Aquatic Conservation-Marine and Freshwater Ecosystems最新文献

Streams and rivers are increasingly threatened by intensifying land cover and land use (LCLU) change and streamflow alteration at a global scale. Stream fishes provide several ecosystem services and thus understanding fish responses to these anthropogenic changes benefits freshwater conservation and management. We compared historical survey data from 1956 to 1957 to replicated surveys conducted in 2023 to assess long-term changes in taxonomic and functional fish assemblage structure brought on by anthropogenic alterations in the Neches River Basin of Texas. We assessed components of temporal beta diversity to find the predominant form of assemblage change, nestedness or replacement, and related the predominant component to LCLU and streamflow change at whole basin and river mainstem extents. We then examined the relationship between temporal beta diversity and functional dispersion for traits related to fish stream size preference, substrate preference, and capacity to host mussels. Replacement was the primary form of temporal beta diversity at both spatial extents. At the basin extent, streamflow alteration was negatively correlated with replacement, while at the mainstem extent, urbanisation was positively correlated with replacement. Taxonomic replacement was positively correlated with functional dispersion change at high urbanisation levels but showed no relationship at low urbanisation levels or across a gradient of streamflow change. This study leverages rare long-term data to test for patterns in temporal beta diversity at taxonomic and functional levels rather than the more commonly used space-for-time substitutions and provides insight for management actions aimed at conserving stream fish assemblages in the face of LCLU and streamflow alterations.

Understanding genetic diversity is essential for conserving and sustainably managing fish populations in riverine ecosystems. However, overexploitation, habitat degradation, pollution, and ineffective fisheries management threaten the genetic integrity of many species, including the bagrid catfish (Rita rita). This study used simple sequence repeat (SSR) markers to assess the genetic diversity and population structure of R. rita across five sites along the Indus River. Genomic DNA was extracted from dorsal muscle tissues, and cross-species microsatellite primers from Bagarius yarrelli were used for polymerase chain reaction (PCR) amplification. Genetic diversity was evaluated using allelic richness (Ar), heterozygosity, inbreeding coefficients (F_IS) and genetic differentiation (F_ST). The results revealed moderate genetic diversity, with allelic richness ranging from 2.400 to 5.800 and expected heterozygosity (He) between 0.617 and 0.699. Lower observed heterozygosity (Ho) across most populations suggests potential inbreeding effects. Significant genetic differentiation (F_ST) indicated moderate population structuring, with a strong correlation between geographic distance and genetic variation. Analysis of molecular variance (AMOVA) showed that 85.72% of genetic variation occurred within individuals, while restricted gene flow (Nm) across certain loci suggested geographical barriers affect genetic diversity. UPGMA clustering and STRUCTURE analysis identified two major genetic clusters, suggesting the presence of distinct evolutionary lineages. These findings highlight the need for targeted conservation strategies to maintain genetic integrity and reduce further genetic loss. This study establishes a molecular framework for future marker-assisted conservation and aquaculture programs to sustain R. rita populations in their natural habitats.

Bycatch from bottom trawling is a major threat to Mediterranean loggerhead turtles. Building on previous trials of Turtle Excluder Devices (TEDs), this study aimed to expand sample size and geographic coverage to assess TED effectiveness in Mediterranean multispecies bottom trawlers. Flexgrid TEDs were tested on nine bottom trawlers operating in the Gulf of Manfredonia and south of the Po River in the Adriatic Sea—areas heavily used by both bottom trawlers and loggerhead turtles. Onboard observers recorded target, discard and turtle catch from different gear configurations, such as an external sac applied to the TED opening (TEDe) as well as nets with and without TEDs. Of the 18 turtles captured, two were decomposed upon capture. Among the 16 potentially captured alive, none were found in the codends of TED-equipped nets. However, some vessels experienced important reductions in commercial catch when using TEDs. Catch loss induced by TED vs. regular gear was estimated as −16.6% by a GLMM, while a mean loss of 19.7% was directly observed in TEDe. Results show high variability among hauls, likely influenced by environmental factors and vessel characteristics, and are consistent with previous studies in the Adriatic Sea. TED design should be further improved, especially with direct involvement of fishers, and should be tested across different fisheries and regions.

No confirmed distribution of seahorses (Hippocampus spp.) is recognized in Bangladesh, apart from a questionable record of Hippocampus kuda (Bleeker 1852). This study documents the occurrence of two newly recorded species, H. spinosissimus (Weber 1913) and H. trimaculatus (Leach 1814), alongside H. kuda, based on specimens collected from the coasts of Chattogram and Cox's Bazar. It provides a detailed account of their key characteristics, including morphometric measurements, meristic counts and photographic evidence. Seahorses in this region are caught as bycatch and are often discarded; however, a portion is channeled into niche markets by local fishers for small-scale trade. The IUCN Red List designated H. kuda, H. spinosissimus and H. trimaculatus as vulnerable species. Major threats to these species include bycatch in artisanal fishing and habitat degradation, highlighting the need for better conservation measures. Accurate species identification is, therefore, a crucial first step in protecting these data-deficient, flagship marine species.