Oudoors: Study throws light on moon factor

Full moon: Lunar phases are only a minor influence on fishing, a university study says. Photo / Simon Baker

The question often arises: does the Maori fishing calendar work?

To obtain a definitive answer one would have to ask the fish, but as this approach is not likely to achieve much it is more useful to look at a study by a university student who tried to reach a conclusion in his thesis.

Just the fact there are different versions of the lunar, or Maori, fishing calendar questions the validity of the approach.

Most successful fishermen seem to agree the moon and its position and phase do have an influence. The lunar calendar is based on the phase of the moon, whereas bite times are determined according to its position.

American Richard Alden Knight publishes Solunar Tables which are based on active feeding patterns. Every 24 hours there is a major period, when the moon is directly overhead in the sky, and a minor period of activity, when it is directly underfoot. These tables predict daily bite times based on this theory and are available here.

An example of this influence is illustrated by taking notice of when cattle and sheep are feeding. They could be all feeding at any time of the day, and if the position of the moon was studied the odds are it would coincide with one of the forecast feeding periods.

The problem arises when a fishing expedition is being planned with elevated levels of anticipation and other factors like tides and weather - which are both just as influential in fishing success - are taken into account with issues like school fairs, kids' Saturday morning sport, holidays, lawns-to-be-mowed, family occasions and rugby matches, and it all starts getting out of hand.

The recent study was undertaken by Ben Stevenson, a student at Auckland University, for his thesis on statistics. It took into account surveys done by, and for, the Ministry of Fisheries over many years. It is the first time we have seen fishing success analysed against the lunar calendar, and it has some interesting conclusions.

The main one is the lunar or Maori calendar is of little value when planning fishing trips.

"Briefly, we were able to provide pretty strong evidence that more snapper are caught at certain times in the lunar cycle than others, and that there are different underlying catch rates for days with different Maori fishing calendar rankings. "However, the differences are very small, and the direction of the effect is not what it should be for the Maori fishing calendar - for example, days rated 'fair' seem to outperform those that are ranked as 'good'.

"Essentially, the effects are so small that there is little use in paying attention to the lunar phase or fishing calendar ranking in terms of deciding when to fish."

Stevenson made some observations of interest to fishermen, such as "significant relationships between catch-per-unit-effort (CPUE) and lunar phase have been found for black marlin, blue shark, short-fin mako sharks, mahi-mahi and yellowfin tuna.

"These effects were found using data from game fishing tournaments held on the coast of New South Wales with catch rates peaking between the new and first-quarter moons for the latter four species, and the highest CPUEs for black marlin occurring near the full moon."

One point he made was that any effect of lunar phases varied between species, so no calendar could apply across the board.

His findings were based on analysis of research which included diaries and interviews from 923 fishermen involved in 5032 fishing trips, involving only snapper as they are the most popular catch. Of these, 1384 (28 per cent) caught nothing and the largest catch was 45 snapper, including 22 in just 90 minutes.

Catch rates are measured as a catch-per-unit-effort, which compares one person's catch for the time spent fishing. There were only eight CPUEs over 10, and the average was 1.11, which basically says the average catch is one snapper per person per trip. In addition, a random phone survey covering 15,015 homes resulted in 3363 being eligible for the survey.

Stevenson said brightness of the moon could have a direct effect on snapper behaviour. "Feeding at night during the full moon is plausibly much easier than it is during the new moon, especially in shallow depths. The extra light available would make it easier to spot potential prey. If this is indeed the case, it is likely that snapper are hungrier during the day following a darker night, therefore biting with more intensity, resulting in higher catch rates.

"What does seem to have a major effect on catch rates is the time of year. Fishing trips in late March and late November seem to be the best times to fish and are surprisingly substantially more successful than trips in late December and January. It is not clear whether this is due to local depletion of snapper stocks (because of increased pressure), or is caused by a seasonal trend in the deficiency of the fishers themselves."

He suggested many people only fished in the summer holidays and were perhaps not as skilled as those who went fishing regularly. The worst months for catching snapper were August and September. Stevenson concluded: "It seems as though the effect of the moon on recreational fishing success is relatively minor. If peak bite times are ignored, the same can be said for the Maori fishing calendar."