430
12 Species Case Studies
The Nassau grouper is known to spawn in large aggregations but its social
behaviour outside of aggregations is little studied due to a lack of areas in its range
with signifi cant populations. Investigations around Lee Stocking Island in the
Exuma Chain of The Bahamas found that the seaward area of the island, bordering
on deep Exuma Sound, had a relatively large undisturbed population (Colin 1992 ) .
A number of specifi c individuals at this location were regularly surveyed, each fi sh
identifi able by individual variations in the markings on the body. Most individuals
moved over several hundred m
2 and many had overlapping home ranges with a
social hierarchy. When a dominant fi sh encountered a smaller conspecifi c the latter
would quickly adopt the “submissive” bicolour pattern seen among aggregated fi sh
as the two fi sh approached each other (Colin 1992 ) . Since Nassau grouper have no
external sex differences, it is impossible to ascribe a sex to the individuals observed.
During the spawning season the largest fi sh within the study area disappeared and
was not seen for 4 weeks. Another, smaller individual had apparently taken over as
the dominant individual during the absence of the larger fi sh and did not allow the
latter to regain its position. There ensued for several weeks a continuing struggle
between these two fi sh manifested by aggressive encounters whenever they met,
and both fi sh displayed tears and scars from their encounters (PLC, personal observation). Similar observations of change to a submissive colour pattern when transiting another Nassau’s territory were made off Little Cayman Island (SAH and Brice
Semmens, personal observation).
The relationship of spawning and larval development to the physical environment is detailed in Chaps. 5 and 7 . Pelagic eggs are produced in the aggregation and
after a pelagic larval (Chap. 7 , Fig. 7.5) period of about 41–43 days (range 37–45)
settlement occurs (Colin et al. 1997 ) . Most information on Nassau grouper larval
recruitment comes from Lee Stocking Island in The Bahamas during the period
1989–1991 (Colin et al. 1997 ; Shenker et al. 1993 ) . Colin et al. ( 1997 ) deployed
moored nets in a tidal channel in early 1989 and 1990 and successfully captured
numerous recruiting Nassau grouper on the new moons of February 1989 and 1990.
While Shenker et al. ( 1993 ) found an association of recruitment through tidal channels with a winter storm event, other years (Colin et al. 1997 ) did not demonstrate
the same relationship of atmospheric conditions with recruitment. Daily otolith
increments back-dated to full moon spawning in December and January, which is
consistent with the known aggregating season for the species in The Bahamas.
Recent satellite-based current drifter tracking in the Cayman Islands indicates that
not only are there eddies that form over the aggregation in the days immediately
after spawning that can potentially retain larvae close to where they are produced,
but that long-term patterns indicate a high likelihood of pre-settlement fi sh being
returned over the ~40 day pelagic larval duration (Fig. 12.10 ) (Heppell et al. 2008 ) .
This suggests that local spawning and its timing may be critical features associated
with the long-term sustainability of local populations.
The habitats into which newly settled Nassau grouper recruit have received some
attention, but because of the cryptic nature of small grouper recruits, it is risky to make
too many assumptions based solely on habitats that can be readily sampled for recruitment versus less accessible ones. Eggleston ( 1995 ) sampled habitats on the Bahama
12 Species Case Studies
The Nassau grouper is known to spawn in large aggregations but its social
behaviour outside of aggregations is little studied due to a lack of areas in its range
with signifi cant populations. Investigations around Lee Stocking Island in the
Exuma Chain of The Bahamas found that the seaward area of the island, bordering
on deep Exuma Sound, had a relatively large undisturbed population (Colin 1992 ) .
A number of specifi c individuals at this location were regularly surveyed, each fi sh
identifi able by individual variations in the markings on the body. Most individuals
moved over several hundred m
2 and many had overlapping home ranges with a
social hierarchy. When a dominant fi sh encountered a smaller conspecifi c the latter
would quickly adopt the “submissive” bicolour pattern seen among aggregated fi sh
as the two fi sh approached each other (Colin 1992 ) . Since Nassau grouper have no
external sex differences, it is impossible to ascribe a sex to the individuals observed.
During the spawning season the largest fi sh within the study area disappeared and
was not seen for 4 weeks. Another, smaller individual had apparently taken over as
the dominant individual during the absence of the larger fi sh and did not allow the
latter to regain its position. There ensued for several weeks a continuing struggle
between these two fi sh manifested by aggressive encounters whenever they met,
and both fi sh displayed tears and scars from their encounters (PLC, personal observation). Similar observations of change to a submissive colour pattern when transiting another Nassau’s territory were made off Little Cayman Island (SAH and Brice
Semmens, personal observation).
The relationship of spawning and larval development to the physical environment is detailed in Chaps. 5 and 7 . Pelagic eggs are produced in the aggregation and
after a pelagic larval (Chap. 7 , Fig. 7.5) period of about 41–43 days (range 37–45)
settlement occurs (Colin et al. 1997 ) . Most information on Nassau grouper larval
recruitment comes from Lee Stocking Island in The Bahamas during the period
1989–1991 (Colin et al. 1997 ; Shenker et al. 1993 ) . Colin et al. ( 1997 ) deployed
moored nets in a tidal channel in early 1989 and 1990 and successfully captured
numerous recruiting Nassau grouper on the new moons of February 1989 and 1990.
While Shenker et al. ( 1993 ) found an association of recruitment through tidal channels with a winter storm event, other years (Colin et al. 1997 ) did not demonstrate
the same relationship of atmospheric conditions with recruitment. Daily otolith
increments back-dated to full moon spawning in December and January, which is
consistent with the known aggregating season for the species in The Bahamas.
Recent satellite-based current drifter tracking in the Cayman Islands indicates that
not only are there eddies that form over the aggregation in the days immediately
after spawning that can potentially retain larvae close to where they are produced,
but that long-term patterns indicate a high likelihood of pre-settlement fi sh being
returned over the ~40 day pelagic larval duration (Fig. 12.10 ) (Heppell et al. 2008 ) .
This suggests that local spawning and its timing may be critical features associated
with the long-term sustainability of local populations.
The habitats into which newly settled Nassau grouper recruit have received some
attention, but because of the cryptic nature of small grouper recruits, it is risky to make
too many assumptions based solely on habitats that can be readily sampled for recruitment versus less accessible ones. Eggleston ( 1995 ) sampled habitats on the Bahama