Freshwater Systems Produce Or Influence More Than Half Of Fish Consumed Globally (Part 1)

From Ancient Egypt to the Zhou Dynasty to first century Palestine, fish have symbolized wealth and abundance, demonstrating the ancient connection between fish and food security.

Thousands of years later, fish are still a critical component of diets for people around the world. This is the first of two posts focused on fisheries from rivers and other freshwater systems, part of a series that explores 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.

Often overlooked, the value of fisheries from freshwater systems—and the role of rivers in food production more broadly—should be front and center at the UN Food Systems Summit, taking place this week in Rome.

Water covers more than 70% of the Earth’s surface, prompting nicknames for our home such as “blue planet” and “water planet”.

It could also be called the salty planet because that is what you would taste if you took a sip of almost any of that water: nearly 97% of water on earth is contained in the oceans. Of the 3% that is freshwater, almost all of that (more than 99%) is either frozen, in polar ice caps and glaciers, or underground - mostly deep underground.

That means that less than one-tenth of one percent of all that water on our water planet is accessible freshwater within lakes and rivers. To help you visualize this disparity: if the world’s oceans were represented by a typical five-gallon tank of an office water cooler (about 20 liters), freshwater habitats would be 1/3 of one teaspoon (just under 2 milliliters).

But…a lot happens in that 1/3 of a teaspoon.

For example, while the oceans hold 10,000 times more water than freshwater habitats, those lakes and rivers support 40% of all fish that we eat.

The first question you may ask is: how can so many fish come from such a tiny (globally speaking) volume of water?

That tiny volume is spread across various types of freshwater habitats, and while the oceans are incredibly deep—and so, by volume, most ocean water is dark and unproductive—most freshwater habitats are relatively shallow. Within these shallow habitats, the sun can drive food webs to support diverse species of plants and animals. In fact, floodplains and wetlands are among the most diverse and productive habitat types on Earth, and the most productive freshwater fisheries come from rivers connected to extensive floodplains, such as the Amazon, Irrawaddy, and Mekong.

From these rivers, lakes, and associated floodplains, fishers haul in approximately 12 million tons of fish per year, about 13% of all capture fisheries around the world, and enough to feed nearly 200 million people.

However, they almost certainly haul in a lot more than 12 million tons. Many freshwater fisheries are quite small scale with catches that are never recorded or sold within formal markets. Because of this, experts believe the harvest from freshwater systems could be more than 60% higher than what is officially reported, or approximately 19% of global capture fisheries.

Further, most aquaculture production (68%) is from freshwater species—dominated by carp, catfish and tilapia—raised in water from lakes and rivers. Because about half of all fish consumed come from aquaculture, that means that rivers and other freshwater systems produce more than 40% of all fish consumed globally each year, equivalent to about 7% of all animal protein.

For hundreds of millions of people in rural regions of the world, freshwater fish are an essential source of protein – and also a range of micronutrients. Freshwater fisheries also employ at least 60 million people worldwide, more than half of them women.

Rivers also exert a strong influence on a significant portion of ocean fish harvests. Nutrients drive productivity, and nutrients are in scarce supply across much of the open ocean – but they are abundant in estuaries.

What are estuaries? They are defined as the places where rivers meet the ocean, where freshwater and saltwater mix. Estuaries encompass a range of habitats distinct to the swirling dance of water and sediments that occurs when river blends with ocean—mudflats, marshes and, in tropical latitudes, mangrove forests—that are crucial for fish spawning and rearing. But most importantly, from the perspective of productive fisheries, they are where rivers dump their nutrients into the oceans.

As a result, estuaries are highly productive. So productive, in fact, that in the United States, 50-75% of the total “marine” fish harvest comes from estuaries. A recent review found similar proportions from estuaries globally.

These fish are being harvested from water that is generally saltier than freshwater, but then again, productive estuarine habitats aren’t randomly distributed along the coasts—they occur only where rivers hold sway. All in all, the outsized role of estuaries in marine fish harvest should shine an even brighter light on the importance of rivers to global fish production.

While estuarine production falls into a grey zone between freshwater versus ocean harvests, if nothing else it’s safe to say 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 a range of threats. The second blog post on fisheries explores these threats and solutions.