507
12 Species Case Studies
For some of the larger parrotfi shes, such as bicolor parrotfi sh, it seems unlikely
they have group-spawning, as they are usually not common on the reef and pairspawning is well known, while no indications (courtship, etc.) of group-spawning
have been seen. Other larger scarids, such as bumphead parrotfi sh appear to spawn
as pairs (and potentially small groups) out of schools which may or may not be true
spawning aggregations (Chap. 1 ).
12.17.4 Conservation and Fisheries Importance
These fi shes are not always thought of as commercially important, but in areas where
reef fi sh resources are highly exploited, they are a major part of the subsistence and
commercial catch. As such, aggregation sites potentially represent an area where
fi shes could be captured by fi sh trap, nets or spearfi shing in some abundance.
These fi shes are important for maintaining the health of coral reef systems, as
they and other herbivores can limit the growth of benthic algae which can threaten
coral populations, particularly during recovery phases after a bleaching event or
storm disturbance. In areas where herbivores have been overharvested, algae quickly
take over much of the rocky bottom where they were previously held in check. They
are also important ecologically in that they convert a large amount of primary and
secondary production into pelagic gametes that are exported from the reef (Hamner
et al. 2007 ) .
12.18 Bigeye Trevally – Caranx sexfasciatus with Notes
on Other Jacks (Carangidae)
Patrick L. Colin
Coral Reef Research Foundation, PO Box 1765 , Koror , Palau 96940
e-mail: crrf@palaunet.com
12.18.1 General
The bigeye trevally, Caranx sexfasciatus Quoy and Gaimard, is a common, mediumsized carangid reaching about 85 cm fork length (FL) found on outer reefs from the
Red Sea to Central America. It often occurs in schools of many hundreds to thousands of individuals swimming in tight whorls which produce amazing images for
underwater photographers (Fig. 12.49 ). The schools might seem to represent spawning aggregations, however, this appears not to be the case, and this case study illustrates the diffi culties in deciding what is and isn’t a spawning aggregation.
12 Species Case Studies
For some of the larger parrotfi shes, such as bicolor parrotfi sh, it seems unlikely
they have group-spawning, as they are usually not common on the reef and pairspawning is well known, while no indications (courtship, etc.) of group-spawning
have been seen. Other larger scarids, such as bumphead parrotfi sh appear to spawn
as pairs (and potentially small groups) out of schools which may or may not be true
spawning aggregations (Chap. 1 ).
12.17.4 Conservation and Fisheries Importance
These fi shes are not always thought of as commercially important, but in areas where
reef fi sh resources are highly exploited, they are a major part of the subsistence and
commercial catch. As such, aggregation sites potentially represent an area where
fi shes could be captured by fi sh trap, nets or spearfi shing in some abundance.
These fi shes are important for maintaining the health of coral reef systems, as
they and other herbivores can limit the growth of benthic algae which can threaten
coral populations, particularly during recovery phases after a bleaching event or
storm disturbance. In areas where herbivores have been overharvested, algae quickly
take over much of the rocky bottom where they were previously held in check. They
are also important ecologically in that they convert a large amount of primary and
secondary production into pelagic gametes that are exported from the reef (Hamner
et al. 2007 ) .
12.18 Bigeye Trevally – Caranx sexfasciatus with Notes
on Other Jacks (Carangidae)
Patrick L. Colin
Coral Reef Research Foundation, PO Box 1765 , Koror , Palau 96940
e-mail: crrf@palaunet.com
12.18.1 General
The bigeye trevally, Caranx sexfasciatus Quoy and Gaimard, is a common, mediumsized carangid reaching about 85 cm fork length (FL) found on outer reefs from the
Red Sea to Central America. It often occurs in schools of many hundreds to thousands of individuals swimming in tight whorls which produce amazing images for
underwater photographers (Fig. 12.49 ). The schools might seem to represent spawning aggregations, however, this appears not to be the case, and this case study illustrates the diffi culties in deciding what is and isn’t a spawning aggregation.