Course:CONS200/2023WT2/Conservation of the Mekong Giant Catfish

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Overview

Mekong giant catfish (Pangasianodon gigas) in captivity

The Mekong giant catfish (Pangasianodon gigas) is one of the largest freshwater fish in the world, and is a species of catfish in the shark catfish family.[1] It has eyes set below its mouth, and no teeth. It can grow to be almost 3 meters long, and up to 300 kg at maturity. This fish is endemic to the Mekong River Basin, and its historical distribution ranged from the coast of Vietnam to northern Lao PDR.[2] Currently, it can be found in Burma, Lao PDR, Thailand, Vietnam, and Cambodia, although sightings are very rare. The population of the Mekong giant catfish has very dramatically declined in the last decades due to its many threats.

In 2001, the Mekong giant catfish was first bred in captivity. Artificial breeding programs have been established, collecting mature specimens and artificially spawning fry. However, these programs are usually without much success, as captive raised fry often do not succeed in the wild. It reaches maturity after around 17 years, and its generation length in captivity is around 35 years.[3]

The Mekong giant catfish lives in the mid-water to bottom levels of the Mekong's tributaries and mainstream. Being mostly vegetarian, its diet consists mainly of aquatic vegetation, particularly plants and algae growing on the rocks that line the Mekong river. For the first few months of their lives, the catfish fry feed mostly on animal plankton.

The Mekong giant catfish migrates very long distances to spawn. Each year from October to December it migrates upstream, from the lower Mekong up to Cambodia, Lao PDR, or Thailand.[4] Little more is known about its spawning habits.

Threats

The Mekong giant catfish is listed as a critically endangered species by the International Union for Conservation of Nature (IUCN)[5]. The population of fish has dramatically declined since the early 1900s. Drastic overfishing in the Mekong region has lead to this species' rapid decline in the wild, with a population that is now facing a multitude of threats as it tries to recover[6]. Chief among these threats are dams, overfishing, habitat loss/degradation, and genetic diversity loss[6].

Dams

A river in Laos being interrupted by a hydropower dam
Hydropower dam in Laos

The biggest issue dams pose for the Mekong giant catfish is that they block their migratory pathways. Although substantial data is absent, it has long been theorized that the Mekong giant catfish are highly migratory fish and can travel very long distances over the course of their lifetimes[5]. As a result, dams prevent individuals from returning to their spawning grounds to reproduce. The spawning grounds are thought to be North East of the Chiang Rai province in Northern Thailand, and South of the headwaters found in China[6].

China first started building dams in the 90s near the headwaters, and "(held) and release(d) water to maximize their own economic gains, with little regard for how their operations alter the river flow downstream"[7]. More recently there's been frenzied dam building in Laos, although mostly on smaller tributaries[7]. One dam near the border with Cambodia is of particular note, because it's proposed to span the only large free-flowing river in the surrounding basin[7]. Preliminary studies show it would have a large impact on local fisheries, despite producing relatively little electricity[7].

One the most concerning proposed dams is the Sayaboury dam in North West Laos[8]. If constructed, it would block the mainstream of the Mekong, effectively acting as an impassable barrier to large bodied fish, including the Mekong giant catfish[8]. To overcome this, serious measures would have to be taken to ensure large adult fish have upstream passage to return to their spawning grounds, and smaller juvenile fish have downstream passage to allow them to mature in the river downstream of the dam[8]. Without these accommodations, this dam could feasibly drive the fish to extinction in the wild[8].

Other proposed dams that would block the mainstream mekong river include the Pak Lay, Pak Beng, Xayaburi, Luang Prabang, Latsua and Don Sahong in Laos, and Stung Treng and Sambor in Cambodia[9].

Overfishing

Waterfall in the Mekong river with a wooden fish trap at the bottom.
Fish traps in the Mekong river

Overfishing is considered by some to be the greatest threat facing the Mekong giant catfish today. Much of the damage was done in the 80s in Thailand due to increased demand for artificial breeding, tourism, and a cultural belief that consuming the fish was good for one’s health[6].

The Tonle Sap is a Cambodian lake in the heart of the Mekong where many fish find fertile feeding grounds[10]. As a result, conservation programs often use it as a place for reintroducing captive raised fish[10]. On the lake, illegal overfishing is rampant and blatant[10]. The use of Illegal fishing gear is common, and fishing boats suited for the high seas can be seen on the lake using large trawling nets[10].

In terms of statistics, the Tonle Sap River bagnet fishery caught roughly 5 fish per year as of 2006[5]. Fishing lots & barrages accounted for 1-2 Mekong giant catfish a year, but the number of juvenile fish is likely much higher[5]. Bycatch in other fisheries, especially “large-mesh gill net fisheries” in Cambodia, and bamboo fishing traps in the South of Laos account for potentially 10 fish a year[5]. Bycatch is defined as "the incidental capture of non-target species" by the WWF, and has been increasing exponentially around the globe[11]. This is largely due to the increase in efficiency that industrial fishing has seen over time, and the fact that the industry is largely unaffected by it despite bycatch being extremely detrimental to a large number of aquatic species, including the Mekong giant catfish[11].

It's theorized that some level of traditional fishing could be maintained without being too detrimental to the population, so long as bycatch doesn’t increase[6]. This could allow for better data regarding the Mekong giant catfish to aid monitoring efforts over longer time frames and maintain investment in the well-being of the population by locals[6]. Bycatch is currently low but could increase if new gear is implemented that unwantedly catches the Mekong giant catfish[6].

Habitat Loss/Degradation

The Mekong giant catfish is also constantly losing valuable habitat, and it's spawning grounds may be in jeopardy[5]. This is primarily due to resource extraction in the lower Mekong, and infrastructure projects near the hypothesized spawning grounds[5][12]. In and around the Tonle Sap, logging projects are clearing the flooded forests[12]. These ecosystems are crucial habitat for the Mekong giant catfish and provide refuge for the fish[12]. The threats posed to their spawning grounds include habitat degradation and hydrological change[5]. This could be disastrous for the population and would only be noticeable roughly 20 years after the damage is done[5]. Potentially harmful projects near the theorized spawning grounds in Thailand include the construction of a port (Chiang Saen), and the removal of rapids with explosives[5]. The rapids would be removed as part of the Mekong Navigation Improvement Project, a project aiming to increase the use of the river for transportation purposes[5]. Additionally there are plans for a bridge to be built between Chiang Khong, Thailand, and Bokeo, Laos[5].

Genetic Diversity Loss

The Mekong giant catfish is also at risk of losing it's genetic diversity from breeding with captive raised fish[6]. Currently the effective population size is estimated to be 2500 individuals[5]. The population may be more genetically robust than previously thought however, as it's been found to "carry the genetic signature of a historically larger population"[13]. In general though, if captive raised fish are introduced into the wild population it could lead to reduced genetic diversity[6]. This is because of the genetic similarity in captive raised fish and the small wild population[6]. The resulting decrease in genetic diversity would be bad for the fish in the long run[6]. As it stands, it’s possible for the wild Mekong giant catfish populations to recover naturally, and breeding with captive raised fish could interfere with that[6].

Climate Change

Furthermore, climate change is exasperating the effects of all of these threats as droughts lead to lower water levels[7]. Droughts reduce the size that the lakes swell to and as a result the habitat they can provide for the Mekong giant catfish. During the wet season, regions like the Tonle Sap (the largest lake in South East Asia) swell to many times their size[10]. This expanded territory is crucial habitat for developing catfish, as much of it is flooded forest which provides shelter for maturing fry[10].

Conservation Efforts

Wonders of the Mekong

Mekong river surrounded by rainforest and mountains
The Mekong River is a complex ecosystem

The Wonders of the Mekong project is working on conservation efforts within the Mekong River Basin which will help the endangered Mekong giant catfish. The project started in 2017 and is based in Cambodia with funding from the United States Agency for International Development (USAID) [14]. Goals of the project are research, training, education and communication about the Mekong River and threats to its biodiversity including the Mekong giant catfish[14]. Seven different types of communication strategies have been used by Wonders of the Mekong to educate Cambodians about the Mekong ecosystem, threats of overfishing and conservation efforts[15]. One of the strategies included in person field trips which has helped generate income for locals[15]. Increased ecotourism to the area could be a potential source of alternative income for locals, who otherwise rely on fishing, in addition to helping fund conservation efforts. Social media is being used as another avenue of communication as Wonders of Mekong have an active Facebook page that highlights the issues that the Mekong is facing along with promoting the work that is being done. Wonders of Mekong have also held release events where captive raised Mekong giant catfish have been released [7]. These fish were tagged prior to their release to allow researchers to study their ecology and gain better insights to inform conservation efforts. The largest of the Mekong giant catfish to be released was 5 feet long and the fish were released into a government operated fish reserve in Tonle Sap Lake with the hopes of finding out how well a fish reserve will work for conservation of threatened species[16]. Engaging local communities in events, like this release, along with educating the general public in Cambodia is helpful to building a foundation of people who will work to protect the Mekong giant catfish and the greater ecosystem the fish needs to thrive.

The World Wildlife Fund's Actions

WWF implemented a study to identify the spawning sites and the migration patterns for the Mekong giant catfish, as there is little known about them. They developed a conservation agreement between the local fishermen communities and authorities in the Chiang Rai Province in Thailand to stop the fishing of the Mekong giant catfish, as well as to compensate fishing communities for the loss of income. This project started in 2007, and is currently in progress.[17] The second conservation effort by WWF is to help involved countries to implement a joint management plan.

In 2004, the first fish conservation zone on Xe Bang Hieng River in Lao PDR was established, with the WWF's assistance developing a co-management plan for the important aquatic habitat. This zone covers a variety of habitats, including the deep water that is an essential habitat for the Mekong giant catfish. The project "encourages communities to use resources sustainably by increasing the capacity of both community residents and government officials to apply indicators of sustainability to manage resources." according to the WWF.[18] These conservation zones aim to protect the diverse and endangered species that inhabit the Mekong river basin.

UNESCO World Heritage Site

The Cambodian government has also put forth a proposal that a portion of the Mekong River be given World Heritage Site Biosphere Reverse designation which would aid in the conservation efforts as it is important habitat for the Mekong giant catfish and the giant freshwater stingray[19], amongst many other species. The hope is that getting this designation would have the same impact on species that has been seen with the Tonle Sap Lake Reserve[19]. There is no information on when a decision will be made by UNESCO. Although a new biosphere reserve could be helpful for the conservation of the Mekong giant catfish it alone will not be enough. A new fish reserve would need to be combined with other conservation efforts to ensure proper protection which would enable the population size to increase to the point where the Mekong giant catfish is no longer endangered.

Conservation Recommendations

Whilst current conservation efforts from projects such as the Wonders of Mekong are making a positive difference to the giant catfish, further action is required to recover the rapidly declining species. As mentioned previously, the Mekong giant catfish is a migratory species that relies on access to upstream spawning grounds to reproduce, and this access is being significantly restricted by the prolific hydroelectric dams being constructed along the Mekong river. Conservation of migratory species often poses the challenge of multilateral cooperation, as the health of a population is dependent on ecosystem health and resources across the entirety of its migratory path. In the case of the Mekong river, the countries such as Myanmar, Laos, Cambodia, and Thailand must pursue a collaborative solution, because even if one country is uncooperative and inhibits giant catfish migration, then the efforts of other countries may be in vain. The importance of multilateral cooperation has been acknowledged in the First Mekong River Commission Summit in 2010 by the four prime ministers of the Lower Mekong[20], but this is only the first step.

One of the strongest recommendations from the WWF is that the cost-benefit analysis of the hydroelectric schemes is thoroughly conducted. Whilst the economic benefits from revenue and environmental benefits of renewable energy are obvious, there are many hidden costs associated with the impending ecosystem collapse that would ensue. Dam construction would completely remove the ecosystem connectivity in the Mekong, contributing to its declining integrity[20]. The lower Mekong region is one of the most agriculturally productive in the world, heavily dependent on the ecologically thriving river system that provides nutrients and life to the neighboring farmland. The economic costs of further dam construction would be significant in the long run, and must be considered in the cost-benefit analysis of this project that the Mekong giant catfish's survival depends on.

The Sayaboury Dam

A photo of a dam wall creating a lake along the Mekong river
One of many dams along the Mekong River

One extremely important action that must be taken in order to conserve the Mekong giant catfish: the management of the Sayaboury dam project. The Sayaboury dam is a hydroelectric dam in the northwest of Laos that will almost certainly guarantee the extinction of the Mekong giant catfish[20]. The dam is affects the main body of the Mekong river and prevents any migration of the lower Mekong populations upstream past this point, where one of the last remaining spawning grounds exists. Without access to these spawning grounds, the population of Mekong giant catfish will inevitably decline into extinction[20]. Therefore, the conservation of this species is dependent on mechanisms that can allow passage of these fish such as fish ladders. Designed to allow the passage of migratory species such as the Mekong giant catfish, fish ladders were pivotal in the negotiations that permitted the dam project to be constructed. However, these fish ladders have proven to be ineffective at sustaining the populations of giant catfish, and are known to ineffective in tropical rivers[21] . Therefore, successful bypassing of the Sayaboury dam and conservation of the Mekong giant catfish relies on the technological innovation of fish ladders to improve their effectiveness.

Flagship Species

In addition to conservation efforts already underway another potential conservation strategy that could be employed is using the Mekong giant catfish or another Mekong megafauna species as a flagship species. Flagship species are characterized as charismatic species, such as pandas or jaguars, that can attract conservation funding and the conservation of these species has been shown in some cases to help protect other species within their habitat range[22]. Highlighting a specific species to be the flagship species to attract funding and attention to the threats that biodiversity in the Mekong River Basin are facing could be beneficial way to ensure not only the conservation of the Mekong giant catfish but to a wide range of species that are also facing many of the same threats from dams, overfishing, and habitat loss and degradation[23].

Giant Freshwater Stingray

Giant freshwater stingray
Urogymnus polylepis

One of the most recently targeted Mekong River flagship species is the giant freshwater stingray (Urogymnus polylepis). This unique species is classified as Endangered by the IUCN, and shares habitat with the Mekong Giant Catfish[24]. The increase in conservation efforts towards the giant freshwater stingray has a specific focus on "regional cooperation... especially in cross-boundary rivers"[24] such as the Mekong river. Even though the giant catfish is not the subject of these initiatives, it will inevitably benefit from more "sensitive development"[24] of infrastructure along the Mekong river as a result of this cross-boundary cooperation between countries. The report recognizes that conservation efforts towards the stingray must aim to increase the overall ecosystem health, which includes the giant catfish, its habitat, spawning grounds, and food sources.

Conclusion

The Mekong giant catfish currently faces many threats and more conservation efforts are needed to ensure their survival. Climate change is likely to further impact many freshwater species including the Mekong giant catfish due to rising water temperatures and changing outflow which will further impact conservation efforts[25]. These threats and mitigating them is also complicated due to the greater Mekong being a transboundary river basin[9]. The decline of the Mekong giant catfish along with the population decline of many other fish in the Mekong presents hardships for locals in the area who rely on fish for their survival and thus make conservation efforts of vital importance[7]. There needs to be a coordinated effort by all the countries in the greater Mekong basin to formulate a strong conservation plan that can be put into action quickly to allow the Mekong giant catfish to recover. Freshwater megafauna has been shown to facilitate many ecosystem service as they play a major role in nutrient cycling and thus the extinction of freshwater megafauna, like the giant Mekong catfish, may have far reaching impacts for the area[26]. Investment into further research is necessary to understand the lifecycle of the Mekong giant catfish and the role it plays in the ecosystem. This research can help facilitate effective conservation plans to bring back this critically endangered species so that future generations can admire the Mekong giant catfish.

References

  1. ↑ "The giant of the Mekong". WWF. Retrieved 4/13/24. Check date values in: |access-date= (help)
  2. ↑ "Mekong Giant Catfish". Asian Species Action Partnership. Retrieved 4/13/24. Check date values in: |access-date= (help)
  3. ↑ "Pangasianodon gigas (Mekong Giant Catfish)". ICUN Redlist. Retrieved 4/13/24. Check date values in: |access-date= (help)
  4. ↑ Hogan, Z.S.; Pengbun, N.; van Zalinge, N. (2001). [chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://thesiamsociety.org/wp-content/uploads/2020/04/NHBSS_049_2m_Hogan_StatusAndConservati.pdf "Status and conservation of two endangered fish species, the Mekong giant catfish Pangasianodon gigas and the giant carp Catlocarpio siamensis, in Cambodia's Tonle Sap River"] Check |url= value (help) (PDF). Natural History Bulletin of the Siam Society. 49: 269–282.
  5. ↑ 5.00 5.01 5.02 5.03 5.04 5.05 5.06 5.07 5.08 5.09 5.10 5.11 5.12 Hogan, Zeb (July 2012). [chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://www.cepf.net/sites/default/files/mgc_report_1.pdf "A Mekong Giant: Current Status, Threats, and Preliminary Conservation Measures for the Critically Endangered Mekong Giant Catfish"] Check |url= value (help) (PDF). WWF Report.
  6. ↑ 6.00 6.01 6.02 6.03 6.04 6.05 6.06 6.07 6.08 6.09 6.10 6.11 Sukumasavin, Naruepon; Lorenzen, K; Hogan, Z. S. (2015). [chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://fisheriessolutions.org/wp-content/uploads/2019/11/Sukumasavin-et-al-2015-SP13-3-Mekong-giant-catfish.pdf "Matching-up the Population Dynamics of Mekong Giant Catfish with Conservation and Management Strategies"] Check |url= value (help) (PDF). Fish for the People. 13: 2–11.
  7. ↑ 7.0 7.1 7.2 7.3 7.4 7.5 7.6 Lovgren, S (2023). "The Wonders of the Mekong Project Shows Both the Wonders and Conservation Challenges of the Mekong River". Fisheries. 48(7): 279–286.
  8. ↑ 8.0 8.1 8.2 8.3 Hogan, Zeb (April 15 2011). [chrome-extension://efaidnbmnnnibpcajpcglclefindmkaj/https://archive.internationalrivers.org/sites/default/files/attached-files/hogan_fisheries_eia_review.pdf "Imperiled Giant Fish and Mainstream Dams in the Lower Mekong Basin: Assessment of Current Status, Threats, and Mitigation"] Check |url= value (help) (PDF). Check date values in: |year= (help)
  9. ↑ 9.0 9.1 Hogan, Z. (2011). "Pangasianodon gigas". IUCN Red List. Retrieved 03/10/2024. Check date values in: |access-date= (help)
  10. ↑ 10.0 10.1 10.2 10.3 10.4 10.5 Lovgren, Stefan (March 18, 2022). "Inside the plan to save some of the biggest freshwater fish". National Geographic.
  11. ↑ 11.0 11.1 "Threats; Bycatch". World Wildlife Fund. Retrieved April 14, 2024.
  12. ↑ 12.0 12.1 12.2 "Mekong Giant Catfish". Asian Species Action Partnership. Species on the Brink.
  13. ↑ Na-Nakorn, U; Sriphairoj, K; Sukmanomon, S; Poompuang, S; Kamonrat, W (31 July 2006). "Polymorphic microsatellite primers developed from DNA of the endangered Mekong giant catfish, Pangasianodon gigas (Chevey) and cross-species amplification in three species of Pangasius". Molecular Ecology Notes. 6 (4): 1174–1176 – via Wiley Online Library.
  14. ↑ 14.0 14.1 "Wonders of the Mekong". U.S. Agency for International Development.
  15. ↑ 15.0 15.1 Loury, E; Eschenroeder, J; Seat, L; Chea, S; Chhut, C; Kritsanavarin, S; Lovgren, S; Ramsay, E; Thao, D (2021). "Communicating for Aquatic Conservation in Cambodia and Beyond: Lessons Learned from In-Person and Media-Based Environmental Education and Outreach Strategies". Water.
  16. ↑ Wolterbeek, Mike (March 22, 2022). "World's largest, most endangered freshwater fishes released in Cambodian lake". Nevada Today.
  17. ↑ "Giant catfish conservation in the Mekong". World Wildlife Fund for Nature. 2020. Retrieved 03/10/2024. Check date values in: |access-date= (help)
  18. ↑ "Fish conservation zone established in Lao PDR". WWF. 5/3/2004. Retrieved 4/13/24. Check date values in: |access-date=, |date= (help)
  19. ↑ 19.0 19.1 Lee, D; Eschenroeder, J; Baumgartner, L; Chan, B; Chandra, S; Chea, S; Chhut, C; Everest, E; Hom, R (May 2023). "World Heritage, hydropower, and earth's largest freshwater fish". Water. 15.
  20. ↑ 20.0 20.1 20.2 20.3 Thompson, Christian (14 May). River of Giants. WWF. Check date values in: |date= (help)
  21. ↑ Fawthrop, Tom (2024). "Where Have All the Mekong River's Fish Gone?". The Diplomat.
  22. ↑ Carrizo, S; Jähnig, S; Bremerich, V; Freyhof, J; Harrison, I; He, F; Langhans, S; Tockner, K; Zarfl, C (September 2017). "Freshwater megafauna: Flagships for freshwater biodiversity under threat". BioScience. 67: 919–927.
  23. ↑ He, F; Zarfl, C; Henshaw, A; Henshaw, A; Darwall, W; Tockner, K; Jähnig, S (February 2017). "Disappearing giants: A review of threats to freshwater megafauna". Wiley Interdisciplinary Reviews. Water.
  24. ↑ 24.0 24.1 24.2 "Species conservation action plan being developed for giant freshwater stingray" (PDF). Catch and Culture - Environment. 29: 10–15. December 2023 – via Mekong River Commission for Sustainable Development.
  25. ↑ Ahmed, S; Kumar, P; Kabir, M; Zuhara, F; Mehjabin, A; Tasannum, N; Hoang, A; Kabir, Z; Mofijur, M (November 2022). "Threats, challenges and sustainable conservation strategies for freshwater biodiversity". Environmental Research.
  26. ↑ He, F; Svenning, J; Chen, X; Tockner, K; Kuemmerle, T; le Roux, E; Moleón, M; Gessner, J; Jähnig, S (September 2017). "Freshwater megafauna shape ecosystems and facilitate restoration". Biological Reviews. 67: 919–927.


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