An article written by researchers at Scripps Institution of Oceanography at the University of California, San Diego, and others provides evidence that fishing activities in the Gulf of California are producing ecosystem-wide changes in the region's coastal marine environment and calls for rigorous new fisheries management in the region.
The group, led by Enric Sala of Scripps Institution, uses data from field surveys, fisheries statistics and interviews with fishers to show that coastal food webs in the region have degraded considerably since the 1970s. In the new issue of Fisheries, a magazine published by the American Fisheries Society, the authors describe how the Gulf of California has been "fished down" during the last 30 years from large, long-living species to small, short-living species.
"The Gulf of California is beautiful and you can still see amazing wildlife there," said Sala, associate director of the Center for Marine Biodiversity and Conservation at Scripps. "But there have been significant changes there in just three decades. Something needs to be done about it."
Despite a low human population density, the Gulf of California, considered a marine biodiversity "hotspot," is subject to intense fishing activities. Major fish families targeted in the southern Gulf of California include sharks, bony fishes and rays.
To arrive at their results, Sala's group looked well beyond an analysis of one or two species, and instead studied a broader "ensemble" of species in the Gulf of California.
Their multi-tiered approach included field surveys to systematically characterize several aspects of the coastal marine environment.
To address a severe lack of historical information on the region's ecology, Sala's group used an approach traditionally associated with social sciences: They conducted independent interviews directly with regional fishers, a group intimately knowledgeable about the area's fishing history. The researchers conducted more than 60 interviews covering various aspects of fishing activities. They obtained data about specific catches from the 1970s through 2000, including the number, type and location of fished species.
Sala's group then turned the responses into a database of information that was cross-referenced with data from fisheries statistics. The two sources matched with remarkable consistency.
Overall, the results pointed to a "marked shift" in the composition of the coastal fishery in the region.
Among the results, the study found that the maximum individual length of fish catches has decreased by approximately 45 centimeters in 20 years. The findings also showed that continuing fish stock depletions have forced the fishers to move fishing sites farther away from fishing villages.
"These declines were associated with a dramatic increase in the fishing effort in the region in the late 1970s (and) early 1980s, mostly in the number of gillnets. Fishing not only impacted targeted species, but also caused community-wide changes," said co-author Octavio Aburto-Oropeza, an exchange scholar at Scripps and a professor of marine ecology at the Universidad Autónoma de Baja California Sur in La Paz, Mexico.
Co-author Gustavo Paredes, a native of Saltillo, Coahuila, Mexico, and a graduate student at Scripps, said large predatory fishes such as sharks, gulf groupers, gulf coneys, goliath groupers and broomtail groupers were among the most important catches in the 1970s, but became rare by 2000.
The results also showed that species that were not targeted in the 70s, such as parrotfish, whitefish, spotted snapper, tilefish and creolefish, have now become common catches.
The authors argue that their results exhibit a clear trend that Gulf of California fisheries have fished down the food web, leading to effects on the entire coastal ecosystem well beyond the direct impacts on targeted species.
In fact, the article says coastal fisheries in the Gulf of California are not sustainable and advocates that "their management needs to be re-evaluated with sound regulatory measures to prevent further degradation of coastal food webs."
To prevent further declines, Sala and his group say that fisheries management in the Gulf of California needs to consider fish spawning activities.
"The first thing I would do is make sure the reproductive sites are protected," said Sala. "Some large groupers, for example, meet to reproduce at very specific locations and times, some around a full moon once or twice per year. Without protection we will see the decline of these and many other species. Protection will, in turn, help the fisheries these species support. There is only a limited number of species the fisheries can shift to and once they are gone, then what?"
In addition to Sala, Aburto-Oropeza and Paredes, all with Scripps Institution, co-authors include Miriam Reza of the Gulf of California Program--World Wildlife Fund, Hermosillo, Sonora, Mexico; and Luis López-Lemus of the Centro Regional de Investigaciones Pesqueras, Instituto Nacional de la Pesca, and Universidad Autónoma de Baja California Sur in La Paz, Mexico.
The study was funded by the Moore Family Foundation, the Tinker Foundation, the Robins Family Foundation, and the World Wildlife Fund-Gulf of California Program.