Time‐varying relationships between ocean conditions and sockeye salmon productivity

Abstract

Environmental change is occurring at unprecedented rates in many marine ecosystems. Yet, environmental effects on fish populations are commonly assumed to be constant across time. In this study, I tested whether relationships between ocean conditions and productivity of North American sockeye salmon (Oncorhynchus nerka) stocks have changed over the past six decades. Specifically, I evaluated the evidence for non-stationary relationships between three widely used ocean indices and productivity of 45 sockeye salmon stocks using hierarchical Bayesian models. The ocean indices investigated were the Pacific Decadal Oscillation (PDO), North Pacific Gyre Oscillation (NPGO), and sea surface temperature (SST). I found partial support for time-varying salmon-ocean relationships. Non-stationary relationships were strongest for the NPGO and weaker for the SST and PDO indices. Productivity-NPGO correlations tended to shift gradually over time with opposite trends for stocks in British Columbia (B.C.) and western Alaska; for B.C. stocks, the NPGO correlations shifted from significantly negative prior to 1980 to significantly positive after 1990, whereas for western Alaska stocks, the correlations shifted from positive to negative. Productivity-SST correlations showed declining trends for B.C. and Gulf of Alaska stocks, that is, correlations became more negative (B.C.) or less positive (Gulf of Alaska) over time. For the PDO, correlations weakened during the 1980s for western Alaska and B.C. stocks. Overall, these results provide evidence for time-varying relationships between salmon productivity and environmental conditions over six decades, highlighting the need to recognize that historical responses of salmon populations to environmental change may not be indicative of future responses. K E Y W O R D S climate change, climate index, non-stationary, North Pacific, Pacific salmon, sockeye, temperature, time-varying S U PP O RTI N G I N FO R M ATI O N Additional supporting information may be found online in the Supporting Information section. How to cite this article: Malick MJ. Time-varying relationships between ocean conditions and sockeye salmon productivity.

Unconventional Sea Surface Temperature Regime Around Japan in the 2000s–2010s: Potential Influences on Major Fisheries Resources

“…Our main focus is after 2000, when canonical spatial patterns of the PDO and NPGO mostly disappeared (Litzow et al, 2020). Nonstationary relationships between the PDO/NPGO indices and ecological conditions were also identified particularly in the northeastern Pacific (Schmidt et al, 2014;Litzow et al, 2019;Malick, 2020). Thus, the unconventional regime of SSTs around Japan in the 2000s-2010s should be further studied within a framework of nonstationarity.…”

Quantifying a Novel Climate Through Changes in PDO‐Climate and PDO‐Salmon Relationships

“…These results have important and possibly urgent implications for stakeholders in GOA salmon fisheries. Current management practices, such as a high degree of reliance on hatchery salmon, have arisen during the post‐1988/1989 period, when both hatchery and wild salmon were largely unaffected by ocean climate (Litzow et al, 2018; Malick, 2020). Past experience in the southern range of Pacific salmon indicates that unanticipated outcomes are possible when management approaches fail to respond to change in the sets of abiotic factors controlling fish production in the system (Schindler et al, 2008).…”

Relationships among somatic growth, climate, and fisheries production in an overexploited marine fish from the Gulf of California, Mexico

“…Despite the value of this information for regulating the fishery, we refrained from providing specific predictions on future landings of the fishery due to several sources of uncertainty that require additional research. First, analyses using longer time series (e.g., Malick, 2020) have revealed time‐varying relationships between climate, ocean conditions, and fisheries productivity. Related to this, the physical and ecological effects of the two largest El Niño events (1982–1983; 1997–1998) on ecosystems within the northern GoC were different, the characteristics of El Niño events are predicted to change with global warming, and the projected changes to coastal ecosystems in the northern GoC due to sea‐level rise are unknown (Herrera‐Cervantes et al, 2010; Páez‐Osuna et al, 2016; Yeh et al, 2009).…”

“…The combination of taxonomy, life‐history traits, exploitation history, and management tactics (i.e., catch and effort controls) determine the response of fish populations to climate and the utility of including environmental drivers within stock assessments and forecasting models (Free et al, 2019; Haltuch et al, 2019; Myers, 1998). Therefore, caution must be exercised to guard against spurious predictions that fail to consider time‐varying relationships between oceanic conditions and fisheries production, changes in fishing effort, the reliability of landings data to estimate stock abundance, and other factors (Malick, 2020; Pauly et al, 2013). More empirical studies are needed to understand which life‐history patterns benefit most from the inclusion of environmental covariates within stock assessment models (Haltuch et al, 2019; King & McFarlane, 2003).…”