Overharvest of animals is an acute human impact on many aquatic ecosystems, affecting ecosystem functioning and services. Marine reserves—areas where harvest is prohibited—have gained widespread support to mitigate against the effects of overfishing by enhancing fish diversity and biomass. Spillover effects can also improve harvests in adjacent areas. Many inland waters are facing fishery depletion, but no regions have proposed systematic reserves in response. The potential for protected area benefits in freshwaters may differ from oceans due to physical constraints on dispersal, but such disparities have not been demonstrated. In Southeast Asia, many communities have instituted no-take reserves, which prohibit all forms of harvest within designated river reaches while maintaining high fishing pressure elsewhere. These systems provide an ideal test of whether benefits of reserves proven in marine ecosystems also apply to riverine reserves. We compared fish diversity, density, and trophic structure using time- and area-standardized visual surveys within reserves and adjacent fished areas in a tributary system of the Salween River Basin to test whether benefits of riverine reserves were evident.
Results/Conclusions
Our 3,570 fish observations from seven paired reserve/fished reaches indicate strong response to protection. Fish densities were three times higher inside compared to outside of reserves. Additionally, reserves contained higher species richness, having 54% more taxa on average. Fish community composition also differed between reserve and fished areas. Within reserves, fish species attaining maximum lengths > 30cm had densities 10 times higher than in fished areas, while species having a maximum size < 10cm made up 76% of observations from fished areas. Only three fish taxa were observed in greater numbers in fished areas, glass perch (Parambassis spp.), loaches (Schistura spp.), and spiny eels (Mastacembelus armatus), which are highly cryptic and infrequently harvested. Large piscivores were only observed in reserves, suggesting reserves help retain trophic structure diversity. Anecdotal harvest reports suggest local catches benefit from spillover of fish from reserves, and harvest effort is highly concentrated at reserve boundaries. Our results indicate that riverine reserves currently have strong benefits for the diversity, abundance, and trophic structure of freshwater fishes. Incorporating riverine reserves into existing fisheries management plans may help to improve both ecological and human nutrition outcomes in countries where dependence on inland fisheries is high.