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Bottom-up and top-down control of small pelagic forage fish: factors affecting age-0 herring in the Strait of Georgia, British Columbia

Jennifer L. Boldt1,*, Matthew Thompson1, Christopher N. Rooper2, Douglas E. Hay3, Jacob F. Schweigert3, Terrance J. Quinn II4, Jaclyn S. Cleary1, Chrys M. Neville1

1Fisheries and Oceans Canada (DFO), Nanaimo, BC V9T 6N7, Canada
2National Marine Fisheries Service, Alaska Fisheries Science Center, Seattle, WA 98115, USA
3Emeritus, Fisheries and Oceans Canada, Nanaimo, BC V9T 6N7, Canada
4Juneau Center, School of Fisheries and Ocean Sciences, University of Alaska Fairbanks, AK 99801, USA
*Corresponding author:

ABSTRACT: Small pelagic fish are key planktivores and prey in marine ecosystems, and their population abundances undergo strong temporal and spatial variability. Top-down (predator controlled) and bottom-up (prey-driven) processes during early life history are important for determining forage fish survival and recruitment. We examined biological and environmental factors hypothesized to influence age-0 Pacific herring Clupea pallasi in the Strait of Georgia (SOG), British Columbia, Canada. Primarily bottom-up processes affected interannual variability in age-0 herring abundance and condition, with some evidence of top-down effects on condition. Age-0 herring abundance increased with increasing adult spawning biomass and peaked when most adults spawned about 20 d prior to the peak spring primary production bloom. This timeline would temporally align first-feeding herring larvae with their prey, such as small copepods. Age-0 herring abundance also increased with increasing juvenile salmon abundance, indicating that conditions favourable for herring were also favourable for their predators and competitors. Age-0 herring condition decreased with increasing spawning biomass, increased when most adults spawned closer to the peak spring bloom, increased with increasing temperatures above 8.2°C, and increased then stabilized with increasing prey zooplankton density. Age-0 herring condition had a dome-shaped relationship with predator abundance, indicating that high predator abundances negatively affected fish condition. Study results suggest that density-dependent processes, such as intraspecific competition, may be important in the SOG. A positive correlation between age-0 herring abundance and subsequent age-3 recruit abundance may provide a leading indicator of low recruitment years.

KEY WORDS: Age-0 herring · Abundance · Condition · Bottom-up · Top-down · Forage fish · Strait of Georgia · Density dependence

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Cite this article as: Boldt JL, Thompson M, Rooper CN, Hay DE, Schweigert JF, Quinn TJ II, Cleary JS, Neville CM (2018) Bottom-up and top-down control of small pelagic forage fish: factors affecting age-0 herring in the Strait of Georgia, British Columbia. Mar Ecol Prog Ser

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