121
5 Timing and Location of Aggregation and Spawning in Reef Fishes
today are “drop off” areas were steep escarpments at the water’s surface dropping
away quickly. Shallow lagoon or fore reef areas would have been uncommon, and
during glacial low sea levels no other habitat was available for aggregation and
spawning. Once sea level rose to present levels, if spawning on drop-off areas is
selectively neutral or somewhat advantageous, and traditionally transmitted sites
important for encountering mates, there would be no selective pressure for fi shes to
change where they aggregate (e.g. move inshore or elsewhere).
Outer reef areas facing the open ocean at the edge of insular and continental
shelves are a common location for spawning aggregations of many commercially
important species (Fig. 5.1 ) (Sadovy de Mitcheson et al. 2008 , www.SCRFA.org ).
The “drop offs” where the bottom slopes away into deep water are a nearly ubiquitous geomorphologic feature of outer reefs varying from gently sloping to vertical,
with the width of the reef comprising the slope duly infl uenced. In the TWA nearly
all TAs are found at or very near shelf edge sites. RAs in the TWA occur both on the
shelf edge and also in areas far removed. The limited migration distance RA species
can cover each day may limit the areas where they aggregate. Areas are probably
selected due to certain features (Randall and Randall 1963 ) (Chap. 4 ), but continued
use of sites may be traditional and learned (Warner 1988, 1995 ) .
Fig. 5.1 Examples of areas with and without spawning aggregation sites located on outer reefs
adjacent to deep ocean. ( a ) Nassau grouper, Epinephelus striatus , transient aggregation ( TA ) site
without sharp projections at the southern end of Long Island, Bahamas. ( b ) TA area for three species
of groupers, Kehpara Marine Reserve in Pohnpei, Caroline Islands, is an arching section of reef
( c ) resident aggregation site for two surgeonfi shes on the shelf edge reef off SW Puerto Rico; an
area without any major projecting reef features. ( d ) A promontory at Agupelu Reef, Palau, similar
in appearance of other aggregation areas, without any known spawning aggregations
5 Timing and Location of Aggregation and Spawning in Reef Fishes
today are “drop off” areas were steep escarpments at the water’s surface dropping
away quickly. Shallow lagoon or fore reef areas would have been uncommon, and
during glacial low sea levels no other habitat was available for aggregation and
spawning. Once sea level rose to present levels, if spawning on drop-off areas is
selectively neutral or somewhat advantageous, and traditionally transmitted sites
important for encountering mates, there would be no selective pressure for fi shes to
change where they aggregate (e.g. move inshore or elsewhere).
Outer reef areas facing the open ocean at the edge of insular and continental
shelves are a common location for spawning aggregations of many commercially
important species (Fig. 5.1 ) (Sadovy de Mitcheson et al. 2008 , www.SCRFA.org ).
The “drop offs” where the bottom slopes away into deep water are a nearly ubiquitous geomorphologic feature of outer reefs varying from gently sloping to vertical,
with the width of the reef comprising the slope duly infl uenced. In the TWA nearly
all TAs are found at or very near shelf edge sites. RAs in the TWA occur both on the
shelf edge and also in areas far removed. The limited migration distance RA species
can cover each day may limit the areas where they aggregate. Areas are probably
selected due to certain features (Randall and Randall 1963 ) (Chap. 4 ), but continued
use of sites may be traditional and learned (Warner 1988, 1995 ) .
Fig. 5.1 Examples of areas with and without spawning aggregation sites located on outer reefs
adjacent to deep ocean. ( a ) Nassau grouper, Epinephelus striatus , transient aggregation ( TA ) site
without sharp projections at the southern end of Long Island, Bahamas. ( b ) TA area for three species
of groupers, Kehpara Marine Reserve in Pohnpei, Caroline Islands, is an arching section of reef
( c ) resident aggregation site for two surgeonfi shes on the shelf edge reef off SW Puerto Rico; an
area without any major projecting reef features. ( d ) A promontory at Agupelu Reef, Palau, similar
in appearance of other aggregation areas, without any known spawning aggregations