Assessment of efficiency and impacts of gillnets on fish conservation in a tropical freshwater fishery

Silvano, Renato Azevedo Matias; Hallwass, Gustavo; Juras, Anastácio Afonso; Lopes, Priscila F. M.

doi:10.1002/aqc.2687

Cited by 29 publications

(22 citation statements)

References 66 publications

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“…On the other hand, the medium‐sized fish showed an increase in citations over time in all PAs, which partially confirms our third hypothesis regarding temporal trends on size of exploited fish. This pattern of a fishing directed to catch medium‐sized fish also has been observed in the Tocantins River, another clear water Amazonian tributary (Silvano et al ., ). Indeed, some medium sized fish, including jaraqui and pescada, are among the most exploited fishes throughout the Amazon (Hallwass & Silvano, ), indicating a pattern of reduction in the size of target species over time (Castello et al ., ), as observed in other tropical freshwater ecosystems experiencing high fishing pressure (Welcomme, ).…”

Section: Discussionmentioning

confidence: 97%

Fishers’ knowledge indicates temporal changes in composition and abundance of fishing resources in Amazon protected areas

Hallwass

Schiavetti

Silvano

2019

Animal Conservation

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The local ecological knowledge (LEK) of fishermen has been applied to reconstruct temporal patterns of resource abundance and to assess resource exploitation, especially in tropical ecosystems. Protected areas (PAs) are the main conservation measure in the Amazon, but their efficacy to improve fisheries is poorly known. The main goal of this study was to apply fishermen' LEK to evaluate temporal changes in composition and abundance of exploited fish species among three different categories of PAs in the Tapaj os River, Brazilian Amazon. We interviewed 203 fishers about their highest fish catches, and the main fish caught at two time periods: the beginning of their fishing careers and currently. Fishers' LEK indicated decreases in citations of larger-bodied fishes and in reported catches over time, evidencing a gradient of conservation according to PA's time of establishment and management rules. We noticed higher changes (reduced catches and smaller fish exploited) in the Environmental PA, established 10 years ago and lacking management plan and buffer zone. In National Forest, which was created 40 years ago with more restrictive management rules, fish composition and catches included larger commercial fish. The Extractive Reserve, which was created 15 years ago and lacks specific fishing rules, may be in an intermediate stage, as large fish and highest catches decreased over time, but medium and large fish are still exploited. Fishers' LEK can be an invaluable but neglected source of data on temporal patterns of fishing pressure and conservation needs, especially in tropical megadiverse, poorly known and threatened rivers.

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Section: Discussionmentioning

confidence: 97%

Fishers’ knowledge indicates temporal changes in composition and abundance of fishing resources in Amazon protected areas

Hallwass

Schiavetti

Silvano

2019

Animal Conservation

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“…The change of human footprint showed the human pressure increased over time, which accelerated the extirpation of some fish species (Dudgeon et al, ; Fu et al, ; Xie, ). Many factors, such as dam construction, sand mining, water pollution, overfishing, and species invasions, have been threatening fish biodiversity either directly or indirectly (Dudgeon et al, ; Raghavan, Prasad, Anvar‐Ali, & Pereira, ; Silvano, Hallwass, Juras, & Lopes, ; Trombulak & Frissell, ; Wu, Huang, Han, Xie, & Gao, ).…”

Section: Discussionmentioning

confidence: 99%

Biodiversity pattern of fish assemblages in Poyang Lake Basin: Threat and conservation

Liu

Qin

Yang

et al. 2019

Ecology and Evolution

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Poyang Lake Basin is of great importance to maintain regional ecological balance. However, fish biodiversity in this basin has rapidly declined as the result of anthropogenic habitat alteration, such as dam construction, sand mining, and water pollution. Here, we aimed to analyze the temporal and spatial changes in biodiversity patterns of fish in Poyang Lake Basin over the last 37 years. The number of fish species underwent a significant decrease in the current period. In particular, 36.7% of the migration of fish was extirpated. Twenty‐seven fish species have been formally assessed using the Chinese Red List were currently listed as Critically Endangered (9), Endangered (3), Vulnerable (10), and Near Threatened (5). Alpha and gamma diversity revealed that fish diversity had also decreased, and beta diversity showed significant composition dissimilarity in two periods. PCoA showed that the historical fish composition dissimilarity was significantly different from that of the current period. We found a significant effect of the geographical distance on the spatial turnover component for the historical and current periods. In addition, the nestedness component was the main contributor to beta diversity, which indicated one large protected area should be established in Poyang Lake and the Ganjiang River Basin with higher species richness. These results indicated that fish biodiversity declined in the current period likely caused by anthropogenic habitat alteration and other threatened factors. Therefore, we suggest that the habitat reconstruction and biodiversity conservation for fish have become imperative in this basin, and a complete management plan should be carried out.

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“…First, the removal of large fish, some of which may be top predators (Castello et al, ) or better competitors, could lead to an ecological compensatory effect, hence increasing the abundance and diversity of non‐exploited fish. Second, there are many rare fish species in the Brazilian Amazon (Hercos, Sobansky, Queiroz, & Magurran, ; Silvano, Hallwass, Juras, & Lopes, ). Most of these rare species might not be affected by fishing, which is usually selective and directs most fishing effort on a few preferred fish species (Hallwass & Silvano, ; MacCord, Silvano, Ramires, Clauzet, & Begossi, ).…”

Section: Discussionmentioning

confidence: 99%

Ecological influences of human population size and distance to urban centres on fish communities in tropical lakes

Keppeler

Souza

Hallwass

et al. 2018

Aquatic Conservation

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1. Human population growth is a major cause of species extinction worldwide, and tropical fresh waters are among the most imperilled ecosystems. The identification of major drivers of human impacts on fish can benefit conservation programmes and management plans.2. The influences of the proximity to urban centres and human population size on six ecological indicators of fish communities (abundance, biomass, richness, diversity, average size, and size dominance pattern) were investigated in 48 floodplain lakes of five main rivers of the Brazilian Amazon (Tocantins, Tapajós, Negro, Solimões, and the Lower Amazon). These ecological indicators were also compared among the rivers studied and checked for any influence of the environmental variables of lakes (size, shape of natural shoreline, distance to the main river channel, depth, transparency, conductivity, and dissolved oxygen).3. Lake distance to urban centre was positively related to average fish size and dominance of large fish, indicating direct human effects caused by fisheries or indirect effects by habitat alteration (e.g. deforestation). Unexpected positive relationships between human population size and the richness and diversity of fishes were found, and may be caused by ecological compensatory effects, the abundance of rare non-fished species, or the proximity of an urban centre to ecotone areas.The other ecological indicators were unrelated to anthropogenic variables. Environmental factors affected fish communities, but did not change the conclusions regarding the effect of the anthropogenic variables. River basin was strongly related to species richness, diversity, biomass, and abundance of fish. Distance to the river channel was positively related to fish biomass. 4. The disappearance of large fish threatens the food security of riverine communities, and may harm essential ecosystem services. Conservation measures, including local management initiatives, protected areas, fisheries monitoring, and the

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Assessment of efficiency and impacts of gillnets on fish conservation in a tropical freshwater fishery

Cited by 29 publications

References 66 publications

Fishers’ knowledge indicates temporal changes in composition and abundance of fishing resources in Amazon protected areas

Fishers’ knowledge indicates temporal changes in composition and abundance of fishing resources in Amazon protected areas

Biodiversity pattern of fish assemblages in Poyang Lake Basin: Threat and conservation

Ecological influences of human population size and distance to urban centres on fish communities in tropical lakes

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