You Are Wrong About Moon Phases

By Dr. Hal Schramm

Most anglers have an opinion about how moon phase affects bass catch. In many cases, these opinions are supported by many years of fishing, so I do not discount them. But who to believe? A lot of anglers swear by the full moon, but others claim better catch rates on a new moon. With 20 million bass anglers in the U.S., every phase of the moon probably has some fans.

To sort through this confusion, it may help to divide fishing into day fishing and night fishing. I can more easily understand an attachment to a particular moon phase by night fisherman. Everything about fishing is more difficult at night. First and foremost, a full moon on a clear night provides sufficient light to navigate to fishing spots. Certainly that was important 20 years ago, but now we have GPS. Nevertheless, a full moon still simplifies night fishing. Of course, none of these benefits accrue to “dark moon” fans.

For daytime anglers, support for the full moon or any other moon phase, is less obvious. Not encumbered by the difficulty of navigating and fishing in the dark, I am more inclined to think that their favored lunar conditions are based solely on past catch rates.

It would seem the moon, or more specifically the lunar cycle, would affect bass. The moon has a powerful effect on tides, and tides organize fish behavior. The dramatic spawning of the grunion that use the moon-influenced tides to deposit their eggs high on southern California beaches come to mind. Bass in tidal rivers position themselves at drains to gorge on the forage pulled from the marsh during falling tide. But there are no tides in inland freshwater systems. Does the moon affect bass in the vast inland acres where most bass anglers fish?

The simple answer is that there is no direct scientific evidence to support a lunar effect on bass. Numerous studies have assessed largemouth and smallmouth bass movement. These studies have found that bass have home ranges, select certain habitats, and exhibit seasonal and even day-night changes in movement and habitat use. A few of these movement studies have looked for lunar effects and found none. But these are movement studies; although feeding can be inferred from movement, these studies do not measure feeding behavior or angler catch rate.

While there is no scientific evidence to support an effect of the moon on bass catch, I suggest there is strong evidence, at least for daytime fishing, that moon phase does not affect bass catch rate. Upper-tier bass tournaments fished by highly skilled bass anglers happen every week from early spring through late fall. Consistently, winning anglers catch limits of big fish. You don’t need a calendar to verify that, collectively, these tournaments occur during every possible moon phase. Maybe someday some obsessed statistician will assemble all these tournament stats and relate them to moon conditions, but I can tell you that when catch rates vary little (which seems to be the case, at least for the top-finishing tournament anglers) you are not going to find much of a relationship with a fluctuating variable like moon phase.
Trophy bass
The Toyota ShareLunker Program encourages anglers to donate live and healthy largemouth bass over 13 pounds caught in Texas to Texas Parks and Wildlife Department for selective breeding. In exchange, anglers are provided a fiberglass replica of their trophy catch. Since 1986, 548 bass have been entered in the ShareLunker Program, and catch date and moon phase are available for each fish. The figure below derived from those data tells me that moon phase has little to do with catching oversize bass.


A few thoughts on bass spawning
Bass anglers have especially strong opinions about the effect of the moon on bass spawning. As for catch, many anglers swear by the full moon; others claim another spawning surge occurs with the new moon. Fish hatchery managers have no evidence to support a strong tendency for bass to spawn on any particular phase of the moon. Below are some data from Charlie Silkwood, hatchery manager at Mississippi Department of Wildlife, Fisheries and Parks’ North Mississippi Fish Hatchery. At North Mississippi, brood bass are held in outdoor ponds and then transferred to raceways to spawn. In both 2013 and 2014, there was no tendency for the bass to spawn on either the full moon or the new moon.

So, without scientific evidence, we’re left with the opinions of experienced anglers, many who say the moon has a tremendous affect on fishing and catching. Maybe they’re simply more confident fishing during those moon phases, and you know how much confidence plays into success. Some anglers plan all of their trips according to moon phase, so they have no experience fishing the other phases. Whatever the reasoning behind the creation of their beliefs, the moon phase is an important topic for many bass fishermen.