Field Observations on Courtship and Spawning Behavior of the Giant Sea Bass, Stereolepis gigas
Aspects of the reproductive behavior of Giant Sea Bass, tereolepis gigas, were observed and monitored at Goat Harbor, Santa Catalina Island, California from June 2014 to August 2015. The site was visited daily during the summer months (the known spawning season); aggregations were not present during the rest of the year. Numbers of Giant Sea Bass observed at Goat Harbor ranged from 1 to 19 individuals with an average of 6. Giant Sea Bass produced booming sounds (40–80 Hz), which were often associated with aggressive behavior but may also be associated with courtship. Courtship behavior was observed during the late afternoons and was most prominent around dusk (1900–2100 h). Courtship involved sexually dimorphic, temporary color changes and displays such as circling in pairs and the nudging of the abdominal area of the presumed female by the snout of the presumed male. The courtship behaviors observed were similar to those observed for Giant Sea Bass in captivity. Although spawning was not observed directly, the available evidence suggests that spawning occurs just after dusk. Confirmation of spawning at or near the aggregation site was obtained through DNA barcoding with CO1 primers of eggs sampled from Goat Harbor near dusk. This study provides insights into courtship behavior that can be used to identify potential Giant Sea Bass spawning aggregations in the wild that are crucial for management of the species.
Map depicting Santa Catalina Island, California. This study was conducted at Goat Harbor within the Long Point State Marine Reserve.
The counts of Giant Sea Bass observed at Goat Harbor by survey date for 2014 and 2015. Counts at this site varied from 1 to 19 individuals (mean of 6 fish per visit).
The average number of Giant Sea Bass per transect (n = 9) at four depths (m) at Goat Harbor (±SE) in 2015 (* denotes significantly different mean based on post hoc Tukey HSD test).
The mean number of individuals observed by time of day from diver surveys within Goat Harbor for both 2014 and 2015 (±SE).
Sexual dimorphism between male (A) and female (B) Giant Sea Bass in the wild during spawning season, with both in situ photographs and drawings of these individuals to show greater contrast. Arrows depict key features in males (A): a slim body profile lighter in color with concave abdominal profile; and in females (B): a very dark mask under the eyes, a more rotund body shape, and a noticeable white patch on the sides above the vent (left to right). (Image Credit: LGA).
Pair of Giant Sea Bass photographed off Goat Harbor, Catalina Island, California by Parker House, July 2014.
Diagrammatic depictions of the three common courting behaviors: Following (A), Circling (B), and Nudging (C). (Image Credit: LGA).
Proposed depiction of spawning behavior exhibited by Giant Sea Bass. The final stages of courtship and actual spawning are believed to occur near and just after dusk as represented by the light to dark gradient (left to right) in the illustration. (Image Credit: LGA).
Contributor Notes
Associate Editor: K. Martin.