Let’s move your cursor around the background GRIB until you once again see the green bar extend outward from the left axis to the red Thermocline line. The portion of this bar which lies ABOVE your Maximium Fishing Depth represents the Fishing Volume (temperature x depth) for your target species at this location.
In general, the bigger this area above the Max Fishing Depth the more opportunity to find your target species at this location. That is a really important point. For example, if all the preferred temperatures (and thus the green Fishing Volume bar) for the species you are targeting are deeper than you can fish, then your fishing volume is zero.
Move your cursor around the downloaded Thermocline file and observe how the Thermocline, the OTD bar and the Fishable Volume triangle change with location. Again, bigger bars mean there is more water at this location which is at temperatures that match your target species Optimum Temperature. Smaller bars mean there is less such water. Other factors being equal, opportunities for successful fishing outcomes should increase as the size of the Fishable Volume increases.
