Full Moon and Bite Activity

[jurelometer]

In the thread: https://alantani.com/index.php/topic,36879.0.html

we were debating about whether fish could detect and therefore respond to changes in atmospheric pressure.  The subject started to wander into the full moon thing, specifically the commonly held belief that fishing during the full moon can be less productive. I was laid up for a day, and decided to dive into the scientific literature.

This full-moon-is-bad theory always bothered me a bit.   First of all, it makes it harder to motivate my fishing buddies. Secondly, the moon phase change is gradual and consistent- not an on/off switch, so why wouldn't the story be that the bite gradually slowed down and then ramped up as the moon phase progressed (other then it being bad for the charter business)?

A more detailed version of this theory is that  fish can feed under the moonlight and therefore would be less interested in feeding during the day when most fishermen were active.  OK, this is a bit better, but still seems kind of weak, and still doesn't answer the ramp-up/ramp down question.

And there are lots of different types of predators, prey, and environments out there. It can't be the same for all of them.

I went to see what the scientific literature had to say.  It turned out a lot!   There is a ton of material of catch/effort rates based on environmental conditions for commercial fishing, and a bit for sportfishing as well.

I do want to limit the discussion a little.  Moon phases will effect tides and therefore currents, but the big tides come with both new and full moons. Spawning cycles are often synchronized around full moon events, but they don't hasppen on each full moon cycle.  Hopefully we can stick to what is unique and repeats with each full moon.

I am going to beak this up in a few chunks to make it more readable. If you want to skip the comments between the chapters:

Part 2 : How much extra light does a full moon make?  https://alantani.com/index.php?msg=436256

Part 3:   Vertical Migration vs. Thermoregulation .  https://alantani.com/index.php?msg=436966

And the usual note that I am not trained in any of this stuff, just a science fanboy, so I would appreciate any corrections from the experts out there.

-J

[jurelometer]

Part 2 : How much extra light does a full moon make?

So lets start with the "just a day or two around the full moon" theory.  I was sure that this was nonsense, but there is a sliver of science to support it.

A rough surface (like the surface of the moon) is a poor reflector of light, but will have a sudden jump up in effectiveness when the source of light is directly or nearly directly perpendicular to the surface .  This is called the lunar opposition surge, and works for about four degrees or so on each side of the full moon.  I have seen numbers between 20% to 40% brightness increase- but as a non-astronomer, I have no clue which is correct and under what conditions . Source: https://www.sciencedirect.com/science/article/abs/pii/S0019103596902250?via%3Dihub

But hold your horses:  For reasons we can get into later, for many gamefish species, piscivorous feeding effectiveness (and therefore activity) peaks in a range of low light conditions – not too bright, and not to dark).  This usually occurs right around sunrise and sunset.  Sunlight is many orders of magnitude brighter than moonlight, so at sunset,  the vast majority of the light is still coming from the sun.  A full moon is essentially just stretching out that magic hour a bit, but on its own is not providing nearly enough illumination to keep the magic bite going without the help of the sun.

Furthermore, the sunlight reflecting off the moon is red shifted- so we are not getting as much of the higher frequency light waves that penetrate water more effectively- plus many  (most?) saltwater gamefish species have no red vision- so red light doesn't do much for them.

That is not to say that for some species, especially in shallow fresh  water,  that there might be enough light (and red vision)  to feed much farther into the night, but on the ocean side, I am still a skeptic. To support the believers,  here is an interesting study on largemouth bass and feeding success at various light levels and water clarities.  It supports the claim that bass  can feed effeciently under a full moon in the right condtions:  https://www.montana.edu/mcmahon/documents/LMB%20light.pdf

The bass study has a bit of a hack, as they used fluorescent light bulbs  that were not adjusted simulate the frequencies of true moonlight.

(Side note: Low light can also occur due to cloud cover, but fish generally lack the ability to quickly adapt to light level changes, and the "night vision" switchover is usually driven by time of day and not available light).

Now this doesn't mean that a full moon is not a factor in oceanic fish feeding behavior.  In fact,  the catch/effort rates show moon phase based variation in the open ocean, where tides are not really much of a factor. But it is much more complicated than a bunch of species feeding by moonlight.  More on this next.

-J

[JasonGotaProblem]

So you're telling me the science says they don't turn into werewolves?

[Finest Kind]

Interesting discussion here about the full moon and also the thread on atmospheric pressure. My take on these things is probably a bit different from most of you guys who I gather fish on the West Coast. Around NY, my experience with fishing around the moons is that they most definitely affect the fishing. And not just the full moon, the new moon as well. It is because the current is significantly stronger for about two or three days before and after the moons. Doesn't mean it's always better or worse. It depends on the area, and the species. Better for some, worse for others.Don't think it has anything to do with the brightness of the moon. Kind of an impossible subject to generalize about in my opinion. For example; I have a spot where I usually hammer the bass around the moons and the fish reliably turn on at the max current, which runs about 3.5 kts. I have another spot about ten miles away where the fishing is also great around the moons. Except here the fish usually only hit for one hour on either side of slack water. Same fish, same moon, ten miles apart, opposite behavior. I think it's important not to psych yourself out about some reason you should not bother to go fishing. Just go.
John

[jurelometer]

I think this stuff is environmental and not regional.  Fish don't know what coast they are on, just whether the water is moving, how well they can see, etc.

As to full moon/ new moon and tides.  I don't think there is any debate that tide has a major effect, especially for inshore fishing.  The tidal swings happen equally at both ends of the full moon/new moon cycle, so I don't consider the tidal effect as part of any potential full moon phenomenon.  The open ocean is a good place to look, because tides have a much smaller effect on water movement.

But the catch/effort ratio is definitely affected by moon phase, even in the open ocean. I'll try to write some of this up next.

-J

[jurelometer]

So you're telling me the science says they don't turn into werewolves?

They  keep telling us that it is just shark attacks, but why should we believe a bunch of scientists?  It has to be werewolves.   Look at those teeth marks!


-J

[Keta]

I don't think there is any debate that tide has a major effect....

Yup

So you're telling me the science says they don't turn into werewolves?

Come on now  werewolfs do not have gills  they are werewolf eels.

[oldmanjoe]

   I will throw my hat in the ring .    Let`s put down the binoculars and start looking at the whole picture .   Everything living thing on planet earth has a electric charge in it .

   The earth is surrounded with magnetic fields .  The moon phases change the flux line as well as other occurrences , such as solar flare ups .

Wild animals will feed at different times, Human behavior changes when the moon comes to full .

I believe all things are reacting the the surrounding electric charge . 

Electric charge is for ever changing , air density ,hot and cold .  Water temperature  including the currents in water , the salinity of the currents

Humans are domesticated , fish are not .   Fish have a lateral line and they use it ,       
 

   

[Benni3]

,,??? ,,,,,,voodoo,,,,,, Wichcraft and folklore,,,,,,,a fish finder just makes me mad when I run over so many fish with the right bait and can't catch anything,,,,,,,,,

[Midway Tommy]

I'm certainly not a fish, but I can tell you that I sleep like $ hit for 5 days around, 2 days on either side of, and a full moon. 

[jurelometer]

I'm certainly not a fish, but I can tell you that I sleep like $ hit for 5 days around, 2 days on either side of, and a full moon. 

Definitely one of the signs of turning into a werewolf.  Check for bristles under the tongue

-J

[jurelometer]

On the magnetic field theory: From a strictly science side, we would first have to find a magnetic phenomenon that was unique to just the full moon, then a reason why it might cause fish to eat differently, than an observation of fish actually behaving that way. 


Marine  biologists would  agree with Joe that detection of the earth's magnetic field  plays a direct role in the behavior of at least some fish species, but probably just for navigation. I haven't seen anything in terms of effecting cyclical feeding behavior.  The tides do move seawater around, and seawater is a conductor, so the earths magnetic field is slightly affected by tides - but we would still have to have a theory about how small magnetic field changes would affect a fishes daily feeding habits.  The moving water from tides is a more likely cause, as it improves predation success. And big tides are not unique to a full moon, they happen on a new moon too.

Magnetism seems to be useful for long range crude navigation.  For example, they think that salmon imprint both magnetic signals and scents.  To get back to the natal river to spawn, magnetic sensors are first used (they still haven't nailed down the biological mechanism yet), and once they are in the general vicinity, smell (taste?) takes over and leads them back to the river mouth and up to the spawning grounds.

On a side note on the comment on humans: For as far back as history goes and across many cultures, societies have always believed that full moon affects human behavior, but from what I have read, when the studies try to nail this down with hard data, the results are inconclusive.  ER docs, cops and EMTs would probably disagree, but the numbers don't seem to support this belief.

-J

[jurelometer]

On the lateral line and magnetism:  I do agree that we tend to over-focus on fish vision, and that is only one of the fishe's sensory systems.


The lateral line detects motion by detecting small changes in water pressure, not magnetism.  Cilia  (sort of like hairs) in special cells in the lateral line move enough to change the cell's electrical charge, which is detected and acted upon  by the nervous system of the fish. Or something like that

The lateral line is used for detecting objects in the near vicinity of the fish (sometimes up to 30 feet, generally under 6 feet, closer is more accurate), and to maintain orientation.

OTOH, cartilaginous fish  species  (sharks, sturgeon, etc.) can have some sensitive electromagnetic sensors on their heads which are used to detect the faint  electrical impulses from the nervous systems of prey, usually  something up close trying to hide in the sand or weeds.  Look up " Ampullae of Lorenzini" for more info. 

Something to run with, but still a bit thin in my opinion.

-J

[Shellbelly]

This is an interesting subject.

As a surf guy, I rely on tide and current charts.  I've caught plenty of fish when the science says I shouldn't have.  I'm not dismissing lunar influence because it's the primary tide engine.  About light levels.  You can't dismiss water clarity.  I've seen trout come up late in the morning because of murky water.  Some fishermen, who rely on the clock, would leave the spot instead of waiting for enough light to reach the lurking fish and stimulate them to rush the shallows.  Sometimes the water is just too muddy and causes them to change patterns.

In my little world, I look at the tide charts and note the odd patterns that occur around the full moon.  Not because of the light, but for the consistency of water levels covering the bottom structure I choose to fish. There's less tidal swing.  In addition, I get to fish during multiple tide and current changes in a shorter period of time.

Now, I'm gonna spin some heads and talk about phosphorus.  Based on my experience, when bait agitates the water during periods of high phosphorus, the agitated water glows green.  Humans only see this at night and it's very cool.  I have no proof, but I believe certain, or maybe all, saltwater fish "see" this in any light and have adapted to using it. I have thrown spoons in pitch-dark conditions and caught trout in the surf during these "glowing" conditions.  I have found that daylight fishing is generally better in these conditions.

Based on these experiences where I fish, I believe light is a major factor, but water movement and structure are the first orders of business.  The light change has to occur upon something that is holding bait. 

[oldmanjoe]

I'm certainly not a fish, but I can tell you that I sleep like $ hit for 5 days around, 2 days on either side of, and a full moon. 

I am the same way , I took notice as a child the effect of the moon .   And I will say their may be Two full moons  a year that are not as strong . But for the rest , I am charged up , thought process , creative .and all around body energy goes up .

      I want to say that we have to keep in mind fresh water fish , mainly pond fish , where there is no tides .
Yet they still feed on the Major and minor periods .  Food can float for hours when they are not hungry ..