433
12 Species Case Studies
The Nassau grouper was the fi rst species scientifi cally documented to spawn in
spectacularly abundant aggregations (Smith 1972 ) . Although the species has never
been observed to spawn outside of aggregations, this possibility cannot be excluded
(Sadovy and Colin 1995 ) . Although the occurrence of aggregations had long been
known (e.g. Vilaro Diaz 1884 ; Sadovy 1993 b ) , until publication of Smith’s ( 1972 )
remarkable underwater photos and description of a spawning aggregation in The
Bahamas, estimated at between 30,000 and 100,000 fi shes, the number of fi sh that
gathered was not quantifi ed. The smallest aggregation of Nassau grouper observed to
spawn numbered about 20 fi sh (Colin 1992 ) and only a single spawning, with a few
individuals participating, was seen in these fi sh. The group was observed for some
time without other evidence of spawning. It may be that the presence of large numbers of fi sh (or greater than some threshold number) in an aggregation may be important for inducing spawning amongst clusters of fi sh from within the aggregation
(Sect. 8.4.2 ). The Grouper Moon project, run by the Reef Environmental Education
Foundation (REEF), has also documented (Brice Semmens, personal observation)
that aggregation dynamics change for depleted aggregations. Fish at a small aggregation on Cayman Brac (~1,500 fi sh) aggregated for a longer period of time than those
at a larger aggregation on an adjacent island, and larger fi sh aggregate for longer than
smaller fi sh. This means that fi sh in aggregations that are being depleted potentially
become more vulnerable to fi shing because they are present for a longer period of
time, and the largest, most reproductively valuable fi sh are the most susceptible.
Aggregations occur at a predictable time and place each year around the time of
the full moon, usually between December and March, although in Bermuda aggregation-spawning occurred in the northern summer period (Sadovy and Eklund
1999 ) . Spawning in the aggregation has been documented to occur within 20 min of
sunset in The Bahamas (Colin 1992 ) but as early as an hour before sunset to 20 min
after sunset in the Cayman Islands (Whaylen et al. 2007 ) . Individual fi sh are known
to travel as far as 220 km to spawn (Bolden 2000 ) , migrating in groups to aggregation sites which tend to be located close to deep waters on outer reefs (Colin 1992 ;
Carter et al. 1994 ) (Fig. 12.12 ). Not only are spawning aggregations stable in location over many years, but individual animals are known to repeatedly use the same
aggregation: uniquely patterned individual animals (“natural tags”) were observed
returning to the same aggregation over multiple years (Whaylen et al. 2007 ) and by
acoustic telemetry (Semmens et al. 2006, 2009 ) . The acoustic telemetry work demonstrates that Nassau grouper not only return to their specifi c aggregation between
years (Semmens et al. 2009 ) , but that individuals can return to the same aggregation
to spawn in different months within a year (Semmens et al. 2006 ) .
12.6.4 Fishery and Commercial Importance
The Nassau grouper once formed what were almost certainly the largest aggregations of any western Atlantic grouper, and perhaps any grouper in the world.
Aggregation fi sheries formed the basis of large and important seasonal fi sheries,
12 Species Case Studies
The Nassau grouper was the fi rst species scientifi cally documented to spawn in
spectacularly abundant aggregations (Smith 1972 ) . Although the species has never
been observed to spawn outside of aggregations, this possibility cannot be excluded
(Sadovy and Colin 1995 ) . Although the occurrence of aggregations had long been
known (e.g. Vilaro Diaz 1884 ; Sadovy 1993 b ) , until publication of Smith’s ( 1972 )
remarkable underwater photos and description of a spawning aggregation in The
Bahamas, estimated at between 30,000 and 100,000 fi shes, the number of fi sh that
gathered was not quantifi ed. The smallest aggregation of Nassau grouper observed to
spawn numbered about 20 fi sh (Colin 1992 ) and only a single spawning, with a few
individuals participating, was seen in these fi sh. The group was observed for some
time without other evidence of spawning. It may be that the presence of large numbers of fi sh (or greater than some threshold number) in an aggregation may be important for inducing spawning amongst clusters of fi sh from within the aggregation
(Sect. 8.4.2 ). The Grouper Moon project, run by the Reef Environmental Education
Foundation (REEF), has also documented (Brice Semmens, personal observation)
that aggregation dynamics change for depleted aggregations. Fish at a small aggregation on Cayman Brac (~1,500 fi sh) aggregated for a longer period of time than those
at a larger aggregation on an adjacent island, and larger fi sh aggregate for longer than
smaller fi sh. This means that fi sh in aggregations that are being depleted potentially
become more vulnerable to fi shing because they are present for a longer period of
time, and the largest, most reproductively valuable fi sh are the most susceptible.
Aggregations occur at a predictable time and place each year around the time of
the full moon, usually between December and March, although in Bermuda aggregation-spawning occurred in the northern summer period (Sadovy and Eklund
1999 ) . Spawning in the aggregation has been documented to occur within 20 min of
sunset in The Bahamas (Colin 1992 ) but as early as an hour before sunset to 20 min
after sunset in the Cayman Islands (Whaylen et al. 2007 ) . Individual fi sh are known
to travel as far as 220 km to spawn (Bolden 2000 ) , migrating in groups to aggregation sites which tend to be located close to deep waters on outer reefs (Colin 1992 ;
Carter et al. 1994 ) (Fig. 12.12 ). Not only are spawning aggregations stable in location over many years, but individual animals are known to repeatedly use the same
aggregation: uniquely patterned individual animals (“natural tags”) were observed
returning to the same aggregation over multiple years (Whaylen et al. 2007 ) and by
acoustic telemetry (Semmens et al. 2006, 2009 ) . The acoustic telemetry work demonstrates that Nassau grouper not only return to their specifi c aggregation between
years (Semmens et al. 2009 ) , but that individuals can return to the same aggregation
to spawn in different months within a year (Semmens et al. 2006 ) .
12.6.4 Fishery and Commercial Importance
The Nassau grouper once formed what were almost certainly the largest aggregations of any western Atlantic grouper, and perhaps any grouper in the world.
Aggregation fi sheries formed the basis of large and important seasonal fi sheries,