Solunar theory in plain English
Anglers have planned around the moon longer than they've planned around the weather. Every fishing-tackle catalogue from the last hundred years has a solunar table in the back, claiming to predict when fish will bite. The theory has a name and a long folk-history, and it shows up enough in actual logs that most working fishers take it half-seriously. It is not a forecast model. It is not endorsed by marine biologists. But it is also not nothing — and once you understand what it actually claims, you can decide for yourself whether the moon transits on this site's tide pages are worth checking before you head out.
What solunar theory actually says
John Alden Knight published the original solunar theory in 1926. The claim: fish are most active around four moments each day, called major and minor periods. Majors fall when the moon is at upper transit (directly overhead) and lower transit (directly underfoot, on the other side of the planet). Minors fall when the moon is at the horizon — moonrise and moonset. Each major period is roughly three hours long, centred on the transit; each minor is roughly two hours, centred on the rise or set. Fish-bite-likelihood, the theory says, peaks during these windows, especially the majors.
Why the moon transit and not the sun
The lunar argument is that the moon is the dominant gravitational driver of tides — twice the pull of the sun, even though the sun is vastly bigger. Tides are when fish-feeding behaviour shifts most clearly: bait moves with current, predators follow bait, the whole intertidal zone reshuffles every cycle. Solunar theory takes the next step and says these gravitational effects shape feeding even outside the tide-driven part of the day. Whether that holds up in clean experiments is contested. Whether it holds up in fishing logs is something every angler decides for themselves.
The tidal coefficient adds another layer
On top of the moon-transit theory, the size of the swing on a given day matters too. The tidal coefficient is a French-Spanish convention that puts a number from 20 to 120 on each tide, where 120 is the biggest possible spring tide and 20 the smallest neap. Bigger coefficient means more water moving, more bait dislodged, more predator activity in coastal estuaries. A solunar major that lands during a high-coefficient day is the strongest signal the system gives — by its own logic, that should be the prime window. The pages on this site flag the coefficient on every day-by-day breakdown.
Crossover with sunrise and sunset
Most experienced fishers will tell you that golden hour at sunrise or sunset is when they catch the most fish — light is changing, surface temperatures are dropping or rising, baitfish are moving from open water to cover or vice versa. This is empirical, not theoretical, and it doesn't depend on the moon. When a solunar major happens to coincide with sunrise or sunset, the theory rates it the highest possible window. That might be because solunar is real, or it might just be that golden hour was always going to be the best window and the moon transit lined up by coincidence. Either way, the recommendation lands the same.
How to actually use it
Don't take it as gospel. Take it as one of three or four signals you check before a session. The wind matters more for surface presentation. The water temperature matters more for species behaviour. The tide stage matters more for current and bait flow at your specific spot. Solunar is the tiebreaker — when two days look equally good on every other axis, the one with a major period overlapping sunrise and a coefficient above 80 is the one to pick. Read the spreadsheet of your last fifty trips and decide whether the moon entries clustered around your better days. If they did, the theory works for you. If they didn't, check it less.