Grunion shrimp. An isopod, two species of flies, sandworms, and a beetle have been found preying on the eggs. Some shorebirds such as egrets and herons prey on grunion when the fish are on shore during spawning. Seagulls, sea lions, and larger fish such as sand sharks have also been observed feeding on grunion during a grunion run. The reduction of spawning habitat due to beach erosion, harbor construction, and pollution is believed to be the most critical problem facing the grunion species. Despite local concentrations, the grunion is not an abundant species. While the population size is not known, all
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