Impact of Shrimp Farming on Mangrove Forest and Other Coastal Wetlands: The Case of Mexico - Aquaculture and the Environment: A Shared Destiny - page 26

which reveals that Ecuador's mangrove loss and conversion was close to 90% of
approximately 54000 ha at the nation level and 67% at the regional level (Machala-Puerto
Bolivar), where mangrove loss was estimated at approximately 1400 ha. Honduras in the
early 1970s accounted for more than 11500 ha of shrimp ponds in the Gulf of Fonseca,
approximately 65% of which were constructed on mangrove sites.
In Mexico, the highest conversion ratio from mangrove to shrimp ponds has been recorded for
San Blas, at Nayarit state, and northern Sinaloa, with 44.1% and 23.6%, respectively,
amounting to a total of approximately 260 converted hectares. In relative terms, these numbers
represent 12.1% and 0.3% of the total pond area constructed by region, respectively, at
approximately 12 000 ha in total. Other studies in Mexico on mangrove conversion attributable
to shrimp farming show output ratios less than 7% of lost mangrove cover. It is also
remarkable that two independent works conducted in Sinaloa state found an increase in the
mangrove cover, and, with some differences, they even found that the mangrove area
occupied by shrimp farm developments represents between 1.7 and 2.2% of a pond surface
estimated above 40 000 ha (De la Fuente & Carrera, 2005; Ruiz-Luna et al., 2005).
5. Discussion
Intense debate about the environmental impacts caused by shrimp farming has been
engaged in Mexico since the beginning of this activity, particularly by environmentalists,
regarding the denunciation of the environmental risks associated with shrimp farming
development. Considering the international background of this issue and bearing in mind
the importance of the environmental services offered by mangroves and the possible impact
caused by land cover changes, the general opinion is that Mexico could confront
environmental risks similar to Indonesia, Philippines, Thailand and Ecuador, where
extensive deforestation of mangrove forests is associated with the construction of shrimp
ponds.
This perception has been maintained and consistently declared even though there are few
studies documenting changes in mangrove at a national extent or the possible causes of
mangrove deforestation when it is proved. It is common that some differences in mangrove
cover estimations obtained by the extrapolation of local values or using different inputs and
evaluation techniques would be misinterpreted as deforestation (Ruiz-Luna et al. 2008).
Thus, the studies conducted by Hernández-Cornejo & Ruiz-Luna (2000), Alonso-Pérez et al.
(2003), De la Fuente & Carrera (2005), Ruiz-Luna et al. (2005), Berlanga-Robles & Ruiz-Luna
(2007), and Berlanga-Robles et al. (2011), among others, have attempted to verify the extent
and intensity of the impact of shrimp farming in Mexico.
Most of the above papers mainly describe the conditions observed in Sinaloa and Nayarit, in
northwest Mexico. This paper is the first attempt to document changes at a nationwide level
based on our own and other authors findings obtained with remote sensing techniques,
analyzing very high spatial resolution satellite imagery (Landsat, Spot, QickBird, GeoEye)
and updating the existing information up to 2010. The main restriction imposed to these
studies is the lack of reference data to validate the accuracy of the earlier dates' estimates.
Even so, the similitude among the results from independent analyses give confidence to the
general trends followed by shrimp farm growth and its impact on mangrove forests in
Mexico, making a comparison possible with analogous developments elsewhere.