The past decade has seen increased international recognition of the importance of the services provided by natural ecosystems. It is unclear however whether such international awareness will lead to improved environmental management in many regions. We explore this issue by examining the specific case of fish migration and dams on the Mekong river. We determine that dams on the Mekong mainstem and major tributaries will have a major impact on the basin's fisheries and the people who depend upon them for food and income. We find no evidence that current moves towards dam construction will stop, and consider two scenarios for the future of the fisheries and other ecosystems of the basin. We conclude that major investment is required in innovative technology to reduce the loss of ecosystem services, and alternative livelihood strategies to cope with the losses that do occur.

Caspian terns Sterna caspia and double-crested cormorants Phalacrocorax auritus that colonize dredge-spoil islands in the Columbia River estuary prey upon millions of juvenile Pacific salmonids annually. We estimated the relative vulnerability of various salmonid stocks to these predators by using data from passive integrated transponder (PIT) tags detected on these colonies; 96,382 tags were detected from the 1998-2000 migration years. On tern colonies, detection rates were highest for tags from steelhead Oncorhynchus mykiss and lowest for tags from yearling chinook salmon O. tshawytscha. However, detection rates on cormorant colonies were similar for tags from steelhead and coho salmon O. kisutch but lower for tags from yearling chinook salmon. Analyses based on migration history showed tags of transported fish were frequently detected in lower proportions than those of their counterparts that migrated in-river, the pattern being most pronounced in steelhead. Analyses based on origin (hatchery versus wild) showed similar detection proportions for the tags of wild versus hatchery steelhead on both tern and cormorant colonies. In contrast, 3.1% of hatchery versus 1.1% of wild chinook salmon tags previously detected at Bonneville Dam were detected on a colony, the greater vulnerability of hatchery fish being more pronounced on tern colonies. These tags accounted for 11.5% of steelhead, 4.6% of coho salmon, and 2.6% of yearling chinook salmon detected at Bonneville Dam, the last downstream impoundment encountered by seaward migrants. These estimates of predation are minimal because detection efficiency was not 100% and tags from many salmonid prey were not deposited on a nesting colony.

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.

We evaluated the survival of juvenile salmon through turbines in Columbia River dams and found no differences between two operations but strong evidence of delayed mortality from turbine passage. After tagging with a passive integrated transponder (PIT) tag and a radio tag, yearling Chinook salmon Oncorhynchus tshawytscha were released at McNary Dam on the Columbia River through a turbine operating both within 1% of peak efficiency (a discharge rate of 317 m3/s) and outside the 1% range at the maximum blade angle (464 m3/s). Estimated relative survival to a detection array 15 km downstream was 0.871 at 317 m3/s and 0.856 at 464 m3/s and 0.858 and 0.814, respectively, to an array 46 km downstream. The highest point estimates of survival occurred under the lower discharge, suggesting that operating turbines within 1% of peak efficiency is a useful guideline for fish protection at McNary Dam. In a concurrent evaluation using balloon tags, estimated mean direct survival ranged from 0.930 to 0.946. Radio tag estimates were significantly lower than balloon tag estimates under both operations. Based on these differences, we estimated that delayed mortality comprised from 46% to 70% of total estimated mortality. We reviewed the literature and concluded that delayed mortality was caused by sublethal impacts to fish sensory systems, which increased vulnerability to predation in the tailrace. We recommend that future research to improve turbine designs and operations for fish passage focus on this major component of mortality.