1. Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Uncertainty studies for hydroacoustic estimate of fish DeWelopment workshop, Warsaw, February 10, 2011 Małgorzata Godlewska, Atle Rustadbakken & Thrond Haugen

2. Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Replicated sampling (independent estimates) Spatial variability Temporal variability (interannual/seasonal) Investigated sources of uncertainty for hydroacoustic estimate of fish abundance:

3. Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund

9. Kiełpińskie Clearly a spherical covariance structure with defined nugget (i.e., intercept>0) and kappa (sill) parameters The spatial autocorrelation becomes neglible at distances > 227 or 289 meters

10. Rumian Clearly a spherical covariance structure with defined nugget (i.e., intercept>0) and kappa (sill) parameters The spatial autocorrelation becomes neglible at distances > 900 (sA- tot) or 600 (sA-SED) meters

11. Lidzbarskie No clear spherical omnidirectional covariance structure Should probably fit a directional variogram as there seems to be a longitudinal gradient in abundance

12. Dąbrowa Wielka Not a clear spherical covariance structure with defined nugget and kappa (sill) parameters The spatial autocorrelation becomes neglible at distances > 524 (total) or 640 (SED) meters Should be used with caution

13. Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund Rumian

14. Polsko-Norweski Fundusz Badań Naukowych / Polish-Norwegian Research Fund

17. Conclusions Uncertainty due to replicated sampling is within 5 %, on the condition that the coverage > 5. The spacial variation must be accounted for when designing the survey or when analyzing the data. For Wel lakes the autocorrelation distances are between 200 and 1000 m. This may change with changes in fish spacial distribution. Rumian data do not show statistically significant differences between 2009 and 2010, however temporal variation may change both seasonally and annually. There is for sure potential variability due to operator handling, both during collecting and analyzing the data. There is therefore an urgent need for a standard operation proceedure to assure comparability of results.