Novel life history tactic observed in fall‐run Chinook Salmon

Life history diversity allows species from bacteria to trees to persist through disturbance and competition (Cole 1954). Diversifying risk through various life history strategies across space and time maintains genetic diversity, population persistence, and range and habitat expansion. Here, we observed for the first time, a novel life history tactic in age 1 (~ 1 yr post fertilization) Chinook salmon (Oncorhynchus tshawytscha), attempting to spawn in the wild alongside large adult (3 yr old) fish that returned from the ocean (Fig. 1). Pacific salmon (Oncorhynchus spp.) have plastic life history tactics that depend on genotype and environmental conditions (Taylor 1990, Gross 1991, Quinn 2005, Bourret et al. 2016). Environmental conditions that dictate these tactics are often associated with growth by a specific time of the year and include factors such as latitude, water temperature, parental spawn timing, nutrients, and food source (Taylor 1990). A “decision” on which tactic to pursue likely happens annually when salmon either remain in freshwater, migrate to the ocean, return to freshwater to spawn, or remain in the ocean for another year (Bourret et al. 2016). Chinook salmon juveniles typically express one of two life history tactics across populations: migrate to the ocean during their first year (ocean type) or remain in freshwater and emigrate during the second year or later (stream type; Quinn 2005). Juveniles that remain in freshwater may also express a third life history tactic, maturation during their second summer as age 2 parr to spawn with returning adults from the ocean, sometimes referred to as precocious parr or microjacks (Quinn 2005). There is also a fourth tactic, where male parr mature in their first summer in their natal stream and spawn with returning adults. This fourth tactic has not been directly observed in the wild before now; instead, it has been described through circumstantial evidence of mature juveniles or mortalities during spawning surveys (Rutter 1903, Rich 1920, Gebhards 1960, Flain 1970, Mullan et al. 1992, Johnson et al. 2012). For this study, snorkel surveys were conducted in the Shasta River, California over a six-year period from 2006 to 2012. During these surveys, mature Chinook salmon parr (age-1; ~1 yr post fertilization) were observed spawning for the first time in the wild. Although the majority of the Chinook salmon leave as age-0 fry during the spring, approximately 4% of juvenile Chinook salmon remained in the Shasta River throughout the summer months (California Department of Fish and Wildlife, unpublished mark–recapture data). A portion of the fish that remained apparently matured and spawned with large adult females after their first summer and without leaving their natal stream. To better understand how mature parr were spawning, underwater cameras were placed adjacent to active redds and approximately 400 min of recordings were made. During snorkel surveys, the most parr observed at a single redd was two, but from the video footage, as many as four parr were present in or near a single redd while spawning activities were taking place. A hierarchy was often observed among mature parr near the redd. A dominant parr, generally the largest, would chase other parr away when they would attempt to enter the redd. After chasing subordinate parr away, the dominant parr would return to