Modelling daily catches of silver-phase European eel (Anguilla anguilla) in two hydropower-regulated rivers

Estimation of silver eel production,Anguilla anguillaL.,is fundamental for the management of eel stocks. In the hydropower-regulated rivers Shannon and Erne, Ireland, production is calculated using catch data from a conservation trap and transport programme. However, in both rivers gaps in silver eel catch datasets tend to occur, which can lead to biases in production estimates. Generalised additive models (GAMs) were used to model daily catch in these rivers based on a variety of environmental variables. Final models for the Shannon and Erne explained 83.7% and 78.8% of deviance in daily catch, respectively. A second model on the Erne included catch from a nearby fishing site in an attempt to increase explanatory power and explained 91.7% of deviance. Although model accuracy was increased, reliance on catch from another site may limit the applicability of the model. Model predictions were combined with estimates of fishing efficiency to predict production for the Shannon (36,210 kg; 0.85 kg/ha) and Erne (66,899-67,047 kg; 2.55-2.56 kg/ha). These values represented a 9.3% and 2.8%-3.0% increase on production estimated from incomplete catch records alone for the Shannon and Erne, respectively.

Automated summary

Estimation of silver eel production is crucial for managing eel stocks. Generalised additive models were used to model daily catch in rivers Shannon and Erne, explaining 83.7% and 78.8% of deviance in daily catch. Incorporating catch data from a nearby fishing site in the Erne river model improved explanatory power, explaining 91.7% of deviance.