Biocomplexity in Pacific Herring (Clupea pallasii) of the Salish Sea

Identifying local sources of genetic and demographic diversity in populations is important for understanding the prospects for stability in the face of environmental change. Here, we examine demographic diversity in 19 stocks of Pacific herring (Clupea pallasii) in the Salish Sea, USA using a multivariate auto-regressive state-space (MARSS) model, and data from both acoustic surveys paired with trawls and subtidal egg surveys, to estimate population growth trends. We used states obtained from MARSS analysis to measure portfolio effects in Salish Sea herring, and found that the Salish Sea population as a whole is stabilized by the presence of several separate spawning subpopulations. Biomass time trends of herring populations associated with individual spawning beaches are asynchronous, but share a common negative growth rate across the all stocks. Last, we tested correlations between herring biomass and local environmental conditions using a state-space model. Inclusion of environmental covariates did not improve model fits; environmental factors affecting early life stages of herring may not be manifested in year-to-year fluctuations in adult spawning biomass.  The biocomplexity in the Salish Sea herring stock complex shown here demonstrates the importance of habitat and demographic diversity in Pacific herring for maintaining resilience to environmental perturbations.