142
P.L. Colin
Among other factors, salinity may play a role in where reef fi shes aggregate
because high salinities (over 30–32 ppt) may be necessary for reef fi sh eggs to be
positively buoyant in order to rise towards the surface rather than drifting towards
the bottom (Colin et al. 1996 ; Ellis et al. 1997 ) . It seems unlikely that any reef fi shes
will migrate to low salinity areas to spawn (Chap. 2 ). Unverifi ed information, such
as that of Craig ( 1969 ) reporting goliath grouper , Epinephelus itajara , to migrate to
mangrove channels in Belize to spawn (which may have somewhat lower salinity
than reef areas), has not been confi rmed by subsequent work which indicates the
species migrates offshore to spawn (Chap. 12.4 ). It is believed oxygen will not
normally be a factor infl uencing locations and timing of spawning, as waters where
aggregations occur are generally near saturation. Most aggregation areas on reefs
have relatively clear water, although the turbidity can vary over a normal range for
reef areas where RA species spawn.
5.8 Spatio-Temporal Factors
Aggregations exist in several different time frames: annual, seasonal, lunar month
and diel. The time spent on direct courtship and spawning is very low for large TA
species, on the order of 0.1–0.2% per annum for adult Nassau grouper, but if migration is included might represent 5–10% of total time. RA species spend more time
engaged in courting and spawning, perhaps as much as 3% for humphead wrasse
(Colin 2010 ) , and if daily migration time is included, the value is similar to that for
TA species. Many RA species, despite their regular spawning, can maintain activities
such as feeding when en route during migration and while at aggregation sites
(Chap. 2 ). TA species are often benthic predators, and while migrating or aggregating
the fi sh may either go for periods without feeding or range out from aggregation
areas to feed elsewhere at times (Chap. 2 , Nemeth et al. 2007 ) . Noticeably skinny
squaretail coralgrouper have been seen in markets at the end of the spawning season
in Palau and other locations, suggesting that their feeding does not keep up energy
requirements during the spawning season (Yvonne Sadovy de Mitcheson 2009).
5.8.1 Time of Day for Spawning
The time of day when spawning in reef fi shes occurs varies with species and
conditions (Thresher 1984 ) and activity patterns vary among aggregating species.
At the equator there is no difference in day length throughout the year, with day and
night being approximately equal at all times. As one moves away from the equator,
the lengths of day and night change during the year. For example, at the latitude of
Palau (7°N), day length is 11:41 h on the winter solstice, 12:34 on the summer
solstice; a change of only 53 min or 7.5% annually. At the northern limits of coral
P.L. Colin
Among other factors, salinity may play a role in where reef fi shes aggregate
because high salinities (over 30–32 ppt) may be necessary for reef fi sh eggs to be
positively buoyant in order to rise towards the surface rather than drifting towards
the bottom (Colin et al. 1996 ; Ellis et al. 1997 ) . It seems unlikely that any reef fi shes
will migrate to low salinity areas to spawn (Chap. 2 ). Unverifi ed information, such
as that of Craig ( 1969 ) reporting goliath grouper , Epinephelus itajara , to migrate to
mangrove channels in Belize to spawn (which may have somewhat lower salinity
than reef areas), has not been confi rmed by subsequent work which indicates the
species migrates offshore to spawn (Chap. 12.4 ). It is believed oxygen will not
normally be a factor infl uencing locations and timing of spawning, as waters where
aggregations occur are generally near saturation. Most aggregation areas on reefs
have relatively clear water, although the turbidity can vary over a normal range for
reef areas where RA species spawn.
5.8 Spatio-Temporal Factors
Aggregations exist in several different time frames: annual, seasonal, lunar month
and diel. The time spent on direct courtship and spawning is very low for large TA
species, on the order of 0.1–0.2% per annum for adult Nassau grouper, but if migration is included might represent 5–10% of total time. RA species spend more time
engaged in courting and spawning, perhaps as much as 3% for humphead wrasse
(Colin 2010 ) , and if daily migration time is included, the value is similar to that for
TA species. Many RA species, despite their regular spawning, can maintain activities
such as feeding when en route during migration and while at aggregation sites
(Chap. 2 ). TA species are often benthic predators, and while migrating or aggregating
the fi sh may either go for periods without feeding or range out from aggregation
areas to feed elsewhere at times (Chap. 2 , Nemeth et al. 2007 ) . Noticeably skinny
squaretail coralgrouper have been seen in markets at the end of the spawning season
in Palau and other locations, suggesting that their feeding does not keep up energy
requirements during the spawning season (Yvonne Sadovy de Mitcheson 2009).
5.8.1 Time of Day for Spawning
The time of day when spawning in reef fi shes occurs varies with species and
conditions (Thresher 1984 ) and activity patterns vary among aggregating species.
At the equator there is no difference in day length throughout the year, with day and
night being approximately equal at all times. As one moves away from the equator,
the lengths of day and night change during the year. For example, at the latitude of
Palau (7°N), day length is 11:41 h on the winter solstice, 12:34 on the summer
solstice; a change of only 53 min or 7.5% annually. At the northern limits of coral