Changing salmon: An analysis of body mass, abundance, survival, and productivity trends across 45 years in Puget Sound

Abstract

Pacific salmon and trout (Oncorhynchus spp., Salmonidae) of the Puget Sound region of Washington State, USA, have experienced recent and longer‐term (multidecadal) variability in abundance while supporting robust fisheries. As part of the post‐season salmon management process, population‐specific estimates of total adult abundance to Puget Sound (Strait of Juan de Fuca) for pink (O. gorbuscha), chum (O. keta), coho (O. kisutch), sockeye (O. nerka), and Chinook (O. tshawytscha) salmon and steelhead trout (O. mykiss) are calculated annually. We compiled annual estimates of body mass, abundance and survival of hatchery‐ and naturally produced salmon from 1970 to 2015 to compare spatial and temporal patterns across species. Average weights of adult salmon and steelhead returning to Puget Sound, with the exception of coho salmon, have decreased since the 1970s. Temporal trends in abundance, survival and productivity varied by species and origin (hatchery vs. naturally produced). Generally, abundance and survival rates of natural‐origin species decreased whereas those of hatchery‐produced species did not, which is in contrast with other studies' general conclusions of decreasing survival among Puget Sound salmonids. Species diversity has decreased in recent years, with salmonids that rely on a short freshwater rearing phase in the natural environment (hatchery‐produced fish and naturally produced pink and chum) representing >90% of total returns in most years. This new information reveals patterns of body size, abundance, survival and productivity across species, life history and rearing type over the past 45 years and, in doing so, demonstrates the strength in multidecadal, multifactor time series to critically evaluate salmonid species.

A mobile sex-determining region, male-specific haplotypes, and rearing environment influence age at maturity in Chinook salmon

“…In concert with behavioral and size differences, individual sneaker males outcompete dominant males under sperm competition (Vladić et al 2010, Young et al 2013) and as a group can sire large portions of offspring in a population (Ford et al 2015b). Despite the importance of variation in age at maturity, many populations are exhibiting long-term declines in size and age at maturity (Ricker 1981, Lewis et al 2015, Ohlberger et al 2018, Losee et al 2019) that can lead to loss of life history diversity and decreases in population stability. Potential mechanisms for these widespread declines in size and age at maturity include fisheries induced evolution (Sharpe and Hendry 2009), size-selective marine predation (Ohlberger et al 2019, Seitz et al 2019), and hatchery breeding and rearing practices (Hankin et al 2009).…”

Ecological implications of changing hatchery practices for Chinook salmon in the Salish Sea

“…7. Further, the differences between juvenile salmon of hatchery and natural origin we identify here may be helpful in explaining their disparate marine survival rates (Losee et al 2019) and even illuminate strategies to improve hatchery performance in the future. The size of the circle in each region is proportional to the relative contribution to each population.…”

“…These changes may have implications for interactions between young salmon and marine mammal, avian, and fish predator assemblages in the Salish Sea, in addition to salmon of natural origin. Further, the differences between juvenile salmon of hatchery and natural origin we identify here may be helpful in explaining their disparate marine survival rates (Losee et al 2019) and even illuminate strategies to improve hatchery performance in the future.…”

“…Distributions for natural Chinook from the Puget Sound are based on trap data (see Materials and Methods). Chinook salmon of natural origin, which are typically smaller than hatchery fish, also survive at significantly higher rates (Claiborne et al 2014, Neville et al 2015, Losee et al 2019. The length range associated with Lance et al (2012) is based on the season with the highest percentages of juvenile Chinook in the seal diet (July-September).…”

“…Since 2010, the number of Chinook released after June 15 in the Salish Sea has been reduced by 63%, compared to years prior to 1990. Chinook salmon of natural origin, which are typically smaller than hatchery fish, also survive at significantly higher rates (Claiborne et al 2014, Neville et al 2015, Losee et al 2019.…”