Changing central Pacific El Niños reduce stability of North American salmon survival rates

Abstract

Pacific salmon are a dominant component of the northeast Pacific ecosystem. Their status is of concern because salmon abundance is highly variable-including protected stocks, a recently closed fishery, and actively managed fisheries that provide substantial ecosystem services. Variable ocean conditions, such as the Pacific Decadal Oscillation (PDO), have influenced these fisheries, while diminished diversity of freshwater habitats have increased variability via the portfolio effect. We address the question of how recent changes in ocean conditions will affect populations of two salmon species. Since the 1980s, El Niño Southern Oscillation (ENSO) events have been more frequently associated with central tropical Pacific warming (CPW) rather than the canonical eastern Pacific warming ENSO (EPW). CPW is linked to the North Pacific Gyre Oscillation (NPGO), whereas EPW is linked to the PDO, different indicators of northeast Pacific Ocean ecosystem productivity. Here we show that both coho and Chinook salmon survival rates along western North America indicate that the NPGO, rather than the PDO, explains salmon survival since the 1980s. The observed increase in NPGO variance in recent decades was accompanied by an increase in coherence of local survival rates of these two species, increasing salmon variability via the portfolio effect. Such increases in coherence among salmon stocks are usually attributed to controllable freshwater influences such as hatcheries and habitat degradation, but the unknown mechanism underlying the ocean climate effect identified here is not directly subject to management actions.salmon | synchrony | persistence |

Marine growth patterns of southern British Columbia chum salmon explained by interactions between density-dependent competition and changing climate

“…Regardless of salmon biomass, predicted total scale size was positively associated with increases in NPGO. Changes in observed total scale size were associated with changes in NPGO, particularly when PDO was negative, reflecting cooler sea surface temperatures (Mantua and Hare 2002) that increased coastal primary productivity (Di Lorenzo et al 2008;Kilduff et al 2015). Metabolic costs decline when water is cooler, resulting in faster growth, especially when coupled with an increase in food availability (Farley et al 2011;Siddon et al 2013).…”

“…Weakening of subpolar and subtropical gyres decreases primary productivity (Schwing et al 2002;Behrenfeld et al 2006;Di Lorenzo et al 2008) and has been associated with decreased salmon abundance (Kilduff et al 2015), growth (Wells et al 2006), and body size (Jeffrey et al 2017) due to changes in prey species (Kaeriyama et al 2004). As a result of lower metabolic costs (Farley et al 2011;Siddon et al 2013), cooler temperatures have been shown to increase the growth potential of Pacific salmonids.…”

Forcing of Multiyear Extreme Ocean Temperatures that Impacted California Current Living Marine Resources in 2016

“…Warm periods in the CCLME are characterized by sharp reductions in cool, nutrientrich, highly productive upwelled and subarctic water (Chavez et al 2002;Checkley and Barth 2009), a shift from lipid-rich to lipid-poor zooplankton (Peterson and Schwing 2003), and an inf lux of predators to the nearshore areas critical for salmon early marine survival (e.g., Pearcy 1992; Wells et al 2017). These shifts in the prey base and predator distributions favor reduced growth and survival rates for CCLME salmon (e.g., Daly et al 2017), and anomalously warm CCLME SSTs are associated with low post-release survival rates for hatchery-origin coho and Chinook salmon from southeast Alaska to California (Sharma et al 2012;Kilduff et al 2015). While links between salmon abundance (or catch) and SST are not easily evaluated with time series correlations (see online supplement material), a strong link between record-warm 2014-16 CCLME SSTs and negative impacts on the West Coast salmon fishery in 2016 is evidenced by a shift to subtropical species and widespread negative impacts (increased mortality rates, reduced reproductive success and/or abundance) on top predators like sea birds, salmon, and marine mammals that typically thrive under neutral or cool SST conditions (Cavole et al 2016;Peterson et al 2016;Welch 2016).…”

Impact of El Niño Southern Oscillation on infectious disease hospitalization risk in the United States

“…Furthermore, although ENSO effects are global, there is variability in the magnitude of impact of ENSO effects, with some regions considered "teleconnected" to ENSO (i.e., they experience climatic anomalies linked to ENSO anomalies despite being many thousands of kilometers away) whereas other regions are nonteleconnected (12,14). As such, ENSO represents a useful natural experiment that may be used to infer effects of altered climatic patterns on a variety of phenomena, including conflict (12), vegetation abundance (17), health of fisheries (20), agricultural productivity (21), and infectious diseases (22).…”