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• 31. [Article] Downstream rearing of juvenile Chinook salmon abundance, distribution and growth in the Upper Mainstem of the John Day River

  Abstract -- Juvenile spring Chinook (Oncorhynchus tshawytscha) emerge from the gravel in the late winter or early spring, and most follow a life history pattern known as Natal Reach Rearing (NRR) in which ...

  Citation × Citation Citation Abstract Copy Title: Downstream rearing of juvenile Chinook salmon abundance, distribution and growth in the Upper Mainstem of the John Day River Abstract -- Juvenile spring Chinook (Oncorhynchus tshawytscha) emerge from the gravel in the late winter or early spring, and most follow a life history pattern known as Natal Reach Rearing (NRR) in which juvenile fish remain in the stream reaches where they were spawned until their second spring of life when they start migrating towards the ocean (Healey 1991). However, in Columbia River tributaries, some juveniles have been observed following a Downstream Rearing (DSR) life history, in which they start moving downstream during their first spring towards other nursery habitats or perhaps ocean rearing (Copeland & Venditti 2009; Schroeder et al. 2016). Rearing in different habitats during their first year gives fish with these two life histories access to diverse food resources and, it is hypothesized that, this leads to different survival and growth advantages for these two groups. Differences in growth are of interest in efforts to conserve this threatened species because size is positively correlated to survival for salmon across multiple stages of their life cycle (Groot & Margolis 1991; Healey 1991; Quinn & Peterson 1996; Roni et al. 2012) Chinook salmon in the upper John Day River, Oregon, exhibit both NRR and DSR life history patterns. Fish following the DSR life history pattern are larger than NRR fish late in the spring, possibly due to factors such as higher fish density, lower stream productivity, and colder water temperatures in their natal reach than in the downstream reaches. However, this size advantage may be lost due to adverse summer conditions. Hot summer days combined with the withdrawal of water for agriculture lead to stream water temperatures well above lethal thresholds for salmon in many downstream reaches. DSR fish have been observed in tributaries of the mainstem John Day River, however their growth and survival during summer is unknown. Title: Downstream rearing of juvenile Chinook salmon abundance, distribution and growth in the Upper Mainstem of the John Day River Abstract -- Juvenile spring Chinook (Oncorhynchus tshawytscha) emerge from the gravel in the late winter or early spring, and most follow a life history pattern known as Natal Reach Rearing (NRR) in which juvenile fish remain in the stream reaches where they were spawned until their second spring of life when they start migrating towards the ocean (Healey 1991). However, in Columbia River tributaries, some juveniles have been observed following a Downstream Rearing (DSR) life history, in which they start moving downstream during their first spring towards other nursery habitats or perhaps ocean rearing (Copeland & Venditti 2009; Schroeder et al. 2016). Rearing in different habitats during their first year gives fish with these two life histories access to diverse food resources and, it is hypothesized that, this leads to different survival and growth advantages for these two groups. Differences in growth are of interest in efforts to conserve this threatened species because size is positively correlated to survival for salmon across multiple stages of their life cycle (Groot & Margolis 1991; Healey 1991; Quinn & Peterson 1996; Roni et al. 2012) Chinook salmon in the upper John Day River, Oregon, exhibit both NRR and DSR life history patterns. Fish following the DSR life history pattern are larger than NRR fish late in the spring, possibly due to factors such as higher fish density, lower stream productivity, and colder water temperatures in their natal reach than in the downstream reaches. However, this size advantage may be lost due to adverse summer conditions. Hot summer days combined with the withdrawal of water for agriculture lead to stream water temperatures well above lethal thresholds for salmon in many downstream reaches. DSR fish have been observed in tributaries of the mainstem John Day River, however their growth and survival during summer is unknown. Close