Fishing for Herring Eggs Beats Catching Adults for Ocean Health

Our research examines how different ways of fishing Pacific herring affect both the fish populations and the predators that depend on them for food. Along the coasts of British Columbia and Alaska, fishers target the same herring populations in two completely different ways: some catch spawning adults, while others harvest the eggs those adults produce.

We built stochastic, age-structured models that could simulate herring populations over 40 years under different combinations of egg and adult harvest. We tracked how various fishing intensities affected herring biomass, catch amounts, and whether populations stayed above thresholds needed to sustain seabirds, marine mammals, and other herring predators.

What we discovered was a dramatic asymmetry between the two fishing approaches. High adult harvest rates (above 0.50) could push mean spawning biomass below the fishery closure limit, while egg harvest didn't have this devastating effect until harvest rates exceeded 70-90%. Even then, mean biomass always exceeded 10,000 metric tons until egg harvest exceeded 90%. The trade-offs were equally striking: slightly increasing adult harvest caused dramatic declines in egg catch, but egg harvest had relatively minor effects on adult catch.

"The trade-offs were equally striking: slightly increasing adult harvest caused dramatic declines in egg catch, but egg harvest had relatively minor effects on adult catch."

What struck us most was how our findings challenged conventional thinking about ecosystem-based fisheries management. We expected that ecosystem thresholds designed to protect herring predators would impose the strictest constraints on fishing. Instead, we found that conventional fishery closure rules—designed simply to avoid depleting the herring themselves—were often more restrictive than ecosystem considerations.

These results matter because Pacific herring exemplify a global challenge in marine conservation. Forage fish like herring are nexus species—central to marine food webs and heavily targeted by fisheries. Global estimates suggest forage fish are worth twice as much to other fisheries as they are to the forage fisheries themselves.

Citation

Shelton, Andrew Olaf; Samhouri, Jameal F.; Stier, Adrian C.; Levin, Philip S. (2014). Assessing trade-offs to inform ecosystem-based fisheries management of forage fish. Scientific Reports.

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This paper is Open Access.