Assessing Trade-Offs Between Forage Fish Fisheries and Ecosystem Services in the California Current Ecosystem

Marine fisheries are exploiting multiple trophic levels at once, creating multiple commercially valuable stocks and leading to trade-offs between catching one species versus another. Such trade-offs are prevalent with small pelagic fish, called forage fish, such as anchovy, sardine. Forage fish are the main energy source for many commercial predator species, as well as predators that have no direct market value but may have existence value. We constructed a mass-balanced ecosystem model of the California Current to describe the energetic interactions between forage fish, their predators, and fisheries. Then, using a yield trade-off model, we quantified trade-offs between the direct yield of forage fish and the value of leaving forage fish as prey. For predators without commercial catch (seabirds, whales, etc.), this same model was used to determine a change in predator biomass given a change in forage fish yield. The ecosystem model contains 12 forage species and 63 predators. Of those predators, 28 rely on forage fish for at least 25% of their diet. Based on the trophic connections of this food web, we reveal variation in yield trade-offs across forage species and predator and identify the taxonomic scale of fisheries at which trade-offs are more readily predictable.