Susana D. Amaral

Potamodromous fish movements under multiple stressors: Connectivity reduction and oxygen depletion.

Rivers are impacted by multiple stressors that can interact to create synergistic, additive or antagonistic effects, but experimental studies on fish encompassing more than one stressor are seldom found. Thus, there is the need to study stressors through multifactorial approaches that analyse the impact of fish exposure to multiple stressors and evaluate fish sensitivity to stressor combinations. Some of the most common impacts to Mediterranean rivers are of two natures: i) water abstraction and ii) diffuse pollution. Therefore, the present study aims at studying the responses of potamodromous fish facing combinations of: 1) a primary stressor (two levels of connectivity reduction due to water scarcity), and 2) a secondary stressor (three levels of oxygen depletion due to increase organic load - of anthropogenic nature). Schools of five wild fish from a cyprinid species (Luciobarbus bocagei) were placed in a flume, equipped with see-through sidewalls to allow for behavioural analysis, and subjected to different combinations of the stressors. Results show that at the unconnected level the primary stressor (lack of connectivity) overrode the effect of the secondary stressor (oxygen depletion), but when connectivity existed oxygen depletion caused a reduction of fish movements with decreasing oxygen concentrations. This multifactorial study contributes to improved prediction of fish responses upon actual or projected pressure scenarios.

Do small barriers affect the movement of freshwater fish by increasing residency

River fragmentation due to artificial barriers directly impacts fish communities by limiting migratory movements. This work aims to understand how small barriers affect the movements of a potamodromous cyprinid species - the Iberian barbel (Luciobarbus bocagei (Steindachner, 1864)) - in a 5.6km upstream segment of a stream impacted only by the presence of physical barriers. Fish were marked with Visible Implant Elastomer tags (VIE), and barriers were seasonally characterized. A total of 683 fish were tagged, with 104 recaptures, during five sampling seasons (spring 2012 - early summer 2013). Eleven of the recaptured fish moved past a barrier, without any preference in terms of direction of movement. There were no differences in length, either between migrants and residents, or between upstream and downstream migrants. The results show that although barbel are able to negotiate small barriers, part of the population did not move between fragmented reaches - an indication that under such conditions, fish species populations may adjust their life-history strategy to augment residency as it was hypothesized from the results.

Modeling water quality in reservoirs used for angling competition: Can groundbait contribute to eutrophication?

Abstract Inland recreational fishing is a popular leisure activity in Portugal, which has close to 219,000 anglers. This study aimed to determine if the groundbait used to attract fish to the area in angling competitions contributes to eutrophication of reservoirs. We conducted a quantitative and qualitative assessment of commercial groundbait to examine the relationship between eutrophication and groundbaiting in angling competitions performed in Maranhão Reservoir, one of the most important southern Portugal angling reservoirs. Simulations using the CE-QUAL-W2 model were performed from January 2001 to February 2007 considering the number of anglers present in angling competitions and the chemical characteristics of commercial groundbait. The results indicated that the use of 5–10 kg of groundbait per angler (3–20 tons of groundbait per year) did not alter the ecological functioning of Maranhão Reservoir; however, higher angling pressures may lead to a significant increase in nutrient concentrations and consequent increases in primary production in the waterbody. Based on these concerns, we combined modeling with simulations to evaluate the environmental effects of groundbaiting in recreational angling and its relation to reservoir eutrophication. This study represents a contribution to more practical and holistic management of recreational fisheries.