The Columbia River was first dammed in the late 1930s, and following the construction of the Bonneville dam numerous other dams were built to harvest the hydro electric potential of this large river. As concerns about fish passage started to be raised fish ladders were installed to allow movement of adult fish – however, fish ladders do not accommodate juvenile fish. Today the options for salmon smolts migrating downriver include a) passage through the turbines b) bypass systems which allow juvenile fish to go around the dam to an area downstream c) going through spill gates (water fall) d) collection and transport downstream in barges or tank truck to avoid passage through the dams.
Cumulative survival estimates (± 95% CIs) for In-River and Transported Chinook smolts from the Snake River basin, 2006, 08, 09, Panels represent survival conditional on survival to McGowans Channel below Bonneville Dam (i.e., survival of IR smolts was adjusted to exclude mortality occurring prior to McGowans Channel).
Barging of salmon smolts has increased over the years – at great expense – to 20 million fish per year or more, in an attempt to lower in-river mortalities and subsequently boost the adult returns to the river. Although transportation of spring Chinook smolts from the Snake River basin has resulted in minor improvements in adult returns, the question remains as to why these improvements are neither consistently nor substantially better than for in-river migrating smolts. The variability in survival, or returns, has led to the hypothesis that transportation induces additional stress, and thereby reductions in survival after the transported smolts are released, a theory usually termed differential-delayed mortality.
From 2006 to 2009 Kintama used acoustic technology to test the differential-delayed mortality hypothesis in the Columbia River by comparing post-Bonneville Dam survival of Snake River smolts that migrated in-river to smolts transported around dams by barge and released below the Bonneville Dam.
We found that Post-Bonneville survival to the coastal ocean arrays, to the northern tip of Vancouver Island, was either statistically indistinguishable or better for the transported groups. Therefore, our study does not support the hypothesis that transportation causes significant differential delayed mortality.
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