Deforestation Is Making Fish Weak and Skinny

The loss of trees could eventually spell trouble for the human food chain, say researchers.

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Young perch pulled from Daisy Lake in Ontario. (Andrew Tanentzap)

Humans mistreating the forest might not immediately suggest collateral damage in the aquatic realm. But the link is there, according to researchers who allege deforestation is making fish thin and puny.

To establish a harmful connection – and one that could potentially come around to damage our own food resources – scientists at the University of Cambridge trekked across the ocean to Ontario's Daisy Lake, located on the edge of the historical mining city of Sudbury. They chose this body of water due to an ecological disaster it suffered in the mid-1900s; the nickel-smelting industry produced acid rain that withered and literally blackened the landscape. Today, there are areas of Daisy Lake's shoreline where the trees have grown back, and other parts where the vegetation is still patchy and poor-looking.

The researchers caught yellow perch from both areas, and the physical differences they found were astounding: Fish taken from water near heavy woodland were "fatter" and "larger and stronger," they say. However, perch pulled from places with fewer trees were "much smaller, and consequently much less likely to survive and breed."

The researchers catching fish around the lake shore. (Andrew Tanentzap)

What's to account for these scaly weaklings? It's likely due to their diets, says Cambridge's Andrew Tanentzap. Forest streams carry a lot of carbon-rich material from leaves and other organic detritus into the lake, which is consumed by bacteria. Zooplankton eat this bacteria and then fish eat the plankton, gaining a nutritional boost. 

Fish living in areas with less access to woodland-derived nutrients presumably eat poorer. "Where you have more dissolved forest matter you have more bacteria, more bacteria equals more zooplankton; areas with the most zooplankton had the largest 'fattest' fish," says Tanentzap. He says his team found perch with almost 70 percent of their biomass coming from chemically identified tree carbon, as opposed to carbon that came from other aquatic food sources.

Trouble similar to what's happening in Lake Daisy could reach deeper into the boreal ecosystem, a huge climate zone in the upper Northern Hemisphere that's full of ancient forests. More than 60 percent of the planet's fresh water lies in boreal zones, including Canada and Siberia. "These areas are suffering from human disturbance such as logging, mining, and forest fires resulting from climate change – all occurrences predicted to intensify in coming years," says Tanentzap.

And if deforestation continues, we might expect to eventually see a harmful impact on the human food chain:

"It's estimated that freshwater fishes make up more than 6% of the world's annual animal protein supplies for humans – and the major and often only source of animal protein for low income families across Bangladesh, Indonesia and the Philippines," added Tanentzap.

"While we've only studied boreal regions, these results are likely to bear out globally. Forest loss is damaging aquatic food chains of which many humans are a part."

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