Declining fish populations in the Amazon could result in major nutritional shortages for the people who live there, even if efforts are made to supplement the supply with other food sources, according to new research.

The study, published Friday in Science Advances, builds upon previous studies on the effects of changing climate on fish diversity, and also expands upon current understanding of fish ecology by connecting it to human communities.

"In the ecological world, there's almost an axiom at this moment where we consider biodiversity to be important in terms of driving ecosystem function. This is really well known," said first author Sebastian Heilpern, a presidential postdoctoral fellow at Cornell University in the Department of Natural Resources and the Environment. "But we oftentimes fail to link those ecological theories or that basic ecological knowledge to some of these services that have a direct impact on human well-being."

The study focused on freshwater fish in the department of Loreto in the Peruvian Amazon, a large rural area where some 800,000 people rely on fish for survival.

"This is a region where people depend very heavily on fish for their food security, and so they eat upwards of 50 kilograms of fish per year," said Heilpern, who went on to explain that this would be the equivalent of substituting half the meat Americans eat for fish.

While the study focused on a specific region, the implications are far-reaching. Around the world, over a billion people rely on non-cultivated food sources, also known as wild food. And though they are often neglected in studies of fisheries and fish diversity, freshwater fish feed 200 million people around the world, and their fisheries employ 60 million.

However, global freshwater ecosystems are under threat from rising global temperatures and human activities such as pollution. Nearly one-third of freshwater fish are currently threatened with extinction.

"Biodiversity loss crisis is global in scale. And wild food species that we consume, primarily fish, are being hit hard by that," Heilpern said. "A lot of the academic conversation in ecology [is] not informed about the services that people get from inland waters."

To fill this gap in knowledge, the researchers collected samples of 56 of the 60 main food species for the people in Loreto, which they sourced by shopping at local markets and wholesalers. The samples were then analyzed at a government lab in Lima for their nutritional content, focusing on protein, fatty acids and mineral micronutrients such as zinc.

By plotting this information against the fishes' likelihood of surviving ongoing biodiversity loss, the researchers were able to create a mathematical model to predict how this loss would affect the food security of the local population as species die out.

"If fish decline, the quality of the diet will decline," said the study's senior co-author, Shahid Naeem, director of Columbia University's Earth Institute Center for Environmental Sustainability. "Things are definitely declining now, and they could be on the path to crashing eventually."

The model predicted that for every individual species lost, overall nutrient supplies could reduce by 1.76%, which could spell disaster if large numbers of species end up going extinct.

The researchers were also able to adjust their model to keep the overall mass of available food constant as species die out, simulating what happens if surviving species expand in population and fill the gap. They also examined what happens when this loss in fish is supplemented by aquaculture and chicken farming, both common practices in Loreto. These results were published in an earlier study in Nature Food.

"As you [lose] this freshwater fish diversity and you put that biomass or that production into either aquaculture, or chicken, you see these really kind of staggering changes in the types and the amount of nutrients that are supplied," Heilpern said.

In other words, even if the amount of food people in Loreto are eating stays constant as wild fish die out, their nutritional needs will still be under threat. Specifically, people will have less access to omega-3 fatty acids and iron, nutrients that are "major drivers of malnutrition and anemia, which are prevailing across again many of these geographies," according to Heilpern.

Heilpern is now working with the Wildlife Conservation Society on an illustrated field guide for the region's fish, which will also include information about their nutritional value to help inform consumers and fishermen on the natural resources around them.

On a larger scale, the researchers hope that their work will contribute to a more holistic understanding of the intricate relationships between natural resources and biodiversity, a relationship that has been neglected in contemporary ecological research.

"The perspective of bringing what's on your plate and linking that to both biodiversity, and the production of ecosystem services, was something that for me is really interesting and motivating from both an intellectual perspective but also from how important it is in terms of sustainability and making the world a better place," Heilpern said.

The study, "Declining diversity of wild-caught species puts dietary nutrient supplies at risk," Published May 28 in Science Advances, was authored by Sebastian A. Heilpern, Columbia University and Cornell University; Ruth DeFries, María Uriarte and Shahid Naeem, Columbia University; and Kathryn Fiorella, Alexander Flecker and Suresh A. Sethi, Cornell University.