The Grunion fish


Here’s a fish that seems to know the Tide Tables!

Grunion fish.
Grunion fish.

The Grunion fish of Californian beaches lays it’s eggs on land at high-tide on a full moon night, so that they get exactly the right interval of two weeks to incubate in the sand before the next extra high tide pops the eggs and washes the young fry out into the sea.

The periodic appearance of the grunion on Southern California beaches, and the act of catching them, is locally known as a ‘grunion run’.
A fishing license is required for persons 16 years and older to catch grunion, and they may be taken by sport fishermen using their hands only.
No appliances of any kind may be used to catch grunion, and no holes may be dug in the beach to entrap them.
Grunion may be taken on specified dates between March and the end of August, but not during the months of April and May.
There is no limit, but fishermen may take only what they can use, as under Californian law it is unlawful to waste fish.
With these regulations, the resource seems to be maintaining itself at a fairly constant level.”

‘Grunion’ Wikipedia [ii]

The life cycle of the grunion is intimately associated with the tidal cycle on the sandy shoreline.
The highest tides occur twice a month, at the times of the new and full moons every two weeks.
These tides are called the semilunar tides.
Grunion may spawn on a particular beach on any or all of the 4 or 5 nights following either a new or a full moon, or none of them.
The runs usually occur after the time of the daily highest high tide, which is always at night during the grunion spawning season.
The form of the waves and swells may alter the timing of spawning on any given night.
Runs may be brief or last over an hour.
Spawning fish time their runs so they are on shore at a height that will enable their eggs to be buried in sand above the water line for their entire incubation period.
They may wait until the tide is lower but ride on larger waves or swells, higher on the beach to spawn.
The embryos incubate nestled in the damp sand until they are ready to hatch.
During these days, the highest tides do not reach the level of the eggs on shore, however occasionally large swells will encroach and some eggs will be swept out and lost.
As the next new or full moon approaches, the daily high tides get higher and the embryos within their eggs are finally washed free.
The larvae quickly hatch out and swim to begin the next phase of their lives.”

‘Introduction to Grunion Biology’ by Karen Martin, Ph.D.

Designed, or trial and error?

I would suggest that the Grunion was given it’s knowledge of the tides by God the great Designer.

References:
[i] ‘Introduction to Grunion Biology’ by Karen Martin, Ph.D
[ii] ‘Grunion’ Wikipedia

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