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Why the Littlest Fish Matter a Whole Lot

Littlest Fish

Top predators along the California coast are having a rough year. Recently starving sea lions have showed up on California beaches and are clamoring for fish at the mouth of Oregon's Columbia River; tens of thousands of dead Cassin’s Auklets have washed up on shores from Alaska to California. Although we cannot say precisely why these animals are having such a hard time finding food, we can point to a problem with their food source, forage fish.

What exactly are forage fish? They are the small, pelagic, schooling fish that form large "bait balls" in the ocean. Think anchovies, sardines and herring, but also lesser-known species such as sand lance, smelt, and saury. Forage fish eat microscopic plants and animals called plankton and become, in turn, a nutrient-rich superfood for everything from larger fish such as salmon and cod, to seabirds like puffins and auklets, and marine mammals like humpback whales and sea lions. (Perhaps somewhat confusingly, forage “fish” also comprise non-fish species such as krill and squid, which play a similar role in the ecosystem.) Their critical role in the marine food web makes forage species so important to wildlife enthusiasts and fisheries alike.

However, forage fish are also pursued by people. Scientists estimate that these species now account for over a third of the global marine fish catch. The majority of this catch (around 90 percent) isn't consumed directly by people; rather, it is processed into fish meal. Fish meal is used to feed farmed fish, livestock and poultry, and even our pets. Other uses include bait for larger fisheries, fertilizers, and dietary supplements.

With this increasing global demand comes intense fishery pressure—but it can be hard to tell when forage fish are overfished. Forage fish populations naturally fluctuate widely (see why in the next paragraph), which means that a sudden population drop doesn't necessarily indicate overfishing. Additionally, even when their populations are low, catches often remain high because of the tendency of these species to form dense bait balls, which are relatively easy to spot and scoop up. It sounds counterintuitive, but research has shown that commercial fishing of predators on forage fish can make crashes in forage fish populations more severe. Together, these characteristics make forage fish very susceptible to overfishing.

Forage fish populations are threatened further because they are sensitive to environmental conditions like changing ocean temperatures and currents. Warmer water supports less plankton that forage fish need. Less food for forage fish means less food for their predators, and so the effect of warming ocean temperatures reverberates through the food web. It's not yet known whether changing ocean conditions or overfishing is the major driver for recent reduced forage fish populations in the California Current.

Regardless of the cause, recent research has shown how important it is to safeguard large populations of forage fish. In 2012, the Lenfest Forage Fish Task Force released a report that found that forage fish are worth about twice as much if they’re left in the ocean as food for other commercially valuable fish ($11.3 billion) than they are as direct catch ($5.6 billion). That’s huge! Other research has found that at least a third of forage fish biomass needs to be left in the water if we want to have a reasonable chance of sustaining seabird populations.

The Pacific Fisheries Management Council, responsible for regulating fish in the California Current, recently made news when it ruled that currently unregulated forage species should be managed using this precautionary approach. This landmark decision means that if anyone wants to open a new fishery on something like smelt or pelagic squid, they must first demonstrate that the ecosystem will not be impacted. In short, things just got a little bit more secure for marine life in the California Current, and this is big news for fish, seabirds, marine mammals and people alike.


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