509
12 Species Case Studies
location where this occurs might (or might not) be different from the normal range.
Whether carangid spawning is considered “aggregation” or “simple migratory” the
fi sh are effectively releasing their gametes within a restricted area at specifi c times,
so the oceanographic mechanisms that affect them would be similar or identical to
those for aggregation spawners. Whether carangid spawning is more like transient
or resident aggregations is also a question. Data are scarce, but some species may
well act as resident aggregators, while other more resemble transient.
Hamilton and Walter ( 1999 ) reported on traditional knowledge of movements of
carangids in the Roviana lagoon, Solomon Islands. Some species were reported to
move back and forth through channels on the tides. Bigeye trevallies were found to
have their movements infl uenced by lunar phase in the Honiavasa Passage and were
present most often during the full moon period. In Palau there is little traditional
knowledge of aggregation of bigeye trevally (e.g. Johannes 1981 does not list it).
The only published report on a spawning aggregation of bigeye trevally is that of
Sala et al. ( 2003 ) from the Gulf of California in the eastern Pacifi c. They reported
bigeye trevally to spawn there around the full moon of July–September at an offshore islet with about 500–1,500 fi sh usually present. The school was absent at
other times of year. The fi sh spawned during the day as pairs at 10–20 m over a 30 m
deep bottom out of the larger group. The aggregation area as a whole covered about
10,000 m
2 .
This same behaviour is seen in the western Pacifi c locations. In Palau, a school
of several hundred fi sh is often present at Blue Corner and the fi sh stay near or over
the drop-off. In the afternoon they remain in the same area, but pairs break away and
swim slightly inshore over a 20 m deep bottom during courtship (Fig. 12.50 ). The
males become quite dark, almost black, while the female retains normal colour, and
the male stations himself slightly below and occasionally slightly behind the female.
If another male tries to approach the female, the intruder is kept away by the male
blocking any attempt of its rival to approach from behind the pair. Figure 12.50 a
shows how widely dispersed the pairs are during courtship, each pair a unit from the
school which still retains its integrity a short distance away, and the pairs swim
slowly into the current, maintaining their position over the bottom.
Elsewhere, bigeye trevallies are often seen in schools with pairs subsequently
separating themselves out. Near Port Moresby in Papua New Guinea, a swirling
school of bigeye trevally on the “horseshoe reef” barrier reef switched their location
to the opposite side of the reef as the current changed (PLC unpublished data).
12.18.3 Other Species of Carangids
Sala et al. ( 2003 ) also reported aggregation spawning in amberjack, Seriola lalandi .
They observed a school with about 80 fi sh for 3 days starting 3 days before the April
full moon, and while they did not observe spawning, females had hydrated eggs and
the density of fi sh was much greater than normal. By SCRFA criteria, this is considered a valid spawning aggregation record (Chap. 1 )
12 Species Case Studies
location where this occurs might (or might not) be different from the normal range.
Whether carangid spawning is considered “aggregation” or “simple migratory” the
fi sh are effectively releasing their gametes within a restricted area at specifi c times,
so the oceanographic mechanisms that affect them would be similar or identical to
those for aggregation spawners. Whether carangid spawning is more like transient
or resident aggregations is also a question. Data are scarce, but some species may
well act as resident aggregators, while other more resemble transient.
Hamilton and Walter ( 1999 ) reported on traditional knowledge of movements of
carangids in the Roviana lagoon, Solomon Islands. Some species were reported to
move back and forth through channels on the tides. Bigeye trevallies were found to
have their movements infl uenced by lunar phase in the Honiavasa Passage and were
present most often during the full moon period. In Palau there is little traditional
knowledge of aggregation of bigeye trevally (e.g. Johannes 1981 does not list it).
The only published report on a spawning aggregation of bigeye trevally is that of
Sala et al. ( 2003 ) from the Gulf of California in the eastern Pacifi c. They reported
bigeye trevally to spawn there around the full moon of July–September at an offshore islet with about 500–1,500 fi sh usually present. The school was absent at
other times of year. The fi sh spawned during the day as pairs at 10–20 m over a 30 m
deep bottom out of the larger group. The aggregation area as a whole covered about
10,000 m
2 .
This same behaviour is seen in the western Pacifi c locations. In Palau, a school
of several hundred fi sh is often present at Blue Corner and the fi sh stay near or over
the drop-off. In the afternoon they remain in the same area, but pairs break away and
swim slightly inshore over a 20 m deep bottom during courtship (Fig. 12.50 ). The
males become quite dark, almost black, while the female retains normal colour, and
the male stations himself slightly below and occasionally slightly behind the female.
If another male tries to approach the female, the intruder is kept away by the male
blocking any attempt of its rival to approach from behind the pair. Figure 12.50 a
shows how widely dispersed the pairs are during courtship, each pair a unit from the
school which still retains its integrity a short distance away, and the pairs swim
slowly into the current, maintaining their position over the bottom.
Elsewhere, bigeye trevallies are often seen in schools with pairs subsequently
separating themselves out. Near Port Moresby in Papua New Guinea, a swirling
school of bigeye trevally on the “horseshoe reef” barrier reef switched their location
to the opposite side of the reef as the current changed (PLC unpublished data).
12.18.3 Other Species of Carangids
Sala et al. ( 2003 ) also reported aggregation spawning in amberjack, Seriola lalandi .
They observed a school with about 80 fi sh for 3 days starting 3 days before the April
full moon, and while they did not observe spawning, females had hydrated eggs and
the density of fi sh was much greater than normal. By SCRFA criteria, this is considered a valid spawning aggregation record (Chap. 1 )