Overfishing As Significant as Environmental Factors as Cause of Sardine Fishery Collapse

A team of researchers led by Scripps Institution of Oceanography at UC San Diego finds that overfishing and environmental changes are nearly equal contributors to the demise of the Gulf of California sardine fishery, which has collapsed four times in the last 30 years.

Not only do these collapses have ecological impacts, as populations of birds, marine mammals, and fish rely on them for food, they also have economic impacts  on Gulf of California communities that rely on fishing for subsistence. The new study, published in the May 4 issue of the Canadian Journal of Fisheries and Aquatic Sciences, reports on the effectiveness of a model that predicts sardine landing volumes that diminish the species’ vulnerability to boom and bust cycles.

“For over 20 years, the sardine fishery in the Gulf expanded, reaching new high records almost every year, until in 1991 it collapsed for the first time. It has not really recovered ever since,” said Alfredo Giron, a marine biologist at the Stanford Center for Ocean Solutions who conducted the research as part of his PhD dissertation at Scripps Oceanography.

The Gulf of California alone produces roughly half of all of Mexico’s seafood catch. The coastal city of Guaymas in Sonora is the epicenter of the country’s sardine fishery. The fishery experienced its first collapse in 1991 when sardine landings dropped from 300,000 tons in 1989 to only 10,000 tons in 1991. Since then there have been three other collapses.

There have been conflicting narratives about why the collapses happen. Some parties, including Mexican fisheries management authorities, believe that environmental shifts and recurring phenomena such as El Niño, which is characterized by a warming of waters in the Eastern Pacific Ocean off Mexico, are their dominant cause.

Giron and other researchers, however, note that lack of clear and precautionary fishery guidelines is also an important factor to consider. The goal of this study was to quantify the contribution of overfishing to the collapse in sardine catch. Eliminating the prevailing practice to simply continue fishing until the endeavor is no longer profitable, needs to become a priority.

Giron, Scripps Oceanography marine ecologist Octavio Aburto, and colleagues from UC Riverside, UC Santa Cruz, NOAA, and Instituto de Ciencias Marinas y Pesquerías in Veracruz, Mexico created a mathematical model that has the potential to provide future catch limits and guide managers and fishers towards a more sustainable and profitable fishery. Including the effects of fishing as a variable improved the predictability of fishery yields.

The issue in Mexico resembles a problem that  has challenged California for decades. The variability of sardine and anchovy catches have been known to fishing fleets and resource managers as far back as the 1940s, when the state’s fisheries for both species collapsed for unknown reasons. Scripps Oceanography and collaborators launched the California Cooperative Fisheries Investigations (CalCOFI) in 1949 to better understand what was happening to these species. To this day, the CalCOFI program continues to measure physical and biological variables that may affect these economically vital fisheries through quarterly cruises. 

Even with seven decades of data, the role of overfishing in declining sardine populations relative to environmental variability is still an open question among CalCOFI researchers. However, unlike in Mexico, California state officials implement caution and will close the sardine fisheries if stock assessments reveal that populations have fallen below a set threshold, such as occurred during the most recent stock assessment in 2019.

The researchers highlighted that considering the couple effects of fishing effort and environmental variability on sardine populations in the Gulf of California is a first step towards a more sustainable fishery. They recommend that the annual catch shouldn’t exceed 200,000 tons per year, compared to the current historical maximum of almost 600,000 tons in 2008. Moreover, in years when environmental conditions are less favorable for sardines, management strategies should be more conservative and better enforced, giving the population an opportunity to recover.

This work was supported by the Walton Family Foundation, the Sugihara Family Trust, the Deutsche Bank-Jameson Complexity Studies Fund, the McQuown Fund and the McQuown Chair in Natural Sciences, University of California, San Diego. Grants from the Department of Defense, National Science Foundation, and Department of Interior supported contributing work by Scripps oceanographer George Sugihara and Scripps graduate Ethan Deyle, currently a professor at Boston University.