Freshwater reserves improve fish stocks – study

Boats by Salween River - main
Boats by Salween River. A new study indicates that freshwater reserves can increase fish density. Copyright: Christophe95 (CC BY-SA 4.0).

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  • Freshwater reserves important in buffering fish populations
  • Overfishing, pollution, invasive species are threats to freshwater fish species
  • Network of community reserves can enhance fish diversity, abundance

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[NEW YORK] Freshwater reserves can significantly increase fish richness, density and biomass relative to adjacent areas where fishing is unrestricted, says a new study conducted in Thailand’s Salween river basin.

Creating reserves helps to buffer fish populations against intensive fishing pressure, land use change and other factors, says Aaron Koning, postdoctoral researcher at the University of Nevada, Reno and lead author of the study, published late November in Nature. He explained that they did the study to test whether benefits documented from marine conservation reserves might also apply to freshwater systems.

“Community-created reserves can enhance fish diversity and abundance locally, and that there are additional benefits of having many reserves in the same river network”

Peter McIntyre, Cornell University

Peter McIntyre, a co-author and a Dwight Webster Sesquicentennial faculty fellow and associate professor of natural resources and the environment at Cornell University, says the findings prove that “community-created reserves can enhance fish diversity and abundance locally, and that there are additional benefits of having many reserves in the same river network”.

“The next step is to try implementing a similar approach in other rivers where the local cultural traditions make reserves enforceable,” McIntyre tells SciDev.Net. “Long-term sustainability of these fisheries may require additional actions but reserves where fishing is prohibited are an excellent first step.”

The researchers focused on the Mae Ngo River along Thailand’s border with Myanmar because South-East Asia has a long history of freshwater conservation reserves. Koning documented more than 50 reserves spread over 1,000 square kilometres of the river valley in 2012. Each of these reserves had been created by a local community to support its own nearby fishing grounds.


Salween River is located in the border of Thailand and Myanmar.
Image credit: Takaeaway (CC BY-SA 3.0).

The researchers surveyed fish communities in 23 separate reserves that ranged in length from 300 metres to two kilometres. Compared to adjacent areas where fishing is unrestricted and intense, the grassroots reserves contained on average 27 per cent more fish species and 124 per cent higher fish density, with a more than twenty-fold increase in overall biomass, they note.


“Our work shows that community-based reserves can be highly successfully at protecting fish,” says Koning.  “Doing this provides some guidelines for how similar reserves may be implemented in other river systems around the world, particularly where human reliance on freshwater fisheries is high.”

Koning acknowledges that inland or freshwater fisheries are a challenge to manage, especially where freshwater fish are important food and nutritional resources, resulting in overfishing or unsustainable harvest practices.

“Many governments don’t have the capacity to monitor inland fisheries or enforce existing regulations where they do exist,” says Koning. “Our study provides a model of community-based, bottom-up conservation and a form of fisheries management that hasn’t often been considered for freshwaters.”

He adds: “Providing fish a refuge from intensive harvest is an important starting point for protecting fish diversity, but many systems will require additional conservation plans that address land-use, pollution, climate change, and things like dams or irrigation infrastructure that can dramatically alter river habitats.”

Steven Cooke, a professor of biology at Carleton University, Ottawa, Canada, says the research is of great importance for freshwater biodiversity conservation for several reasons. “Most notably, this is community-based approach recognising that changes in fish populations will most directly influence the local communities that depend on inland fish and fisheries for their livelihoods and nutritional security.”

He adds: “Community-based approaches incorporate local knowledge and reflect collective goals. This unique model has potential to be adopted in other regions. Indeed, there has been opposition to the use of freshwater protected areas in many locations because efforts have been top-down and fail to incorporate or address concerns of local stakeholders and rights holders.”

According to the International Union for Conservation of Nature, 55 per cent of all fishes rely on freshwater habitats for their survival. Freshwater species are important to local ecosystems, provide sources of food and income to humans and are key to flood and erosion control. But freshwater species are disappearing faster than their marine counterparts due to habitat loss, introduction of alien species, pollution and over harvesting.

Abigail Lynch, research fish biologist, US Geological Survey’s National Climate Adaptation Science Centers, tells SciDev.Net that even though freshwater covers less than one per cent of the earth’s surface, it holds more fish species than all the world’s oceans. “In fact, freshwaters are home to ten per cent of all species. Yet, few freshwater ecosystems have a protected area status.”

“To date, reserves and protected areas, common in marine systems, have had limited evaluation in freshwater systems,” says Lynch. “The researchers demonstrate that ‘no-take’ riverine reserves clearly work in Thailand’s Salween basin.

This piece was produced by SciDev.Net’s Asia & Pacific desk.