470
12 Species Case Studies
(10 replicate counts of school depth), which varies over time, the speed of movement
and the time taken for the entire school takes to pass the focal location (Fig. 12.26b ).
These groupings form twice a year and, at other times, the site does not contain the
species. Water temperatures during aggregation are generally 28.0°–29.5°C (Patrick
Colin, personal communication, 2008). All three sites appear to have distinctive
promontory-like features and are located on outer reefs. Aggregation has a lunar
pattern, starting after the full moon, with fi sh numbers peaking at around the third
quarter and disappearing by the following new moon. During the aggregating season, the species makes diel migrations of about 2 km moving from sheltered areas
in daylight hours to shallow areas at night, with a minor migration to the deeper
spawning site at dawn. Interestingly, the stomachs of fi sh during the aggregation
period were found to be empty and they would not take bait at this time.
Spawning occurs in small sub-groups that form from within the large aggregations
which appear to move up and down in depth in response to prevailing water movements (Fig. 12.27a ). Fish stay near the substrate and are more spread out over a large
area in strong currents and become more concentrated and three-dimensional as fi sh
move up in the water column when currents are less strong. The sub-groups are
believed to be composed of a single female and several males. Males take on a temporary and distinctive colouration during courtship with the blue lines and the inner side
of the dorsal and caudal fi ns becoming darker with the body colour in general intensifying. As spawning approaches, the dark coloured males of a single subgroup approach
females, which are lighter coloured and have clearly swollen abdomens, to chase and
nuzzle them (Fig. 12.27b ). Several males may simultaneously engage in this courtship
behaviour with a single female. The female then begins to rush into the upper layers
of the aggregation followed by several males and she leads the male group at high
speed and with rapidly changing direction. The spawning occurs in a rapid burst of
swimming either vertically or horizontally that culminates in a release of gametes at
its apex and the rapid return of the fi sh to the substrate and the aggregation.
The eggs are pelagic, 0.80 ± 0.01 mm in diameter, with a single oil globule, and
hatch about 24 h after fertilization into larvae of 2.3 mm TL that appear to be typical
of lutjanid larvae.
12.11.3 Management and Conservation
In Palau the species is not common in the local markets and was not reported as
aggregating recently by fi shers interviewed on species exploited from spawning
aggregations (Sadovy 2007 ) . However, fi shers reported being aware of schools of
this species in the 1980s and commented that these could be fi shed out from areas
by spearfi shing (Johannes 1981 ) . Since the species does not appear to be common
on Palau reefs, each spawning aggregation may draw fi sh in from a wide catchment
area, making them susceptible to overfi shing (Johannes 1981 ) . The blue-lined seabream is listed as an important marine resource for a number of western Pacifi c
countries (e.g. Nichols 1991 ; Hamilton et al. 2004 ) .
12 Species Case Studies
(10 replicate counts of school depth), which varies over time, the speed of movement
and the time taken for the entire school takes to pass the focal location (Fig. 12.26b ).
These groupings form twice a year and, at other times, the site does not contain the
species. Water temperatures during aggregation are generally 28.0°–29.5°C (Patrick
Colin, personal communication, 2008). All three sites appear to have distinctive
promontory-like features and are located on outer reefs. Aggregation has a lunar
pattern, starting after the full moon, with fi sh numbers peaking at around the third
quarter and disappearing by the following new moon. During the aggregating season, the species makes diel migrations of about 2 km moving from sheltered areas
in daylight hours to shallow areas at night, with a minor migration to the deeper
spawning site at dawn. Interestingly, the stomachs of fi sh during the aggregation
period were found to be empty and they would not take bait at this time.
Spawning occurs in small sub-groups that form from within the large aggregations
which appear to move up and down in depth in response to prevailing water movements (Fig. 12.27a ). Fish stay near the substrate and are more spread out over a large
area in strong currents and become more concentrated and three-dimensional as fi sh
move up in the water column when currents are less strong. The sub-groups are
believed to be composed of a single female and several males. Males take on a temporary and distinctive colouration during courtship with the blue lines and the inner side
of the dorsal and caudal fi ns becoming darker with the body colour in general intensifying. As spawning approaches, the dark coloured males of a single subgroup approach
females, which are lighter coloured and have clearly swollen abdomens, to chase and
nuzzle them (Fig. 12.27b ). Several males may simultaneously engage in this courtship
behaviour with a single female. The female then begins to rush into the upper layers
of the aggregation followed by several males and she leads the male group at high
speed and with rapidly changing direction. The spawning occurs in a rapid burst of
swimming either vertically or horizontally that culminates in a release of gametes at
its apex and the rapid return of the fi sh to the substrate and the aggregation.
The eggs are pelagic, 0.80 ± 0.01 mm in diameter, with a single oil globule, and
hatch about 24 h after fertilization into larvae of 2.3 mm TL that appear to be typical
of lutjanid larvae.
12.11.3 Management and Conservation
In Palau the species is not common in the local markets and was not reported as
aggregating recently by fi shers interviewed on species exploited from spawning
aggregations (Sadovy 2007 ) . However, fi shers reported being aware of schools of
this species in the 1980s and commented that these could be fi shed out from areas
by spearfi shing (Johannes 1981 ) . Since the species does not appear to be common
on Palau reefs, each spawning aggregation may draw fi sh in from a wide catchment
area, making them susceptible to overfi shing (Johannes 1981 ) . The blue-lined seabream is listed as an important marine resource for a number of western Pacifi c
countries (e.g. Nichols 1991 ; Hamilton et al. 2004 ) .