570
Y. Sadovy de Mitcheson and P.L. Colin
consideration of economic and management implications, or can be misleading
when testing hypotheses on why when and where aggregations form. For example,
an area where sharks congregate to release their young may be vulnerable to fi shing,
and possibly in need of management, but would be an inappropriate location to test
hypotheses on why some bony fi shes (teleosts) release pelagic eggs in spawning
aggregations. Like any defi nition, however, there are challenges and few defi nitions
are perfect. For example, for species that live and also spawn in schools, such as
many jacks and trevallys (Carangidae) and the bumphead parrotfi sh ( Bolbometopon
muricatum ), how is the defi nition best applied to meet its objectives?
Defi nitions aid communication and understanding, and their careful crafting and
consistent application are important. Throughout this book we tried to clarify terms
referred to in various ways in the literature, e.g. ‘promontory’, ‘group’-spawning,
‘spawning aggregation’, etc. In the case of ‘aggregations’, for example, to verify that
a given grouping of fi sh is a spawning aggregation, we specify that one or more of
the following conditions must be met as direct indicators of spawning; (1) undisputed
spawning observations, (2) females found with hydrated eggs, or (3) presence of
post-ovulatory follicles in the ovaries of aggregating females. Indirect indicators are
also identifi ed in Chap. 1 . The suggestion that a ‘grouping’ represents a minimum
four-fold or more increase in numbers at a spawning site is somewhat arbitrary but
intended to distinguish it from background levels of abundance in the non-spawning
season. Most aggregating fi shes have considerably higher relative densities when
aggregated.
Two basic types of spawning aggregation, termed ‘resident’ (RA) and ‘transient’
(TA) appear to be useful concepts, distinguishing whether fi shes remain “within or
nearby” (resident) or “well outside” (transient) their home range during aggregation. However, as more species are studied in more detail, it appears that the scope
of aggregation type is likely to be more of a continuum, with clear distinctions at the
extremes but with no absolute dividing line between TA and RA. Examples include
the leopard coralgrouper, P. leopardus and the blackfi n snapper, Lutjanus fulvus (see
case studies for these species in Chap. 12.10 for details).
In attempting to understand the wider ecological role of aggregating species,
Rick Nemeth addresses the part they may play in ecosystem function in Chap. 2 . He
develops the concept of a ‘functional migration area’ that encompasses a mosaic of
habitats through which a species migrates, including the specifi c spatial components of catchment area, staging area, courtship arena, and inclusive of the spawning aggregation site. The fl ux in fi sh biomass and the energy transfer between
feeding grounds and spawning sites is a hitherto overlooked ecological and ecosystem
component of adult connectivity. Information on predator-prey dynamics indicates
that some fi shes feed during migration and at spawning sites, while certain piscivores
and egg predators feed on aggregated fi shes or their spawning products. Mapping
fi sh movements and documenting the physical and ecological components of
functional migration areas are important steps in the management of multi-species
tropical fi sheries and shallow marine ecosystems.
Phillip Molloy, Isabel Côté and John Reynolds take a broad behavioural ecology
perspective of aggregation-spawning in Chap. 3 in which they ponder the important
Y. Sadovy de Mitcheson and P.L. Colin
consideration of economic and management implications, or can be misleading
when testing hypotheses on why when and where aggregations form. For example,
an area where sharks congregate to release their young may be vulnerable to fi shing,
and possibly in need of management, but would be an inappropriate location to test
hypotheses on why some bony fi shes (teleosts) release pelagic eggs in spawning
aggregations. Like any defi nition, however, there are challenges and few defi nitions
are perfect. For example, for species that live and also spawn in schools, such as
many jacks and trevallys (Carangidae) and the bumphead parrotfi sh ( Bolbometopon
muricatum ), how is the defi nition best applied to meet its objectives?
Defi nitions aid communication and understanding, and their careful crafting and
consistent application are important. Throughout this book we tried to clarify terms
referred to in various ways in the literature, e.g. ‘promontory’, ‘group’-spawning,
‘spawning aggregation’, etc. In the case of ‘aggregations’, for example, to verify that
a given grouping of fi sh is a spawning aggregation, we specify that one or more of
the following conditions must be met as direct indicators of spawning; (1) undisputed
spawning observations, (2) females found with hydrated eggs, or (3) presence of
post-ovulatory follicles in the ovaries of aggregating females. Indirect indicators are
also identifi ed in Chap. 1 . The suggestion that a ‘grouping’ represents a minimum
four-fold or more increase in numbers at a spawning site is somewhat arbitrary but
intended to distinguish it from background levels of abundance in the non-spawning
season. Most aggregating fi shes have considerably higher relative densities when
aggregated.
Two basic types of spawning aggregation, termed ‘resident’ (RA) and ‘transient’
(TA) appear to be useful concepts, distinguishing whether fi shes remain “within or
nearby” (resident) or “well outside” (transient) their home range during aggregation. However, as more species are studied in more detail, it appears that the scope
of aggregation type is likely to be more of a continuum, with clear distinctions at the
extremes but with no absolute dividing line between TA and RA. Examples include
the leopard coralgrouper, P. leopardus and the blackfi n snapper, Lutjanus fulvus (see
case studies for these species in Chap. 12.10 for details).
In attempting to understand the wider ecological role of aggregating species,
Rick Nemeth addresses the part they may play in ecosystem function in Chap. 2 . He
develops the concept of a ‘functional migration area’ that encompasses a mosaic of
habitats through which a species migrates, including the specifi c spatial components of catchment area, staging area, courtship arena, and inclusive of the spawning aggregation site. The fl ux in fi sh biomass and the energy transfer between
feeding grounds and spawning sites is a hitherto overlooked ecological and ecosystem
component of adult connectivity. Information on predator-prey dynamics indicates
that some fi shes feed during migration and at spawning sites, while certain piscivores
and egg predators feed on aggregated fi shes or their spawning products. Mapping
fi sh movements and documenting the physical and ecological components of
functional migration areas are important steps in the management of multi-species
tropical fi sheries and shallow marine ecosystems.
Phillip Molloy, Isabel Côté and John Reynolds take a broad behavioural ecology
perspective of aggregation-spawning in Chap. 3 in which they ponder the important