Illegal and unmanaged aquaculture, unregulated fisheries and extreme climatic events combine to trigger invasions in a global biodiversity hotspot

Raj, Smrithy; Kumar, Appukuttannair Biju; Tharian, Josin; Raghavan, Rajeev

doi:10.1007/s10530-021-02525-4

Cited by 23 publications

(8 citation statements)

References 26 publications

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“…Also, unlike temperate species of anguillid eels, A. Freshwater eels are also exposed to multiple threats in their habitats, with these stressors acting either individually or synergistically (Jacoby et al, 2015). In the study region (Chalakudy, Periyar and Muvattupuzha rivers), there are several continuing, as well as predicted, future threats to freshwater biodiversity, including flow alterations as a result of the cascade of hydropower dams, high levels of pollution, and extreme climatic events (Dahanukar et al, 2011;Raj et al, 2021). The combined effects of these threats will certainly result in changes to the habitat use, growth, and reproduction of the two species of freshwater eels, making them more vulnerable to drastic declines and local extinctions, as has already been witnessed in the northern part of the Western Ghats (Kharat et al, 2003;Kumkar et al, 2017).…”

Section: Challenges For the Conservation And Management Of Anguillid ...mentioning

confidence: 99%

Demographics and exploitation of two Near Threatened freshwater eels, Anguilla bengalensis and Anguilla bicolor, in small‐scale subsistence fisheries and implications for conservation

Shanmughan

Dahanukar

Harrison

et al. 2022

Aquatic Conservation

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Tropical freshwater eels (Anguilla bengalensis and Anguilla bicolor) contribute a major share of the world's wild‐caught eel production, having become the next major target owing to the declines in availability of both Anguilla japonica and Anguilla anguilla, species that have traditionally contributed to eel aquaculture and trade. Although both A. bengalensis and A. bicolor are assessed as Near Threatened on the International Union for Conservation of Nature Red List, these assessments are primarily based on anecdotal information and local knowledge on population declines. Demographics and exploitation levels of A. bengalensis and A. bicolor were determined from small coastal river systems, and their adjoining aquascapes in the Western Ghats hotspot of southern peninsular India, and the value of these data for future conservation planning discussed. The computed estimates of annual catch data for freshwater eels from the study region are between 0.17 (A. bicolor) to 0.30 t (A. bengalensis). Virtual population analysis of exploitation showed a drastic decline (in number) in the length groups >45 cm for both species, suggesting that they were less likely to attain their asymptotic length in the region. Current exploitation rates of A. bengalensis are unsustainable, and those for A. bicolor are almost close to reaching this level. Exploitation of all life stages from yellow eels to adults (29–171 cm) is likely to cause recruitment failure and significant mortality of spawning individuals of both species. An integrative conservation approach, including raising awareness (leading to voluntary restrictions), fishing closures in reservoirs, village‐level quotas, and regular monitoring of populations, will ensure a sustainable future for the freshwater eel species in the Western Ghats hotspot, and elsewhere in the tropics where these species are exploited.

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Section: Challenges For the Conservation And Management Of Anguillid ...mentioning

confidence: 99%

Demographics and exploitation of two Near Threatened freshwater eels, Anguilla bengalensis and Anguilla bicolor, in small‐scale subsistence fisheries and implications for conservation

Shanmughan

Dahanukar

Harrison

et al. 2022

Aquatic Conservation

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“…This finding suggests that rising extreme rainfall and flood incidents in the region, global warming and climate change events would aid and expedite the establishment of Pirarucu in the region. Raj et al (2021) report that the Western Ghats are also home to unlicensed aquarium fish breeding and farming operations that operate in the flood plains of major rivers prone to yearly floods. There have been documented cases of indiscriminate and illegal fishing of a fish species, the African Catfish Clarias gariepinus , in central Kerala, which resulted in the species' escape and spread into Vembanad Lake (Krishnakumar et al, 2011).…”

Section: Discussionmentioning

confidence: 99%

Ensemble modelling of Pirarucu (Arapaima gigas) distribution in biodiversity hotspot to understand its invasion risk

Nisin

Sreenath

Sreeram

et al. 2023

Ecology of Freshwater Fish

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Invasive species pose a severe threat to biodiversity around the world. Managing the consequences of invasion is difficult in aquatic settings, as the rate at which invaders establish typically outpaces the resources available to eradicate them. For proactive management measures to be implemented, prior knowledge of the probability of invasion is required. In this study, we created a spatial model of the probability of the Pirarucu (Arapaima gigas) invasion in the Western Ghats. The Western Ghats, one of the world's top biodiversity hotspots, is home to numerous endemic species, many of which are now threatened. An ensemble modelling approach using 10 models, including machine learning techniques such as Artificial Neural Network (ANN), Maximum Entropy (MaxEnt), Random Forest (RF), Generalised Boosted Regression Model (GBM) and Classification Tree Analysis (CTA), was adopted. The model was built using the species' occurrence data and nine climate variables. The findings revealed that southern regions of the Western Ghats have a high risk of Pirarucu invasion. Sri Lanka also has a much greater geographical area with a higher percentage of appropriate habitats for the species. The study becomes vital as this exotic species was repeatedly reported from the rivers since the extensive floods in the region in 2018. The developed model will assist managers in prioritising locations and initiating monitoring and management steps to prevent the spread before they establish in the wild. With earlier Pirarucu invasions in Bolivia, Peru and East Asia and recent climatic vagaries in the Western Ghats, the native biodiversity of the region is in grave danger of being displaced.

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“…The recent catastrophic flood in August 2018 in Kerala resulted in the release of large-sized predators such as A. gigas and A. spatula into the natural waterbodies of SWG, revealing the existence of unpredicted changes in the inland waters. Further, unregulated, unscientific, mostly illegal and thriving aquaculture and aquarium fisheries sector based on alien species along the riverine floodplains are posing uncontrolled threats (Biju Kumar et al, 2019;Raj et al, 2021). Given the increasing evidence of habitat changes (dams and the resultant flow alterations), climate change and expansion of alien fishes, further research is urgently needed to understand the spread of invasive fish, and associated declines in ecosystem services (Radinger et al, 2019).…”

Section: Discussionmentioning

confidence: 99%

Distribution of alien invasive species in aquatic ecosystems of the southern Western Ghats, India

Raj

Prakash

Reghunath

et al. 2021

Aquatic Ecosystem Health &Amp; Management

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We present results of the first major attempt to record the distribution of aquatic alien species in the Western Ghats Biodiversity Hotspot using Geographical Information System. A total of 32 alien species, including four macrophytes (Salvinia molesta, Pistia stratiotes, Eichhornia crassipes and Cabomba furcata) and 28 fish were recorded from the southern part of the Western Ghats. Seven of these have established natural populations and are invasive, which includes Oreochromis mossambicus, O. niloticus (Cichlidae), Poecilia reticulata, Gambusia affinis (Poeciliidae), Pterygoplichthys pardalis (Loricariidae), Cyprinus carpio (Cyprinidae) and Clarias gariepinus (Clariidae). Oreochromis mossambicus is the most extensively distributed invasive fish in the region. Major reservoirs serve as a spawning hub for species such as C. gariepinus and C. carpio. Significant pathways for the establishment of most alien species in Western Ghats were aquarium trade and aquaculture. Given the increasing records of alien species and proliferation of invasive species in the southern region of the Western Ghats, urgent research and policy interventions are suggested, including the development of a comprehensive database on distribution, trade, invasion biology, as well as determining both short-term and longterm impacts on endemic fauna.

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Illegal and unmanaged aquaculture, unregulated fisheries and extreme climatic events combine to trigger invasions in a global biodiversity hotspot

Cited by 23 publications

References 26 publications

Demographics and exploitation of two Near Threatened freshwater eels, Anguilla bengalensis and Anguilla bicolor, in small‐scale subsistence fisheries and implications for conservation

Demographics and exploitation of two Near Threatened freshwater eels, Anguilla bengalensis and Anguilla bicolor, in small‐scale subsistence fisheries and implications for conservation

Ensemble modelling of Pirarucu (Arapaima gigas) distribution in biodiversity hotspot to understand its invasion risk

Distribution of alien invasive species in aquatic ecosystems of the southern Western Ghats, India

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