Quantifying the Magnitude and Mechanisms Driving Pacific Herring (Clupea pallasi) Egg Loss on the Central Coast of
British Columbia, Canada

Pacific herring (Clupea pallasi) play a fundamental ecological and socio-economic role in marine ecosystems and have exhibited declining trends in British Columbia, Canada, over the past decade. The rate of herring egg loss following spawning events is a key parameter used to estimate population productivity, however, it is highly uncertain. We quantified the magnitude, spatial variation and mechanisms driving egg loss along BC's Central Coast using observational surveys and an experiment. Depending on the modeling approach, we estimated regional egg loss rates (Z) ranging from 0.152 ± 0.022 to 0.177 ± 0.027, the equivalent of 59-75% eggs loss over 6.8 days, the average lag between spawn deposition and survey. Loss rates varied by 4.5 orders of magnitude among sites. Spawn area was found to positively influence egg loss rates based on our observational study, while evidence from our experiment suggests that predation and habitat type were strong drivers of loss. Modeling approach, parameter uncertainty, and site-level variability in egg loss rates need to be accounted for when estimating Pacific herring abundance and its associated uncertainty.