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Gewählte Master / Diploma Thesis:

Daniel Hayes (2014): The Influence of Recreational Fishery on Salmonid Populations in the Ois River & Comparison of Two Sampling Strategies for Estimating Salmonid Stocks.
Master / Diploma Thesis - Institut für Hydrobiologie, Gewässermanagement (IHG), BOKU-Universität für Bodenkultur, pp 112. UB BOKU obvsg FullText

Data Source: ZID Abstracts
Abstract:
This thesis studies the influence of recreational fishery on the stock of brown trout (BT), rainbow trout (RBT), and European grayling in the Ois River. It has been examined if the harvest of RBT in the study reach affects populations of these three species. Data of yearly conducted fish stock assessments from 2008 to 2013 were analyzed and compared with electrofishing data of 2012 and 2013 collected in an upstream reference reach experiencing no angling pressure. Additionally, fish stocks in both river reaches were assessed via day-time snorkeling and results were compared to those of the electrofishing surveys. In the study reach, total salmonid density averaged 763 ind./ha (range 549–1,153 ind./ha), biomass 74.3 kg/ha (range 52.3–102.7 kg/ha). An increasing ratio between adult RBT >25 cm and BT >22 cm from 1:2 in 2008 to 1:7.4 in 2013 indicates that harvest of RBT influences adult BT and RBT stocks in the study reach. Total salmonid abundance and biomass was on average 230 ind./ha and 15.6 kg/ha higher in the reference reach than in the study reach. The non-fished reference reach had 7–10% greater RBT shares than the study reach. The abundance and biomass values of rainbow trout >25 cm indicated the influence of fishing pressure. In the reference reach, a higher percentage (32–39%) of these fish survived the 2012 season to tribute to the >32 cm size class in the following year. In the study reach this was 12–17%. So far the extent of the influence does not yet impair or weaken the population. If the allowed number of 400 RBT/year would be harvested, it is expected that the stock will be reduced beyond the natural capacity. The comparison of electrofishing and snorkeling revealed a correlation between both methods (R² = 0.77). On average, total snorkeling abundance was 86% (Δ 21 ind./100 m) of the electrofishing estimates. The comparison revealed a high variability in regards to species-specfic density per habitat type.

Beurteilende(r): Jungwirth Mathias
1.Mitwirkender: Pinter Kurt

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