Since the late 1990’s, NOAA's Northwest Fisheries Science Center (NWFSC) has been studying the physical, biological and ecological mechanisms that control the early marine survival of juvenile salmonids originating from the Columbia River Basin.   The overall purpose of this study is to identify the mechanisms that determine the importance of the Columbia River plume and near coastal ocean environments to overall salmonid survival and adult returns and then provide this information to managers in the Columbia River Basin.  Periods of high or low ocean productivity can mask underlying trends in freshwater habitat productivity and could lead to a misinterpretation of the proximate cause of trends in survival or adults returns.

We have found that early ocean growth and survival of Columbia River Basin juvenile salmonids are determined by physical processes operating at multiple scales that affect both bottom-up (food web) and top-down processes (predation and competition).  Many aspects of the early marine ecology of juvenile salmon such as ocean distribution, diet, time and size of ocean entry vary between species, population groups, and life history types.  Although we have not fully analyzed all species and population groups within the Basin, results of our work to date suggest that much of the variability in overall survival from the smolt-to-adult life stage (SAR) of Columbia River Basin salmonids is a function of ocean conditions.  In particular, for a number of species and populations groups, early ocean life is a critical period.  Early ocean residence can vary within and between genetic stocks and life history types but we define it in this proposed work as approximately the first 60 days the fish are in the near coastal ocean (which includes the plume).  Conditions the fish experience during this period can be strongly related to adult returns and overall SAR rates, although no single ocean factor or set of factors account for variability in ocean survival for all species and population groups we are studying.

Purpose:  
This plume and nearshore ocean research addresses RPA (Reasonable and Prudent Alternatives) actions 58.3, 58.4, 61.1, 61.2 and 61.4.  Overall, this work seeks to evaluate how the experience of juvenile salmonids in the estuary, plume, and near coastal ocean interact to affect their survival. Information derived from plume and nearshore ocean research is needed to increase our ability to adaptively manage FCRPS mitigation actions and implement Reasonable and Prudent Alternatives (RPAs).  This includes informing FCRPS mitigation actions to improve the survival of juveniles during residence in and migration through the estuary and plume.