How Tides Work

Gravity at Play

While most anglers are aware that all of the world's oceans experience tides, not all anglers are aware that tides are caused by the gravitational attraction between the Earth, the Sun, and the Moon and their resultant centrifugal force due to the relative motion of the Moon around the Earth and the orbit of both of these celestial bodies around the Sun. Although these forces are, on average, in precise balance with each other, there is a localized difference on the Earth's surface which creates a horizontal force directed towards the surface points closest to, and farthest from, the Moon and the Sun. 

Therefore, the relationship between the masses of the Earth, Moon, and Sun and their distances to each other play a critical role in affecting the Earth's tides. In fact, although the Sun is 27 million times more massive than the Moon, it is 390 times further away from the Earth than the Moon. Also, Tidal Generating Forces vary inversely as the cube of the distance from the tide-generating object. Therefore, the Sun’s tidal generating force is reduced by 3903 (about 59 million times) compared to the tide-generating force of the Moon. Consequently, the Sun’s tide-generating force is about half that of the Moon, and thus, the Moon is the dominant force affecting the Earth’s tides.

In addition, because the Earth's crust is somewhat elastic, these opposing gravitational forces cause both Lunar and Solar tidal bulges in the Earth's crust at the points closest to, and farthest from, the Moon and Sun respectively. Thus, both gravity and inertia act in opposition to each other on the Earth’s surface which, in turn, creates tidal bulges on opposite sides of the planet. Therefore, on the “near” side of the Earth (the side facing the Moon), the gravitational force of the Moon pulls the ocean’s waters toward it, creating one bulge while inertia dominates on the far side of the Earth where it creates a second tidal bulge on the opposite side of the Earth.

Translation into Tides

As a consequence of these influences, the tidal gravitational forces generated by the Sun and the Moon cause these bulges in the Earth's surface to move from west to east around the globe each day and result in two Solar and two Lunar high tides each day (in most locations) and each high as well as each low tide are spaced approximately twelve hours apart.

However, it should also be noted that these periods of high and low tides advance by roughly one hour each day. Therefore, a high tide that occurs at 12:00 PM one day will occur at 1:00 PM the following day and 2:00 PM the day after that. But, it should also be noted that while some locations experience two nearly equal high and low tides each day (aka Semi-diurnal tide), other locations experience only one high and one low tide each day (aka Diurnal Tide) while other locations experience two uneven tides per day (aka Mixed Tide).

How Tides Affect Fish

First of all, it should be noted that 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. Whereas, current is defined as the horizontal movement of water and is caused by rising water levels on an incoming tide and by gravity as water levels fall on an outgoing tide. So tides translate into currents.

Therefore, while tides are of extreme importance to the inshore saltwater fisherman, they are of less importance to the offshore fisherman and, of course, of no significance at all to the freshwater fisherman except when fishing in the mouths of rivers near the sea. The reason for this is because baitfish are small, they have less ability to hold in a given position in the current than the larger predator species do and thus, baitfish are often forced to move with the current on either incoming or outgoing tides.

On the other hand, because of their larger bodies, piscivorous (fish-eating) species require deeper water in which to swim than baitfish species do and thus, baitfish tend to seek out shallow waters in order to gain protection from their predators. Consequently, baitfish will often move onto flats or into estuaries and swamps where they can find cover when the tide is rising but are forced to move back out again as the tide falls in order to prevent themselves from becoming stranded.

Therefore, because predator fish species are forced to follow their prey, they are well of this daily migration of their food source and thus, they 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

Tidal Speeds

It should also be noted that 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 fact, the tidal current speed increases and decreases approximately 8% the first hour, 16% the second hour, and 24% during hours 3 and 4 and then decreases to 16% 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.

Species Preference

However, is should also be noted that different species of piscivorous fish tend to have different preferences for the speed of the current in which they feed. For instance, Cobia, Mackerel, Kingfish, Trippletail, and Sheepshead will often feed most avidly during a slow moving tidal flow, but Spadefish seem to display a distinct preference for feeding during a slack tide.

In addition, certain species of forage feeders such as Bonefish and Permit will move into the shallows and onto flats as the water level rises and then move back out to deeper water as the water level falls. Therefore, 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 the height of the tide for forage species such as Bonefish and Permit.

Where to Fish During Tidal Flows

Also, because most species of piscivorous fish are ambush predators, anglers 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.

However, when the water level is at its height, both baitfish and piscivorous fish species tend to spread out; making them much more difficult to locate. Also, it should be noted that low tide is an excellent time to scout beaches for surf fishing locations because the low water levels will reveal the presence of depressions and holes behind the break line as well as channels that enable the water to escape back out to sea as it is pushed onto shore by the wind because these channels often cause rip currents and subsequent eddies. Therefore, many predator fish species will station themselves either in these depressions and holes or near these rip currents where they can ambush their prey as the water levels rise and fall.

Also, during the warmer months of the year, most inshore fish species will be found along the edges of sounds, beaches, and inlets. Therefore, you should search for fish near the shallows of small islands as well as channels that drain marshes. In addition, you should search for them near the bends in creeks that flow past shell mounds or points with shell or sandy bottoms since most of these places will be productive during the first hour or two of the flood and during the last hour or two of the ebb.

In fact, Sea Trout will often be found away from structure in 6 to 8 feet of water whereas Red Drum and Flounder are most often found close to structure in less than 2 feet of water. On the other hand, during the cooler months of the year, fish will often be found inhabiting sounds and estuaries as well as the lower ends of coastal rivers and, because the ambient water temperature is lower, they will often move into the depressions and holes in these locations where they can find slightly warmer waters.