A preliminary analysis of 53 spawning runs of the Gulf grunion, Leuresthes sardina (Jenkins and Evermann) from 1968 to 1973 in the northern Gulf of California suggests that the initiation of a spawning run is strongly dependent on tidal amplitude. Gulf grunion runs occur fortnightly from January to May following a descending series of higher high tides after the new and full moon phases. The runs begin about 3.5 days after the time of full moon and about four days after the new moon. The daytime runs of L. sardina result from a mid-season shift in the time of the higher high spring tides from early morning (0300 to 0500) to late afternoon (1500 to 1700).
The accelerated spawning act of the Gulf grunion appears to be an adaptation to the short period, low amplitude sea waves typical of the protected coasts of the upper Gulf of California rather than increased daytime predation of spawning fish by sea birds.