File:Bulletin (1971-) (20423409685).jpg

Title: Bulletin
Identifier: bulletin7477sout (find matches)
Year: 1971- (1970s)
Authors: Southern California Academy of Sciences
Subjects: Science; Natural history; Natural history
Publisher: Los Angeles, Calif. : The Academy
Contributing Library: New York Botanical Garden, LuEsther T. Mertz Library
Digitizing Sponsor: The LuEsther T Mertz Library, the New York Botanical Garden

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200 BULLETIN SOUTHERN CALIFORNIA ACADEMY OF SCIENCES VOLUME 75 MARCH 1970 â 17 NIGHT a DAY RUNS
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APRIL 1970 DAY RUNS ONLY CO .21 22 23 24 25 26 1\ fi/ll ^ 0921 ) ^ / 7 ^ i/^ v/ '^ / V^ 7 < vA Figure 2. Gulf grunion runs at El Golfo showing transition of higher high tide to daytime and beginning of daytime runs. Shaded area denotes darkness; clear areas denote daylight: numbers under tide curves mark the number of high tides after each moon phase. Tide curves are those predicted for Puerto Peiiasco, Sonora. tide from night to day, runs were often observed on successive high tides (Fig. 2). These successive night and day runs occurred when the height dif- ference between consecutive high tides was less than 0.5 m, indicating that the grunion were "com- paring" the height of each high tide during a run series. Walkers (1949) scheme of relating the timing of runs to the moon phases involved predicting runs beginning 2.5 days after a new moon and 4 days after a full moon. This permits a 17.9 day egg maturation period since it correlates with the short and long intervals between new and full moon (14 days) and full and new moon (15.5 days). The relationship of Gulf grunion runs to the moon phases is nearly opposite to that pre- dicted by Walker for California grunion. After a full moon Gulf grunion runs start and reach their peak earlier than runs following a new moon. Full moon runs usually begin 2.5 days to 3.5 days after the moon phase and new moon runs begin 3.5 to 4.5 days after the moon phase. The mean difference in days between new and full moon runs is about half a day or one high tide. Although this difference is slight, it is highly consistent and statistically significant (P< 0.001; see Table 1). Does such a run sequence permit a uniform egg maturation period to be set by the second preced- ing moon phase? L. sardina's runs show a mean 19.5 day interval after a full moon and 17.5 day interval after a new moon. However, the mid- point of a Gulf grunion run series occurs at about 18.5 days after either moon phase, ranging from 17.4 to 19.8 days after the new and full moon. This duration closely agrees with Walker's (1949, 1952) egg maturation period of 17.9 days for California grunion, based upon the mid-point of spawning runs. The timing of the Gulf grunion's runs seems to be related to tide height rather than to moon phase per se. During our period of observation of Gulf grunion runs (January to May, 1968 to 1973) new moon tides were significantly higher than full moon tides. If grunion are selecting a tide height new moon runs might be expected to occur later after the moon phase than full moon runs. Mean tide heights at the start and end of new and full moon grunion runs were quite similar, differ- ing only by 0.21 and 0.11 m respectively (Table 1). Comparison of tide heights between night and day runs showed no significant differences and provided even better agreement betwen the means of these tide level parameters (Table 2). Therefore, it appears that the stimulus for initiating a grunion run is a descending high tide of the proper tidal amplitude. Runs occurred at

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