Reservoir ecosystems support large pools of fish biomass

Humans increasingly dominate Earths natural freshwater ecosystems, and many freshwater fisheries resources are imperiled and at-risk of collapse. Yet despite this, the productive capacity of intensively modified freshwater ecosystems is rarely studied. We digitized, and provide open access to, a legacy database containing empirical fish biomass from 1,127 surveys on 301 USA reservoirs. In parallel, we developed a slate of reservoir classification schemas that were deployed to better understand distributions of biomass and secondary production. By fusing these data products, we generated a predictive capacity for understanding the scope of fisheries biomass and secondary production across all USA reservoirs. We estimate total potential fish total standing stock in USA reservoirs is 3.4 billion (B) kg, and annual secondary production is 4.5 B kg y-1. In southern USA alone, total standing stock and secondary production are 1.9 B kg and 2.5 B kg y-1, respectively. We also observe non-linear trends in reservoir fish production and biomass over time, indicating that these ecosystems are quite dynamic. Results demonstrate that reservoirs represent globally relevant pools of freshwater fisheries, in part due to their immense spatial and limnetic footprint. This study further shows that reservoir ecosystems play major roles in food security, and fisheries conservation, even though they are frequently overlooked by freshwater scientists. We encourage additional effort be expended to effectively manage reservoir environments for the good of humanity, biodiversity, and fishery conservation. Significance StatementGlobally, many freshwater fishes and fisheries resources are imperiled and at-risk of collapse. However, previous research overwhelmingly focuses on freshwater fisheries in natural rivers and lakes. This study provides evidence that novel and reconciled ecosystems, such as reservoirs, hold massive pools of freshwater fisheries biomass and may have higher ecological value than previously thought. While dams are patently ecological catastrophes, ecosystem services including secondary fish production provided by reservoirs are nonetheless substantial. Indeed, in many locations (e.g., arid regions), reservoirs are the only remaining fisheries resource. We suggest considerable conservation management is warranted for reservoir fisheries worldwide. Data DepositionCode is available on GitHub (https://github.com/caparisek/res_biomass_USA; DOI 10.5281/zenodo.8316696). All data and reservoir classifications are available on Zenodo (DOI 10.5281/zenodo.8317007). Furthermore, data will also be deposited in the Environmental Data Initiative repository upon acceptance of this manuscript.