June 17, 2024

Freshwater Systems Produce Or Influence More Than Half Of Fish Consumed Globally (Part 2)

For millennia, fish have symbolized wealth and abundance. Thousands of years later, fish are still a critical component of diets for people around the world. This is the second of two posts focused on fisheries from rivers and other freshwater systems, part of a series examining how rivers underpin food security and how managing rivers as systems will be crucial for maintaining their ability to produce food and a range of other benefits.

The first post quantified the amount of global fish consumption that depends on rivers and other freshwater systems. This second post examines threats to freshwater fisheries and solutions to maintain healthy rivers and abundant fisheries.

The first post summarized data and research showing that rivers and other freshwater systems produce—or strongly influence—well over half of all global fish production. All from less than 1% of the surface extent of global water and 0.01% of global water volume!

While it is impressive that so much fish is produced from such a tiny area, globally speaking, it also underscores the vulnerability of that production. Freshwater fisheries can be negatively impacted by pollution, overfishing, and invasive species.

Moreover, freshwater species have been dramatically impacted by the infrastructure built to manage rivers – including dams and levees built to promote food production. An earlier post, focused on irrigation, described how dams built largely to store water for irrigation have led to dramatic declines of fish populations and fisheries in rivers such as the Colorado, San Joaquin and Sacramento. Migratory fish often comprise the most important species within freshwater fisheries and dams are one of the leading causes of the 76% decline of migratory freshwater fish since 1970.

The expansion of hydropower dams is perhaps the greatest current threat to the remaining healthy populations of migratory fish. Studies on the Mekong—the most productive freshwater fishery in the world—found that construction of 11 hydropower dams on the lower mainstem river would reduce populations of migratory fish by 42% while hydropower dams on tributaries of the Mekong could reduce populations by over 20% (i.e., collectively, a two-thirds decline of migratory fish populations).

Many of the dams—including two on the lower mainstem river along with dozens of dams on tributaries—have since been built, and fisheries are declining. Laos is continuing to move forward with additional dams on the Mekong. Migratory fisheries in free-flowing rivers such as the Amazon, Irrawaddy and Salween, are also at risk from proposed hydropower dams.

These examples underscore the urgent need to manage rivers as overall systems – systems that are capable of producing a range of benefits, including food.

I explored solutions to these challenges in past posts, and will continue to explore them with some upcoming posts focused on the Mekong, but will summarize them here:

1. Sustainably manage river systems across multiple sources of food production. As described in the post on irrigation, managing rivers to support irrigated agriculture can negatively impact fisheries, from rivers and floodplains upstream in a basin to the deltas and estuaries where rivers meet the sea. While management decisions often require tradeoffs between services, rivers can be managed to maintain diverse benefits. For example, future expansion of irrigation systems should be done with careful planning such that the needed infrastructure minimizes negative impacts on migratory fish and the transport of sediment needed by deltas (the subject of the next post). Existing systems can be re-operated, including through the release of environmental flows from dams to mimic ecologically important patterns of water levels that are crucial for fish habitat. This flow restoration can be made possible through improvements in irrigation efficiency – but only when coupled with governance mechanisms that allocate the saved water to river ecosystems. On Orgeon’s Wychus Creek, a combination of irrigation efficiency improvements and transfers of water rights improved flow conditions on the creek for fish, increasing the attainment of environmental flow targets from 20% of days to nearly 80%.

2. Nature-based Solutions. Flood risk is rising for much of the world, driven both by climate change and increased development in flood-prone areas. Reconnecting floodplains to rivers can give floodwaters room to spread out and reduce risk for people and property – an example of a Nature-based Solution in which protection or restoration of ecosystems helps address a societal challenge. These interventions can also allow fish to access highly productive floodplain habitats. On the Sacramento River, reconnected floodplains are key to both reducing flood risk and providing habitat for fish. As a Nature-based Solution, floodplain reconnection offers another food-related benefit: the recharge of groundwater that can be used for irrigation. California’s Department of Water Resources has launched a program for Managed Aquifer Recharge, directing floodwaters onto floodplains where the water can infiltrate into the ground, boosting water storage in the soils and aquifers that can be used for irrigation, potentially reducing the amount of water diverted from rivers.

3. Renewable revolution provides substitute for new hydropower dams with high impacts. Although hydropower is currently the world’s largest source of renewable energy, the contribution of other renewable technologies is growing rapidly. It is becoming increasingly clear that the world can meet climate targets without further loss of free-flowing rivers to fragmentation from hydropower dams, with the accompanying loss of migratory fish and sediment for deltas. This opportunity arises due to the renewable revolution: the rapidly falling costs for wind and solar generation and storage technologies, alongside significant advancements in energy efficiency, demand side management and grid management. Due to the renewable revolution, governments no longer have to accept the loss of food sources as an unavoidable tradeoff of providing low-carbon electricity to their people and economies. However, in the Mekong and other places, decisions and funding still need to align around these renewable options at scale before further fragmentation of rivers occur (the subject of upcoming posts).

These solutions for managing rivers to maintain or restore fisheries are focused on how infrastructure is planned and operated. Other solutions include the control of invasive species and the sustainable management of capture fisheries and aquaculture. These solutions are explored further in the Emergency Recovery Plan for Freshwater Biodiversity (I was a co-author) and the WWF report Forgotten Fishes.

Fish have been fundamental to people’s food security for thousands of years. While most attention to fisheries is focused on the oceans, freshwater systems support more than 40% of all fish consumed globally. Adding in estuaries—the habitats defined as being the mixing zone between rivers and ocean—and freshwater systems produce or strongly influence well more than half of all the world’s fish supplies.

The value of fisheries from freshwater systems should be front and center at the UN Food Systems Summit, taking place this week in Rome – and in subsequent fora and policies focused on ensuring global food security.

Rivers are not just flows of water. They are also flows of fish…and food.

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