June 13, 2011
The Amazon River Basin encompasses the world’s largest remaining tropical rainforest, and the largest freshwater system with the highest fish species diversity on earth, but global climate change is predicted to cause the loss of 7–12% of fish species by 2070. The severe drought anomaly of 2005, caused by warming of Atlantic surface waters, provided a unique opportunity to examine the impact of a major climatic disturbance on a tropical fish assemblage. We monitored fish species diversity in six Brazilian floodplain lakes along the Solimões River from 2004 to 2007 (before, during, and after drought). Statistical analysis revealed changes in species composition of these lakes following the drought, with both positive and negative responses observed. The response to drought was not uniform among species with regard to trophic guild or migratory behavior. SIMPER analysis showed that planktivores on the average increased in abundance in the years following the drought, carnivores and omnivores decreased, and herbivores and detritivores increased. Some of these changes were transitory, others persisted through monitoring. Migratory species disproportionately increased in abundance post-drought compared to non-migratory species. Interlake (β) diversity of fish declined during the drought year, indicating that lakes were becoming less heterogeneous in species composition, but showed a trend toward recovery of pre-drought level in the following years. According to both global climate change models and recent experience, the intensity and frequency of droughts in this region of the world is increasing. Given the sensitivity of resident fish species to the single, short-term, perturbation reported here, assessment of how tropical freshwater fish populations respond to drought will be crucial to understanding the consequences of this kind of perturbation to these communities and to the human inhabitants who depend upon this important protein source.
The study tests whether diurnal microhabitat use by Hatcheria macraei depends upon specific environmental parameters and/or the abundance of other fish. We carried out a 1-year field study in a low-order river of northern Patagonia, Pichileufu River, and used experimental trials to determine substrate preferences. Fishes were captured during daylight and physicochemical environmental variables were recorded. Headwater zones were dominated by rainbow trout (Oncorhynchus mykiss) and brown trout (Salmo trutta), while native fishes, H. macraei and the creole perch (Percichthys trucha) were more abundant downstream. H. macraei inhabited mostly shallow microhabitats with fast water velocity and substrates having significant interstitial spaces, independently of the abundance of other fishes. Experimental trials pointed out that H. macraei preferred mostly coarser substrates (>6 cm), avoiding fine ones. This study highlights the importance of erosional zones with high water velocity, large substrates, and suitable interstitial space in the microhabitat selection ofH. macraei. The knowledge of microhabitat use by native fish populations is critical for management and conservation strategies and should be taken into account before any river modification.
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