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Most coastal residents and frequent visitors to the coast
take tides for granted unless they work on the water or
they are planning a day of fishing in Louisiana’s
vast marshes. Tides are the result of powerful gravitational
forces on Earth’s waters by the Moon, and to a lesser
extent the Sun. While all water bodies on Earth are affected
by the gravitational pulls, it is most evident on our oceans.
Since
tides are dictated by the alignment of the Moon, Sun and
Earth, it seems quite logical to understand why tides can
be forecast far into the future. These predictions are baseline
estimates and assume normal weather variables. However,
tides can vary greatly from forecasted predictions due to
weather conditions such as frontal passages, wind and tropical
weather systems. This makes exact tidal movements and amplitudes
somewhat more complicated.
Louisiana’s tides are influenced most by the Moon’s
declination. Declination is the distance in degrees latitude,
north or south of the equator, of the orbit path the Moon
takes around Earth. As the Earth tilts on its axis, the
declination of the moon constantly changes. The greatest
difference between tides is when the Moon is over the equator.
In Louisiana, our tides are long and undulating, rising
and falling over several hours, rarely deviating more than
two feet above or below sea level. In contrast, the Bay
of Fundy in Maine experiences tidal fluctuations of 40-50
feet per day.
Twice each month, when the Moon is new (dark) and again
when it’s full, we have the greatest tidal fluctuations.
The highest highs and the lowest lows are experienced during
this time known as spring tides. Between these extreme Moon
phases, during first and last quarter phases, we have more
moderate tides.
Louisiana’s robust seafood production and the myriad
of estuarine dependent species complete their life cycles
around the lunar phases and the accompanying tides. Larval
fishes ride the tides into coastal bays and marshes where
they avoid predators and feed on the riches of the tidal
ecosystem.
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