Distribution patterns and trophic characteristics of salmonids and native species inhabiting high altitude rivers of Pampa de Achala region, Argentina

Abstract

The Pampa de Achala in central Argentina is an area with low fish species richness where salmonids were first introduced at the beginning of the twentieth century. A total of 19 rivers of different order were sampled during the low water period by using portable electrofishing equipment. We covered different identified macrohabitats (pools, riffles, glides and cascades) in reaches of 300-500 m length. The native species Trichomycterus corduvensis and two exotic salmonids such as Salvelinus fontinalis and Oncorhynchus mykiss represented the most common species, showing allopatric and sympatric distribution in some streams. Stomach contents and diet overlapping were also analyzed. Cluster results showed a first main group comprised those streams with high diet similitude between T. corduvensis and O. mykiss whereas a second main group consisted of streams with high diet similitude between O. mykiss and S. fontinalis. Mean niche width was similar among all these species but T. corduvensis showed that widest range whereas S. fontinalis exhibited the narrowest trophic niche. We were able to document a direct predation on T. corduvensis by O. mykiss in two stream although distribution overlapping among native and exotic species were low. In turn diet overlapping among species were negligible. Trophic niche amplitude of S. fontinalis was inversely related to stream order, providing clues that geomorphology and hydrology may exert also influence of trophic characteristics and can be used for predicting the potential for food competition with native species. Analysis by Tokeshi plot revealed that T. corduvensis ranged from specialist to generalist whereas both salmonids showed generalist feeding habits with a heterogeneous and homogeneous diet.El área de Pampa de Achala, en el centro de Argentina, posee una baja riqueza específica y donde los salmónidos fueron introducidos al comienzo del siglo XX. Se muestrearon 19 ríos de diferente orden durante el período de aguas bajas utilizando un equipo de pesca eléctrica portátil. Se cubrieron diferentes macrohábitats (pozones, correderas, tablas y cascadas) en tramos de 300 a 500 m de longitud. Las especie nativa Trichomycterus corduvensis y dos salmódios exóticos, Salvelinus fontinalis y Oncorhynchus mykiss, representaron las especies más comunes mostrando distribuiciones alopátricas y simpátricas en algunos de estos ríos. Se analizaron los contenidos estomacales y la superposición de sus dietas. El análisis por agrupamiento puso en evidencia un primer gran grupo compuesto por aquellos ríos con alta similitud de dieta entre T. corduvensis y O. mykiss, ancho medio de nicho fue similar entre estas especies pero T. corduvensis exhibió el rango de mayor amplitud y S. fontinalis que la superposición de distribución entre especies nativas y exóticas fue escasa. Por su parte, la superposición de dietas entre estas especies fue muy baja. La amplitud de nicho trófico de S. fontinalis estuvo inversamente correlacionada con el orden del río, proporcionando indicios que la geomorfología y ...

Endemic amphibians cornered in headwaters by trout invasion in a mountain range in Argentina

“…A total of six basins were surveyed, some of which were located within Quebrada del Condorito National Park and some outside this protected area. Lotic water bodies from the study area are first‐ to fourth‐order streams with a mean depth of 0.36 m, ranging from 0.06 to 3.66 m (Ferriz et al, 2010 and data from the present study). The pH of the streams is slightly alkaline, with an average pH of 8.17 (range 6.5–9.13); water electrical conductivity varies between 19 and 67 μS cm −1 , with an average of 44.29 μS cm −1 (Ferriz et al, 2010).…”

“…Lotic water bodies from the study area are first‐ to fourth‐order streams with a mean depth of 0.36 m, ranging from 0.06 to 3.66 m (Ferriz et al, 2010 and data from the present study). The pH of the streams is slightly alkaline, with an average pH of 8.17 (range 6.5–9.13); water electrical conductivity varies between 19 and 67 μS cm −1 , with an average of 44.29 μS cm −1 (Ferriz et al, 2010). Temperature and dissolved oxygen range between 6.9 and 17°C and between 7.7 and 10.2 mg l −1 , respectively (Ferriz et al, 2010).…”

“…The pH of the streams is slightly alkaline, with an average pH of 8.17 (range 6.5–9.13); water electrical conductivity varies between 19 and 67 μS cm −1 , with an average of 44.29 μS cm −1 (Ferriz et al, 2010). Temperature and dissolved oxygen range between 6.9 and 17°C and between 7.7 and 10.2 mg l −1 , respectively (Ferriz et al, 2010).…”

“…As well as the restricted distribution range, amphibians from this area face threats such as landscape modifications by human activities, and chytridiomycosis (Cingolani et al, 2014; Lescano et al, 2015; Lescano, Longo, & Robledo, 2013). Rivers and streams in the high‐altitude grasslands of the SPC were free from predator fishes until 1930 when two trout species were introduced: rainbow trout ( Oncorhynchus mykiss , Salmonidae) and brook trout ( Salvelinus fontinalis , Salmonidae) (Baigun & Quiros, 1985; Bistoni & Hued, 2002; Ferriz, Baigún, & Dominino, 2010). At present, most rivers and streams of the SPC have been invaded by trout (Bistoni & Hued, 2002; Ferriz et al, 2010); however, their impact on the biodiversity of the area has not yet been evaluated.…”

“…Rivers and streams in the high‐altitude grasslands of the SPC were free from predator fishes until 1930 when two trout species were introduced: rainbow trout ( Oncorhynchus mykiss , Salmonidae) and brook trout ( Salvelinus fontinalis , Salmonidae) (Baigun & Quiros, 1985; Bistoni & Hued, 2002; Ferriz, Baigún, & Dominino, 2010). At present, most rivers and streams of the SPC have been invaded by trout (Bistoni & Hued, 2002; Ferriz et al, 2010); however, their impact on the biodiversity of the area has not yet been evaluated. There is an urgent need, therefore, to understand the impact of trout on the aquatic ecosystems of the SPC in order to establish management priorities for conservation purposes and to raise awareness among environmental authorities with jurisdiction in this extra‐Andean mountain range of great importance for conservation.…”