Potential Effects of Dams on Migratory Fish in the Mekong River: Lessons from Salmon in the Fraser and Columbia Rivers

Abstract

We compared the effects of water resource development on migratory fish in two North American rivers using a descriptive approach based on four high-level indicators: (1) trends in abundance of Pacific salmon, (2) reliance on artificial production to maintain fisheries, (3) proportion of adult salmon that are wild- versus hatchery-origin, and (4) number of salmon populations needing federal protection to avoid extinction. The two rivers had similar biological and physical features but radically different levels of water resource development: the Fraser River has few dams and all are located in tributaries, whereas the Columbia River has more than 130 large mainstem and tributary dams. Not surprisingly, we found substantial effects of development on salmon in the Columbia River. We related the results to potential effects on migratory fish in the Mekong River where nearly 200 mainstem and tributary dams are installed, under construction, or planned and could have profound effects on its 135 migratory fish species. Impacts will vary with dam location due to differential fish production within the basin, with overall effects likely being greatest from 11 proposed mainstem dams. Minimizing impacts will require decades to design specialized fish passage facilities, dam operations, and artificial production, and is complicated by the Mekong's high diversity and productivity. Prompt action is needed by governments and fisheries managers to plan Mekong water resource development wisely to prevent impacts to the world's most productive inland fisheries, and food security and employment opportunities for millions of people in the region.

Integrated watershed management: evolution, development and emerging trends

“…Most of the salmonid species migrate up the Fraser River to reach their spawning grounds, which have been severely altered due to human development and increasing population. The gold rush of the mid-to-late ninth century led to the establishment of mines and dams, such as that in Quesnel, which decimated a run of 10 million sockeye salmon (Ferguson et al 2011). Dams were also constructed throughout the basin for log storage in the early twentieth century, which blocked migratory routes and destroyed eggs when the log booms were floated downstream.…”

“…The five salmon species are commercially harvested with an economic value of C$41.7 million annually (Ferguson et al 2011), although this has fluctuated markedly in recent years because of government restrictions on catch limits. Additionally, there are several Indigenous communities within the basin that depend on salmon for non-economic purposes such as cultural and spiritual ceremonies and subsistence needs (Ferguson et al 2011). Most of the salmonid species migrate up the Fraser River to reach their spawning grounds, which have been severely altered due to human development and increasing population.…”

“…4). Its headwaters lie in the province's central interior Rocky Mountains, where it flows 1400 km to the southernmost part of the province where it discharges into the Pacific Ocean via the Strait of Georgia (Watson 2004;Ferguson et al 2011;FBC 2015a). The major environmental issues within the basin include ecosystem degradation and water pollution from agriculture, mining, forestry, and industrial and human development; water depletion; and biodiversity loss from habitat destruction and environmental degradation (Gustavson et al 1999).…”

“…The Fraser River is the greatest salmonid-producing system in the world, with seven salmonid species living in the basin-sockeye (Oncorhynchus nerka), pink (Oncorhynchus gorbuscha), chum (Oncorhynchus keta), coho (Oncorhynchus kisutch), and Chinook salmon (Oncorhynchus tshawytscha); and steelhead (Oncorhynchus mykiss) and cutthroat trout (Oncorhynchus clarki) (FBC 2015a;Ferguson et al 2011). The five salmon species are commercially harvested with an economic value of C$41.7 million annually (Ferguson et al 2011), although this has fluctuated markedly in recent years because of government restrictions on catch limits.…”

“…Dams were also constructed throughout the basin for log storage in the early twentieth century, which blocked migratory routes and destroyed eggs when the log booms were floated downstream. Despite the popularity of hydropower dams in British Columbia, there are no dams along the main stem of the Fraser River (Ferguson et al 2011). There are however seven dams along its tributaries that have altered the downstream flows along the migratory routes of all five salmon species (Ferguson et al 2011).…”