Time-Lapse Photography of an ASDIC Echo-Sounder PPI-Scope as a Technique for Recording Fish Movements During Migration
The use of time-lapse photography in combination with sonar as a means of observing the sockeye salmon (Oncorhynchus nerka) smolt migration in a large lake is discussed. A description of the gear used is given with some examples of the type of information that can be derived from this technique.The scanning rate of the sonar equipment used, combined with time-lapse photography, resulted in a compression of time to [Formula: see text] when scanning at a range of 400 ft and to [Formula: see text] at a range of 800 ft. A 24-hr period may thus be viewed on film in respectively S and [Formula: see text] when projected at a speed of 24 frames/sec. This speeded-up process facilitates separation of moving targets from stationary ones, even in the clutter of surface and/or ground echoes.Although subject to all the usual vagaries of target identification which accompany use of all echo-sounding gear, analysis of the movies with a time-motion projector appears to give meaningful information on such parameters as the speed and direction of migration or movement, and the distribution of migratory activity throughout a 24-hr period.