The storied sardine fishery in the northeast Pacific may be tottering on the brink of another collapse, like one that shut down sardine fishing there for years in the middle of the last century.
Signs of trouble that foreshadowed the last collapse are recurring, warn two researchers at the Southwest Fisheries Science Center in La Jolla, Calif. A shift toward the cooler phase of an oceanic cycle is coinciding with evidence that the sardine population is struggling to reproduce in abundance, report fisheries biologist Juan Zwolinski and research engineer David Demer online February 27 in Proceedings of the National Academy of Sciences.
This fishery was once the largest for any single species in the Western Hemisphere, says Boris Worm of Dalhousie University in Halifax, Canada. “It continues to be important today, not just for people, but also for the large numbers of whales, seabirds and predatory fish who depend upon that stock.” U.S. fishing fleets landed an estimated $12.3 million worth of Pacific sardine in 2010.
Last century, harvesting flourished during the early 1940s as the sardine populations spawned in the spring off southern and central California, and larger, older fish slowly migrated northward. But only five years after the peak 1943–44 season, the fishery’s sardine population had plunged and northern migration was dramatically curtailed. By 1952, sardine fishing north of Monterey Bay had ended, and the industry took nearly two decades to recover.
Just what caused that collapse — overfishing, ocean conditions or a combination — remains a matter of debate. But looking back at fisheries and oceanographic data from those years, Zwolinski and Demer have identified precursors of the collapse. An oceanic cycle called the PDO, for Pacific Decadal Oscillation, entered its cooler phase, which does not favor sardine growth. Also, fishing fleets in the 1940s were increasingly targeting the migrating fish, which are bigger and older and have the most reproductive capacity.
With the PDO chilling again, and catches today also including bigger fish, the researchers warn that acoustic-trawl surveys show 2011 populations at only one-fifth their numbers in 2006. Also, surveys report that normally sardine-rich waters have had abundant jack mackerel, which can lead to mixed-species schools that compromise sardine feeding and migration.
“The hopeful story here is that we have much better technology and understanding for monitoring the health of this stock today than we had in the 1950s,” says Worm. With more regulation now, fisheries managers can adjust quotas. “We have a conscious choice to keep sardines around or to collapse them.”