Aquatic Conservation-Marine and Freshwater Ecosystems最新文献

Fish hybridization is common in aquaculture worldwide, including in Brazil, with cross-breeding between species of the genera Piaractus and Colossoma taking the lead. However, little is known about the genetic damage caused by hybrids that escape into natural environments. In the upper Paraná River region, hybrid fishes are overproduced; therefore, the use of molecular techniques for their monitoring and identification is necessary. This study aimed to detect the presence of possible hybridization between Piaractus and Colossoma in the upper Paraná River using the molecular markers cytochrome c oxidase subunit 1 (COI) and α-tropomyosin (TROP). Fragments from 53 fish samples were analysed, and 41 samples were considered hybrids, with 12 confirmed pure, six as Piaractus mesopotamicus (pacu) and six as Piaractus brachypomus (pirapitinga). This is the first record of P. brachypomus, which is an invasive species in this basin, while Colossoma macropomum has not been observed. Molecular markers efficiently detected hybrids in the Ivinhema and Paraná rivers. The results showed a predominance of hybrid specimens from P. mesopotamicus × P. brachypomus. Our study suggests that more restrictions on hybridization and better supervision of fish farms are needed to prevent the escape of hybrids and the consequent ecological and genetic damage to native populations. We warn of the risk of a decline in the population of P. mesopotamicus, as this species is of great importance for fishing and maintaining the ecosystem.

North American river otters (Lontra canadensis) are semiaquatic mammals distributed throughout the North American continent. They are generalist carnivores with a high potential to affect community structure and dynamics. However, habitat degradation and ecosystem changes have the potential to impact their trophic interactions. Therefore, investigating their diet is critical to understand how anthropogenic disturbances can affect their ecological roles, particularly in the urbanised ecosystems in Florida, where such diet information is currently unavailable. Due to their elusive nature, direct observation of feeding events is a major challenge. Here, we have applied DNA metabarcoding of faecal matter (fDNA), opportunistically collected from river otters killed by road traffic in eastern Florida. Two mitochondrial markers were used to identify prey species' DNA—one for fish and one for vertebrates. A total of 23 unique exact sequence variants (ESVs) were identified, the majority belonging not only to teleosts but also to amphibians, reptiles, birds and mammals. The prey species identified are known dietary resources for river otters and the recovered dietary profiles provided independently by the fish and vertebrate assays were similar. Among the identified teleost prey, three fish species are considered invasive. Here, we show that when sufficient reference sequences are available, fDNA metabarcoding provides high prey species resolution. The collection and metabarcoding of faecal samples is particularly advantageous for scaling diet studies, both geographically and longitudinally, highlighting the potential of fDNA metabarcoding for the investigation of the diet of predators. This can provide foundational information on the organisation of ecological networks, which is vital for implementing successful ecosystem-based conservation management.

Greater Caribbean manatees Trichechus manatus manatus face complex conservation challenges throughout their distribution range, many of which are associated with human factors; and in consequence, the subspecies is considered Endangered (EN) by the International Union for Conservation of Nature (IUCN). Human-related threats as hunting for meat consumption, collisions with boats, entanglement in fishing nets, pollution and loss of habitat put the Greater Caribbean manatee at risk in Colombia. Studies aiming to describe traditional knowledge and local perceptions provide information that can be useful to design local manatee conservation programmes. We analyse the fishers' perceptions regarding manatees in Ayapel, Córdoba. One hundred semi-structured interviews were conducted, focusing on personal data, fishing practices, perceptions and knowledge about the manatees. According to the interviews, bycatch is the greatest threat to manatees (56%), followed by pollution (16%), whereas boat collisions (12%), hunting (11%) and drought (5%) are lower ranking threats. Our results demonstrated that participants have a good understanding of manatee biology and ecology. However, a human–manatee conflict was evidenced, as 39% of fishers consider that manatees negatively impact fishing by competition for the fishing resources and/or by damaging fishing gear. We recommend strengthening awareness about the importance of manatee to guarantee an optimal management of this subspecies and its habitat. Fishers should be directly involved in the formulation of management and conservation plans for the subspecies, as their knowledge becomes critical to understanding and mitigating the risks to manatee populations. This work has a clear application to understand the human factor in manatee recovery not only in our study area but also in other locations where manatees share habitat with people, particularly in marginalized human communities.

Stocking density has a significant influence on animal homeostasis, and so is a crucial factor in the management of organisms in captivity and an important role in ex situ conservation of endangered species. Hypancistrus zebra is an endemic fish species from the Xingu River, Brazil—considered Critically Endangered since the early 2000s due to fishing pressure and, more recently, due to habitat changes resulting from the construction of the Belo Monte Hydroelectric Dam. The implementation of appropriate management in captivity is of utmost importance for its conservation, particularly in enhancing ex situ breeding techniques. This study aimed to evaluate the growth of juvenile H. zebra in aquaria with three different stocking density levels. The juveniles were distributed between three treatments, each with three replicates. We found no correlation between biomass and aquarium volume. The highest correlation coefficients were found between growth rates and densities related to the number of individuals per shelter area. Mortality rate was directly related to the initial number of fish in the aquariums, with larger populations showing higher mortality rates. The treatment with lower stocking density displayed the highest growth rate, while the treatment with higher density had the lowest growth rate, with a 23.38% difference between them.

The introduction of invasive fish for aquaculture can significantly impact native aquatic fauna, especially in regions where native amphibians have a biphasic life cycle. We conducted three laboratory experiments to assess the effects of introduced rainbow trout (Oncorhynchus mykiss) aquaculture on the native showy leopard frog (Lithobates spectabilis) in Mexico. We aimed to understand the effects of trout visual and chemical cues on tadpole behaviour, and the long-term effects of chemical cues (in interaction with tadpole density) on tadpole growth, development and survival. In Experiment 1, we exposed groups of tadpoles to the visual cue of a trout, comparing their refuge use and position within the tank to a control group. In Experiment 2,we exposed groups of tadpoles to trout chemical cues contrasting their refuge use to a control group. In Experiment 3, we exposed tadpoles at different densities to trout chemical cues for a prolonged period, recording their growth, development and survival. Results showed that tadpoles did not alter refuge use in response to trout visual cues but positioned themselves farther from these cues compared to controls. Tadpoles increased refuge use in response to chemical cues. Long-term exposure to chemical cues did not affect tadpole growth, development or survival, but higher densities led to lower survival rates. Our findings suggest that trout farming, through fish escapement or untreated farm water discharge containing trout chemical cues, could trigger behavioural responses in L. spectabilis larvae, increasing refuge use and local tadpole densities, ultimately compromising their survival and, potentially, species persistence.

Rhodolith beds are one of the major marine coastal ecosystems. Knowing the spatial distribution, environmental characteristics and composition is not only scientifically pertinent but also crucial to allow comparisons in case of changes due to local and global anthropogenic pressures. With slow algal growth rates, high associated diversity and potential importance as nursery grounds, rhodolith beds are present along the Brazilian coast of the Southwest Atlantic Ocean. This study provides an updated map of shallow and mesophotic rhodolith distribution after a systematic literature review. The prevailing oceanographic conditions along most parts of the Brazilian coast render the environment suitable for the developing rhodolith beds (a total of 68 taxa in this review), with 63 taxa along the East Brazilian Shelf, seven taxa for the North Brazilian Shelf and 10 taxa in the South Brazilian Shelf. According to composition, shallow and mesophotic communities were more similar in each large marine ecosystem than among them. In addition to gaps in terms of distribution, there are uncertainties about the taxonomic composition of the rhodoliths, associated fauna and flora and oceanographic and geological characteristics of the bottoms, which call attention to the importance of further studies, mainly in the mesophotic. This review provides a more precise distribution of these habitats along the Brazilian coast of the Southwest Atlantic Ocean. It contributes to a more detailed taxonomic composition of calcareous algae in an extremely relevant marine ecosystem, which is crucial for many species, including the endemic kelp, Laminaria abyssalis.

The last populations of Danube salmon (Hucho hucho) in Croatia are found in the Kupa and Una rivers. However, the size of the suitable area that could serve as the best spawning ground for the remnant Danube salmon population in these rivers is not known. This study aimed to leverage anglers' experiences to determine the sections of the Una and Kupa rivers where the last populations of Danube salmon (Hucho hucho) in Croatia are most abundant, identify potential spawning sites and assess threats that could impact the species' existence. The Kupica river emerged as a tributary of the Kupa river with a large Danube salmon population in Croatia. Experienced divers conducted three dives along a 350-m transect in the Kupica river, estimating a total of 13 Danube salmon individuals ranging from 50 to 115 cm in total length, in pool and run mesohabitat types. In the Kupa and Kupica rivers, the survey identified 25 Danube salmon spawning sites. The primary local threats identified for the Danube salmon population include small hydropower plants, the construction of a radioactive waste disposal site, water abstraction, the removal of riparian vegetation, overfishing and climate change. Based on the results of this study, we strongly recommend the implementation of protective measures against these threats and the establishment of an ichthyological reserve specifically for Danube salmon in the Kupica river. This recommendation aligns with the EU Biodiversity Strategy, emphasizing the need to identify designated areas by 2030.