Food resources and cyprinid diet in permanent and temporaryMediterranean rivers with natural and regulated flow

Abstract

This study addresses the differences in food availability, diet and feeding activity of the Iberian barbel, between permanent and temporary nonregulated rivers, and the effect of flow regulation on feeding parameters. A total of 267 adult barbels were seasonally collected in four nonregulated and regulated rivers from permanent and temporary basins, and their gut content was analysed. Locally available food sources were evaluated across sites and seasons. Barbels from the permanent nonregulated river exhibit a more variable and diversified diet in which invertebrates assumed a large importance, especially during high flows. Barbels from the temporary nonregulated river presented a more uniform diet composed of plant material and detritus, particularly in drought seasons. Flow regulation affected different flow components in both systems, but the effects on food resources and barbels' diet were similar, resulting in an intra‐annual stabilisation of resource availability and fish diet, with a higher consumption of plants and detritus. Changes in fish diet and feeding activity in both nonregulated and regulated rivers were strongly associated with the seasonal variability of streamflow components, particularly between low‐ and high‐flow periods, and with the reduction in flow variability in the case of dam regulation. Results from this study can be used to improve guidelines for flow requirement implementation.

Dietary niche divergence between two invasive fish in Mediterranean streams

“…In particular, we have found a tendency for sympatric fish decreasing niche width in the permanent stream relative to their allopatric counterparts in intermittent streams, which can be associated with higher availability of preferred prey in the former systems. There was, however, no apparent decrease in the consumption of plants by the cichlid in the permanent river despite that prey availability was likely higher (Magalhães, 1993b;Alexandre et al, 2015). This suggests that our findings might not be an artefact of local conditions.…”

“…Regardless of its direct cause, this divergence in plant use may influence trophic interactions between the two species, with advantages for the cichlid. Plant material is a highly accessible and persistent resource in Mediterranean streams (Alexandre et al, 2015) and may constitute an alternative and efficient buffer strategy against prey scarcity (Magalhães, 1993a).…”

Life‐cycle responses of a Mediterranean non‐migratory cyprinid species, the Northern Iberian chub (Squalius carolitertii Doadrio, 1988), to streamflow regulation

“…The Northern Iberian chub, as well as other species of this genera, is generally described as an omnivorous species, feeding on both animal and plant items, with a strong ontogenic variation on its dietary habits (e.g., Garrido, Sanchéz‐Polaina, & Prenda, ; Magalhães, ; Sánchez‐Hernández & Cobo, ). As described by these authors, smaller chubs tend to feed more on small soft‐bodied invertebrates, which in this case are more available at the NRR river (Alexandre, Sales, et al, ), contributing for the higher condition of these fish in the nonregulated watercourse. As they grow, chubs tend to decrease animal prey breadth and feed more on larger items, such as smaller Decapoda and detritus or plant materials (Garrido et al, ; Magalhães, ), whose constantly higher abundance and availability is incremented in the studied regulated river by the environmental homogenization caused by its storage dam and respective EFR (Alexandre, Sales, et al, ), contributing to the higher body condition of adult chubs in RR.…”

“…A more detailed characterization of the studied rivers and of the main streamflow (30‐year time series, 1974–2004, collected from the Portuguese Environmental Agency Database; SNIRH, ) and thermal (obtained with data loggers Water Temp Pro V2 from HOBO during the study period) regimes differences between them is presented by Alexandre et al (, ) and Alexandre, Sales, et al (). In short, only slight differences are observed between the two rivers regarding their seasonal temperature variation pattern, which occur mostly in the end of spring and summer when the NRR presents higher average daily temperatures.…”

“…However, most models and other studies addressing this relationship were developed to analyse variability in life‐cycle traits at the assemblage level, and the aspects of the links between fish bioecological cycles and environment remain relatively unknown at the population level. Intraspecific variability in the life histories of fish determined by environmental conditions has been demonstrated to occur in numerous cases (e.g., Alexandre, Ferreira, et al, ; Alexandre, Sales, Ferreira, & Almeida, ; Blanck, Tedesco, & Lamouroux, ; Spranza & Stanley, ). Described patterns are, generally, in accordance to previous theories about fish life‐history strategies (Winemiller & Rose, ) and include changes in diet composition and feeding strategy (Alexandre, Sales, et al, ); differences in age at first reproduction due to flow effects or food availability (Alexandre, Ferreira, et al, ), longevity (Baltz & Moyle, ), brood size, and size at first reproduction (Baylis, Wiegman, & Hoff, ).…”