This is from the
WTides application help page:
The Maori Fishing Calendar
There is a thing called the Maori Fishing Calendar. It is published in various forms in New Zealand. The Maori (and many other Pacific peoples) found that on certain days of the lunar cycle, fishing was better than at other times. These days are mainly the few days surrounding the New Moon.
Does this stuff really work? It's not infallible. There are, after all, still the effects of weather and season to be factored in. However, many people are quite convinced that, on balance, you will catch more “fish per unit effort” on a day when the Maori calendar predicts good fishing than on other days. At least there’s more chance it is valid than the astrological predictions published daily by even the most respectable journals.
The moon's gravitational pull is said to directly affect animal appetites. When the moon is overhead, for some reason, it makes fish hungry. When the moon is underfoot, it also seems to make fish hungry. This is true for both fresh and salt water fish. The gravitational pull of the sun must have a similar, if lesser effect. So, when the sun and the moon are ‘up’ or ‘down’ at roughly the same time – as happens near new and full moon – fishing should be the most productive. Some people say the hour around moonrise and moonset have a similar, if lesser, stimulating effect.
In addition to the effect of gravity, light must play a good part in the ability to catch fish. If the fish can’t see the bait, it is unlikely to find it. Many predatory fish have eyes that see better in low light than the eyes of their prey. This makes dawn and dusk two valuable contributors to good fishing. Bright moonlight is probably similar from the perspective of the fish, so full moon nights are also favoured fishing times.
Finally, a good current is helpful in carrying the food supply (and your ground bait) towards the fish.
So, basically they assign values to factors such as sunrise/set,moonrise/set, moon/sun overhead/underfoot and tidal movement to make the graph. You'll notice that the peaks correspond to the portion of the tide graphs with the greatest slope. Those are the times with the greatest water movement. At times of peak tidal flow you get the most feeding activity.
Not exactly proven by rigorous scientific experiment, but probably supported by time on the water experience. I don't know if I absolutely accept the validity of the graphs. After all; I've proven that I can't catch fish at peak tidal flow just as well as at slack tide. Maybe that's just me, though
