39
2 Ecosystem Aspects of Species That Aggregate to Spawn
and Creole wrasse, Clepticus parrae , whereas Nassau grouper guts contained
mainly crustaceans (e.g. Justitia longimanus ) but also Creole wrasse (RSN
unpublished data).
Not all species necessarily feed while aggregated but may use staging areas for
maintenance. Individuals of squaretail coralgrouper in Palau, the males of which
defend temporary spawning territories, become thin during the spawning season
suggesting that some are not feeding or not feeding enough (Yvonne Sadovy de
Mitcheson personal communication). Transient aggregating species may spend
brief periods at aggregation sites but individual fi sh may spend several weeks to
months between spawning peaks feeding in staging area habitats (Figs. 2.3 and 2.4 )
that surround the aggregation site (Starr et al. 2007 ) . More detailed studies of feeding
habits by aggregating species during migration and at FSA sites are needed to
understand if, when or where feeding takes place and how important local prey
populations are for aggregating species and their subsequent reproductive output.
2.4.2 Predation by Piscivores on Spawning Adults
Potential predators on fi sh in spawning aggregations are composed of a diverse
group of which 22 species within 13 families attacked and occasionally consumed
spawning adults (Table 2.1 ). Predation attempts are more commonly reported from
resident aggregating species than from transient aggregators (14 vs. 2 species listed
in Table 2.1 ) and evidently more common in the Indo-Pacifi c (Robertson 1983 ;
Sancho et al. 2000a ) than in the Caribbean (Colin and Clavijo 1988 ; Robertson et al.
1999 ) . The higher number of observations of predation attempts on resident aggregating species probably results from their extended spawning seasons (Chap. 5 )
during which they spawn nearly every day during daylight hours, when visibility is
good for behavioural observations. Transient aggregating species, on the other hand,
typically spawn over short time periods at sunset or during the night, and are often
associated with deeper water or challenging diving conditions, making direct observations by divers diffi cult (Colin et al. 2003 ) . Transient aggregating species are also
larger in body size making them vulnerable to only the largest of piscivores (Juanes
1994 ) . Reports of sharks attacking transient spawning aggregations appear to be
most commonly associated with fi shing-induced predation where sharks and other
large predators attack groupers that are hooked on fi shing lines (Olsen and LaPlace
1978 ; Nemeth 2005 ; Matos-Caraballo et al. 2006 ; Heyman and Kjerfve 2008 )
(Chaps. 5 and 7 ).
Evidence for predation on spawning adults comes from direct observations of
successful strikes and predation attempts or from an increase in the number of potential predators at FSA sites when fi sh are aggregated compared to non-aggregation
periods. Although observations on successful predation attempts are rare (Colin and
Clavijo 1988 ) , a few studies have provided quantitative data of predation on aggregating species (Chaps. 5 and 7 ). These studies indicate that when predation attempts
were observed, most piscivores attacked during the spawning rush, with an overall
2 Ecosystem Aspects of Species That Aggregate to Spawn
and Creole wrasse, Clepticus parrae , whereas Nassau grouper guts contained
mainly crustaceans (e.g. Justitia longimanus ) but also Creole wrasse (RSN
unpublished data).
Not all species necessarily feed while aggregated but may use staging areas for
maintenance. Individuals of squaretail coralgrouper in Palau, the males of which
defend temporary spawning territories, become thin during the spawning season
suggesting that some are not feeding or not feeding enough (Yvonne Sadovy de
Mitcheson personal communication). Transient aggregating species may spend
brief periods at aggregation sites but individual fi sh may spend several weeks to
months between spawning peaks feeding in staging area habitats (Figs. 2.3 and 2.4 )
that surround the aggregation site (Starr et al. 2007 ) . More detailed studies of feeding
habits by aggregating species during migration and at FSA sites are needed to
understand if, when or where feeding takes place and how important local prey
populations are for aggregating species and their subsequent reproductive output.
2.4.2 Predation by Piscivores on Spawning Adults
Potential predators on fi sh in spawning aggregations are composed of a diverse
group of which 22 species within 13 families attacked and occasionally consumed
spawning adults (Table 2.1 ). Predation attempts are more commonly reported from
resident aggregating species than from transient aggregators (14 vs. 2 species listed
in Table 2.1 ) and evidently more common in the Indo-Pacifi c (Robertson 1983 ;
Sancho et al. 2000a ) than in the Caribbean (Colin and Clavijo 1988 ; Robertson et al.
1999 ) . The higher number of observations of predation attempts on resident aggregating species probably results from their extended spawning seasons (Chap. 5 )
during which they spawn nearly every day during daylight hours, when visibility is
good for behavioural observations. Transient aggregating species, on the other hand,
typically spawn over short time periods at sunset or during the night, and are often
associated with deeper water or challenging diving conditions, making direct observations by divers diffi cult (Colin et al. 2003 ) . Transient aggregating species are also
larger in body size making them vulnerable to only the largest of piscivores (Juanes
1994 ) . Reports of sharks attacking transient spawning aggregations appear to be
most commonly associated with fi shing-induced predation where sharks and other
large predators attack groupers that are hooked on fi shing lines (Olsen and LaPlace
1978 ; Nemeth 2005 ; Matos-Caraballo et al. 2006 ; Heyman and Kjerfve 2008 )
(Chaps. 5 and 7 ).
Evidence for predation on spawning adults comes from direct observations of
successful strikes and predation attempts or from an increase in the number of potential predators at FSA sites when fi sh are aggregated compared to non-aggregation
periods. Although observations on successful predation attempts are rare (Colin and
Clavijo 1988 ) , a few studies have provided quantitative data of predation on aggregating species (Chaps. 5 and 7 ). These studies indicate that when predation attempts
were observed, most piscivores attacked during the spawning rush, with an overall