Growth dynamics of juvenile Atlantic salmon, Salmo salur L., from two sections of the Narcea River and one of the Esva River (Northern Spain) were examined in relation to the development of bimodality in their sizefrequency distributions. Sizebimodality was clearer under intermediate growth (section A) than under relatively fast or slow growth. The proportion of fishentering the upper modal group increase with growth intensity. Composition of upper and lower modal groups became fixed prior to December, and at this time both groups separated on the 90-95 mm interval. Fish exhibiting smolt appearance in late March (larger than 130 mm) had already been upper group fish in December, while parr-like fish and those that remained in the river by May (potential 2-year-old smolts) had formed the lower modal group. Anadromous salmon catch in the Narcea River was mostly of previously 1-year-old smolts (97.6%), of which 94% were larger than 100 mm by their first winter. In the Esva River, slow growth ofjuveniles is consistent with a large proportion of 2-year-old smolts (47.9%) among anadromous salmon. Both juvenile samples and scale analysis of anadromous salmon indicate that 2-year-old smolts were larger than I-year-olds. Early disappearance of the former (before March) is, at least, partially related to earlier migration of large fish, since sexual maturity of parr does not provide a complete explanation. The Narcea stock have a minimum length at smolting of about 130 mm and an optimum smolt size in the 155-175 mm interval. Mean smolt lengthdid not vary although the winter length changed between years.
Relationships between the fish community and selected habitat features were examined in a set of short temperate streams located at the northern end of the Iberian Peninsula . The fish fauna in these streams consists mostly of diadromous or estuarine species . Species richness and diversity increased with stream order, depth and width and decreased with elevation and distance from the sea . Stream order (positively) and elevation (negatively) were the two variables most highly correlated with species richness and diversity ; higher order streams (order 3-4) showed greater values of species diversity than lower order ones (order 1) even when the elevation effect was removed . Addition of species in the downstream direction, but no replacement or loss was evidenced . We also compared the observed values of species diversity with those predicted from habitat features for a set of locations above unpassable dams . A great majority of the sites showed lower than predicted diversity values, which is an expected outcome for this mainly migratory fish fauna .
Effects of angling exploitation on brown trout populations were assessed by comparing fished sections with close ones unfished for at least 20 years, in mountain streams of Asturias (Northern Spain) . Both the fish size and age structure significantly differed among sections in the expected direction according to their exploitation status . The main effects were a significant decrease in age structure complexity (diversity), life span, and percent individuals above the legal limit size in the exploited stocks versus the unexploited ones . Trout above the minimum length limit for fishing (18 cm) averaged 19 .47% of the fish caught in the unfished sections (sd = 4.01 ; n = 5), and 4 .72% (sd = 3.46 ; n = 4) in those subjected to angling . Furthermore, fish older than 4 years represented 39.84% (sd = 8 .53) and 1 .19% (sd = 1 .60) of the catch, respectively . Effects on recruitment (density of young fishes) and growth rates (length at age 1 + to 3 + ) were not absolutely consistent, though maximum values were associated with fished sections .
Frugivorous birds are able to track spatiotemporal changes in fruit availability. Food resource fluctuations, characteristic of seasonal environments, can be affected by the naturalization of exotic ornithocorous plants. In the mountain forest of central Argentina, invasive shrubs of the genus Pyracantha provide a new temporal resource that modifies fluctuations of natural resource availability because the invasives fructify in autumn-winter (largely uncoupled with the fruiting of native species). The contrasting patterns of resource fluctuation between non-invaded and invaded areas throughout the year provide a good study system to test predictions of the fruit-tracking hypothesis, and to understand the relationship between food resources offered by fleshy fruited invasives and abundances of avian trophic guilds. By means of point counts conducted during five time periods at invaded and non-invaded sites we found that the presence of Pyracantha, and time periods, significantly affected frugivorous bird abundance, which in autumn-winter was greater in invaded sites and in spring-summer similar between invaded and non-invaded sites. On the other hand, granivores and insectivores did not show a significant relationship with the presence of Pyracantha. Abundances of the most common seed disperser were significantly affected by the interaction between time period and presence of Pyracantha. These results indicate that the abundances of birds that legitimately disperse Pyracantha seeds are temporally and spatially associated with fruit abundance provided by this exotic plant. This underscores fruit availability as an important ecological factor affecting frugivorous bird abundance, and suggests that Pyracantha seed dispersers are capable of detecting changes in the availability of its fruit, likely contributing to the effectiveness of its dispersal.
Nuevo registro del huroncito patagónico (Lyncodon patagonicus, Carnivora: Mustelidae) para el centro de Argentina y aportes sobre su historia natural ä Resumen -El huroncito patagónico (Lyncodon patagonicus) habita regiones áridas y semiáridas de Argentina y Chile. La mayor cantidad de referencias proviene de registros antiguos, existiendo escasas observaciones recientes. Si bien la especie es conocida desde hace más de un siglo y posee una amplia distribución, el conocimiento sobre su historia natural es limitado. En este trabajo se da a conocer una nueva localidad para esta especie en base a un ejemplar observado y fotografiado en la Reserva Natural Chancaní, provincia de Córdoba, Argentina. Además aportamos información sobre su historia natural, ya que el individuo fue visto durante el día, alimentándose de un ejemplar de Ctenomys sp. Por lo tanto, confirmamos la presencia del huroncito patagónico en la provincia de Córdoba, cuyo registro más fehaciente data del Pleistoceno Tardío.Palabras clave: Alimentación, Argentina, distribución, Reserva Chancaní.ä Abstract -The Patagonian weasel (Lyncodon patagonicus) inhabits arid and semiarid regions of Argentina and Chile. Most references come from ancient records, recent observations are scarce. Although the species has been known for more than a century and has a wide distribution, knowledge about its natural history is limited. In this work, a new locality is documented for this species, based on a single specimen observed and photographed at Chancaní Natural Reserve, Córdoba Province, Argentina. It also provides information about its natural history, since the individual was seen feeding on a specimen of Ctenomys sp. during the day. Therefore, we confirm the presence of the Patagonian Weasel in the province of Córdoba, whose most reliable record of the species comes from Late Pleistocene.
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