Grunion until the next tide series high enough reaches them 10 or more days later. Grunion eggs can extend incubation and delay hatching if tides do not reach them for an additional four weeks after this initial hatching time. Most of the eggs will hatch in 10 days if provided with seawater and the agitation of the rising surf. The mechanical action of the waves is the environmental trigger for hatching. The rapidity of hatching, which occurs in less than one minute, indicates it is probably not an enzymatic function of a softening of the chorion as in some other fishes.
Grunion research points to a restricted resource that is adequately maintained at current harvest rates under existing regulations. In the 1920s, recreational fishing of grunion caused definite signs of depletion resulting in a regulation passed in 1927 that established a closed season of three months from April until June. Grunion stocks improved and in 1947 the closed season was shortened to the months of April and May. This closure is still in effect to protect grunion during their peak spawning period. The periodic appearance of the grunion on Southern California beaches, and the act of catching them, is locally known as