42
R.S. Nemeth
success rate of 2–4% (Moyer 1987 ; Sancho 2000 ; Sancho et al. 2000a ) . The possible
impact of predation on spawning aggregations can be calculated for at least one
species. At Johnston Atoll, Sancho et al. ( 2000a ) found that piscivores (bluefi n
trevally Caranx melampygus and small jobfi sh Aphareus furca ) successfully consumed spawning bullethead parrotfi sh ( Chlorurus sordidus ) at about 0.1 fi sh per
hour. Since bullethead parrotfi sh spawns about 1 h each day (Sancho et al. 2000b ) ,
this equals a predation rate of about three fi sh per month. The maximum spawning
population size observed by Sancho et al. ( 2000b ) at Johnston Atoll was 300 individuals, so piscivores may consume about 1% of the bullethead parrotfi sh spawning
population each month or 12% each year during spawning episodes.
Other non-quantitative studies report an increase in the number of predators at
spawning aggregation sites during the spawning period including sharks, large pelagics (marlin-Istiophoridae, tunas and wahoo-Scombridae), large green moray eels and
snappers (Nemeth 2005 ; Heyman and Kjerfve 2008 ) . One recent acoustic tagging
study in the USVI found that lemon sharks ( Negaprion brevirostris ) frequented
red hind, yellowfi n grouper and Nassau grouper spawning sites during the spawning
season but were mostly absent the remainder of the year (Brad Wetherbee, Mahmood
Shivji and RSN unpublished data). These observations suggest that feeding patterns of piscivores may be synchronized with the seasonal spawning activity of transient aggregations. However, the importance of spawning aggregations to the overall
diet of predators that target spawning adults requires further investigation.
2.4.3 Egg Predation at Spawning Aggregations
Evidence for predation on newly released eggs or sperm at spawning aggregation
sites comes from several quantitative studies, and direct observations including an
observed increase in the number of potential oophagous predators. A review of the
literature found that 35 species within 13 families were egg predators with the
majority of observations coming from the Pacifi c (Table 2.2 ). In most cases, egg
predators rapidly swim to the centre of a visible gamete cloud and pick at newly
released eggs or swim through gamete clouds and ram fi lter feed (i.e. bigmouth
mackerel Rastrelliger kanagurta and whale shark Rhincodon typus ) (Colin 1976 ;
Moyer 1987 ; Sancho et al. 2000a ; Heyman et al. 2001 ) .
The percent of spawning events attacked by oophagous predators was calculated
for a variety of species and varied from <1% to >40% (Robertson 1983 ; Moyer
1987 ; Samoilys 1997 ; Sancho et al. 2000a ) . A number of factors contributed to this
variability including spawning location, the species aggregating, spawning mode
and time of day. For example, in Palau Robertson ( 1983 ) found that egg predation
was similar among pair-spawning bristletooth tang and brown surgeonfi sh (<5%)
but was considerably higher during group-spawns in these two species (27% and
42%, respectively). Egg predation rates for pair-spawning leopard coralgrouper
(10–27%) and group-spawning cupid wrasse, Thalassoma cupido , (42%) also fell
within this range (Moyer 1987 ; Samoilys 1997 ) . While there are no estimates of the
R.S. Nemeth
success rate of 2–4% (Moyer 1987 ; Sancho 2000 ; Sancho et al. 2000a ) . The possible
impact of predation on spawning aggregations can be calculated for at least one
species. At Johnston Atoll, Sancho et al. ( 2000a ) found that piscivores (bluefi n
trevally Caranx melampygus and small jobfi sh Aphareus furca ) successfully consumed spawning bullethead parrotfi sh ( Chlorurus sordidus ) at about 0.1 fi sh per
hour. Since bullethead parrotfi sh spawns about 1 h each day (Sancho et al. 2000b ) ,
this equals a predation rate of about three fi sh per month. The maximum spawning
population size observed by Sancho et al. ( 2000b ) at Johnston Atoll was 300 individuals, so piscivores may consume about 1% of the bullethead parrotfi sh spawning
population each month or 12% each year during spawning episodes.
Other non-quantitative studies report an increase in the number of predators at
spawning aggregation sites during the spawning period including sharks, large pelagics (marlin-Istiophoridae, tunas and wahoo-Scombridae), large green moray eels and
snappers (Nemeth 2005 ; Heyman and Kjerfve 2008 ) . One recent acoustic tagging
study in the USVI found that lemon sharks ( Negaprion brevirostris ) frequented
red hind, yellowfi n grouper and Nassau grouper spawning sites during the spawning
season but were mostly absent the remainder of the year (Brad Wetherbee, Mahmood
Shivji and RSN unpublished data). These observations suggest that feeding patterns of piscivores may be synchronized with the seasonal spawning activity of transient aggregations. However, the importance of spawning aggregations to the overall
diet of predators that target spawning adults requires further investigation.
2.4.3 Egg Predation at Spawning Aggregations
Evidence for predation on newly released eggs or sperm at spawning aggregation
sites comes from several quantitative studies, and direct observations including an
observed increase in the number of potential oophagous predators. A review of the
literature found that 35 species within 13 families were egg predators with the
majority of observations coming from the Pacifi c (Table 2.2 ). In most cases, egg
predators rapidly swim to the centre of a visible gamete cloud and pick at newly
released eggs or swim through gamete clouds and ram fi lter feed (i.e. bigmouth
mackerel Rastrelliger kanagurta and whale shark Rhincodon typus ) (Colin 1976 ;
Moyer 1987 ; Sancho et al. 2000a ; Heyman et al. 2001 ) .
The percent of spawning events attacked by oophagous predators was calculated
for a variety of species and varied from <1% to >40% (Robertson 1983 ; Moyer
1987 ; Samoilys 1997 ; Sancho et al. 2000a ) . A number of factors contributed to this
variability including spawning location, the species aggregating, spawning mode
and time of day. For example, in Palau Robertson ( 1983 ) found that egg predation
was similar among pair-spawning bristletooth tang and brown surgeonfi sh (<5%)
but was considerably higher during group-spawns in these two species (27% and
42%, respectively). Egg predation rates for pair-spawning leopard coralgrouper
(10–27%) and group-spawning cupid wrasse, Thalassoma cupido , (42%) also fell
within this range (Moyer 1987 ; Samoilys 1997 ) . While there are no estimates of the