Mexican native trouts: a review of their history and ... - Webspace

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wild habitats. We apparently have found areas where
introgression of native and non-native gene pools
is advanced, though substantiation of that requires
additional analyses. In other areas, we have not yet
detected indications of hybridization, but our sampling
to date is likely inadequate for elucidation of this
possibility. There is little doubt in our minds that
future sampling will reveal more and more widely
distributed occurrences of introgression of rainbow
and native gene pools. The extent of the area involved,
its general topographic complexity, and the (even
now) remoteness of many of its headwater tributaries,
should help assure that small, isolated native populations
will remain unexposed to non-native stocks in
the near future, but we feel it is important to quickly
discover and protect those populations before they
become contaminated.
In this contribution we have concentrated on real
or potential problems created by introductions of nonnative
trouts, but other non-native fishes also have
their potential impacts on the system. Our collections
and those of others have documented the presence of
several species of exotic centrarchids and ictalurids
within the general range of native Mexican trouts.
Largemouth bass surely will feed on trout if given
the opportunity, as might large catfishes, and smaller
centrarchids likely compete with trout for food, as
well as prey on fry and juveniles. Nonetheless, all
of these exotics are being increasingly introduced
into a surprising number of high-elevation, man-made
ponds and (eventually) natural waterways which could
harbor native trouts. Ways need to be found to limit
or, at least, rigorously manage the continued introduction
of species now being promoted by government
agencies and others.
Threats from logging, grazing and other agriculture
Logging will continue to expand in the region,
although accelerated harvest has resulted in a shortfall
of commercially-sized secondary growth. Pulpwood
markets have recently promoted commercial exploitation
of smaller material, including oak, and sawmills
are still touted as value-added economic development.
Supporting out anecdotal observations, Guerrero and
colleagues (Guerrero et al., 2001) reported that the
number of registered sawmills in Chihuahua increased
from 108 in 1993 to 309 in 1998. As it was in the
1950s, sawdust waste entering watercourses is again
a concern, along with leakage of associated oil-based
pollutants into streams and groundwater.
Forestry policies have changed numerous times
over the past century through efforts to make Mexico
more competitive and sustainable in the global forest
products market. Evolving policies often offer incentives
that tend to increase pressure to cut more forest
to make ends meet (Guerrero et al., 2001). A relatively
new Agrarian Code now allows privatization of
parcels within ejidos (a community-based land ownership
system which has existed in one form or another
for centuries, but instituted in its present format
following the 1910 revolution) to attract capital and
promote efficient management. However, the socioeconomics
of rural Mexico make changing forestry
practices in the direction of habitat protection very
difficult. Approximately seventy percent of forest
land in Chihuahua is under ejido ownership (Association
of Mexican Professional Foresters, 1996),
and much of that includes native trout habitat. The
complexity of negotiating conservation agreements
with ejidos is illustrated by the experience of McDonnell
and Vacariu (2000), who found it necessary
to provide economic alternatives in order to reach
an agreement protecting the most critical remaining
nesting site of the endangered thick-billed parrot.
Thoms and Betters (1998) outline four components
favorable to implementing ecosystem management in
ejidos: (1) communication and cooperation between
numerous agencies; (2) diversifying the economy
to reduce pressure to log; (3) environmental education
and both short- and long-term planning; and (4)
expanded administration capacity to address resources
other than timber. García and collaborators (1994)
surveyed residents of Ejido Largo Madera, one of
the larger and more successful ejidos in Chihuahua,
extending from Madera, Chihuahua to the headwaters
of the Río Gavilán. Their study exemplifies the
importance of providing economic alternatives. Those
they interviewed were keenly interested in economic
diversification and fearful of over-reliance on traditional
forestry practices, but lacked capital to try new
initiatives. In such settings, government-financed initiatives,
such as rainbow trout culture, can be popular.
Even if agreements are reached that appear sustainable,
illegal practices can remain a concern despite
proper changes in forestry laws and land management.
Barry (1994) indicates that environmental laws
in Mexico can often be more stringent than in the
U.S., but enforcement is almost always problematic
(Guerrero et al., 2001; Klooster, 1999). Regardless of
such concerns, progress is being made in some areas.
Aguirre-Bravo and Reich (1998) promoted an inte-