The California Current flows southward from British Columbia bringing cool waters along the West Coast and producing a nutrient-rich upwelling that supports diverse species of forage fish. These play an important and often underappreciated role in the "middle" of the food web. Species, such as the Pacific sardine and northern anchovy, eat plankton and nourish predators such as whales, sea lions, seabirds, sharks, salmon, and tuna. Changes in the availability of forage fish— abundance, size, timing, and location —have been shown to affect populations of predators. In addition, fisheries targeting forage fish may indirectly or directly compete with predator needs. Although some forage fish are consumed by humans, most are used for nonfood products such as animal feed, pet food, and fishing bait.
Forage fish populations are influenced by environmental variation, natural processes, and human activities such as fishing, coastal development, and pollution. They are also subject to natural population cycles. These factors are not always well-understood and are difficult to incorporate into most management approaches. Few forage fisheries are managed, and of those that are, managers rarely consider factors such as predator needs or environmental conditions. Yet economic and ecosystem research indicates that forage fish may be more valuable as prey than as catch.
Several large-scale studies have also recently suggested thresholds of forage fish biomass that should remain in the ocean for predators. Considering the increasing number of threats to forage fish, scientists recommend that efforts should be made to control those factors that we can, such as fishing, to help ensure the maximum resilience possible to factors that we cannot easily control, such as climate change. This approach is important for the health of both forage fish stocks and the predators that rely on them.
Figure: Common forage fish species in the California Current (illustrations are not to scale)