Biodiversity of Mexican Trout (Teleostei: Salmonidae: Oncorhynchus): Recent Findings, Conservation Concerns, and Management Recommendations
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BIODIVERSITY OF MEXICAN TROUT (TELEOSTEI: SALMONIDAE: ONCORHYNCHUS): RECENT FINDINGS, CONSERVATION CONCERNS, AND MANAGEMENT RECOMMENDATIONS Biodiversidad de Truchas Mexicanas (Teleostei: Salmonidae: Oncorhynchus) : recientes hallazgos, preocupacion de conservaci6n, y recomendaciones de manejo RICHARD L. MAYDEN Department of Biology. 3507 Laclede Ave. Sa int Louis University St. Louis, Missouri 63 l 03-20 l 0 USA [email protected] ABSTRACT. Until very recently the diversity of trout in Mexi south to the Rio Acaponeta. Th ese trout forms are highly can rivers of the Sierra Madre Occidental has been very differentiated and distinctive, and are considered native poorly understood and only the Rainbow Trout, to these high-elevation river systems in pine-dominated Oncorhynchus mykiss, and the Mexican Golden Trout, 0. forests. The increased occurrence of trout growout facili chrysogaster, have been recognized. Recent efforts in the ties and hatcheries within the range of these native last decade by a binational organization of sc ientists and Oncorhynchus and the escapes from these facilities laypersons interested in the diversity and conservation of threaten the native trout diversity through both introgres Mexican trout, Truchas Mexicanus, have revea led consid sive hybridization and through resource competition, end erable diversity within the river systems of the Pa cific Slope products already known to occur in other trout popula- H OM EN A JE A L DOC TOR A NDRES R ES ENDEZ MED INA BIODIVERSITY OF MEXICAN TROUT (T ELEOSTEI : SALMONIDAE : 0NCORHYNCHUS ): RECENT FINDINGS, CONSERVATION CONCERNS , AND MANAGEMENT RECOMMENDATIONS tions in the other areas of North America exposed to ex Key Words: Biodiversity, Trouts, Conservation, Mexico oti c hatchery trout. Other threats to the native and previ ously unknown trout biodiversity in Mexico include timber RESUMEN. Hasta recientemente la diversidad de las harvesting, some pollutions associated with these activi truchas en rios mexicanos de la Sierra Madre Occidental ties, and siltation of critical habitats. Recommendations ha sido entendida pobremente y solo la trucha arcoiris, are provided to aid in the safe management and protec Oncorhynchus mykiss, y la trucha dorada mexicana, 0. tion of this diversity which center around the future use of chrysogaster, hon sido reconocidas. Los esfuerzos sterile trout in growout facilities and the use of undisturbed recientes durante la ultimo decada por una organizaci6n buffer zones along streams. Th e divergence observed in binacional de cientfficos y legos interesados en la forms of Mexican trout is equivalent to the levels of diver diversidad y conservaci6n de las truchas mexicanas, hon gence found between currently recognized subspecies of revelado una considerable diversidad dentro de los trout in the Rainbow and Cutthroat trout groups. Upon sistemas flu via les de la vertiente Pa cifica al sur del Rio review of the diversity and divergence known to exist in Acaponeta. Estas formas de truchas estan a ltamente these groups and our current understanding of diferenciadas y distintas, y son consideradas nativas a estos conceptualizations of species, it is argued that the recog sisemas riverinos de alto elevaci6n en bosques domino dos nition of subspecies within these highly diverse trout lin por pino. La creciente presencia de establecimientos para eages is inconsistent with the natural evolutionary history la crfas de truchas y piscifactorfas dentro del area de estas of these groups. Th e long-term use of the Biological Spe Oncorhynchus nativas y los escapes de estas faci lidades cies Concept for these species is argued as not only inap amenazan la diversidad de truchas nativas a consecuencia propriate but an inadequate and illogica l characteriza de ambas, hibridizaci6n introgresiva y por competencia tion of diversity. The logica l consequences of hanging on por recursos, y productos finales ya conocidos por suceder to this concept as the operational and theoretical frame en otras poblaciones de truchas en otras areas de Norte work of trout diversity would necessitate the synonymization America expuestas a truchas ex6ticas de criadero. Otras of all Rainbow and Cutthroat trout taxa as subspecies amenazas a las truchas y diversidad nativas previamente because of the known propensity of these groups to dem desconocidas in Mexico incluyen tala de bosques, alguna onstrate introgressive hybridzation in some areas. These poluci6n asociada a esta actividades, y el azolve de subspecies are considered va lid evolutionary lineages that habitats criticos. Se proveen recomendaciones para are demonstrate divergence at morpho logical, genetic, ayudar en el manejo seguro y la protecci6n de esta and ecological characters that are we ll known to many dive rsidad que se centran sobre el uso futuro de truchas trout taxonomists and biologists. All of these therefore esteril es en las instalaciones de engorda y el uso de zo qualify as Evolutionary Species that are easi ly diagnos nas buffer no perturbadas a lo largo de las corrientes. La able under the Phylogenetic Species Concept and should divergencia observada en las formas de trucha Mexicano be recognize d as valid species. es equivalente a los ni veles de diverg encia que se encuentran entre las subespecies actualmente reconocidas f ACULTAD DE C IENCIAS B IOLOGICAS , LJ NIVERSIDAD AUTONOM A DE N UEVO L EON RICHARD L. M AYDEN de subespecies de trucha en las grupos arcoiris y cuello people know of North American trout diversity almost cortado. Sabre la revision de la diversidad y divergencia entirely because of the common Rainbow Trout, que se sabe existe en estos grupos y nuestro entendimiento Oncorhynchus mykiss {formerly known as Oncorhynchus actual de las conceptualizaciones de especies, se or Sa/mo gairdneri), a species that is the dominate "form" argumenta que el rconocimiento de subespecies en estos used in stocking streams from hatcheries or "grow out linajes altamente diversos es inconsistente con la historia facilities" to appease the avid fishermen. The Rainbow natural evolutiva de estos grupos. El prolongado uso del Trout is also known as a distinct lineage with a number of Concepto de la Especie Biol6gica para estas especies se distinctive forms currently referred to as subspecies (Table argumenta que no solo es inapropiado sino tambien una l ), all inhabiting streams of western North America. Un inadecuada e il6gica caracterizaci6n de la diversidad. Las fortunately, this trout is also famous as a species that has consecuencias 16gicas de apegarse a este concepto coma been introduced into just about every possible stream el armaz6n operativo y te6rico de la diversidad de truchas outside of its native range where conditions are tolerable. necesitarfa la sinonimizaci6n de todos las taxa de trucha Other North American trout that are likely of interest to arcoiris y cuello cortado coma subespecies debido a la many include the cutthroat trout complex (0. clarki), which propensi6n conocida de estos grupos de mostrar also consists of a large number of subspecies under this hibridizaci6n introgresiva en algunas areas. Par lo single polytypic species (Table l ), and the California contrario, estas "subespecies" son consideradas linajes Golden Trout (0. mykiss aquabonita), the latter species evolutivos v6lidos que demuestran divergencia en gaining its notoriety for its beautiful colors and demand in caracteres morfol6gicos, geneticos, y ecol6gicos que son fishing. Some of the less commonly known species in bien conocidos a muchos tax6nomos y bi6logos de North America include the Gila Trout (0. gilae gilae), truchas. Todas ellas en consecuencia califican coma Apache Trout (0. g. apachae), and the various forms of Especies Evolutivas que son f6cilmente diagnosticables rainbow and cutthroat trout concealed as subspecies un bajo el Concepto de Especies Filogeneticas y deben ser der presumed single lineages. The recent publications by reconocidas coma especies v6lidas. Behnke (l 992, 2002) discussing trout diversity and hy potheses as to their origins and the heroic efforts by na Palabras Clave: Biodiversidad, Truchas, Conservaci6n, tional organizations focusing on the restoration and con Mexico servation of trout and their habitats have brought consid erable attention to the existence and diversity of these INTRODUCTION aquatic predators, especially in the United States . In fact, today, unlike a few decades ago within the United States Most scientists and laypersons alike are very familiar with there is considerable emphasis on the management of the North American trout species of the genus native trout and "bringing back the natives" rather than a Oncorhynchus from their popularity in angling, aquacul need for introducing "hatchery" rainbows for fishing plea ture, and as a food resource. Likewise, most of these same sure. Trout advocates have been exceedingly successful HOMENAJE AL DOCTOR ANDRES RESENDEZ MEDINA BIODIVERSITY OF MEXICAN TROUT (TELEOSTEI : 5ALMONIDAE : 0 NCORHYNCHUS ): RECENT FINDINGS, CONSERVATION CONCERNS, AND MANAGEMENT RECOMMENDATIONS in drawing attention to the protection of some trout and this diversity, determine possible threats to the divers ity, salmon species, subspecies, and ESUs (Evolutionarily Sig and identify reasonable conservati on and management nificant Units; Nielsen, 1995), restoration of habitats for native efforts that can be developed to carry on this exceptional taxa , elimination of exotic trout populations, and manage natural resource of