Influences of ocean conditions and feeding ecology on the survival of juvenile Chinook Salmon (Oncorhynchus tshawytscha)

Abstract

Recruitment variability in many fish populations is postulated to be influenced by climatic and oceanographic variability. However, a mechanistic understanding of the influence of specific variables on recruitment is generally lacking. Feeding ecology is one possible mechanism that more directly links ocean conditions and recruitment. We test this mechanism using juvenile Chinook Salmon (Oncorhynchus tshawytscha) collected off the west coast of Vancouver Island, British Columbia, Canada, in 2000-2009. Stable isotopes of carbon (d 13 C), an indicator of temperature or primary productivity, and nitrogen (d 15 N), an indicator of trophic position, were taken from muscle tissues of genetically stock-identified salmon. We also collated large-scale climate indices (e.g., Pacific Decadal Oscillation, North Pacific Gyre Oscillation), local climate variables (e.g., sea surface temperature) and copepod community composition across these years. We used a Bayesian network to determine how ocean conditions influenced feeding ecology, and subsequent survival rates. We found that smolt survival of Chinook Salmon is predicted by their d 13 C value, but not their d 15 N. In turn, large-scale climate variability determined the d 13 C values of salmon, thus linking climate to survival through feeding ecology, likely through qualities propagated from the base of the food chain.

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

“…for a year or more. Therefore, populations from the same basin likely share common rearing habitat within the first few months of marine entry and may be affected by more localized environmental factors (Ohlberger et al, 2016;Hertz et al, 2016). Regional specificity in the foraging ecology of juvenile Chinook salmon supports this hypothesis (Hertz et al, 2015).…”

“…Notably, many Chinook salmon populations reside within 100–200 km of their source river systems until their second year at sea (Orsi & Jaenicke, ; Trudel et al., ; Tucker et al., , ), so common rearing habitat may persist for a year or more. Therefore, populations from the same basin likely share common rearing habitat within the first few months of marine entry and may be affected by more localized environmental factors (Ohlberger et al., ; Hertz et al., ). Regional specificity in the foraging ecology of juvenile Chinook salmon supports this hypothesis (Hertz et al., ).…”

“…() utilized regional average annual survival rates for their analyses whereas we included survival rates for individual populations. Although region‐ and basin‐scale marine conditions such as sea surface temperature can be driven by larger climatic processes occurring at the scale of the North Pacific Ocean (Moore et al, b), which in turn can affect the survival rates of Chinook salmon (Hertz et al., ; Sharma et al., ), their effects may be dampened by localized environmental drivers within the Salish Sea.…”

Broader foraging range of ancient short-tailed albatross populations into California coastal waters based on bulk tissue and amino acid isotope analysis

“…In contrast, δ 13 C baseline values ranged from −18.5 to −22.0 ‰ at lower latitudes such as the NPSG, which is likely caused by a combination of lower [CO 2 ] in warmer waters and correspondingly lower δ 13 C, higher phytoplankton growth rates, nutrient limitation, and fractionation effects associated with small phytoplankton cell size (Bidigare et al 1997, Popp et al 1998. The AKDS also had higher δ 13 C values, likely linked to enhanced productivity and larger cells (Pomerleau et al 2014, Hertz et al 2016. While downwelling systems are typically associated with low productivity, the AKDS is highly productive due to eddies and advection that delivers resuspended nutrients to the continental shelf (Stabeno et al 2004).…”

Conservation planning for freshwater–marine carryover effects on Chinook salmon survival

“…Local ecosystem dynamics (e.g., high-lipid copepods at lower trophic levels relate to higher salmon survival) are linked to large-scale oceanographic forcings as indexed by the PDO (Bi et al, 2011). As well, salmon recruitment links to NPGO through food web processes and feeding ecology (Hertz et al, 2016). Multiple ecological pathways link large-scale climate indices to salmon recruitment, but the PDO appears to be more influential than the NPGO or Oceanic Niño indices (Malick, Cox, Peterman, Wainwright, & Peterson, 2015).…”