Up to three-quarters of the biological makeup of freshwater lake fish comes from land vegetation, study finds

Forest loss leads to smaller, less healthy fish living in the lakes they surround, and human activities that reduce vegetation have a greater impact on the aquatic food chain than previously thought, according to a new report.

“Fish are a forest product,” said Andew Tanentzap, lecturer in Plant Sciences at University of Cambridge and an author of the report. The study, “Forests Fuel Fish Growth in Freshwater Deltas,” was published Wednesday in online journal Nature Communications.

For the report, scientists studied yellow perch, an important sport and commercial fish, in freshwater lakes in Sudbury, Ontario — a location that offered a unique perspective because of its history of environmental degradation from mining and metal smelting. This intense industrial activity created acid rain that killed off much of the area’s forest cover.

Former U.S. president Jimmy Carter’s approval of the Clean Air Act in 1977 helped reduce sulfate emissions. Consequently, lake waters in the Sudbury area have recovered in terms of PH levels and metal contamination.

But fish stocks have not, the report points out. Researchers were aware that terrestrial recovery was also slow, and wondered how much of an effect that had on fish growth.

When they studied the fish, researchers found that 30 to 70 percent of their biological makeup came from land resources. Looking deeper, they discovered that organic material from terrestrial sources makes up an important food source for aquatic life in every level of the food chain, from microscopic zooplankton to yellow perch.

With that supplemental food source from land vegetation, fish grow larger, survive longer, and are less susceptible to disease, according to the report.

That means loss of forest cover — from industrial activities such as mining and logging — could have more far-reaching consequences for aquatic ecosystems that previously thought, the report found.

“Should we plant trees around lakes? If so, what types of trees? These are the issues we’re interested in feeding into,” Tanentzap said. “It’s also important for industries, which invest billions but haven’t been able to restore the damage they’ve caused.”