The suitability of rehabilitated floodplains along the lower River Rhine for rheophilic cyprinids was assessed by investigating the spatial distribution of 0-group fish among, and within, three newly created secondary channels, an oxbow lake reconnected at its downstream end and several existing groyne fields. Fish were sampled during April through September 1997-1999 with seine nets and trawls and, for each sample, the habitat (physical environment) was characterized (flow, depth, substrate and inundated terrestrial vegetation). The new water bodies provide more suitable habitats for 0-group fish than the groyne fields. Their beneficial value differs, however, between reproductive guilds and depends on the morphological and hydrological conditions. Total fish density increased along a gradient of decreasing water flow whereas the proportion of rheophilic species (Barbus barbus, Gobio gobio, Leuciscus idus and Aspius aspius) decreased. Flow velocity and water depth were the most important factors determining habitat utilization. Rheophilic fish were spatially separated from eurytopic fish (e.g. Abramis brama, Rutilus rutilus and Stizostedion lucioperca). During flood events, inundated terrestrial vegetation was an important habitat for the larvae of all species. To enhance the riverine fish community, floodplain water bodies should have complex shorelines, and a high variability of flow velocities. Their slopes should be moderate to maximize the probability of terrestrial vegetation getting inundated during spring and summer. Future management of similar floodplains should focus on more diverse and accessible aquatic habitats to increase overall fish species diversity, since different types of water body clearly have complementary values.

Here we report the occurrence of the two non-native brown macroalgal species Sargassum horneri (Turner) C. Agardh and Undaria pinnatifida (Harvey) Suringar in San Diego County and describe expansions in their ranges and new invasions on the California and Baja California coasts. Both species have exhibited characteristics of successful invaders: establishing in new areas, spreading locally, and persisting through multiple generations in areas that have been invaded. These species now occur primarily in harbors, but have also invaded open coast sites, suggesting that they can invade areas with relatively high wave action and with well-established native benthic communities. The rapid and uncontrolled spread of these species to date has serious implications for their expansion along the west coast of North America. The ecological and economic consequences of these invasions require further research.

In the Netherlands, Burbot Lota lota have severely declined due to aquatic system modifications and agricultural intensification. The aim of this study was to evaluate the species' distribution and population trends and to interpret its decline for conservation and management-planning. Historic and present distributions were examined by GIS analysis, while the decline was quantified using binary logistic regression of presence-absence data. Records suggest that at the beginning of the twentieth century the overall Burbot population was relatively stable but reached a turning point from a positive to a negative population phase around 1950. Today, only two areas with spawning populations remain. Recently, increasing numbers of Burbot have been recorded in one of these areas, viz. the lakes in the confluence area of the rivers Vechte and IJssel. This increase could be attributed to annual stockings in German reaches of the River Vechte since 2001, with stock material originating from the rivers Elbe and Weser. Because of the low numbers in which Burbot populations were present and the risks of introduction of non-local stock, Burbot requires imperative tools and action plans for recovery and conservation in the Netherlands.

Two monitoring programmes in estuarine and freshwater systems in the Netherlands both show a recent increase in anadromous North Sea houting Coregonus oxyrhynchus after it disappeared there in the 1940s. Most houting were immature and caught during the feeding season indicating that at present the riverine and estuarine waters in the Netherlands mainly function as a feeding habitat.

The Water Framework Directive (WFD) recognizes fish as a biological quality element to determine the ecological health and quality of waterbodies. Therefore fish monitoring is carried out using conventional methods like electrofishing and seine fishing following standardized protocols. This data is then used in metrics that calculate ecological quality ratios (EQR) for waterbodies. eDNA-metabarcoding could prove an alternative to this conventional WFD-monitoring by offering high sensitivity, possibly lower costs and less invasive sampling. A large project was set up in the Netherlands together with STOWA and the waterboards to explore the possibilities to use eDNA-metabarcoding as an alternative way to carry out the WFD-monitoring for fish. In 2015 in a total of 55 WFD transects (250 meter) were sampled using eDNA-metabarcoding in parallel to the conventional WFD-monitoring. On average 60% mores species were detected with eDNA-metabarcoding. In 2016 a total of 9 whole waterbodies (small rivers/ lakes / canals) were samples in parallel. A sample strategy that mixed water collected from 3 long transects was compared to a strategy that sampled the 3 transects individually. The results showed that the strategy with mixed water samples resulted in nearly the same results at far lower costs. Furthermore a first comparison was made between the relative abundance in eDNA sequences and the relative abundance in biomass and numbers caught. Building on this project between 2018 and 2020 a total of 73 waterbodies were sampled with eDNA-metabarcoding in parallel to conventional WFD-monitoring. Those included streams, rivers, canals, lakes and brackish waterbodies. The final goal is to assess if eDNA-metabarcoding fish can provide similar EQR-scores compared to the conventional WFD-monitoring. This can be done by either renovating the current metrics used or to build new ones based on eDNA data. This presentation will discuss the advantages and disadvantages of both options and gives some insight in the steps still needed for implementation of eDNA-metabarcoding methods in standardized WFD-monitoring.