Lutjanus bohar

Grzelak, Katarzyna & Sørensen, Martin V., 2022, Echinoderes landersi Grzelak & amp; Sørensen 2022, sp. nov., Zoological studies 55 (44), pp. 1-15 : 9-12

Lutjanus bohar

The spawning aggregate of L. bohar formed early in the morning before dawn. The actual spawning took place within groups composed of one female with several males occurring in the upper peripheral part of the aggregation ( Fig. 7b ). Once a female made an upward rush, several males followed the female, and spawning took place at the apex of the rushing group.

Lutjanus bohar shared the same spawning site with S. spilurus but its sub-aggregating site was on the opposite side of the reef to that of S. spilurus ( Fig. 2 ). The number of fish in the aggregation was several thousands and the aggregation duration was shorter than that of S. spilurus . The spawning season of L. bohar was not limited to spring and autumn but occurred almost throughout the whole year.

Characteristics of fertilized eggs

The size of fertilized eggs of S. spilurus was 0.80 ± 0.01 mm in diameter, single oil globule and pelagic. That of L. bohar was slightly larger 0.82 ± 0.01 mm in diameter, single oil globule and pelagic also.

Spawning duration and interval

We observed the spawning duration of S. spilurus over seven years. Data collected by direct observations (diving) and interviews with other divers were gathered to summarize all-daytime fish behaviors for eight days as shown in figure 8. The spawning started 6 days before every new moon. Core spawning lasted about one hour while sporadic spawning occurred prior to and after the core spawning. On the second day, the spawning time shifted about 90 minutes later from that of the first day, and the spawning duration expanded to one and half hours. The third day, spawning took place about 90 to 120 minutes later than on the second day (spawning occurred in the early afternoon). Similar time shift was observed on the fourth day. On day five, however, spawning took place after dawn and the mode of spawning was sporadic. On the last day of spawning in the new moon period, sporadic spawning lasted from dawn to early afternoon. Thus, the whole spawning activity lasted for one week on every new moon. On some occasions, the actual spawning did not take place on the last day. The tendency of overall behavior was consistent throughout the years of 2009 to 2015.

The spawning duration tendency of L. bohar was also observed for six years as shown in figure 9. The first spawning takes place two days before the full moon when the aggregation started about 1.5 hour before sunrise and the fish spawned frequently at around sunrise for about half an hour. On the second day, the aggregation started at almost the same time with the first day, but the core spawning time was delayed by about half an hour. On the third day, the aggregation started again the same time with the first day, but the onset of core spawning was delayed by about an hour. The duration of the core spawning was one hour. On the fourth day, no spawning behaviors were observed. This tendency was also consistent throughout the years of 2010 to 2015.

Water temperature in spawning site

Fluctuation of water temperature at the spawning site between March 3rd and April 18th, was recorded in 2015. The water temperature of the spawning site changed between 21.4 and 29°C)(n = 3033, average 27.7 ± 0.81°C in the spawning season ( Fig. 10a ). The water temperature, recorded when spawning of fish actually was observed, changed between 25.0 and 28.7°C (n = 15, average 27.2 ± 1.23°C) for S. spilurus , and between 24.2 and 28.6°C (n = 15, average 27.5 ± 1.22 for L. bohar . No significance between spawning and the grand average was found in both species ( Fig. 11a). When waters from deeper layers upwelled into the site, it resulted in a large decrease in temperature to 22 or even 21°C). Spawning behaviors in both species, however, were not affected even by such a large fluctuation of water temperature. Of note, on the day when the water temperature went down below 21°C. S. spilurus showed the same spawning behavior. These data suggested that there is no clear correlation between the temperature and the behavior of the fish within the fluctuations observed in the present study. Larger fluctuations in temperatures, however, may occur because of “unusual” climate factors such as El Nino, continuous observations are necessary to draw conclusions as to the temperature dependence of the spawning behavior.

Current velocity in spawning site

Fluctuation of the current velocity at the spawning site between March 3 and April 18, the mean current direction ranging from 150.1 and 259.4° with an average of 215.7° ± 35.5 (n = 15) ( Fig. 10c ). No significant difference was evident between the grand average and the average value ( Fig. 11c). It is interesting to note however, the distribution of the current direction when L. bohar spawned ( Fig. 10c ) is narrower than that of average, suggesting that L. bohar actually has a “preferred” direction.

These data illustrated that the spawning behavior of S. spilurus is influenced largely by the current direction. The difference in the current direction between the two species is about 60° and the direction of transportation of fertilized eggs was estimated to be SES in S. spilurus and WSW in L. bohar ( Fig. 12 ).

Although the rhythmicity and the regular daily spawning for both species as shown in figures 8 and 9 were consistent, no spawning occurred at the expected time when the current was minimal (less than 0.23 km /h) in both species. Probability of such a slow tide was about 2.7% from the normal distribution curve.

Figures

Fig. 7. Photographs of actual spawning of (a) S. spilurus and (b) L. bohar. Dotted yellow trace indicates a locus of a rushing female individual.

Fig. 2. Observation site: southernmost reef of Peleliu Island. The “resting area” where sub-aggregate schools of S. spilurus and L. bohar gather are highlighted in yellow and red, respectively. The spawning ground is marked in white circle.

Fig. 10. Normal distributions of: (a) Ambient water temperature (bold line), that at the time S. spilurus (circles), and L. bohar (triangles) spawn. (b) Current velocity of spawning site (bold line), that at the time S. spilurus (circles), and L. bohar (triangles) spawn, (c) Current direction of spawning site (bold line), that at the time S. spilurus (circles), and L. bohar (triangles) spawn. Above data were recorded between February 2 and April 18, 2015.

Fig. 12. Averaged current directions for the spawning days of L. bohar (Lb), and S. spilurus (Ss).