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San Felipe Grunion
Run
It's better than the a command performance
of the Imperial Russian Ballet. It's like watching a Master
Silversmith spill his creations on the beach. A thousand
little watch mecahnisms ticking and twirling on the damp
sand. It's the rarely-seen magical grunion run of San
Felipe, Baja, Mexico.
 Grunion
are small slender fish with bluish green backs, silvery
sides and bellies. Their average length is between 5 and
6 inches.
Native Americans called this fish by
various names. The Kumeyaay (Diegueno) word for grunion
was Hashuupill, which meant fish out of water.
The Paipai called it Ha-il or water worm. Early
Spanish settlers called this fish grunion, which means
grunter. The word was later anglicized into grunion. Grunion
are known to make a faint squeaking noise while spawning.
The scientific name for the California
grunion is Leuresthes tenuis and they belong to the family
Atherinidae, commonly known as silversides. Other more
abundant atherinids found in California are the topsmelt,
Atherinops affinis, and jacksmelt, Atherinopsis californiensis.
Silversides differ from true smelts, family Osmeridae,
in that they lack the trout-like adipose fin.
The principal range of the grunion
is between Point Conception in southern California and
Punta Abreojos in Baja California, Mexico. However, there
are small populations both north and south of these points.
Occasionally grunion appear in fair numbers as far north
as Morro Bay, California, and spawning has been reported
as far north as MontereyBay, California.
The grunion that
are seen on the beaches here in San Felipe are the gulf
grunion (Leuresthes sardina), a relative of the California
grunion. They differ from their Californian relatives
in that they spawn both day and night, while the California
grunion spawns only at night.
Spawning
The spawning season extends from late
February or early March to August or early September,
varying slightly in length from year to year. Actual spawning
runs are restricted to relatively few hours during this
period. Grunion spawns are associated with the highest
tides of each full or new moon and then only for a 1 to
3 hour period following high tide.
Spawning runs typically begin with
single fish (usually males) swimming in with a wave and
occasionally stranding themselves on the beach. Gradually,
more and more fish come in with the waves and by swimming
against the outflowing wave strand themselves until the
beach is covered by a blanket of grunion. Spawning normally
starts about 20 minutes after the first fish appear on
the beach. Typically a run lasts 1 to 3 hours, but the
number of fish on the beach at any given moment can vary
from none, to thousands. Peak activity is reached about
an hour after the start of the run and lasts from 30 to
60 minutes. Finally, when the tide has dropped a foot
or more, the run slackens and then stops as suddenly as
it started. No more fish will be seen and they will not
appear again until the next the next series of runs.
Observing grunion can be much more
interesting than catching them. Females ride a far reaching
wave onto the beach accompanied by as many as eight males.
If no males are present,a female will return to the ocean
with the outflowing wave. In the presence of males, she
swims as far up on the beach as possible and literally
drills herself into the sand as the wave recedes. This
is accomplished by arching her body with the head up,
and at the same time vigorously wriggling her tail back
and forth. As her tail sinks into the semifluid sand,
she twists her body and drills herself downward until
she is buried up to the pectoral fins. Occasionally she
may bury herself completely. The male (or males) curves
around her as he lies on top of the sand, with his vent
close to or touching her body. The female continues to
twist, emitting her eggs 2 or 3 inches beneath the surface
of the sand. Males discharge their milt onto the sand
near the female and then immediately start to wriggle
towards the water. The milt flows down the body of the
female and fertilizes the eggs. The female then frees
herself from the sand with a violent jerking motion and
returns to the sea with the next wave to reach her. This
entire process takes about 30 seconds, but individual
fish may remain on the beach for several minutes. Larger
females are capable of producing up to 3,000 eggs every
2 weeks. As the mature eggs are deposited in the sand,
another group of eggs are developing that will be spawned
during the next series of runs. This cycle continues throughout
the season. During the early part of the season only older
fish spawn, but as the season progresses fish hatched
the previous year come into spawning condition and join
the runs. Fish of all ages will spawn by April and May.
Fate
of the Eggs
The eggs are initially deposited 2
to 3 inches below the surface of the sand by the female.
The outgoing tide deposits sand onto the beach covering
the eggs to a depth of 8 to 16 inches. Here the eggs remain
in the moist sand. They will be ready to hatch in about
10 days, but remain viable until they are freed from the
sand by the next series of high tides to reach them. The
baby grunion hatch 2 or 3 minutes after the eggs are freed
from the sand and are washed out to sea.
Age
and Growth
Young grunion grow very rapidly and
are about 5 inches long by the time they are 1 year old
and ready to spawn. The normal life span is 2 or 3 years,
but individuals 4 years old have been found. The maximum
size attained is between 6 and 7 inches. The growth rate
slows after the first spawning and stops completely during
the spawning season, consequently the fish grow only during
the fall and winter. This cessation of growth during spawning
causes a mark to form on each scale, and the age of the
fish can be determined by counting these marks, much like
the age of a tree can be determined by counting its “growth”
rings. The life history of grunion while at sea is not
well known, but these fish apparently spend most of their
life close to shore in water 15 to 40 feet deep. Return
to Top of Page
Tides
Tides are caused by forces exerted
on the earth by celestial bodies in direct proportion
to their mass. Theoretically all celestial bodies affect
the tides but realistically only the sun and moon need
be considered. Since the sun has 26 million times the
mass of the moon, one might expect it to be the dominant
tide producing force. However, the force exerted by a
celestial body decreases rapidly as its distance from
earth increases (inversely proportional to the cube of
the distance). Consequently the sun, being almost 400
times farther from earth than the moon, exerts less than
half as much force as the moon. Tidal highs and lows vary
according to the relative positions of the sun, earth,
and moon. Highest and lowest tides occur when the sun,
earth, and moon are most in line, such as during full
moon (sun and moon on opposite sides of the earth) and
new moon (sun and moon on the same side of the earth).
These tides are known as “spring” tides. The tides occurring
during the first and last quarters of the moon, when the
sun and moon are least in line, are known as “neap” tides
and are intermediate in range.
Grunion
Behavior in Relation to Tides
Grunion have adapted to tidal cycles
in a precise manner. Along the Pacific coast of North
America the two daily high tides vary in height, and the
higher of the two occurs at night during spring and summer
months. Grunion spawn only on these higher tides, and
after the tide has started to recede. Since waves tend
to erode sand from the beach as the tide rises and deposit
sand as the tide falls, it is obvious that if grunion
spawn on a rising tide the succeeding waves would wash
the eggs out. This danger is eliminated since spawning
usually is confined to the falling tide. In addition,
grunion nearly always spawn on a descending series of
tides when succeeding tides are lower than tides of the
previous night. The eggs would be washed out prematurely
by succeeding tides if spawned during the ascending tidal
series. The eggs mature and are ready to hatch in about
10 days or about the time of the next series of high tides.
Thus spawning must take place soon after the highest tide
in a series if the eggs are to have adequate time to develop
before the next series of high tides. Looking at a tidal
cycle, it becomes apparent that there are only 3 to 4
nights following the highest tide that spawning conditions
are right, and it is on these nights that grunion spawn.
Internal
Clock
How does the grunion know when the
time is right to spawn? Evidently some biological mechanism
or“internal clock” that can detect some change in the
environment sounds an alarm at exactly the right moment.
The exact stimulus is not known, but it is suspected that
they may be able to detect minute changes in water pressure
caused by the rising tides. Without this ability to spawn
at precisely the right moment the grunion would not survive.
The Grunion
Run of 2010, A Video
For a chart of predicted Southern
California Grunion Runs in 2008, click HERE.
WESTWAYS
article about the grunion.
The
Grunion Greeter Project.
Boyd W. Walker, a modern Ed Ricketts,
studied the habits of the grunion in southern California
during the '40s. He wrote his theasis on the periodicity
of their spawning (you can read it HERE
in pdf format). Later, he wrote about the ecology of the
Salton Sea, California, in relation to the sportfishery.
While on the faculty of UCLA, Walker began his study of
the fishes of the Gulf of California (Sea of Cortez).
He and his students built a large and important collection
of eastern Pacific fishes, much of which has since been
transferred to the Los Angeles County Museum of Natural
History. This work resulted in the discovery of many new
species of fishes and produced large amounts of information
about fish distributions, abundances, ecology, and behavior.
For more about Boyd W. Walker, visit:
http://www.universityofcalifornia.edu
http://links.jstor.org
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