Fish catch and fishing practices in the Nam Theun 2 Reservoir and watershed (Lao <scp>PDR</scp>)

Cottet, Maud; Visser, T.A.M.

doi:10.1111/lre.12196

Cited by 4 publications

(15 citation statements)

References 21 publications

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“…The Nam Theun 2 hydropower Reservoir (NT2) area [33] was selected for this survey. Numerous villages are settled along the reservoir [34] and the two rivers downstream that are the Nam Theun River (NTH) and the Xe Bangfai River (XBF). Fisheries are further recognized as an important source of income for those villages and might be affected by the evolution of fish diversity.…”

Section: Introductionmentioning

confidence: 99%

Direct fishing and eDNA metabarcoding for biomonitoring during a 3-year survey significantly improves number of fish detected around a South East Asian reservoir

Gillet

Cottet²,

Destanque

et al. 2018

PLoS ONE

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Biodiversity has to be accurately evaluated to assess more precisely possible dam effects on fish populations, in particular on the most biodiverse rivers such as the Mekong River. To improve tools for fish biodiversity assessment, a methodological survey was performed in the surroundings of a recent hydropower dam in the Mekong basin, the Nam Theun 2 project. Results of two different approaches, experimental surface gillnets capture and environmental DNA metabarcoding assays based on 12S ribosomal RNA and cytochrome b, were compared during 3 years (2014–2016). Pitfalls and benefits were identified for each method but the combined use of both approaches indisputably allows describing more accurately fish diversity around the reservoir. Importantly, striking convergent results were observed for biodiversity reports. 75% of the fish species caught by gillnets (62/82) were shown by the metabarcoding study performed on DNA extracted from water samples. eDNA approach also revealed to be sensitive by detecting 30 supplementary species known as present before the dam construction but never caught by gillnets during 3 years. Furthermore, potential of the marker-genes study might be underestimated since it was not possible to assign some sequences at lower taxonomic levels. Although 121 sequences were generated for this study, a third of species in the area, that exhibits high endemism, are still unknown in DNA databases. Efforts to complete local reference libraries must continue to improve the taxonomic assignment quality when using the non-invasive and promising eDNA approach. These results are of broader interest because of increasing number of hydropower projects in the Mekong Basin. They reveal the crucial importance to sample tissues/DNA of species before dam projects, i.e. before the species could become endangered and difficult to catch, to obtain more precise biomonitoring in the future as we believe eDNA metabarcoding will rapidly be integrated as a standard tool in such studies.

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Section: Introductionmentioning

confidence: 99%

Direct fishing and eDNA metabarcoding for biomonitoring during a 3-year survey significantly improves number of fish detected around a South East Asian reservoir

Gillet

Cottet²,

Destanque

et al. 2018

PLoS ONE

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“…The NT2 Reservoir was impounded in 2008 and tends to reach an ecological equilibrium, despite significant exploitation of the ichtyo resources (Cottet et al, 2016;Cottet and Visser, 2017). More than 2000 households rely on the O. niloticus for food.…”

Section: Discussionmentioning

confidence: 99%

“…This reservoir was impounded in April 2008 and after a classical trophic upsurge, the system seems to have reached ecological stabilization in 2011 (Cottet et al, 2016). The Nile tilapia represents the major part of the catch by the local fishery and is of significant economic importance (52% of relative biomass contribution of total catch, (Cottet and Visser, 2017). Biological parameters of this fish species constitute essential data to assess population dynamic and the exploitation level for fisheries management.…”

Section: Introductionmentioning

confidence: 99%

Investigating key biological parameters of Nile tilapia (Oreochromis niloticus L.) in a large Asian reservoir to better develop sustainable fisheries

Beaune

Guillard²,

Cottet³

et al. 2020

Hydroécol. Appl.

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The Nile tilapia (Oreochromis niloticus) was introduced in Southeast Asia, such as in Thailand, in the mid-1960s for aquaculture purposes (Pullin et al., 1997; De Silva et al., 2004). The species was later promoted for aquaculture development in the early 1990s in Lao PDR (Garaway et al., 2000). In Lao People’s Democratic Republic (PDR), like in other countries, this exotic species is well established due to its self-reproduction (De Silva et al., 2004; CABI, 2018) facilitated by its particular life history traits and plasticity (Ishikawa et al., 2013). The species was then suspected to be introduced in the seventies in Laos and subsequently in the Nam Theun watershed where the NT2 Reservoir was impounded in 2008. Population parameters of this alien fish were investigated using the FiSAT II software with the most popular methods of bioparameters assessment to check their interchangeability within a same stock and the same year 2016. The length-at-age data analysis (using otoliths analysis, N = 258) gave slightly different results with the length frequency distribution analysis of fish landings (11 820 individuals). Furthermore, experimental fishing data provided irrelevant parameters due to insufficient representativeness of the sample size. The growth parameter K was estimated to be 0.23 year−1, with asymptotic length L∞ = 52.5 cm based on the length frequency distribution analysis with the fish landing data. According to these landing data, the total, natural and fishing mortality were Z = 1.41 year−1, M = 0.30 year−1 and F = 1.11 year−1. The exploitation rate E = 0.79 is over the Emax = 0.594 obtained by relative yield and biomass per recruit. This estimated stock of 165 tons (more than 700 000 tilapias) was characterized by high mortality (no population growth). These results showed that the population is overfished with too many juveniles caught (L50 = 210.4 mm; 50% mature stages at 295 mm). To maximize the yield per recruit, increase the biomass and sustain this fishery, enlarging the gillnet mesh size of the gill-net is recommended. This example highlights the variability of the parameters calculated from different methods and thus weaken worldwide and even inter-site comparisons. Despite this issue, the Growth Performances Indices (φ′) gathered into the literature can serve as baseline and confirmed the wide phenotypic plasticity of the species due to environmental factors. Analyses revealed difference between fast growing domesticated fish rose for aquaculture with φ′ higher to the tilapia growing in natural and challenging environments.

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“…The Nam Theun 2 reservoir impounded in 2008 is shallow (8 m depth on average) and its surface area varies between 489 km 2 at full supply level to 86 km 2 in the dry season. Sixteen hamlets are established along the reservoir, a part from resettlement, with a total households of more than 2,000 in 2014 and around 85% of that population is involved in fishing [21].…”

Section: The Nam Theun 2 Reservoirmentioning

confidence: 99%

“…Catch monitoring based on landings started in 2008 [21] and has been regularly implemented since then. The catch varied between 6.2 kg/household/day in 2009 just after impoundment and 2.8 kg/ household/day in 2012-2013, with a rebound after 2013 (4.3 kg/ household/day in 2015; [22].…”

Section: Fish Supplymentioning

confidence: 99%

A Case Study of Fisheries Governance and Management in a Reservoir of Lao PDR: Perspectives for Improvement

et al. 2021

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The focus is on the fishery as a whole, i.e. the combination of fish, environment, fishers, and economic and policy context [11,12]. The need to integrate customer demand and marketing to sustainable fisheries management is highlighted in several studies, in particular in the Mekong basin [13]. Thus, we consider here fish supply, fish demand/marketing and the environment policy as the three main pillars of a sustainable fishery, knowing that several other factors such as biological productivity, algae blooms, limnological aspects, landuses in the catchment areas, fishing gears are also important [14]. Our study focuses only on a reservoir fishery, it does not include upstream or downstream fisheries. We set the stage by identifying the various components of a generic tropical reservoir fishery, and then document how much is known and has been done about each component in the case of Nam Theun 2. This highlights strengths and weaknesses in the knowledge base needed for the management of the system. Ultimately, the various degrees of control of managers over the fishery system and its components are identified. Components of a Fishery: the Conceptual PerspectiveThis case study review is based on the analysis of Nam Theun 2 environment, fish resource, fishing, fishers, fish trade, and policies

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Fish catch and fishing practices in the Nam Theun 2 Reservoir and watershed (Lao PDR)

Cited by 4 publications

References 21 publications

Direct fishing and eDNA metabarcoding for biomonitoring during a 3-year survey significantly improves number of fish detected around a South East Asian reservoir

Direct fishing and eDNA metabarcoding for biomonitoring during a 3-year survey significantly improves number of fish detected around a South East Asian reservoir

Investigating key biological parameters of Nile tilapia (Oreochromis niloticus L.) in a large Asian reservoir to better develop sustainable fisheries

A Case Study of Fisheries Governance and Management in a Reservoir of Lao PDR: Perspectives for Improvement

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