Factors driving spatial variation in egg survival of an ecologically and culturally important forage fish

Abstract

1. Low trophic-level forage fish are experiencing global declines, influencing coupled humanocean systems worldwide. Along the northwest coast of North America, declining trajectories of Pacific herring (Clupea pallasii) have prompted interest in improving the understanding of its population and community dynamics to better guide future conservation and management strategies.2. To improve future population estimates and understanding of the ecological factors governing herring egg survival, the magnitude, spatial variation and mechanisms driving herring egg loss rates were quantified. This was achieved by way of repeated observational field surveys and a predator exclusion experiment.3. Observational surveys revealed that regional egg loss rates (Z) were substantial and ranged from 0.101 ± 0.019 to 0.134 ± 0.028, the equivalent of 88-94% egg loss over a 21 day incubation period, or 50-60% egg loss over 6.8 days, the average time lag between spawn deposition and annual egg surveys. Furthermore, spatial variation was high, with egg loss rates varying 5-fold among study sites. Depth, time since spawn, and spawn area were primary spatial drivers of egg loss, but predator abundance and exposure were secondarily important. 4. Experimental evidence showed that benthic predation and habitat type were strong drivers of egg loss, suggesting that a high proportion of eggs, particularly those spawned on benthic substrates, are consumed by predators. 5. These results have important conservation implications for managers and ecologists seeking to estimate herring biomass and to understand the environmental influences on predator-prey interactions that affect herring dynamics.

Measuring social-ecological resilience reveals opportunities for transforming environmental governance

“…4, Tables A3.1 and A4.1). These declines in system diversity based on expert knowledge are supported by multiple sources of empirical evidence from quantitative scientific sources (Martell et al 2012, Shelton et al 2014, Keeling et al 2017. Importantly, we also detected slight but nonsignificant signs of recovery among several resilience metrics in the most recent environmental justice regime (Fig.…”

Herring supports Northeast Pacific predators and fisheries: Insights from ecosystem modelling and management strategy evaluation

“…Raising B lim to 0.70–0.80 B 0 , also suggested by the Task Force [ 2 ], would likely be even more effective, but our EwE model could not consistently produce herring biomasses at this level, likely due to poor herring recovery or inadequate herring prey availability in the current Northeast Pacific ecosystem. A recent study [ 72 ] also recommended using B lim > 0.25 B 0 in British Columbia herring fisheries to account for the ecosystem role of herring and for stock assessment error due to variable egg loss rates and spawn survey catchability.…”

High pCO2 does not alter the thermal plasticity of developing Pacific herring embryos during a marine heatwave

“…High P CO 2 also increased time to hatch in embryos of the northern sand lance, Ammodytes dubius , where the delay was thought to be caused by low pH interfering with the hatching process directly ( Murray et al, 2019 ). Regardless of the mechanism, a longer time to hatch is unlikely to be adaptive because it would exacerbate the very high rates of predation inflicted upon Pacific herring eggs ( Keeling et al, 2017 ). However, these small effects should not be overstated and our findings join the bulk of experimental evidence showing that high P CO 2 conditions consistent with near-future ocean conditions have limited effects (<±10%) on the physiological rates of most marine fish embryos ( Flynn et al, 2015 ; Lefevre, 2019 ; Leo et al, 2018 ; Schwemmer et al, 2020 ).…”