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Fishing Factors

How Weather Factors Affect Fishing

How many times have you had the experience where you have chosen what seemed to be the perfect day for going fishing only to have the fish completely ignore your bait, lure, or fly seemingly without reason? You’ve gone to the trouble of sourcing a variety of fresh baits or lures, the sun is setting, the water is calm, it’s a beautiful day but you don’t get a touch and end up leaving for home wondering why the fish weren’t biting. Fish have to eat just like people do and if they refuse to feed on any given day there must be a reason for it. However, the answer to why fish don't bite on any given day is likely dependent on several variables ranging from water temperature, to barometric pressure, to turbidity, to wind speed and direction. In fact, most fishermen do not truly understand just how different a fish's environment is from our own and because they have a drastically different anatomy from Humans, atmospheric conditions and even the lunar cycle that have little direct effect on Humans can actually have a huge effect on fish.

The purpose of this article is to examine in depth the question of exactly how various factors affect fishing by examining each aspect of the weather and how it affects the fish's behavior.

Water Temperature

Water temperature can either positively or negatively impact the quality of fishing because it affects the fish's willingness to feed. Fish are cold blooded creatures and unable to regulate their body temperature meaning the colder the water the slower the fish's metabolism is and the more torpid they are. A slow metabolism makes fish less inclined to feed as they require fewer calories to maintain their slower bodily functions. In contrast, the warmer the water is the faster a fish's metabolism rate and the more active they are. In warm water fish are more inclined to feed as their metabolism and energy requirements are significantly higher.

Fish also require oxygen in order to live and, regardless of how high their metabolic rate is, will not feed if they are having difficulty breathing. Fish do not use their gills to break down water molecules to extract oxygen but instead use their gills to extract dissolved oxygen from the surrounding water. Dissolved oxygen is a free roaming oxygen atom found in water that is not attached to a pair of hydrogen atoms. It enters the water in two ways - when aquatic plants engage in the process of photosynthesis and when air becomes trapped in water via the action of rapids, breaking waves or rainfall. The colder the water is the more dissolved oxygen it can hold and the warmer the water is the less dissolved oxygen it can hold. Each fish species therefor has a minimum water temperature below which it will not feed due to a low metabolic rate and a maximum water temperature above which it will not feed due to a lack of oxygen.

It is interesting to note the paradox that in cold water the dissolved oxygen level is at its highest yet the fish’s metabolic rate is at its lowest - the fish requires the least amount of oxygen when the most dissolved oxygen is available. And in warmer water the dissolved oxygen level is at its lowest yet a fish's metabolic rate is at its highest - the fish requires the greatest amount of oxygen when the least amount of dissolved oxygen is available.

Water temperature also affects the activity levels of a fish’s prey such as insects, crustaceans and small fish which are also cold blooded and therefor less active in colder water and more active in warmer water just like the predators that pursue them. Both fish and the prey they feed on are ruled by water temperature which is in turn controlled by the weather.

How rain affects water temperature

While direct sunlight inevitably warms the water and cloudy skies or a low ambient air temperature cause it to cool somewhat, it is important to note that rain can rapidly raise or lower the ambient water temperature depending on the size of the body of water. It can also rapidly raise the water level and wash a significant amount of food into the water at the same time. Of course, we all know that the Sun's radiation causes objects to heat up (just try leaving your car in the sun with the windows rolled up) and thus, it also heats both small and large bodies of water when it shines upon them. Therefore, when it's cloudy such that the Sun's rays are blocked, then the water cools slightly by radiating the heat it has absorbed from the Sun to the surrounding air. However, when the ambient air temperature is exceptionally cool, then the water temperature often remains cool despite the heat absorbed from the Sun. Furthermore, water is a poor conductor of heat and thus, it both heats and cools relatively slowly. Consequently, minor fluctuations in either sunlight or air temperature have little effect on water temperature in small bodies of water and almost none in large bodies of water; especially where currents exist to distribute the absorbed heat.

Rain however can rapidly raise or lower water temperatures in small bodies of water and while it does affect larger bodies of water in the same way it does so more slowly. On the other hand, rain can also significantly raise the water level and increase turbidity in any given body of water. Plus, it can also wash an abundance of food into the water in the form of organic matter and terrestrial insects and so cause fish to congregate in schools near inflowing creeks and streams.

How streams, surface area and water depth affect water temperature

Most creeks and streams start as ground water meaning the temperature of the water of creeks, streams and rivers is often significantly lower than water contained in ponds, lakes or the ocean. This is due to its emergence from the ground as well as the fact that gravity causes water to flow downhill and the current in bodies of water located at higher elevations distributes any heat the water absorbs from the sun. Bodies of water that are fed by creeks, streams and even some rivers are often significantly cooler than those fed by rainwater alone.

The level to which inflowing creeks, streams or rivers can lower the ambient temperature of any given body of water depends on the surface area and depth of the body of water. The larger a body of water the larger its surface area. The larger the surface area the greater the amount of sunlight that shines upon it and the quicker it heats on sunny days. Small or shallow bodies of water heat quickly as there is a smaller volume of water to be heated. The deeper a body of water the slower it heats as there is a larger volume of water to be heated.

Fish can often be found congregating near inflowing creeks, streams and rivers as well as hydro-electric power plant outlets due to the significantly cooler or warmer water temperatures which affect both the fish's metabolic rate and the amount of dissolved oxygen the water holds.

Barometric Pressure

Anatomy of a fish
The internal organs of a fish.

Due to the fact that fish live in a drastically different environment than humans they also have a drastically different anatomy. As fish live in a liquid environment their bodies enable them to pursue prey and elude predators in a dense medium. They need to suspend themselves in the water column or they will either sink or be forced into continual forward motion in order to maintain lift on their fins. Most fish species have evolved an internal organ known as a swim bladder - a sack similar to a stomach that the fish can inflate or deflate with oxygen that enables them to suspend themselves in the water column. So not only does the availability of dissolved oxygen in the water affect a fish’s ability to breathe, barometric pressure can also affect their willingness to feed due to the way it affects their swim bladder.

What is barometric pressure?

Air has mass and so it is affected by gravity. The amount of pressure that the earth's atmosphere exerts on the earth's surface can be measured in a number of units including: pounds per square inch (psi), hecto Pascal’s (hPa), millibar (mb) and inches of mercury (inhg, aka Torr). Depending on your location barometric pressure generally ranges from 985 hPa to 1040 hPa and average air pressure at sea level (MSLP) is 1013 hPA.

Falling barometric pressure usually indicates a storm is coming. Rising barometric pressure usually indicates clear skies ahead. When barometric pressure is low the earth's atmosphere is exerting little pressure on the earth's surface and when barometric pressure is high the earth’s atmosphere is exerting a greater amount of pressure on the earth's surface. The same amount of pressure that is exerted on the earth's surface is also exerted on the surface of bodies of water so changes in barometric pressure causes the water to exert more pressure on fish.

How does barometric pressure affect fishing?

Rising and falling barometric pressures change the pressure on the surface of a body of water. Fish experience this change in their environment as either increased or decreased pressure on their swim bladder. Although we don’t know the definitive answer why, changes in barometric pressure affect fish behavior. Fish with small swim bladders such as dolphin fish, mackerel and king fish are not as affected by changes in barometric pressure as much as fish with large swim bladders such as snapper, trout and redfin. Some fish such as tuna and sharks do not have swim bladders so changes in their behavior are less significant and likely the result of other factors such as changes in behavior of their prey.

Rising barometric pressure indicates improving weather (by human standards) and falling barometric pressure indicates degrading weather (by human standards) as well as incoming warm and cold fronts. It is the change in barometric pressure that either positively or negatively affects fishing.

  • Stable weather. Fish prefer stable, consistent, weather patterns regardless of the conditions - sunny and warm, cold and raining, or windy. Stability is the key to normal fishing. Fish are most active and their behavior most predictable during a stable weather pattern. The best fishing usually occurs after the third day of a stable weather period. By then the fish have acclimated to the weather conditions and their activity levels have stabilised.
  • Rapidly changing weather. Fish react to weather changes by changing their feeding patterns as well as where they choose to hold in the water column and the senses they use to locate prey. Fish are first and foremost sight feeders so if heavy rains cause widespread turbidity fish will need to rely heavily on their lateral line and hearing to locate prey. Often fish will move location to clearer or less turbid water. If the turbidity is not widespread but confined to the mouths of creeks, streams or run-off points, fish may move to these locations and ambush their prey at the edge of the discolored water.
  • Cold fronts. During a cold front masses of cold air move in to displace the warm air and ambient air temperatures can drop as much as 15°C in an hour. Before a cold front arrives Barometric pressure tends to fall steadily and reach a minimum. As the front passes pressure rises sharply then tapers off to a steady rise until the front has stabilised. Cold fronts also generate shifting or gusty winds.
    Just before the arrival of a cold front fish tend to feed with gusto although this is only for a short period. After that fish seek cover until they become acclimated or the weather changes again. The first day after a cold front passes fish in rivers, lakes, mangrove swamps and estuaries tend to hold deep in the available cover and pelagic fish species tend to seek deep water and only make short runs to obtain food. When fishing during cold fronts fishermen should use smaller, slower moving, lures or flies and fish close to cover or in deep water over a dark bottom.
  • Warm fronts. Warm fronts cause masses of warm air to move in and displace the cold air, causing the ambient air temperature to rise. Unlike cold fronts, warm fronts move slowly and bring gentle rains as opposed to violent storms. Before a warm front arrives air pressure tends to decrease slightly. As the front passes pressure levels off then falls steadily until the front has stabilized.
    Warm fronts generate falling barometric pressures, rising ambient air temperatures, cloudy skies and mild winds which often cause fish to feed with alacrity. In these conditions shallow water fish species tend to move out to the edges of cover to feed and are more willing to chase prey. Deep water fish species will move from deep water into transition zones between deep water and shallow water to feed.
    When fishing during warm fronts, fishermen should use larger, faster moving lures or flies and fish on the edges of cover or in transition zones from shallow to deep water such as along ledges, cliffs, and even the continental shelf for pelagic fish species.

It is imperative fishermen be aware of barometric pressure and how it affects both the weather and the fish’s habits. But regardless of the trends in barometric pressure, fish behavior is most adversely affected the day the front arrives and their willingness to feed returns to normal levels three days after the front has passed. Although general trends have been discussed, there is no definitive rule as to how air pressure will affect fish behavior and it can be different for different species and at different locations.

Wind Speed and Direction

Wind can either positively or negatively affect the quality of the fishing depending on its direction and speed. As wind blows across the water surface, friction between the water and air causes the surface of the water to start moving in the direction of the wind which creates waves. Both the distance the wind blows over the water (the fetch) and the duration over which it blows will either increase or decrease the size of the waves as individual peaks join to create larger waves. Without wind there are no waves.

The wind's effect on bodies of water and fish
The wind's effect on bodies of water and fish.

How does wind affect fishing?

Wind affects fishing conditions due to the extent of the fetch as well as nearby geographical features. Most weather travels from west to east so the western shores of large land masses (continents and large islands) most commonly experience inshore winds while the eastern shores most often experience offshore winds. Large land masses tend to slow the wind and geographical features such as hills can block the wind. Valleys and troughs can funnel the wind into a tight stream which creates eddies as the wind disperses out across the water’s surface. Precipices can cause sudden downdrafts as the air rushes down their face and then out across the water. Food sources on the windward side of a large land mass tend to be pushed inshore while food sources on the leeward side of large landmasses are often pushed out to sea. This also applies to smaller bodies of water.

  • Currents. Currents created by wind can improve fishing conditions in several ways. Downwind shorelines bear the brunt of currents which bring with them large quantities of phytoplankton and zooplankton which accumulate near the shoreline. Small baitfish will congregate near windblown shorelines because of the concentration of food. This draws larger predator species. Currents can also affect fishing conditions when they are caused by an angled wind direction. Currents caused by winds that strike the shoreline at a significant angle, or winds that blow parallel to the shoreline and create water movement can significantly increase feeding activity. Fishermen should look for points along these shorelines where calmer water is present on the opposite side as predator fish will often lay in wait in the calmer waters where they can ambush their prey as it passes in the current.
    Currents flowing in the same direction as the wind tend to move faster and currents moving in the opposite direction to the wind tend to move slower. Opposing wind and currents will often generate large waves due to the opposing forces. In the saltwater environment as well as in large freshwater lakes, wind blowing around sand bars, points and jetties can create eddies, current lines and even rip currents. The wind also causes water to collect in shallows, coves and inlets where it is heated by the sun’s rays. Fish are attracted to these solar heated waters on cool windy days when their metabolic rate is higher.
    When choosing a spot to fish wind direction must be taken into consideration. The wind blows phytoplankton, zooplankton, aquatic insects and terrestrial insects towards the windward shore which attracts crustaceans and bait fish. These bait fish attract larger predator species that feed on them. When fishing in the wind it is best that fishermen position themselves on or near the windward shore, even though these can be challenging conditions to fish in.
  • Waves. Wind can also affect fishing by creating waves and waves are often a more important factor to consider than currents. This is because waves on the downwind shoreline can increase dissolved oxygen levels, reduce the visibility of the surface environment and reduce incident sun light hence reducing shadows cast by the fish. As a result, fish find it difficult to see predators, making them inclined to come to the surface to feed. This means windy days are often excellent for fishing topwater or using shallow running lures even in sunny weather conditions. However, in some areas waves can also create turbidity by churning the water which can lead fish to search out less turbid water to feed in.

When fishing in windy conditions, it is important fishermen note the direction and speed of the wind and position themselves accordingly. It often helps to use larger and/or more brightly coloured lures as well as lighter lines which are less affected by wind drag.

Turbidity

Turbidity (aka water clarity) is a measure of the amount of particles suspended in the water and its affect on the depth to which light can penetrate the water. Clear water is said to have low turbidity because light can easily penetrate the water, while muddy water is said to have high turbidity because light is blocked from penetrating the water by the suspended particles. Because fish are primarily sight feeders the turbidity level of the water can significantly affect the quality of fishing and rain and wind can also affect the turbidity of bodies of water.

Increasing Turbidity

What causes turbidity?

Turbidity in streams and estuaries is caused by particles (both organic and inorganic) that are suspended in the water column. Organic particles come from various sources such as algae and decaying plant matter. Inorganic particles come from erosion of the surrounding terrain and are washed into bodies of water by rainfall. When stream flows in moving water are high, inorganic particles such as sand and silt make up most of the suspended sediment. However as the flow decreases the inorganic particles such as sand and silt that cause high turbidity settle out and the lighter organic particles remain. The organic particles that remain suspended cause moderate to low turbidity and decrease the amount of light penetrating the water. Turbidity can also be caused by waves churning the settled sediments in shallow waters such as coves, flats and surf zones. A fisherman is likely to encounter increased turbidity levels on windy days in both freshwater and saltwater environments.

How does turbidity affect fishing?

Most species of fish are primarily sight feeders so, when feeding in turbid water with reduced visibility, they are forced to rely on their rudimentary hearing and their lateral line to locate prey. As well as diminishing their food base, turbidity also makes it harder for fish to see their prey, leading to reduced feeding efficiency, a reduced feeding rate and depressed growth. Smaller bodies of water tend to become turbid quicker than larger bodies of water. Fish living in larger bodies of water will often hold in the clear water on the edges of turbid water where they can ambush their prey on edges of sediment clouds located adjacent to the mouths of creeks or streams. Due to the reduced visibility fishermen should use different lures for fishing in turbid waters than those used to fish in clear waters.

Illustration of fish showing lateral line
Illustration of fish showing lateral line

Do fish see colours?

Most fish species do see colours and the retina of a fish’s eye contains two types of cells which consist of cones and rods. Cones are the cells that discern colour and are used for feeding during the day. Rods are the cells that discern light intensity and are used for feeding at night but cannot distinguish colour.

Light In Water

Light behaves differently in water than in air because various colours of light have different wavelengths. Reds have the longest wavelength, then oranges, yellows, greens, blues and indigos and, finally violet with the shortest wavelength.

Decreasing Wavelength

When light travels through water some of its energy is absorbed with the longest wavelengths absorbed first. So the warmer colors (red, orange, yellow) fade out first and gradually appear darker or even black the deeper a fishing lure runs. Turbidity increases this effect and so impacts the distance various wavelengths of light travel in water. In typical water conditions, Red light is almost completely absorbed within the first 5 metres (16 feet), orange light penetrates 8 metres (26 feet), yellow light 14 metres (45 feet), green light 23 metres (75 feet), and blue light 32 meters (105 feet). In perfect conditions (distilled water) the distance traveled by each wavelength will be much greater but in natural bodies of water suspended particles attenuate light and therefor decrease the distance traveled.

Maximum depth at which various colours
Above: Maximum depth at which various colours are no longer visible due to the absorption and scattering of different wavelengths of light. As the total light available diminishes with depth both the number of colours and the intensity of each colour is reduced.

The intensity of light also decreases as it travels thought water so at a depth of 12 metres, a yellow lure will still appear yellow but will not appear as bright as it did at 6 metres.

How does turbidity affect light transmission and colour?

The quality of turbidity can also affect light transmission. While red may be the first colour to disappear in clear water, the reverse can sometimes occur in turbid waters where blues and greens disappear first and reds are visible to greater depths. This is due to the fact shorter wavelengths from blues and greens are more attenuated by the size of suspended particles than reds and yellows. For this reason, in heavily turbid water, a red lure may appear brighter than a green or blue lure would appear in the same position.

The colour water appears on the surface usually indicates the colour of light most easily transmitted in that body of water. Most bodies of water appear blue because it is the wavelength of light least absorbed and therefor mostly reflected back and visible. Some bodies of water appear green because they transmit light in the green spectrum better than in the blue spectrum. This is due to suspended particles in that water body blocking shorter blue wavelengths more readily than longer wavelengths. Some inland bodies of water often get stained with tannins secreted by nearby plants and trees so absorb blue and green wavelengths more readily than warmer colors such as reds and yellows, therefor making these warmer colored lures more visible.

It is important to note it isn’t depth that impacts the transmission of light under water but distance travelled. The way a lure looks at a depth of 5m will be the same as it looks from a distance of 5m when travelling up near the surface layer.

How does turbidity affect light transmission and colour
The red lure appears dark grey at a depth of 5 meters. It also appears dark grey to a fish 4m away when the lure is at a depth of 1m

What lures should be used when fishing in turbid water?

Fish in turbid waters are forced to rely on their rudimentary hearing and their lateral lines rather than their sight to locate prey. While fish are able to locate the general position of a lure in turbid water using sound, vibration or scent, most fish locate their prey using their sense of sight. Lures that create sound or vibrations in the water such as spinner baits or rattles can help fish to zero in on their position, but most fish species still must be able to see their prey before striking. When fishing in turbid waters fishermen should use lures that create either noise or vibrations or both as well as choosing colours that will enable the fish to see the lure once it is within striking distance.

Ultraviolet Light

Different colours of light have different wavelengths with reds having the longest wavelengths and violets having the shortest wavelengths. There are also other wavelengths of light that extend beyond the human visible spectrum (380-750 nanometers - nm) with ultraviolet light being one of these. Ultraviolet light is called ‘ultra’ because its wavelengths (10-360 nm) are even shorter than those in the violet spectrum.

In perfect conditions (distilled water) ultraviolet light can penetrate water much deeper than the shorter violet wavelengths however suspended particles in natural bodies of water such as the ocean, lakes and rivers usually absorb UV more readily so this doesn’t occur in practice.

Why are fish able to see UV light?

According to Darwinian Theory, any biological adaptation that does not directly contribute to the continued survival of a species is eventually discarded. A prime example of this is the blind, cave dwelling Milyeringa that inhabit streams in the Cape Range National Park of North Western Australia. Because these fish have adapted to live in a dark environment, their eyes have evolved from complex visual structures to simple, convex, eyespots. African cichlids have not only retained their complex eye structures but have also evolved a highly sophisticated ability to see ultraviolet light which they use to indicate both species and sex. And so the ability to see ultraviolet light has not only been retained in some fish species but has become highly refined as it provides greater visual range and enables them to detect phytoplankton and see prey against a camouflage background.

Why do ultraviolet fishing lures cause fish to strike?

Ultraviolet fishing lures first became popular in the 1950s. But the zinc oxide coating that was used to reflect ultraviolet light was not very effective as it was only available in a luminous green colour and the lures had to be ‘recharged’ every few minutes in order to maintain their glow. The coating that was used to create the luminous glow was eventually determined to be a toxic waterway contaminate. Because of this, ultraviolet fishing lures eventually fell out of favour with fishermen. Modern ultraviolet fishing lures employ a new, non-toxic, UV reflector called titanium dioxide that retains its glow for several hours after even short exposure to UV light. Manufacturers of UV fishing lures are now able to infuse the UV reflective coating with bright colour pigments, creating highly realistic colour patterns with a high degree of contrast. The eyes of various species of piscivorous fish contain the necessary rodospin proteins to not only use their ears and lateral lines to locate lures, but to see the lure as they approach making it easier for them to identify the prey and orient it prior to striking (some piscivorous fish species such as salmon consume their prey head first). Because many species of baitfish use ultraviolet light as an indicator of both species and sex, UV reflective fishing lures create an additional level of realism beyond profile and size and are better able to fool fish into believing the lure is a real fish.

Ambient Light

Like humans, fish's eyes also contain Rods and Cones and it is the Rods that are responsible for enabling humans and fish to perceive ambient light levels. Also, Human eyes have pupils that are able to expand or contract as well as eyelids that can either be partially or fully closed to further limit the amount of light entering the pupil; both of which help to prevent damage to the cornea due excessive light levels. However, unlike humans, fish's eyes lack eyelids and their pupils are fixed (with the exception of some species of shark) and thus, their pupils are not able to dilate. Consequently, fish are forced to seek out cover, shade, turbid water, or deep water in order to reduce the amount of ambient light to comfortable levels.

How does turbidity affect ambient light levels?

The amount of light that penetrates the water on any given day is dependent on both the turbidity of the water and the angle of the Sun. Although turbidity will cause less light to penetrate the water it can also make it more difficult for fish to see their prey. On the other hand, many species of piscivorous fish feel safer when the water is slightly stained to moderately turbid and so they are often more inclined to feed in these conditions as they feel less vulnerable to predation themselves.

How does time of day affect ambient light levels?

Due to the angle of which the sun hits the water, there is less ambient light in the water in the morning and the evening hours than during the middle of the day. Fish will therefor feed more readily in the mornings and evenings than during the middle of the day on bright, sunny days.

When a light ray hits a water surface some of it is refracted into the water and some of it is reflected back to the sky. We see this phenomenon with Polarized glasses which help cut out reflected rays and only see those that penetrate the surface and then get reflected back from beneath the water surface.

Diagram of a light ray hitting an air water boundary. Some of the light is reflected back to the sky and some of the light is transmitted into the water
Diagram of a light ray hitting an air water boundary. Some of the light is reflected back to the sky and some of the light is transmitted into the water

The amount of light that gets reflected versus refracted at the surface layer is dependent on the angle at which light hits the water. Fresnel equations model this phenomenon and show that at an angle of 80o degrees approximately 45% of light gets reflected back to the sky and the rest gets refracted. As the angle increases towards 90o degrees the amount that gets reflected increases exponentially. The below chart shows this relationship.

Light Reflected at an Air Water Boundary

In early morning and late evening when the sun is at a steep angle to the water surface, the amount of ambient light in the water is significantly lower than at other times of the day allowing fish to come to the surface more readily due to increased comfort levels.

Light that gets reflected from banks and trees on the edges of water bodies usually does so at steep angles so contributes less to the level of ambient light under water than light reflected from the sky directly above.

How do cloudy skies affect ambient light levels?

Cloud cover can also affect the amount of ambient light penetrating the water leaving fish more inclined to feed on cloudy days than sunny days. Under cloudy skies the various colours of light will not penetrate as deeply as they will on a sunny day. As the intensity of the ambient light decreases, rod cells in the fish’s eye become more active and the fish can no longer distinguish colours. Because of this, when fishing after dark, fishermen should use a shiny lure to reflect any available light or a lure that glows in the dark. Night feeding fish species only use their vision at close range and may also be attracted to a lure by smell and vibration. As dawn approaches and ambient light levels increase, the cone cells in the fish's eyes become active again enabling the fish to see colours once more. Blues, greens, yellows, oranges and – finally - reds begin to reappear. Ambient light also affects the movement of forage fish which move up or down the water column in response to increasing and decreasing ambient light levels which affects the distribution of the piscivorous fish species that feed on them.

How does bright sunlight affect fish behavior?

In addition to aquatic predators, avian predators also pose a significant danger to fish. Fish are more alert during periods of bright sunlight as they are more visible to benthic and pelagic predators when in deep water due to the fact that they are outlined against the bright sky. Fish are more visible to avian predators in shallow water due to the light penetrating the water and the sun casting the fish's shadow. Aquatic invertebrates, crustaceans and bait fish are most abundant in shallow waters where sunlight can easily penetrate the water and enable photosynthesis in aquatic plants which provide both oxygen and cover. Piscivorous fish are often forced to enter these dangerous waters in order to find prey but may only feel safe here during periods of low ambient light such as early morning, late evening or on cloudy days. The movement of phytoplankton and zooplankton (a food source for most species of baitfish) is also affected by light intensity and these microorganisms are usually positioned higher in the water column at dawn and dusk making these prime times for catching piscivorous fish species. Dark, overcast and rainy days can draw fish into the shallows to feed as well. Yet, as the level of ambient light increases, fish often move into deeper water adjacent drop-offs or in channels where they take up ambush positions over stretches with a dark bottom.

How does moonlight affect fish behavior?

During the new moon nights are dark with little or no ambient light from the moon. The increased gravitational pull from the moon during this phase causes increased tide heights which can cause turbid water. It is best to limit fishing during this lunar period to areas with a hard bottom. During the first quarter moon the difference between high and low tides is less which results in slower currents and less turbidity, leaving the fish better able to locate their prey and more inclined to feed. Come the new moon the height of the tides will start to increase approximately three days prior to the full moon and continue for about the same number of days after the full moon causing increased turbidity. Additional light from the moon allows fish to feed more successfully at night resulting in altered feeding habits. Fishing often improves during the period of the waning moon due to the lower ambient light levels and lower levels of turbidity.

Tides

Tides are the rise and fall of sea levels caused by gravitational forces between the earth, sun and moon. Some locations experience one high and one low tide per day (diurnal) whereas others experience two high and two low tides per day (semi-diurnal) and others experience a mixed tide. A mixed tide is one where two high peaks and two low peaks occur in a day but the two high peaks are uneven and the two low peaks are uneven. A receding tide is known as an ebb tide and an incoming tide is known as a flood tide.

The relationship between the masses of earth, moon and sun and their distances to each other play a critical role in affecting the earth's tides. Although the sun is much bigger than the moon it is also much further away and has 46% of the tidal generating force as the moon. Therefor the sun’s tide-generating force is about half that of the moon and so the moon is the dominant force affecting the earth’s tides.

How tides affect fishing

Tides are defined as the vertical movement of water and are caused by the gravitational pull of the sun and the moon on the earth's surface. Current is defined as the horizontal movement of water and can be caused by rising water levels on an incoming tide and falling water levels on an outgoing tide. While tides are of extreme importance for inshore saltwater fishing, they are of less importance to offshore fishing and of no significance to inland fishing.

Since baitfish are small and have less ability to hold in a given position in the current than larger predator species, baitfish are often forced to move with the current on either incoming or outgoing tides. Because of their larger bodies, piscivorous fish species require deeper water in which to swim than baitfish species. Baitfish seek out shallow waters for protection from their predators and often move onto flats or into estuaries and swamps where they can find cover when the tide is rising but they are forced to move back out again as the tide falls in order to prevent themselves from becoming stranded. Predator fish species follow their prey so will often hold in ambush positions on the edges of cover or in transition zones from shallow water to deep water where they can ambush their prey as it moves in the current caused by the rising and falling tides.

When to fish the tides

Currents are at their slowest during the beginning and the end of a change in tide and accelerate as the water levels rise or fall. In semi-diurnal areas the tidal current speed increases and decreases approximately 8% in the first hour, 16% in the second hour, and 24% during the third and fourth hours and then decreases to 16% in the fifth hour and 8% the sixth hour. Consequently, fishing is often least productive during the slack time between both high and low tides and often becomes more productive as the speed of the current increases. Different species of piscivorous fish tend to have different preferences for the speed of the current in which they feed. The best time to fish inshore waters for piscivorous species is most often after the current flow reaches a speed sufficient to force the baitfish into or out of the shallows or during high tide for forage species.

Given high tide enables access to portions of the shoreline previously unreachable, high tides can be a productive time to fish as they allow baitfish and forage feeders to search for food sources that may have washed up on shore or that may exist above the low water line such as clams on rocks or pylons.

Where to fish during tidal flows

Because most species of piscivorous fish are ambush predators, fishermen should position themselves near the ends of reefs or jetties and close to man-made structures when the current is running and near deep depressions, channels and gutters during low tide when the current is not running. When the water level is high both baitfish and piscivorous fish species tend to spread out making them difficult to locate. Low tide is an excellent time to scout beaches for surf fishing as the low water levels reveal the location of depressions and holes behind the break line as well as channels which often cause rip currents and subsequent eddies. Many predator fish species will station themselves either in these depressions and holes or near these rip currents so they can ambush their prey as the water level rises and falls.

During the warmer months most inshore fish species will be found along the edges of sounds, beaches and inlets. Fishermen should search for fish near the shallows of small islands, channels that drain marshes, bends in creeks that flow past shell mounds or points with shell or sandy bottoms as most of these places will be productive during the first three hours of the flood and during the last three hours of the ebb. During the cooler months of the year fish will often inhabit sounds and estuaries as well as the lower ends of coastal rivers and, because the ambient water temperature is lower, they will move into the depressions and holes in these locations in search of warmer waters.

How The Moon Affects Fishing

The length of a lunar cycle is approximately 29.5 days and during that time the moon will go through new moon, quarter moon, full moon and three quarter phases before going back to new. During full moon the sun and moon are positioned nearly opposite each other in their orbits with the earth in the centre and only a few minutes pass without one or the other being in our skies overhead. During a new moon both bodies are in near perfect synchronisation and travel the skies in unison.

Neap and Spring Tides

In new and full moon periods the moons gravitational effects are in alignment with the suns gravitational effects which result in the greatest pull on the Earths surface and the largest high and low tide differences. These are called spring tides. During periods of first and third quarter, the moons gravitational effects are at right angle to the suns gravitational effects hence they are not in alignment and the difference between high and low tides is least. These are called neap tides.

Spring tides result in higher high water and lower low water and the effects from increased water currents and access to areas of land previously unreachable during low tide periods are magnified resulting in increased fish activity. For this reason spring tides are favoured by fishermen.

Daily Lunar Cycle

As the moon is a celestial body orbiting the Earth and the Earth is rotating on an axis, during a 24 hour period the moon will come into view on the horizon (moonrise), reach its zenith in the sky (upper transit), set below the horizon (moonset) then reach its lowest point underfoot (lower transit). The times that each of these points occur and the angle to which the moon reaches at its upper and lower transits varies depending on the observer’s location and time of year. Also, due to the interaction between the numerous solar and lunar cycles, no two days, months or years are the same.

Solunar Theory

Solunar theory is a hypothesis that animals and fish move according to the location of the moon relative to their bodies. It implies the moons position directly affects activity and feeding habits of animals and fish and there are four periods of the day when increased activity is observed - upper transit, lower transit, moon rise and moon set.

Whenever one of these periods falls within 30 to 60 minutes of sunrise or sunset fishermen can expect a peak in fish activity. When these periods occur during either a new moon or a full moon the highest level of activity for the entire season can be expected.

Solunar Theory is not scientifically proven and it is perhaps difficult to do so due to there being many other factors that would need to be controlled to provide a conclusive answer. In any case Fish Ranger provides one day moon elevation charts for each registered location that show times of moonrise, moonset, upper transit and lower transit. Folklore can now be put to the test to see if Solunar Theory holds merit.

Conclusion

As we have seen many different weather factors affect fish behavior - water temperature, barometric pressure, ambient light levels, turbidity, changing water levels due to the rise and fall of tides and even the position of the sun and the moon. Different species respond differently to weather events and what may be good in one area or for one species may not be good in another area or for another species. Successful angling relies on taking all of these factors into account when planning the best time to be on the water.

Glossary

  • torpid: Mentally or physically inactive. Slow or sluggish. Lethargic.
  • turbid: (Of a liquid) cloudy, opaque or thick with suspended matter.
  • alacrity: Brisk and cheerful readiness.
  • ambient: Relating to the immediate surroundings of something.
  • benthic fish: Fish that live on or near the sea-bottom, irrespective of the depth of the sea.
  • forage fish: Small fish which are preyed on by larger predators for food. Also called prey fish or baitfish.
  • lateral line: A system of sense organs found in aquatic vertebrates, mainly fish, used to detect movement and vibration in the surrounding water.
  • pelagic: Relating to the open sea.
  • piscivorous: Feeding on fish; fish-eating.
  • water column: A conceptual cross-section of water extending from the water bed to the surface.
  • spring tides: Tides with the greatest difference between high and low water in a lunar cycle.
  • neap tides: Tides with the lowest difference between high and low water in a lunar cycle
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