Survival of Migrating Salmon Smolts in Large Rivers With and Without Dams

Abstract

The mortality of salmon smolts during their migration out of freshwater and into the ocean has been difficult to measure. In the Columbia River, which has an extensive network of hydroelectric dams, the decline in abundance of adult salmon returning from the ocean since the late 1970s has been ascribed in large measure to the presence of the dams, although the completion of the hydropower system occurred at the same time as large-scale shifts in ocean climate, as measured by climate indices such as the Pacific Decadal Oscillation. We measured the survival of salmon smolts during their migration to sea using elements of the large-scale acoustic telemetry system, the Pacific Ocean Shelf Tracking (POST) array. Survival measurements using acoustic tags were comparable to those obtained independently using the Passive Integrated Transponder (PIT) tag system, which is operational at Columbia and Snake River dams. Because the technology underlying the POST array works in both freshwater and the ocean, it is therefore possible to extend the measurement of survival to large rivers lacking dams, such as the Fraser, and to also extend the measurement of survival to the lower Columbia River and estuary, where there are no dams. Of particular note, survival during the downstream migration of at least some endangered Columbia and Snake River Chinook and steelhead stocks appears to be as high or higher than that of the same species migrating out of the Fraser River in Canada, which lacks dams. Equally surprising, smolt survival during migration through the hydrosystem, when scaled by either the time or distance migrated, is higher than in the lower Columbia River and estuary where dams are absent. Our results raise important questions regarding the factors that are preventing the recovery of salmon stocks in the Columbia and the future health of stocks in the Fraser River.

In situ measurement of coastal ocean movements and survival of juvenile Pacific salmon

“…Only one juvenile BC salmonid was detected on the Alaskan subarray, located some 1,000 km north of QCS, although tagged smolts from the Columbia River and other nonsalmonids were detected there more commonly (21,22). * Steelhead, unlike other species of Pacific salmonids, are thought to move directly offshore (15), so the failure to detect BC steelhead in Alaska may reflect this migration pattern.…”

“…Comparison of marine and freshwater survival rates is complicated because survival may be measured relative to either the time over which fish were observed or the distance they traveled (22,28). We estimated lower overall survival for sockeye and steelhead during their early marine migration than during their down-river migration ( Fig.…”

Seasonal abundance, size, and host selection of western river (Lampetra ayresii) and Pacific (Entosphenus tridentatus) lampreys in the Columbia River estuary

“…2). A single western Table 2 Number of fishes observed with lamprey wounds, by species, in the lower Columbia River estuary during the Estuary Purse Seine study during 2008or 2006. Also provided are the mean percentages of fish of each species with wounds and, for each species, the percentage of cruises in which at least one wounded fish was observed.…”

Reduced flow impacts salmonid smolt emigration in a river with low-head weirs

“…244 - Table 3 half that of 2011 (45%). These levels can be compared with those of conventionally tagged 332 anadromous brown trout smolts in Norway which were estimated to have a survival rate of 24% for 333 their first seaward migration (Berg and Berg, 1987) and with the survival of chinook salmon(Oncorhynchus tshawytscha) smolts migrating down the Snake and Columbia rivers where survival to 335 the sea was estimated to be around 27.5% (Welch et al, 2008). However, the Columbia River system 336 is of much greater size and has much larger impoundments than the Tweed catchment.…”