Transporting Juvenile Salmonids Around Dams Impairs Adult Migration

Abstract

Mitigation and ecosystem-restoration efforts may have unintended consequences on both target and nontarget populations. Important effects can be displaced in space and time, making them difficult to detect without monitoring at appropriate scales. Here, we examined the effects of a mitigation program for juvenile salmonids on subsequent adult migration behaviors and survival. Juvenile chinook salmon (Oncorhynchus tshawytscha) and steelhead (O. mykiss) were collected and uniquely tagged with passive integrated transponder (PIT) tags at Lower Granite Dam (Washington State, USA) on the Snake River and were then either transported downstream in barges in an effort to reduce out-migration mortality or returned to the river as a control group. Returning adults were collected and radio-tagged at Bonneville Dam (Washington-Oregon, USA) on the Columbia River 1-3 years later and then monitored during approximately 460 km of their homing migrations. The proportion of adults successfully homing was significantly lower, and unaccounted loss and permanent straying into non-natal rivers was higher, for barged fish of both species. On average, barged fish homed to Lower Granite Dam at rates about 10% lower than for in-river migrants. Barged fish were also 1.7-3.4 times more likely than in-river fish to fall back downstream past dams as adults, a behavior strongly associated with lower survival. These results suggest that juvenile transport impaired adult orientation or homing abilities, perhaps by disrupting sequential imprinting processes during juvenile out-migration. While juvenile transportation has clear short-term juvenile-survival benefits, the delayed effects that manifest in adult stages illustrate the need to assess mitigation success throughout the life cycle of target organisms, i.e., the use of fitness-based measures. In the case of Snake River salmonids listed under the Endangered Species Act, the increased straying and potential associated genetic and demographic effects may represent significant risks to successful recovery for both target and nontarget populations.

Behavioral thermoregulation and associated mortality trade-offs in migrating adult steelhead (Oncorhynchus mykiss): variability among sympatric populations

“…The general lack of delayed effects may have been because fish were not spatially aggregated after exiting refugia or because there was no clear threshold temperature for refugia exit timing. The single statistically significant delayed effect was that Snake River fish that were barged as juveniles had lower upstream survival, consistent with a broader pattern of reduced homing and increased migration mortality for transported fish (Keefer et al 2008b).…”

“…Some steelhead were almost certainly last recorded in nonnatal locations (i.e., they were ''strays'') and their population assignment was therefore incorrect. In previous analyses, Snake River steelhead were most likely to stray into the Deschutes and John Day rivers (Keefer et al 2008b), and this should be considered in the interpretation of results. For example, some fish assigned to the Deschutes and John Day rivers were likely from upriver populations, adding a small bias of unknown direction to thermoregulatory estimates for these stocks.…”

Influence of pinniped-caused injuries on the survival of adult Chinook salmon (Oncorhynchus tshawytscha) and steelhead trout (Oncorhynchus mykiss) in the Columbia River basin

“…We also considered interbasin strays to be successful migrants regardless of their ultimate destination. Permanent strays were those last detected inside non-natal tributaries downstream from Lower Granite Dam either at fixed-site aerial radiotelemetry antennas or while mobile tracking (see Keefer et al 2008). Mortalities included salmon and steelhead whose final radiotelemetry records were in reservoirs or at dams.…”

Testing for delayed mortality effects in the early marine life history of Columbia River Basin yearling Chinook salmon

“…Haeseker et al (2012) provided further evidence for hydro-DM by demonstrating that freshwater and ocean survival is correlated, and concluded that increased spill and decreased transit time in the hydrosystem improved survival in both environments. Anderson et al (2011) reviewed the numerous potential causes of transport-DM, including physiological or behavioural stress associated with dam bypass facilities (Budy et al 2002), co-transportation with steelhead salmon Oncorhynchus mykiss (Congleton et al 2000), increased disease transmission (Van Gaest et al 2011), smaller body size and earlier ocean entry of transported smolts (Muir et al 2006) and impaired adult homing abilities (Keefer et al 2008). Although there is no consensus on how delayed mortality of transported spring Chinook salmon occurs, timing of transport appears to be important (Muir et al 2006, Smith et al 2013.…”