460
12 Species Case Studies
crustaceans and fi shes. Its yellowish body, yellow anal fi n, dark caudal fi n and large
eye make it easily identifi ed (Allen and Talbot 1985 ) . Due to its relatively small
size, it is of minor fi shing importance throughout its range, with only limited artesanal or commercial catch according to available information (e.g. Sadovy 2007 ) .
Little has been published regarding its spawning biology, although in Tahiti it was
reported to spawn around the full moon (Randall and Brock 1960 ) this section also
includes notes on some other lutjanid species.
12.10.2 Reproduction and Aggregation
At the time of the full moon in January 2007 the blacktail snapper was found in
Palau to form a large spawning aggregation numbering tens of thousands of fi sh on
the side of a deep tidal channel (Fig. 12.20 ). There is no traditional knowledge
recorded regarding such aggregations of this fi sh (Johannes 1981 and later surveys)
but almost certainly the aggregation would have been observed by the numerous
spearfi shermen of Palau (see below). In many other areas of the Pacifi c, however,
the aggregations would be easy targets for fi shing with explosives and might become
a target in Palau if larger fi sh species decline in the reef fi shery.
Spawning has not been observed despite attempts from late afternoon until a half
hour after sunset. Spawning may occur at dawn, at night, or at some other time of
day. The fi sh are disturbed by observers, constantly moving away, perhaps preventing easy observations of spawning. The one known aggregation in Palau occurred
on the slope of a barrier reef channel, but located well inside the channel over 1 km
from the mouth of the channel. The fi sh ranged from the shallow reef fl at along the
channel edge (1 m deep at low tide) down the 30–45
o slope to around 20 m depth.
The aggregating fi sh occurred as 3–4 discrete “schools” along about 150 m of channel edge. At peak numbers schools were estimated at 10,000–20,000 fi sh, based on
the estimated density within small areas and the overall areas covered by the schools.
They are present at the site during the entire day, starting at dawn, but may leave the
area around sunset (see Fig. 9.8). The site was visited for surveys during the full
moon period for 10 months of 2007 (2 months missed due to weather). The aggregation was present all 10 months and it seems likely it occurs every month of the year.
The aggregation duration most months was from the day before the full moon to 3
days after, a total of 5 days with large numbers of fi sh present. In a few months, the
aggregation was not present on the day before the full moon, and in one case it did
not appear until the day after the full moon.
While the presence of tens of thousands of snappers in a limited area where normally there might be only a handful fi sh implied that a spawning aggregation was
likely occurring, without a direct indication of spawning it was not correct to consider this group of fi sh as a spawning aggregation. At least one of the three direct
criteria accepted by SCRFA as direct evidence of a spawning aggregation; observations of spawning, hydrated oocytes and post-ovulatory follicles, needed to be met
(Colin et al. 2003 ; Chap. 1 ). In this case, specimens from the aggregation were
12 Species Case Studies
crustaceans and fi shes. Its yellowish body, yellow anal fi n, dark caudal fi n and large
eye make it easily identifi ed (Allen and Talbot 1985 ) . Due to its relatively small
size, it is of minor fi shing importance throughout its range, with only limited artesanal or commercial catch according to available information (e.g. Sadovy 2007 ) .
Little has been published regarding its spawning biology, although in Tahiti it was
reported to spawn around the full moon (Randall and Brock 1960 ) this section also
includes notes on some other lutjanid species.
12.10.2 Reproduction and Aggregation
At the time of the full moon in January 2007 the blacktail snapper was found in
Palau to form a large spawning aggregation numbering tens of thousands of fi sh on
the side of a deep tidal channel (Fig. 12.20 ). There is no traditional knowledge
recorded regarding such aggregations of this fi sh (Johannes 1981 and later surveys)
but almost certainly the aggregation would have been observed by the numerous
spearfi shermen of Palau (see below). In many other areas of the Pacifi c, however,
the aggregations would be easy targets for fi shing with explosives and might become
a target in Palau if larger fi sh species decline in the reef fi shery.
Spawning has not been observed despite attempts from late afternoon until a half
hour after sunset. Spawning may occur at dawn, at night, or at some other time of
day. The fi sh are disturbed by observers, constantly moving away, perhaps preventing easy observations of spawning. The one known aggregation in Palau occurred
on the slope of a barrier reef channel, but located well inside the channel over 1 km
from the mouth of the channel. The fi sh ranged from the shallow reef fl at along the
channel edge (1 m deep at low tide) down the 30–45
o slope to around 20 m depth.
The aggregating fi sh occurred as 3–4 discrete “schools” along about 150 m of channel edge. At peak numbers schools were estimated at 10,000–20,000 fi sh, based on
the estimated density within small areas and the overall areas covered by the schools.
They are present at the site during the entire day, starting at dawn, but may leave the
area around sunset (see Fig. 9.8). The site was visited for surveys during the full
moon period for 10 months of 2007 (2 months missed due to weather). The aggregation was present all 10 months and it seems likely it occurs every month of the year.
The aggregation duration most months was from the day before the full moon to 3
days after, a total of 5 days with large numbers of fi sh present. In a few months, the
aggregation was not present on the day before the full moon, and in one case it did
not appear until the day after the full moon.
While the presence of tens of thousands of snappers in a limited area where normally there might be only a handful fi sh implied that a spawning aggregation was
likely occurring, without a direct indication of spawning it was not correct to consider this group of fi sh as a spawning aggregation. At least one of the three direct
criteria accepted by SCRFA as direct evidence of a spawning aggregation; observations of spawning, hydrated oocytes and post-ovulatory follicles, needed to be met
(Colin et al. 2003 ; Chap. 1 ). In this case, specimens from the aggregation were