Use of a microcomputer as an aid to identifying objects passing through a resistivity fish counter

摘要

Abstract.The Freshwater Biological Association has operated a salmon counter on the River From, Dorset. England since 1970. In this calcareous river, false upstream counts generated by mats of aquatic macrophytes floating downstream have proved the main constraint to the accuracy of the installation. In addition, time‐delays in the counter logic circuitry prevent the use of still photography to check the identity of downstream records. This paper gives a full description of the technical details and basic program listings for an inexpensive microcomputer‐based system to record the out‐of‐balance voltage signals from the resistivity counter. Comparison with still photographs indicates that the totals recorded can be corrected on the basis of differences in the form of signals generated by salmon and by other objects, including weed‐mats. The fast response time of the microcomputer‐system made it passible to confirm that most objects which generated downstream counts on Ihe River Frome resistivity counter were either salmon