reproductive investment (territoriality, courtship, and brood care) and likelihood of only a single spawning period in their lifetime influenced on higher sensitivity of their antioxidant defence. On the other hand, for females antioxidant defence is considered more important to survive the environmental changes and successfully reproduce in the next season. Our experiments exposed fish to acute thermal stress. Further research should determine the effects of exposure to chronic thermal stress to corroborate our understanding on sex differences in antioxidant defence in the round goby.

Flow, force, behaviour: assessment of a prototype hydraulic barrier for invasive fish

Migration barriers being selective for invasive species could protect pristine upstream areas. We designed and tested a prototype protective barrier in a vertical slot fish pass. Based on the individuals’ swimming responses to the barrier flow field, we assumed this barrier would block the ascension of the invasive round goby, but allow comparable native species (gudgeon and bullhead) to ascend. The barrier was tested in three steps: flow description, quantification of forces experienced by preserved fish in the flow field, and tracking the swimming trajectories of ca. 43 live fish per trial and species. The flow and the forces were homogenous over the barrier, though gudgeon experienced significantly smaller forces than round goby or bullhead. The swimming trajectories were distinct enough to predict the fish species with a random forest machine learning approach (92.16% accuracy for gudgeon and 85.24% for round goby). The trajectories revealed round goby and gudgeon exhibited increased, but varied, swimming speeds and straighter paths at higher water discharge. These results suggest that passage of round goby was prevented at 130 L/s water discharge, whereas gudgeon and bullhead could pass the barrier. Our findings open a new avenue of research on hydraulic constructions for species conservation.

FEEDING OF THE INVASIVE ROUND GOBY Neogobius melanostomus (Perciformes: Gobiidae) IN THE SOUTH-EASTERN BALTIC

The feeding of the Ponto-Caspian invasive round goby Neogobius melanostomus in the coastal zone of the Baltic Sea near the Curonian Spit, in the Vistula Lagoon and in the eastern part of the Gdansk Bay has been studied. The round goby in coastal waters prefers biotopes with various shelters - boulders, large pebbles, etc. In the diet of the round goby, there is a significant proportion of fouling organisms inhabiting these objects. If fouling organisms are absent for some reason, the goby switches to other types of prey: molluscs, free-living crustaceans, insect larvae and other groups of benthic and nektobenthic organisms. There is a connection between the food spectrum and the size of the round goby: large individuals consume larger prey. The round goby implements a food strategy, which consists in the fact that all organisms that are available territorially and in size are used for food. Such food plasticity is one of the reasons for the wide expansion of this species outside the native range.

Status of Freshwater Mussels (Unionidae) in the French Creek Watershed, USA at the Onset of Invasion by Round Goby, Neogobius melanostomus

Freshwater mussels are an imperiled group of organisms that are vital to aquatic ecosystems. Services performed by freshwater mussels, coupled with their use for biomonitoring, make them an invaluable asset. Neogobius melanostomus (Round Goby), a recently introduced invasive species to the French Creek watershed, was once restricted to the watershed of Lake Erie in Pennsylvania. The Round Goby’s propensity to consume Dreissena polymorpha (Zebra Mussel) and Dreissena bugensis (Quagga Mussel) in their native habitat raises concerns about this recent introduction into Pennsylvania’s Allegheny River watershed. Since the discovery of their introduction within the watershed, we have followed the range expansion and dispersal rate of Round Gobies, which makes this study unique. The objectives of this study were to quantify baseline data on the contemporary diversity and abundance of unionid mussels in the upper French Creek watershed, and to explore potential habitat factors that influence or limit the size of the mussel populations. We gathered baseline data on freshwater mussel diversity and abundances across eight sites in the French Creek watershed and examined substrate particle size and host availability as potential limiting factors of the freshwater mussel distribution. Freshwater mussel surveys were conducted during the summer months (July–September) of 2017 using area-constrained surveys. Results showed a significant relationship between mussel diversity and substrate particle size (p < 0.05). From the data collected, we were able to calculate population estimates for the species found across the sample sites. Our results regarding the locations of native mussel populations and characteristics of their habitat provide the needed insight for establishing priority areas for the conservation of freshwater mussels, facilitating planning for protection, mitigation, and adaptation as the invasive Round Goby continues its spread.