Aquatic Conservation-Marine and Freshwater Ecosystems最新文献

The idle crayfish (Austropotamobius bihariensis Pârvulescu, 2019), endemic to Romania's Apuseni Mountains, urgently requires a specific conservation plan. Due to its recent description, conservation efforts have been limited, highlighting the need for immediate and practical recommendations to ensure its protection. Over 13 years, field observations were conducted to evaluate population trends and identify threats following IUCN standards. Additionally, geospatial assessments and predictive modelling were employed to estimate both the optimal habitat and current population size under three distinct scenarios. The primary threats identified include poor forest management, extreme drought, anthropogenic development and riverbed alterations, all contributing to declines in crayfish abundance. The most severe impacts arise when these pressures converge at a single site, compounded by a chronic, low-virulence crayfish plague infection (A-haplogroup). The total population is estimated at 31,150 (± 449.9 SE) individuals, with 1,163,754 m² of suitable habitat, of which only 37.9% lies within 13 protected areas under the most realistic scenario. Poor water quality was found to significantly reduce the modelled population size. In light of these findings, we propose a series of targeted conservation actions tailored for each protected area and highlight the importance of extending measures beyond their current boundaries. Additionally, we recommend implementing the ‘ark sites’ concept in regions with optimal ecological conditions, stable populations and genetic diversity, to reduce pressures and safeguard the species through effective field management.

Environmentally persistent structures of dead individuals represent an unexplored avenue to estimate some population parameters for endangered species that cannot sustain lethal sampling. We used simulations to explore the feasibility of applying catch-curve analysis from dead unionid shells to estimate mortality. We found that when shell persistence was nonconstant across age-classes, weighted regressions produced biassed results. Chapman–Robson estimates, however, were more robust with performance comparable to estimates from catch-curve analysis on live individuals. Application of Chapman–Robson catch curve analysis to dead unionid shells represents a simple, cost-effective and nonlethal approach to increase our understanding of unionid life history.

Instream barriers disrupt the connectivity of rivers worldwide, threatening fish communities by limiting access to essential habitats. Innovative conduit fishways, such as the siphon fishway with flow regulators, have potential for improving native fish passage in Australian rivers but necessitate fish to negotiate pressure reduction below ambient atmospheric pressure. We investigated the volitional passage of juvenile silver perch (Bidyanus bidyanus) against hypobaric pressure gradients to 1-m (~91.5 kPa) and 2-m (~81.8 kPa) elevations inside a pipe, with and without flow. Fish negotiated both elevations (~20% maximum pressure reduction relative to ambient atmospheric pressure) without adverse impacts, and the presence of flow resulted in faster passage across elevations. The probability for a proportion of the group of five fish passing within an hour ranged from 38% to 80% across four treatments, with a predicted 50% chance of passage of three out of five individuals occurring under 45 min for three treatment groups. A reliable comparison of passage performance between treatments, however, was complicated by the possible effect of fish conditioning. In demonstrating fish ability to negotiate hypobaric pressure gradients, we provided a foundation for using the siphon fishways as a cost-effective fish passage for threatened native species. These findings present significant conservation opportunities for improving connectivity at sites affected by low head barriers globally.

The European eel (Anguilla anguilla) is a critically endangered and declining species. Information from traditional fisheries and a fish monitoring scheme in the Ebro Delta reflect the widely reported eel decline onset in the late 1970s and also a recent, sharp and ongoing decline of similar magnitude (> 80%). This recent trend arises from both fishery and monitoring data, is solidly described by time-series analyses and agrees with patterns reported in other areas. Decline drivers could be related to emergent invasions and/or to the exploitation of the already depleted eel stock. There is an urgent need to re-evaluate eel status and associated management strategies.

Rhodolith beds are biogenic marine habitats formed by aggregations of free-living crustose coralline algae. New descriptions of rhodolith beds fill the gaps in our understanding of the global distribution and ecological significance of these understudied habitats. We provide the first characterisation of a network of rhodolith beds associated with coral reefs in the tropical central Pacific. We surveyed the shallow eastern reef flat of Palmyra Atoll to evaluate the spatial extent and biodiversity of rhodolith habitat relative to adjacent coral reefs. We mapped 15 discrete rhodolith beds that collectively covered 1.5 ha. When combined with mixed rhodolith and coral habitat that connected the beds, the total areal coverage of rhodolith habitat was ~15 ha. The benthos of rhodolith beds was markedly different from adjacent reefs. Although coral cover was low in the rhodolith beds, five genera were commonly found as free-living coralliths. Fish abundance did not vary notably between reef and bed habitats, but rhodoliths, particularly Neogoniolithon sp., supported a higher abundance of cryptic invertebrates relative to reef rubble. The dominant rhodolith genera were Neogoniolithon and Porolithon, and a third, less frequent species was Harveylithon munitum. Neogoniolithon sp. was the most abundant and displayed a more structurally complex branching morphology than the encrusting, lobe-forming Porolithon sp. and the encrusting H. munitum. Our description of a previously unknown rhodolith complex in a remote and protected coral reef ecosystem provides novel insights to our understanding of the persistence and function of undisturbed tropical rhodolith bed habitat.

If eradication is not feasible, suppressing a population size of non-native species by removal is an alternative option for the conservation of native species that are impacted by non-native species invasions. This study reports on the suppression of non-native brown trout for the conservation of native white-spotted charr in an upstream of Monbetsu Stream, Hokkaido, northern Japan. Brown trout removals were conducted from 2014 to 2023 by electrofishing. The population size of brown trout was dramatically reduced during the first three years of removals, and the ratio of white-spotted charr to brown trout abundance gradually increased. However, the population size of white-spotted charr did not fully recover, which can be explained by the openness of the system and likely also by the influence of interfering factors observed during the study, such as changes in stream morphology due to flooding and suspected illegal fish stocking. The abundance of young-of-the-year brown trout also tended to be reduced when numerous mature females had been removed in previous years. This study suggests that suppressing non-native fish species, even on a limited scale, can contribute to the conservation of native species. However, when preventing migration from downstream into the target stream reach is unfeasible, ongoing suppression of non-native species becomes essential to ensure the conservation of native species in the area.