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

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the journey leading to and beyond this point, allow us
to place him unambiguously on this date in the Río
Conchos basin, to the north of modern-day Nonoava,
and probably in the Tecubichi, Guacareachi, or Agua
Caliente sub-drainage. Furthermore, his mention of
groves of pine trees along the stream corroborate that
he was potentially in trout habitat, probably at or
above 2000 meters elevation, and argue against the
possibility that his reference was to cyprinids of the
genus Gila, that were sometimes called “trout” in the
southwestern U.S. (Minckley, 1973), instead of to
true trout. Though species of Gila in the region do
range into high-elevation streams in pine forests, they
are more commonly found at lower elevations (DAH
unpubl.).
Why have there been no subsequent collections of
trout from the Río Conchos? Our review of literature
and museum fish collection catalogs reveal that
though lower reaches of the Río Conchos basin have
been moderately sampled, collections in that basin’s
extensive headwater areas have been very rare since
Flechsig’s and Moller’s brief excursion (above).
The basin remains almost completely unsampled
above 1700 m elevation, which our experience in
adjacent drainages indicates to be below the lower
limit for trout in the region. Sydney Anderson
collected at two sites near the town of Bocoyna
in 1958, taking Rio Grande sucker (Catostomus
plebeius) and longnose dace (Rhinichthys cataractae)
at about 2400 m elevation, and one of us (RLM)
collected the same species from a tiny tributary of
the Arroyo Bocoyna in 1987. We found no scientific
collections of fishes from the more than 2000 km 2 of
the Río Nonoava watershed, which reaches 2850 m
elevation. Similarly, the Río Balleza and Río Florido
are apparently unsampled for fishes above 1700 m,
although they reach more than 3300 m.
Did trout have access to the Río Conchos? Evidence
from other fishes. Throughout the Rio Grande basin
in the United States, presence of longnose dace is
considered an indicator that trout formerly had access
to, or might inhabit higher reaches of, the same
streams (Mike Hatch, pers. comm., 2002; Robert
Behnke, pers. comm., 2002). Our survey of museum
collections found at least 14 collections from the Río
Conchos basin that include longnose dace, a species
also ranging to lower elevations (below typical trout
habitat) in New Mexico and Texas. Longnose dace
is thought to have entered the Rio Grande drainage
via stream capture by the Pecos River between 12,000
and 20,000 years ago during the last major pluvial
(Hatch, 1985) and since dispersed throughout the
drainage into headwaters of both the Rio Grande/Río
Bravo and Río Conchos. The climate was much cooler
during this pluvial and “life zones” for flora and
fauna were some 1300 meters lower than present day.
Consequently, we believe the Rio Grande cutthroat
trout could have accessed the Conchos through the
same dispersal corridor. Alternatively, trout could have
arrived to the Conchos via other hydrographic connections
to Pacific drainages. During mid-Pleistocene
or more recently, the Río Papigochi (now the major
far southeastern tributary to the upper Río Yaqui
system – Figure 1) may have been confluent with
the Río Conchos. Many species and groups of fishes
share a Conchos – Yaqui (and beyond) distribution,
and structural geology also supports the likelihood
of past connections between these basins (Brand,
1937; Miller, 1959; Miller, 1976; Hatch, 1985;
Minckley et al., 1986; Echelle and Echelle, 1998,
Minckley et al., 2002; Mayden, in press; Norris
et al., in press). Among the fishes involved are
species of the genus Gila (some still undescribed),
the former Catostomus conchos (of the Río Conchos)
that was synonymized by R.R. Miller with Catostomus
bernardini of the Río Yaqui and Pacific drainages
to its south (Hendrickson, 1984; Hendrickson and
Varela-Romero, 2002), Codoma ornata, Campostoma
ornatum, and the genus Cyprinodon.
Trout phylogenetic relationships and biogeography
The taxonomy, systematics, and biogeography of
western North American trout species and subtaxa in
general are relatively poorly known or in a state of flux
and debate. Especially little understood are diversity
and phylogenetic relationships of native Mexican
trouts. While many historical and recent studies of
variation (genetic and non-genetic data) have been
conducted within and between trout species of the
western United States and Canada, very few comparative
analyses exist at a geographic and taxonomic
scale providing meaningful genealogical information
with respect to the biodiversity of these taxa and
the Mexican trout species and relatives. Without a
doubt, most systematic and evolutionary studies of
western North American trouts have not been done
within a comparative phylogenetic perspective and
have focused on single species, subspecies or populations
within a species, and many of these studies have