Plenary Speaker: Fish Passage in an Era of Broken Rivers: New Approaches a Reason for Hope?

Abstract: Fish passage in an era of broken rivers: new approaches a reason for hope? In an era of decline of large-bodied, migratory fishes, river connectivity has been shown to be increasingly important for the conservation of native biodiversity. From North America to Asia, Europe to South America, issues with river connectivity influence – for better or worse - the life cycle, and population status, of migratory fishes. In the Mekong River Basin, the world’s largest fishes, including the Critically Endangered Mekong giant catfish Pangasianodon gigas and giant pangasius Pangasius sanitwongsei, face extinction because of mainstream dams on the lower Mekong. In China, populations of the Chinese sturgeon, Acipenser sinensis, and Chinese paddlefish, Psephurus gladius, have declined significantly since the construction of the Gezhouba and Three Gorges Dams. In North America, connectivity is increasingly recognized as a determining factor in the health of sturgeon and salmon populations in the Columbia and Fraser Rivers; similarly, American paddlefish, Polyodon spathula, and pallid sturgeon, Scaphirhynchus albus, are impacted by dams and habitat fragmentation. The situation is similar in New Zealand, where a combination of factors – from dams to habitat degradation to overfishing – is resulting in unprecedented population decline of species like the longfin eel Anguilla dieffenbachii. Identifying novel fish passage solutions that maximize environmental benefit and minimize cost is the only way to provide for needs of a rapidly growing human population while also protecting imperiled aquatic fauna. Fish passage broadly interpreted includes a wide range of solutions to increase connectivity and restore fish migrations and populations. New methods of study, technologies, decisions about dam placement and dam removal all offer potential for restoring threatened fish. On a policy level, the Convention on Migratory Species provides a framework for management of transboundary migratory freshwater fish – a neglected biota in urgent need of study and protection

Spatial and Long-Term Temporal Changes in Water Quality Dynamics of the Tonle Sap Ecosystem

Tonle Sap lake-river floodplain ecosystem (TSE) is one of the world’s most productive freshwater systems. Changes in hydrology, climate, population density, and land use influence water quality in this system. We investigated long term water quality dynamics (22 years) in space and time and identified potential changes in nutrient limitation based on nutrient ratios of inorganic nitrogen and phosphorus. Water quality was assessed at five sites highlighting the dynamics in wet and dry seasons. Predictors of water quality included watershed land use, climate, population, and water level. Most water quality parameters varied across TSE, except pH and nitrate that remained constant at all sites. In the last decade, there is a change in the chemical nutrient ratio suggesting that nitrogen may be the primary limiting nutrient across the system. Water quality was strongly affected by development in the watershed i.e., flooded forest loss, climatic variation, population growth, and change in water level. Seasonal variations of water quality constituents were driven by precipitation and hydrology, notably the Mekong’s distinct seasonal flood pulse

Fish community composition and habitat use in the Eg-Uur River System,

Abstract Mongolian rivers and their fi sh communities have suffered severe impacts from anthropogenic activities. However, the remoteness of some systems has allowed for the conservation of unique fi sh faunas, including robust populations of Hucho taimen. Conservation of H. taimen requires understanding the composition and ecology of other fi shes in the community. Using multiple sampling techniques, direct observation, and existing literature, we assessed the composition, relative abundance, and ecological attributes of fi shes in the Eg-Uur watershed (Selenge basin). We collected 6 of 12 species known in the watershed. Phoxinus cf. phoxinus and Lota lota were the most and least abundant species, respectively. We failed to detect H. taimen, indicating low abundance or unknown habitat requirements for juveniles. We compared the effectiveness of different sampling techniques (with electrofi shing producing the highest species richness), constructed length-weight relationships for four species, and identifi ed ecological attributes (i.e., trophic guild, preferred habitat) for resident fi shes

Fish community composition and habitat use in the Eg-Uur River System,

Abstract Mongolian rivers and their fi sh communities have suffered severe impacts from anthropogenic activities. However, the remoteness of some systems has allowed for the conservation of unique fi sh faunas, including robust populations of Hucho taimen. Conservation of H. taimen requires understanding the composition and ecology of other fi shes in the community. Using multiple sampling techniques, direct observation, and existing literature, we assessed the composition, relative abundance, and ecological attributes of fi shes in the Eg-Uur watershed (Selenge basin). We collected 6 of 12 species known in the watershed. Phoxinus cf. phoxinus and Lota lota were the most and least abundant species, respectively. We failed to detect H. taimen, indicating low abundance or unknown habitat requirements for juveniles. We compared the effectiveness of different sampling techniques (with electrofi shing producing the highest species richness), constructed length-weight relationships for four species, and identifi ed ecological attributes (i.e., trophic guild, preferred habitat) for resident fi shes

The Living Planet Index (LPI) for migratory freshwater fish:Technical Report

Migratory freshwater fish (i.e. fish that use freshwater systems, either partly or exclusively) occur around the world and travel between critical habitats to complete their life cycle. They are disproportionately threatened compared to other fish groups but global trends in abun-dance, regional differences and drivers of patterns have not yet been comprehensively described. Using abundance information from the Living Planet Database, we found widespread declines between 1970 and 2016 in tropical and temperate areas and across all regions, all migration categories and all populations. Globally, migratory freshwater fish have declined by an average of 76%. Average declines have been more pronounced in Europe (-93%) and Latin America & Caribbean (-84%), and least in North America (-28%). The percentage of species represented was highest in the two temperate regions of Europe and North America (almost 50%). For the continents of Africa, Asia, Oceania, and South America, data was highly deficient, and we advise against making conclusions on the status of migratory freshwater SUMMARYfish in these areas. Potamodromous fish, have declined more than fish migrating between fresh and salt water on average (-83% vs -73%). Populations that are known to be affected by threats anywhere along their migration routes show an average decline of 94% while those not threatened at the population level have increased on av-erage. Habitat degradation, alteration, and loss accounted for around a half of threats to migratory fish, while over-exploitation accounted for around one-third. Protected, regulated and exploited populations decreased less than unmanaged ones, with the most often recorded actions being related to fisheries regulations, including fishing restrictions, no-take zones, fisheries closures, bycatch reductions and stocking (these were most com-mon in North America and Europe). Recorded reasons for observed increases tended to be mostly unknown or un-described, especially in tropical regions. This information is needed to assemble a more complete picture to assess how declines in migratory freshwater fishes could be reduced or reversed. Our findings confirm that migratory freshwater fish may be more threatened throughout their range than previously documented

A global agenda for advancing freshwater biodiversity research

Global freshwater biodiversity is declining dramatically, and meeting the challenges of this crisis requires bold goals and the mobilisation of substantial resources. While the reasons are varied, investments in both research and conservation of freshwater biodiversity lag far behind those in the terrestrial and marine realms. Inspired by a global consultation, we identify 15 pressing priority needs, grouped into five research areas, in an effort to support informed stewardship of freshwater biodiversity. The proposed agenda aims to advance freshwater biodiversity research globally as a critical step in improving coordinated actions towards its sustainable management and conservation

A global agenda for advancing freshwater biodiversity research

Global freshwater biodiversity is declining dramatically, and meeting the challenges of this crisis requires bold goals and the mobilisation of substantial resources. While the reasons are varied, investments in both research and conservation of freshwater biodiversity lag far behind those in the terrestrial and marine realms. Inspired by a global consultation, we identify 15 pressing priority needs, grouped into five research areas, in an effort to support informed stewardship of freshwater biodiversity. The proposed agenda aims to advance freshwater biodiversity research globally as a critical step in improving coordinated actions towards its sustainable management and conservation.Peer reviewe