Freshwater fishes and water status in México: A country-wide appraisal.

Abstract

México is the southernmost country in North America, and extends into Central America, south of the Isthmus of Tehuantepec. The northern half of México is located on the Temperate belt and is arid in character (Nearctic), while the rest is within the Tropical belt (Neotropical). Climate varies from extremely temperate desert in the north, to tropical humid in the south. México has more than 500 freshwater fish species, about 271 of them country endemics, and approximately 48 endemics from binational basins. There are still some 30–40 fish species not yet described. There are 563 fish species colonizing coastal flood plain species. In addition to the numbers of colonizing fishes, the burden of introduced exotics has also been growing. In 1904, only 4 species were recognized as exotics; by 1997 the number had increased to 94, and by 2008 to 115. The main fish collections in Mexico are at IPN, UNAM, and UANL and are the most representative, being national in scope, although concentrated in the tropics, central region, and general in coverage, respectively. The decline of the native fish fauna has been in focus in recent years, usually as trend-in-time comparisons, where the loss of native forms and increase of exotics and/or colonizer species is evident in many basins, mainly in Río Balsas, Río Grande, and Río Lerma-Santiago. As a result, the numbers of species reported at some degree of risk have been increasing also, from 17 in 1963 to 192 in 2005. The trends in colonizers, exotics, and species at risk among Mexican fishes are parallel. The Index of Biological Integrity (IBI), in either its geographical, or historical form (IBIh), has been applied to the Rio Grande/Río Bravo basin, USA and México. IBIh values go between 0–91 (average 31). Alien species are regarded as detrimental. Overall, the IBI trends have been similar in all regions, starting from 70–95% in upper reaches, decreasing to less than 0–35% in the lower reaches of West central basins, and then down to 15% or less near the Lower Rio Grande delta. Several alien species of plecos have been recognized in the rivers Balsas, Grijalva-Río Usumacinta complex, and, also, one in the Rio Grande. Mexican rivers are notoriously dewatered in the northern half of the country. Until 1962, the Rio Grande had an average runoff of 12,000+ millions of cubic meters/year; however by 2002 it was less than 2% of that value. The river went nearly dry along the Big Bend region and was dry for months in the delta region, both in 2002 and 2004. The Rio Grande is mostly dry north of the Río Conchos junction, its main Mexican tributary, and other tributaries provide now between 1% (Río San Juan) and 20% (Río Conchos) of pre-1960 runoff. A modified Index of Biological Integrity for Rio Grande resulted in grades from 70 to 95% of the baseline in upper reaches, less than 35% in lower reaches, to less than 15% near the coast. The Texan version of the IBI was not representative as it suppresses data on euryhaline fishes. The reports of total toxics were masked, since the sum should have included both organics and heavy metals exceeding USA regulations to the total count, but only one of the two was included.

Recurrencia histórica de peces invasores en la Reserva de la Biósfera Sierra de Huautla, México

“…Los avances en el conocimiento de las especies invasoras en México, permiten reconocer a los grupos exóticos como una de las principales causas de la extirpación de las nativas en más de 100 localidades en el país (Contreras-Balderas et al 2008, AguirreMuñoz & Mendoza-Alfaro 2009, esto las convierte en un componente importante dentro de las amenazas de extinción. El plan de manejo de la Reserva de la Biósfera, no contempla ninguna acción en respuesta a este proceso, a pesar de reconocer la presencia de especies no nativas en el área, (CONANP 2005) algunas clasificadas dentro de las 100 especies invasoras más dañinas a nivel global (Lowe et al 2004).…”

“…La regulación de la actividad acuicultural en México no se cumple o no existe en el caso de las especies de uso ornamental (Contreras-Balderas et al 2008), la incorrecta regulación para la importación e introducción de nuevas especies al mercado, permite que prácticamente cualquier organismo acuático pueda ser introducido para ser cultivado con muy poco control, ha sucedido con la tortuga de concha blanda Apalone spinifera spinifera, ya que ejemplares de la misma han sido obtenidos y observados en el área de la REBIOSH (Castro-Franco & Bustos-Zagal 2004), por lo que forman parte de la fauna exótica, distinta a los peces comercializados en la región.…”

Effects of Exotic Fishes on the Somatic Condition of the Endangered KillifishFundulus lima(Teleostei: Fundulidae) in Oases of Baja California Sur, Mexico

“…Fuller et al, 1999;Contreras-Balderas et al, 2008). Redbelly tilapia is a potential competitor with native fish for food and spawning areas in many places of United States and northwestern Mexico and is implicated in the decline of populations of the desert pupfish Cyprinodon macularius (Fuller et al, 1999;Varela-Romero et al, 2003).…”

“…DISCUSSION-One of the main threats that face the native, freshwater fishes of North America is the introduction of exotic species of fishes (Fuller et al, 1999;Contreras-Balderas et al, 2008). Environments prone to establishment of exotic species include places having either low environmental resistance or low biological resistance (Case, 1991;Moyle and Light, 1996) as well as a low native-species richness (Elton, 1958;Orians, 1986;Lodge, 1993) such as occurs in the springs and oases of North American deserts (Douglas et al, 1994), including those of the Baja California peninsula , 2006b).…”

Exotic and invasive fishes in Mexico

“…It is unknown whether the species is established or not, but there is suspicion that it has hybridized with other species of the genus (Escalante and Contreras 1985). Cyprinella lutrensis (Baird & Girard, 1853) was documented by Contreras-Balderas et al (2008) as introduced, and mentioned it in multiple localities in the north. Ruiz-Campos et al (2012) suggested the species to be probably responsible of the decline of the Desert Pupfish Cyprinodon macularius Baird & Girard, 1853.…”