523
12 Species Case Studies
were not high enough to form aggregations of the size seen. We found a density of
about 4 adult ocean surgeonfi sh per 100 m
2 of bottom during the non-spawning
period (June-August). With an estimated 20,000 individuals in the spawning aggregation, a semi-circular area (since the spawning site is at the shelf edge and surgeonfi shes do not penetrate deep water in abundance) 500–600 m in radius from the
aggregation site would contain that number of fi sh. Although never quantifi ed, it
appeared there were discrete groups of surgeonfi shes (“trains” in the sense of
Myrberg et al. 1988 ) coming to the aggregation sites along specifi c paths across the
sandy basin (“the moat”) shoreward of the outer reef.
The daily patterns of spawning rushes of ocean surgeonfi sh in the aggregation
were documented during the peak spawning season in February; blue tang were too
shy to be counted and fl ed an approaching diver. Typically spawning consists of
fl urries of spawning rushes for 2–5 min followed by short quiescent periods of only
1–2 min (Fig. 12.61 ). When 5 days data were combined, the overall pattern to
spawning activity is apparent with spawning starting about 90 min before, peaking
70–50 min before and ceasing about 30 min before sunset (Fig. 12.62 ). In the limited fi eld of view from which spawning rushes were documented for 5 days during
peak activity in February, the number of rushes seen per afternoon was 198–228. As
this view encompassed only a portion of the aggregation area, only a fraction of the
total numbers of spawnings were recorded.
Gonad indices of aggregated fi shes: There is a clear correlation between increased
gonad indices in both male and female ocean surgeonfi sh and the season for
Fig. 12.60 These histograms show the occurrence of spawning on different lunar phases during
the winter period (December to March) for blue tang ( upper ) and ocean surgeonfi sh ( lower ). The
number of days when observation were made on a given day of the lunar calendar during those
months are shown along the upper axis of the upper histogram. Blue tang showed lunar periodicity
and ocean surgeonfi sh spawned every day of the lunar month
12 Species Case Studies
were not high enough to form aggregations of the size seen. We found a density of
about 4 adult ocean surgeonfi sh per 100 m
2 of bottom during the non-spawning
period (June-August). With an estimated 20,000 individuals in the spawning aggregation, a semi-circular area (since the spawning site is at the shelf edge and surgeonfi shes do not penetrate deep water in abundance) 500–600 m in radius from the
aggregation site would contain that number of fi sh. Although never quantifi ed, it
appeared there were discrete groups of surgeonfi shes (“trains” in the sense of
Myrberg et al. 1988 ) coming to the aggregation sites along specifi c paths across the
sandy basin (“the moat”) shoreward of the outer reef.
The daily patterns of spawning rushes of ocean surgeonfi sh in the aggregation
were documented during the peak spawning season in February; blue tang were too
shy to be counted and fl ed an approaching diver. Typically spawning consists of
fl urries of spawning rushes for 2–5 min followed by short quiescent periods of only
1–2 min (Fig. 12.61 ). When 5 days data were combined, the overall pattern to
spawning activity is apparent with spawning starting about 90 min before, peaking
70–50 min before and ceasing about 30 min before sunset (Fig. 12.62 ). In the limited fi eld of view from which spawning rushes were documented for 5 days during
peak activity in February, the number of rushes seen per afternoon was 198–228. As
this view encompassed only a portion of the aggregation area, only a fraction of the
total numbers of spawnings were recorded.
Gonad indices of aggregated fi shes: There is a clear correlation between increased
gonad indices in both male and female ocean surgeonfi sh and the season for
Fig. 12.60 These histograms show the occurrence of spawning on different lunar phases during
the winter period (December to March) for blue tang ( upper ) and ocean surgeonfi sh ( lower ). The
number of days when observation were made on a given day of the lunar calendar during those
months are shown along the upper axis of the upper histogram. Blue tang showed lunar periodicity
and ocean surgeonfi sh spawned every day of the lunar month