Objectives: Estimate A. spurrelli density by distance sampling and perform a statistical power analysis for an eventual monitoring, based on the sampling and data obtained in the Utria NNP. Methodology: Population density was estimated by distance sampling with the software DISTANCE 6.0 Release 2, using nine transects following the course of the streams with variable length. The statistical power was estimated with the software Monitor 11.0. Results: The estimated density was 0,03 individuals/m 2 (CV=12,8%) of A. spurrelli associated to streams. The statistical power showed that implementing a monitoring program for the species would imply two annual samplings for three years, in order to detect exponential changes up to 12% with a power of 85%. Conclusion: In an eventual monitoring program for A. spurrelli , operational and technical capacity from staff in charge must be assessed, in order to determine sampling periodicity and frequency according to the results obtained in this study.