Published online 21 July 2008 | Nature | doi:10.1038/news.2008.966


Mexican mangroves well worth saving

Fishing survey puts dollar value on endangered ecosystems.

A study of the fishing industry off the west coast of Mexico has measured the financial consequences of mangrove forest destruction.

MangroveA red mangrove in Santispac, Baja California, Mexico.Scripps Institution of Oceanography, Univ. California, San Diego

The scientists behind the study say this is the first detailed research to put a dollar value on the potentially irreparable damage being done to these coastal ecosystems. Mangrove trees form forests that grow at the edge of the sea, and provide a home for a wide variety of species.

Octavio Aburto-Oropeza of the Scripps Institution of Oceanography in La Jolla, California, and his colleagues selected 13 marine regions around the Gulf of California and on Baja California's lower Pacific Coast. Baja California is sparsely populated, and the mainland Gulf states of Sonora, Sinaloa and Nayarit largely have natural coastlines, where fishing is a vital source of food and income.

Within these 13 regions, the authors looked at fisheries records of about 9,150 fish landings between 2001 and 2005. The crucial zone within these regions is the seaward 'mangrove fringe', just 5–10 metres wide, where tide-flooded red mangrove plants (Rhizophora mangle) provide feeding grounds or nursery habitats for many species.

mangrove mapThe researchers studied catches at 13 fishing regions in the Gulf of California (red dashed perimeters). Green areas represent mangroves; black dots indicate the location of the local offices of the Mexican National Fisheries and Aquaculture Commission.National Academy of Sciences, PNAS/CONAPESCA

During that period, fishermen averaged annual hauls of 10,500 tonnes of fish and blue crab, worth US$19 million for the 13 regions combined. Roughly one third of all the small-scale fisheries landings in the area were of fish species which rely on mangroves as a habitat.

This economic value reinforces the need for governments to preserve mangroves, the researchers say. "Without a coastal mangrove ecosystem, the cost of food can only increase," says Aburto-Oropeza.

"One of the beauties of these data is that they come from public sources that anyone can access and use for verification," adds co-author Exequiel Ezcurra, former president of Mexico’s National Institute of Ecology and now Provost of San Diego Natural History Museum. The research is published in Proceedings of the National Academy of Sciences1.

Generational value

The scientists say that Mexico grossly underestimates the mangroves' value in land sales aimed at aggressive tourism development and, by setting low prices for these coastal regions, puts them at high risk of large-scale destruction.

In the past, the Mexican government has sold mangrove areas for around $1,000 per hectare. Yet the study by Aburto-Oropeza et al. shows that, on an annual basis, mangrove zones produce a median value of $37,500 per hectare.

"And governments need to think about a generational value," adds Aburto-Oropeza. His team estimated that, considered over a 30-year-period, the mangroves should be valued at more than $600,000 per hectare.

Mexico, and other governments experiencing weighing the economic consequences of their impact on the environment, need to open legislative debates to address an ecological "management crisis", says Ezcurra.

"The authors have done an excellent job of demonstrating the importance of mangroves to fisheries," says Karl Flessa, head of geosciences at the University of Arizona in Tucson. "This work should have a real impact on coastal development." Mexican government officials did not respond to repeated requests for comment on the study.

Early last year, Mexico enacted a new law outlawing mangrove destruction that was designed to prevent a repeat of past catastrophes. In the La Paz region near the tip of Baja California, for example, 23% of the mangroves were wiped out between 1973 and 1981. Now, the development industry is "investing large amounts of money" in lobbying the Mexican Congress to overturn the protections, Ezcurra says.

The largest mangrove forest in Baja California, at Magdalena Bay on the lower Pacific coast, is under immediate threat, he notes, with a huge development planned for a bay that spawns fish for the entire West Coast. 

  • References

    1. Aburto-Oropeza, O. et al. Proc. Natl Acad. Sci. USA doi:10.1073/pnas.0804601105 (2008).
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