Monday, December 16, 2013

California Grunion (Leuresthes tenuis)

Grunions are two species of fish found off the East coast of the United States and Mexico. They are known for their unique mating ritual, which is referred to as a ‘grunion run’.
Californian grunion spawn from 2-6 nights after the new or full moon soon after high tide. These tides are exceptionally high.
The female rides the wave as far up on the beach as possible, and excavates the semi-fluid sand by twisting her body into the ground. This causes her body to be buried in the sand.
After she is buried, up to 8 males attempt to mate with her by curving around her and releasing their milt as she deposits her eggs in the nest 4 inches below the surface. The milt flows down her body and fertilises the eggs in the sand. After this, the female twists free and returns to the sea.
The eggs incubate a few inches in the sand, above the level of the subsequent waves. They are not immersed in water, but kept moist by residual water in the sand. They will only hatch when the next series of exceptionally high tides reaches them 10 or more days later. If the tide is not high enough, they can delay hatching for an extra 4 weeks.
The mechanical action of the wave is the environment trigger for hatching. The process takes less than 1 minute and the fry return to the ocean through the wave.

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