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

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Findings
Mexican trouts past and present
The Mexican fossil record
The marine anadromous fauna, including salmonids,
that now characterizes North American Pacific drainages
of the United States, extended during Pleistocene
at least as far south as the Mexican Mesa (Plateau)
Central to about 21 ◦ N latitude (Miller and Smith,
1986). Though Mexican salmonid fossils are fragmentary,
and thus difficult to relate to modern forms, they
have been referred to two species in the modern genus
Oncorhynchus (Cavender, 1986; Cavender and Miller,
1982) (or the extinct Rhabdofarío (Smith, 1980;
Smith, 1981). Though salmonids did not persist on the
Mesa Central to modern times, other components of
this same ancestral fauna apparently did; two lampreys
of the genus Lampetra (subgenus Tetrapleurodon)are
landlocked on the Mesa Central (Cochran et al., 1996;
Lyons et al., 1994; Lyons et al., 1996), far south
of their nearest relatives in Baja California (Ruiz-
Campos and Gonzalez-Guzman, 1996).
To our knowledge, the only fossil fishes known
from within or near the present range of Mexican
native trouts include those from the Pliocene fauna
of Yepómera, Chihuahua (southern Río Yaqui –
Papigochi sub-basin). Though mammals, birds and
other components of that fauna have been well studied
(Lindsay and Jacobs, 1985, Smith, 1981), to our
knowledge the fossil fishes have yet to be described
beyond M.L. Smith’s (1981) very brief mention
only of a cyprinid and an unidentified, possible
cyprinodontoid. The site appears, however, to be
the only fossil fish locality within the present range
of native trouts, being in the southern Río Yaqui
(Papigochi) basin. Slightly outside of the currently
known range of native trouts, but perhaps within
prehistoric range, are two fossil fish localities. A Holocene
cave deposit in Durango (Brooks et al., 1962) in
the Río Nazas basin contains three families of fishes
still found in the area, but typical of lower elevations
than trout. The La Brean fauna from Rancho La Brisca
(Van Devender et al., 1985) in the Río Sonora basin
(the next major basin west of the Río Yaqui), had
few fish remains typical of species found today very
near the fossil locality at elevations well below those
typical for trout.
Recent native trouts
Living Mexican native trouts currently consist of
two described forms, the Mexican golden trout, O.
chrysogaster (Needham and Gard, 1964) of the ríos
Fuerte, Sinaloa and Culiacán, and the Baja California
rainbow trout, O. mykiss nelsoni (Evermann, 1908)
of the Sierra San Pedro Mártir in northern Baja
California. Native trouts known from the mainland
north of the Mexican golden trout in the ríos Yaqui,
Mayo and Guzmán systems remain undescribed, but
specimens of these forms are relatively abundant in
museum collections compared to those from further
south from the ríos San Lorenzo, Piaxtla, Presidio,
Baluarte and Acaponeta. Whether these forms from
south of Mexican golden trout are native or introduced
or hybrids of native and introduced forms remains
contested as mentioned above. We recently collected
additional specimens from most of these basins and
discuss them below.
Early explorations, observations and collections
The history of observations of trout in Mexico
goes back further than previously reported. We
report below a number of formerly overlooked early
observations in a chronological review of collections
and observations of specimens from the study area.
Other similar, but site-specific and more habitatoriented
observations and selected extracts from
interviews, archives and personal communications are
reported later in our reviews of habitat and fish faunal
histories.
James Woodhouse Audubon. More than 150 years
ago, James Woodhouse Audubon (son of John James
Audubon) traveled across Chihuahua enroute to northwestern
Sonora as second in command of a group of
about 100 men. Crossing the ríos Florido, Conchos,
and Yaqui, he mentioned in his journal (Audubon,
1906) that on July 3rd, 1849, near the town of
“Tomochi,” he and his crew
... looked in vain for fish in the most tempting
of eddies and holes, but saw very few; little
trout about five inches long were all that rewarded
our search. We crossed and recrossed this stream
twenty-two times in about seven miles, and
encamped on a sandy bottom covered with fine
pines.
Though overlooked by earlier researchers, this
appears to be the first written report of trout in
Mexico and it is not difficult to place the locality