Kevin VanDam recently published an article for Bassmaster Magazine that outlines the importance of moon phases for predicting largemouth bass movement during the spawn. The article can be found here. I’m a huge KVD fan, but this is one case where I believe anglers have let superstition trump science. In High Percentage Fishing, I examined more than 40,000 freshwater catch data points and argued at great length that moon phases do not have any impact on the movements of freshwater fish.
Speaking hypothetically, if such a relationship did exist, how would the moon influence bass? Freshwater lakes are far too small for tidal movements. Given the distances involved, your boat has a greater gravitational influence on a netted bass than the moon. Not to mention the gravitational pull of a full moon is essentially the same as a new moon. The whole moon, is after all, still there. Is it light levels? If so, do we suppose bass sit just below the surface like gators waiting to see if it’s a full moon? What do they do if it’s cloudy?
In Doug Hannon’s 1986 publican “Big Bass Magic,” the bass professor argues for a strong connection between lunar phases and fishing success. Hannon bolstered this claim by creating a graph of world record catches that occurred between 1970 and 1979 as compared to moon phases. In Hannon’s study there appeared to be some correlation between moon phase and world record catches as more catches seemed to take place on or around the new and full moon. He claimed that 73% of catches occurred on three days of either side of the full or new moon, plus the day of each half-moon. While initially this seems impressive, it’s important to note that as defined, Hannon has included more than
half of all the days in a lunar month! I have updated Hannon’s graph to include new World Record catches that have been confirmed since the original publishing date of Hannon’s book. As defined previously by Hannon, peak lunar days which comprise 51% of a lunar month now only yield 55% of the catches as compared to the 73% Hannon noted. The full moon bias has vanished and there isn’t a strong correlation with catch rates and any particular moon phase. This is compelling evidence to further bolster the case that lunar periods have little if anything to do with the feeding cycles of fish.
In addition to my published work, other scientific studies have come to the same conclusion. For those interested, please follow this link to a study conducted by the University of Florida: Do Moon Phases Affect Bass Fishing.
Hard to kill moon myths are great examples of an illusory correlation and confirmation bias. Illusory correlation happens when humans infer causal relationships where none exist. Confirmation bias is the tendency to remember instances that support a particular mental model, but forgetting the data that paints a contrary picture. Fishermen, of which I am one, often do both in spades.
I think John Hope said it best, “Too many fishermen are unknowingly handicapped because they have acquired a zealous belief in what they consider to be gospel-truth facts that are actually nothing more than myths.” So what's a fisherman to do? If you are a passionate believer that the moon influences bass behavior by all means get out there and get on the water during that full moon! If however, you've become a doubting Thomas, don’t ignore moon phases. Plan your trips around them, especially new and full moons. Minimize fishing pressure and maximize your chances by making sure you arrive a few days before the masses!
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