Salish Sea Chinook salmon exhibit weaker coherence in early marine survival trends than coastal populations

Abstract

Identifying factors that influence anadromous Pacific salmon (Oncorhynchus spp.) population dynamics is complicated by their diverse life histories and large geographic range. Over the last several decades, Chinook salmon (O. tshawytscha) populations from coastal areas and the Salish Sea have exhibited substantial variability in abundance. In some cases, populations within the Salish Sea have experienced persistent declines that have not rebounded. We analyzed a time series of early marine survival from 36 hatchery Chinook salmon populations spanning ocean entry years 1980–2008 to quantify spatial and temporal coherence in survival. Overall, we observed higher inter‐population variability in survival for Salish Sea populations than non‐Salish Sea populations. Annual survival patterns of Salish Sea populations covaried over smaller spatial scales and exhibited less synchrony among proximate populations relative to non‐Salish Sea populations. These results were supported by multivariate autoregressive state space (MARSS) models which predominantly identified region‐scale differences in survival trends between northern coastal, southern coastal, Strait of Georgia, and Puget Sound population groupings. Furthermore, Dynamic Factor Analysis (DFA) of regional survival trends showed that survival of southern coastal populations was associated with the North Pacific Gyre Oscillation, a large‐scale ocean circulation pattern, whereas survival of Salish Sea populations was not. In summary, this study demonstrates that survival patterns in Chinook salmon are likely determined by a complex hierarchy of processes operating across a broad range in spatial and temporal scales, presenting challenges to the management of mixed‐stock fisheries.

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

“…These groupings allow for comparisons among groups of salmonids at a finer resolution than would be provided by Evolutionarily Significant Unit groupings as defined by the ESA (National Marine Fisheries Service (NMFS), ) and account for environmental differences among geographically distinct areas. In addition, these groups are consistent with other studies (Ruff et al, ).…”

“…The first documentation of declining abundance of Pacific salmonids occurred following European settlement in the Pacific Northwest (Lichatowich, ). Since that time, a variety of factors including overharvest, rapid habitat alteration and, more recently documented, lower marine survival rates (Kendall et al, ; Ruff et al, ; Zimmerman et al, ) have contributed to the dramatic declines of naturally produced Chinook and coho salmon and steelhead in Puget Sound. The combined narrative of the “4‐H's” of human impacts on salmon and steelhead abundance and survival have helped shape recovery plans (e.g.…”

Declining patterns of Pacific Northwest steelhead trout (Oncorhynchus mykiss) adult abundance and smolt survival in the ocean

“…Because of this overlapping distribution, juvenile steelhead in the Gulf of Alaska experience similar environmental conditions that are correlated at larger spatial scale (Hartt 1980;Mantua et al 1997). The lack of larger-scale covariation in survival rates, consistent in North American salmonid species (Kilduff et al 2014;Pyper et al 2005;Ruff et al 2017;Teo et al 2009;Zimmerman et al 2015), suggests that conditions during the later periods of ocean residence may be less influential in overall marine survival patterns (Logerwell et al 2003;Mueter et al 2005Mueter et al , 2002aPyper et al 2005). The relatively small spatial scale of steelhead populations' smolt survival synchrony, which parallels their early ocean distribution, provides additional support for the second hypothesis above that important processes, including much of the marine mortality of steelhead smolts, occur during their early marine life Pyper et al 2005;Ricker 1976;Welch et al 2011).…”

“…1. e-folding scale (v) is the distance apart at which population correlation coefficients would be reduced to 37% (i.e., e -1 × 100%) of the expected mean correlation at a distance of 0 km, 0 (the intercept). The e-folding scale is an arbitrary measure but provides a common metric to compare the scale of spatial synchrony in smolt survival with that in other studies (e.g., Kilduff et al 2014;Ruff et al 2017;Teo et al 2009;Zimmerman et al 2015). Larger v values suggest similar patterns for populations that are further apart, whereas smaller values imply similarities for close-together populations.…”

“…Recently, there has been increasing concern that poor marine survival of Pacific Northwest (including British Columbia (BC), Washington, and Oregon) steelhead may contribute to their declining abundance and lack of recovery (Moore et al 2015;Ward 2000 Beamish et al 2000;Beetz 2009;Coronado and Hilborn 1998a;Teo et al 2009;Zimmerman et al 2015; and Chinook salmon (Oncorhynchus tshawytscha): Coronado and Hilborn 1998b;Duffy and Beauchamp 2011;Kilduff et al 2014;Ruff et al 2017;Sharma and Liermann 2010;Sharma et al 2013), such an analysis has been done for only one steelhead population -the Keogh River of BC (Ward 2000;Ward and Slaney 1988). There are few large-scale mass mark-recapture or life-cycle monitoring studies (e.g., coded wire tag studies) on steelhead, and few populations are intercepted in marine fisheries, making it more difficult to estimate marine survival rates.…”