Combining Migration History, River Conditions, and Fish Condition to Examine Cross‐Life‐Stage Effects on Marine Survival in Chinook Salmon

Abstract

We examined delayed effects (or carryover effects) on marine survival from the freshwater experiences of migrating Chinook Salmon Oncorhynchus tshawytscha. Juvenile Chinook Salmon that differed in their freshwater experience in passing hydroelectric power dams of the Columbia and Snake rivers (Pacific Northwest) as run-of-the-river or barged fish were tested in challenge experiments at 23.5°C to determine the freshwater survival index m (i.e., the time to 80% mortality). Seasonal patterns of m were best predicted by (1) an index of migration timing (t) at the exit of the hydropower system and a barge index (B) or (2) a temperature exposure index (θ; i.e., 7-d average of river temperatures experienced prior to collection). Other predictors tested included river flow, wet mass, and Fulton's condition factor. Predicted m (m pred ) based on t and B or based on θ was then related to seasonal patterns of marine survival. Significant relationships between m pred and marine survival provide support for the hypothesis that the seasonal patterns of freshwater experiences during hydropower system passage influence the biological condition of juvenile salmon at seawater entry and consequently their seasonal pattern of marine survival to the adult stage. Because temperature is a more direct and biologically relevant variable than migration timing with a barging index offset, further investigation of temperature-related factors affecting the biological condition of anadromous fishes as they exit freshwater-and subsequently their marine survival-is warranted.

Climate change threatens Chinook salmon throughout their life cycle

“…Survival through Columbia and Snake River dams generally now meets recovery targets (>96%) 83 , and cumulative mortality over 500 km of in-river migrating fish (~50%) is similar to that estimated for unregulated rivers of similar length (i.e., Fraser River 84 ). However, slow travel time through slow-flowing reservoirs behind dams, combined with increased surface temperatures in these reservoirs 85 , can potentially result in lower marine survival 86 . Mitigation efforts to increase smolt body size and advance migration timing could increase marine survival 46 , 87 .…”

Review of trap-and-haul for managing Pacific salmonids (Oncorhynchus spp.) in impounded river systems

“…Posttransport survival studies of downstream migrants would help managers understand how factors such as handling and transport methods contribute to delayed mortality of transported fish. There are several good research templates for evaluating post-transport survival questions, with many developed as part of the large-scale juvenile transportation program in the Columbia and Snake rivers (e.g., Muir et al 2006;Rechisky et al 2014;Gosselin and Anderson 2017). Examples include experimental post-transport holding evaluations and a variety of tagging studies to evaluate short-and long-term survival.…”

Survival of prey growing through gape-limited predators

“…Theories have suggested fish need to reach a critical size by a particular life stage [33,34] while others have demonstrated the importance of early marine growth rates [31,35,36]. Furthermore, other studies suggest freshwater growth prior to migration affect adult survival [6,12,37,38]. The properties noted in these studies and others are intrinsic to the model.…”