What is the initial step in the methodical analytical approach used to locate unknown Wels catfish specimens in a new venue?

Map the deepest contours, holes, and trenches using sonar or charts

Successfully locating an unknown Wels catfish requires treating the water body as a complex puzzle based on ecological needs, starting with the fish's primary daytime requirement: security and thermal stability. The systematic, tiered approach begins with using tools like sonar to accurately chart the physical topography of the water body. Identifying the deepest contours, trenches, and holes is prioritized because these represent the fish's necessary daytime refuge. Only after establishing these deep bases of operation does the angler proceed to locate overhead cover and feeding routes.