Solunar tables were first devised by John Alden Knight in the 1920s. His tables are still published, but since then many imitators and innovators have expanded his basic concepts and included new theories. There are many different forms of tables, computer programs, and a watch that compute solunar majors and minors, predicting the best fishing days and best times of day.

Full and new moons rank highest, with days of decreasing fishing strength on either side. The specific hours of predicted good fishing cycle through the clock, regular as the tides.

The moon changes position in the sky at predictable rates that vary with the moon’s position in its orbit and its altitude (declination) relative to Earth. Solunar forces are at their strongest (majors) twice a day, when the sun and moon are closest to perpendicular with a particular longitude on earth—that is, when the moon is directly overhead or beneath that longitude. (That’s when tidal forces are strongest, although actual tides may be delayed.) Minor activity periods theoretically occur when the moon is positioned at 90 degrees to a particular longitude, and tidal forces are weakest. Computers at the U.S. Naval Observatory calculate these times for reference longitudes; solunar calendar makers center their solunar peaks around them, two majors and two minors every 24 hours and 50 minutes.

Of course folklore, literature, and police records suggest that phases of the moon influence the activity levels of werewolves, lovers, and criminals. Why not bass? Science also shows plenty of evidence of specific lunar effects on sea turtles, oysters, worms, crustaceans. (Mollusks moved from the Atlantic to Chicago, for example, reset their biological clocks in two weeks and started opening and closing to the schedule of a Chicago’s tidal cycle––if Chicago had tides.)

Consider that the moon exerts about 1⁄6 as much gravitational pull as Earth, and that, as it orbits us, its pull causes tides that can raise oceans up to 50 feet twice a day, as occurs in the Bay of Fundy. Solunar theorists propose that freshwater fish retain a primal memory of tidal effects, since their ancestors evolved in marine waters. We do know that tides strongly affect the movements and spawning of invertebrates, preyfish, and other marine species.

But it’s complex––marine fish are extremely variable in feeding patterns; water depth and current strength, not tides, usually determine feeding times. Different species feed at high tide, low tide, or in the faster currents in between; furthermore, in estuaries and tidal rivers, the flow of water is impeded so that actual peak tide occurs many hours after peak solunar influence.

If freshwater gamefish retain any ancestral memory of tidal feeding, it isn’t likely that they feed around majors and minors. More likely, fish have inherited abilities to use a biological clock (internal timing mechanism) to predict feeding opportunities in their environment. Lunar forces have been suggested as one kind of zeitgeber, a term for events that resynchronize the biological clocks of organisms. In response to a zeitgeber, an organism will start or stop bodily functions and behaviors to stay in synch with the environment and be ready for optimal conditions for laying eggs, feeding, or migration. Sunrise and sunset can also be zeitgebers, as they are for many gamefish, which have morning and evening activity peaks synchronized to reduced light periods.

Predatory gamefish become active in response to activity cycles of prey that produce improved feeding opportunities; preyfish in turn respond to the activity cycles of simpler organisms. Since many invertebrates use the moon to time behaviors, intermediate predators that eat them might use solunar forces as a feeding cue. Most gamefish are several steps up the food ladder from the simple organisms most likely to react directly to solunar force, suggesting that they will react to solunar force with discretion.

If few prey become available on solunar peaks, these peaks won’t be optimal fishing periods, regardless of the strength of the lunar force. Whenever events such as sudden cloudiness, increased current, or wave action create a feeding opportunity, predators try to feed. If bass feed successfully, they may be inactive at the next routine feeding period, like sunset or a major. Predators won’t ignore a chance to feed just because a major or minor period hasn’t arrived.

Many types of research have demonstrated how lunar forces affect a variety of animals, including humans. But in many cases, behavioral changes may be due to changes in light, day length, angle of the sun’s rays, or tides, rather than gravitational or electromagnetic forces of the moon and sun.