Environmental Engineering Reference
In-Depth Information
Mexican laws protect mangrove forests (Federal Wildlife Law 2000, NOM-022-SEMARNAT-
2003, NOM-059-SEMARNAT-2010). These laws declare all mangrove species endangered,
and they forbid changes on this cover while prohibiting adjacent economic activities (with
some exemptions). Therefore, we defined a 100-m buffer zone around the shrimp farm
polygons to assess the impact on mangroves within this fringe restricted by law. Using this
criterion, the impacted area is almost twice the preceding figure, and Sinaloa was again the
most unsafe area. The results of this analysis are shown in Table 3.
% of farms adjacent Mangrove in 100 m
zone
Nayarit 43 81.4 426
Sinaloa 163 68.7 1635
Sonora 45 26.7 113
Tamaulipas 22 4.5 2
Total 273 58.6 2176
Table 3. Shrimp farms adjacent to mangrove forests in some Mexican states and mangrove
extent (ha) inside the 100 m fringe banned by law for any economic activity. Estimations are
based on a 100 m buffer created around the shrimp farm polygons and overlaid on
mangrove thematic maps.
Shrimp farm
polygons
State
Even when a farm's design excluded the polygon from the mangrove cover, the shrimp
farms were sometimes constructed in the vicinity of mangroves, thus transgressing some
environmental regulations. From our results, close to 60% of the total analyzed shrimp
farms were in proximity with mangroves, almost doubling the lost area estimated here for
this vegetation if the 100 m fringe is considered. Sinaloa and Nayarit, both with the largest
mangrove coverage, were the states with the highest interaction between polygons and the
forbidden perimeter, affecting more than 80% of the farms in the case of Nayarit.
4. Mexican shrimp farming in the international context
Comparing the observed conditions of Mexican shrimp farming with other producing
countries worldwide highlights the fact that most of the declarations about mangrove
deforestation by shrimp farming are not properly documented. Documents with data and
descriptions of the technical process to assess mangrove deforestation are limited and, in
some cases, only generalize observed trends. From the available information, it was possible
to analyze some cases from Asia and America, including six cases in Mexico (Table 4).
At first sight, the situation of the Mexican states can be roughly compared with that from
other countries. In some regions of India, Bangladesh and Vietnam, though not necessarily
at the country level, shrimp ponds are practically the only cause of deforestation, with rates
between 85 and 100%, even when those ponds generally represent a small to medium
fraction (17.6 to 53%) of the activity (Table 4).
Shrimp farming growth in Latin America also had negative effects on mangrove cover,
particularly in Ecuador and Honduras (Gulf of Fonseca), with a decline in total mangrove
cover of approximately 27% and 22% between 1969-1995 and 1973-1992, respectively
(DeWalt et al., 1996; Tobey et al., 1998). These references agree with the present analysis,
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