8
M.L. Domeier
days, (2) last only a few hours or less, (3) occur daily over an often lengthy reproductive
period of the year, and (4) can occur year round. A single day of spawning for an
individual participating in a resident spawning aggregation represents a small
fraction of that individual’s annual reproductive effort.
Transient spawning aggregations draw individuals to a site well outside their
typical adult home range. Transient spawning aggregations often (1) occur during
a very specifi c portion of one or two months of the year; (2) persist for a period of
days or at most a few weeks and (3) do not occur year round. A single transient
spawning aggregation may represent the total reproductive effort for participating
individuals.
The difference between Resident and Transient spawning aggregations is more
than just a matter of scale, there are important functional differences that can be
indirectly observed but not easily described. Indirect measures of these functional
differences include the fact that species that form these different types of spawning
aggregations split fairly well along phylogenetic lines (Appendix, Chap. 4 ).
Furthermore, species that form Transient aggregations are typically large and predatory while those that form Resident aggregations are generally smaller herbivores,
planktivores or omnivores (exceptions do exist; e.g. humphead wrasse, Cheilinus
undulatus ). However, like any defi nition, these will not necessarily capture every
situation and there are species that appear to fall between the two (i.e. leopard
coralgrouper) – this is the nature of many defi nitions and as we learn more about
aggregating species refi nements may be introduced.
The general dichotomy between resident and transient spawning aggregations
has clear management implications. For example, on the Great Barrier Reef,
Australia, the leopard coralgrouper forms seasonal semi-resident (transient on a
home reef, but fi sh do not seem to move between reefs) spawning aggregations
(unusual for a grouper-Serranidae) and is the basis of an important fi shery. In
Australia, where one third of the GBR is protected from fi shing, the (untested)
assumption is that each reef contains resident spawning aggregations, and, therefore
that protecting one third of the reef theoretically could protect 1/3 of the aggregations (Martin Russell personal communication). This could not be assumed for a
transient spawner, since the catchment area for a single transient spawning aggregation can involve many surrounding reefs. To effectively protect a transient aggregation, an MPA would have to be very large or extremely well-placed. It is very
likely that MPAs in the absence of region-wide seasonal closures will not adequately
protect transient spawning aggregations. This is just one illustration of how such
defi nitions can have practical value.
Schooling fi shes are known to join conspecifi c schools at predictable sites and
times to form both transient (e.g. jacks-Carangidae, mackerels/tuna-Scombridae,
croakers-Sciaenidae) and resident (e.g. wrasses-Labridae, parrotfi sh-Scaridae)
spawning aggregations. The movement of a single school of animals to a specifi c
site to spawn falls under the defi nition of Simple Migratory Spawning (Domeier
and Colin 1997 ) . Although this phenomenon does not fall under the defi nition of a
spawning aggregation, due to the absence of a signifi cant density increase, if the
M.L. Domeier
days, (2) last only a few hours or less, (3) occur daily over an often lengthy reproductive
period of the year, and (4) can occur year round. A single day of spawning for an
individual participating in a resident spawning aggregation represents a small
fraction of that individual’s annual reproductive effort.
Transient spawning aggregations draw individuals to a site well outside their
typical adult home range. Transient spawning aggregations often (1) occur during
a very specifi c portion of one or two months of the year; (2) persist for a period of
days or at most a few weeks and (3) do not occur year round. A single transient
spawning aggregation may represent the total reproductive effort for participating
individuals.
The difference between Resident and Transient spawning aggregations is more
than just a matter of scale, there are important functional differences that can be
indirectly observed but not easily described. Indirect measures of these functional
differences include the fact that species that form these different types of spawning
aggregations split fairly well along phylogenetic lines (Appendix, Chap. 4 ).
Furthermore, species that form Transient aggregations are typically large and predatory while those that form Resident aggregations are generally smaller herbivores,
planktivores or omnivores (exceptions do exist; e.g. humphead wrasse, Cheilinus
undulatus ). However, like any defi nition, these will not necessarily capture every
situation and there are species that appear to fall between the two (i.e. leopard
coralgrouper) – this is the nature of many defi nitions and as we learn more about
aggregating species refi nements may be introduced.
The general dichotomy between resident and transient spawning aggregations
has clear management implications. For example, on the Great Barrier Reef,
Australia, the leopard coralgrouper forms seasonal semi-resident (transient on a
home reef, but fi sh do not seem to move between reefs) spawning aggregations
(unusual for a grouper-Serranidae) and is the basis of an important fi shery. In
Australia, where one third of the GBR is protected from fi shing, the (untested)
assumption is that each reef contains resident spawning aggregations, and, therefore
that protecting one third of the reef theoretically could protect 1/3 of the aggregations (Martin Russell personal communication). This could not be assumed for a
transient spawner, since the catchment area for a single transient spawning aggregation can involve many surrounding reefs. To effectively protect a transient aggregation, an MPA would have to be very large or extremely well-placed. It is very
likely that MPAs in the absence of region-wide seasonal closures will not adequately
protect transient spawning aggregations. This is just one illustration of how such
defi nitions can have practical value.
Schooling fi shes are known to join conspecifi c schools at predictable sites and
times to form both transient (e.g. jacks-Carangidae, mackerels/tuna-Scombridae,
croakers-Sciaenidae) and resident (e.g. wrasses-Labridae, parrotfi sh-Scaridae)
spawning aggregations. The movement of a single school of animals to a specifi c
site to spawn falls under the defi nition of Simple Migratory Spawning (Domeier
and Colin 1997 ) . Although this phenomenon does not fall under the defi nition of a
spawning aggregation, due to the absence of a signifi cant density increase, if the