520
12 Species Case Studies
not include details regarding gonad indices, size frequency, and population density,
which are now included here. Colin ( 1996 ) reported on the occurrence of these
aggregations 12 years after their original discovery and described a small aggregation of blue tang in The Bahamas which disappeared shortly after its discovery. In
2011 the site was visited again and while fi shes were still aggregating and spawning
in the same general area, numbers were less than previously.
Location of aggregations: The aggregations occurred in a discrete area of the outer
reef along the SW Puerto Rican shelf edge. The reef was mapped in some detail
using the tape and compass method (see Chap. 9 ) and the locations of the aggregations plotted on this base map (Fig. 12.57 ). The site was revisited in 1988 (Colin
1996 ) and again in 2011. While their locations did not appear to have shifted
between the 1970s and 1988, in 2011 both aggregations were found to have moved
slightly further east (but less than 50 m distance) and a bit more towards the drop off
edge. The consistency of these aggregation locations over 34 years is indicative of
the stability of sites for a surgeonfi sh with resident aggregation.
The aggregation site and sizes of fi sh aggregating : The locations of the aggregation
site in Puerto Rico are shown in Fig. 12.57 . In the late 1970s the aggregation areas
for ocean surgeonfi sh and blue tang overlapped, the smaller blue tang site lying
totally inside the area used by A. bahianus . Currents at the site were mild and did
not have any particular correlation with spawning occurrence. All aggregations of
ocean surgeonfi sh and the largest aggregations of blue tang occurred during the
coldest portion of the year, when water temperatures are about 24–25.5°C. The
water is clearer during the northern winter period also, with visibilities occasionally
of 30 m, but generally 20–25 m. The aggregations sites utilized by the Puerto Rico
surgeonfi shes remained exactly the same for at least 12 years (Colin 1996 ) and varied only slightly over 34 years.
Fishes from the spawning aggregations were speared and data on standard
length, sex and gonad weight were taken. Ocean surgeonfi sh females from the
Puerto Rico aggregation ranged in size from 115 to 150 mm standard length (SL),
while males were 115–205 mm SL (Fig. 12.58 ). There was a signifi cant size
difference in males and females from the aggregation at the p < 0.05 level. Blue
tang from the aggregation ranged in size from 105 to 180 mm SL for females and
110 to 180 mm SL for males. There was no difference in size of males and females
for blue tang.
Seasonal, lunar and daily spawning and migration patterns: Data were obtained on
the presence/absence and, if present, the size of the aggregation and whether spawning was occurring for both species on 139 days during the main spawning season
(December to March), as well as on an additional 40 days in the “off season” of
April to November. Observations were much more diffi cult during the latter period
as the water is much less clear (visibility as little as 9–12 m) making fi nding the
aggregation and observing spawning diffi cult.
During the main spawning period (December to March) the ocean surgeonfi sh
was aggregated and spawning at all lunar phases (Figs. 12.59 and 12.60 ) with low
12 Species Case Studies
not include details regarding gonad indices, size frequency, and population density,
which are now included here. Colin ( 1996 ) reported on the occurrence of these
aggregations 12 years after their original discovery and described a small aggregation of blue tang in The Bahamas which disappeared shortly after its discovery. In
2011 the site was visited again and while fi shes were still aggregating and spawning
in the same general area, numbers were less than previously.
Location of aggregations: The aggregations occurred in a discrete area of the outer
reef along the SW Puerto Rican shelf edge. The reef was mapped in some detail
using the tape and compass method (see Chap. 9 ) and the locations of the aggregations plotted on this base map (Fig. 12.57 ). The site was revisited in 1988 (Colin
1996 ) and again in 2011. While their locations did not appear to have shifted
between the 1970s and 1988, in 2011 both aggregations were found to have moved
slightly further east (but less than 50 m distance) and a bit more towards the drop off
edge. The consistency of these aggregation locations over 34 years is indicative of
the stability of sites for a surgeonfi sh with resident aggregation.
The aggregation site and sizes of fi sh aggregating : The locations of the aggregation
site in Puerto Rico are shown in Fig. 12.57 . In the late 1970s the aggregation areas
for ocean surgeonfi sh and blue tang overlapped, the smaller blue tang site lying
totally inside the area used by A. bahianus . Currents at the site were mild and did
not have any particular correlation with spawning occurrence. All aggregations of
ocean surgeonfi sh and the largest aggregations of blue tang occurred during the
coldest portion of the year, when water temperatures are about 24–25.5°C. The
water is clearer during the northern winter period also, with visibilities occasionally
of 30 m, but generally 20–25 m. The aggregations sites utilized by the Puerto Rico
surgeonfi shes remained exactly the same for at least 12 years (Colin 1996 ) and varied only slightly over 34 years.
Fishes from the spawning aggregations were speared and data on standard
length, sex and gonad weight were taken. Ocean surgeonfi sh females from the
Puerto Rico aggregation ranged in size from 115 to 150 mm standard length (SL),
while males were 115–205 mm SL (Fig. 12.58 ). There was a signifi cant size
difference in males and females from the aggregation at the p < 0.05 level. Blue
tang from the aggregation ranged in size from 105 to 180 mm SL for females and
110 to 180 mm SL for males. There was no difference in size of males and females
for blue tang.
Seasonal, lunar and daily spawning and migration patterns: Data were obtained on
the presence/absence and, if present, the size of the aggregation and whether spawning was occurring for both species on 139 days during the main spawning season
(December to March), as well as on an additional 40 days in the “off season” of
April to November. Observations were much more diffi cult during the latter period
as the water is much less clear (visibility as little as 9–12 m) making fi nding the
aggregation and observing spawning diffi cult.
During the main spawning period (December to March) the ocean surgeonfi sh
was aggregated and spawning at all lunar phases (Figs. 12.59 and 12.60 ) with low