I guess it depends on what you believe. Is fishing bad during a Full Moon because the salmon is “full” from feeding at night – i.e. feeding during the pale light of the moon? Well, I don’t doubt that salmon may feed during the night (commercial line-trawlers sometimes fish at night) but I do doubt that full moon nights are prime feeding times for salmon! If the pale light of the full moon provide enough light for salmon to feed, would not the blazing sun do it even better? Also, is fishing only bad after a CLEAR full moon nights? Or is it perhaps bad even after cloudy ones? I think it’s bad during full moons – clear or cloudy!
My guess is that fishing for salmon is bad during the Full Moons mainly because of tidal currents. Tidal currents are the worst during a full moon because both the Sun and the Moon line up… the Sun in one direction and the Moon in the other. They exert a TWO-WAY gravitational pull on the Earth’s oceans! This produces so called “Spring Tides” at opposite ends of the Earth at the same time! Although full moons do not produce the strongest currents, they are the worst for fishing because they NEVER LET UP – there is no time during the 24h day when it gets quiet. There is almost no difference between HIGH/HIGH and LOW/HIGH , and the period of high and low slacks are very short!
The next worst is the New Moon! This is because during this phase, the Sun and the Moon line up … both of them in the SAME direction. They exert a ONE-WAY gravitational pull on the Earth’s oceans. The combined effect of both Sun and Moon tugging together produces the largest Spring Tides of the entire cycle and hence the strongest currents! However, the saving grace of the New Moon is that there are LONG QUIET TIMES… the so called “Neap Tides”… in between the HIGH/HIGH and the LOW/LOW. Fishing is usually pretty good during Neap Tides … at least compared with Spring Tides.
If this is correct, then the best fishing time is during a Half Moon! In this lunar phase, the Sun and the Moon are separated by 90° when viewed from the earth. The gravitational pull of the Sun partially cancel those of the Moon, thus producing minimal tidal exchange… i.e. Neap tides throughout the day and less currents than during any other time!
The lunar cycle is no doubt related to the tides in the ocean and thus to the currents. But these currents vary, not only because of the Sun and the Moon, but also because of GEOGRAPHY! For example: Flooding and ebbing currents in Johnstone Strait are affected by the Moon and Sun but follow a cycle that have a LONGER FREQUENCY than the rising and falling tides. Another example is the currents under the Lion’s Gate Bridge in Vancouver (the mouth of the Capilano River). They do not follow the high and low tides exactly – sometimes they could be separated by hours! This is because of the geography of these areas and they are not the only ones in BC! When I fish in the mouth of the Cap, I am much more concerned about being there when there is no current, than I am about being there during high water or low water!
Therefore, when trying to figure out the best fishing times, I think we would be better off by concentrating more on what the tides and the geography might be doing to the currents, and less on what the moon and sun might be doing to the tides!