5
1 Revisiting Spawning Aggregations: Defi nitions and Challenges
is actually a list of species that were believed or observed to spawn at the same
aggregation site as the aggregating leopard coralgrouper, Plectropomus leopardus .
However, many of these species had never been documented to form a spawning
aggregation (Melita Samoilys personal communication). The unfortunate use of
this informal list from the GBRMPA report has erroneously perpetuated a large
number of species as examples of aggregate spawners. If these species, and those
from another anecdotal source (Johannes 1981 ) , are removed from Claydon’s
review, approximately two thirds of the species now drop off his list of species
that aggregate to spawn. This is an important example of why great care need be
taken when discussing and identifying species that aggregate to spawn and why the
primary literature needs to be referred to and evaluated in such cases.
The defi nition of a spawning aggregation proposed in this chapter is more
restrictive than Claydon’s ( 2004 ) defi nition and clarifi es the original intent of
Domeier and Colin ( 1997 ) ; however, the substitution of the word ‘animal’ for ‘fi sh’
is much less restrictive than previous defi nitions and allows the consideration of
additional phyla. When considering new phyla, the word ‘spawn’ may appear too
restrictive since it is generally used to describe the release of eggs and sperm or a
large number of offspring; this would exclude mating/breeding aggregations that
may only involve copulation. From strictly a management perspective, a periodic,
predictable mass gathering of economically valuable marine organisms presents
similar challenges, regardless of the function of the aggregation, but it is the mass
gathering of adults, release and subsequent dispersal of large numbers of offspring
that make this phenomenon biologically unique and distinct from other types of
aggregations. The selection of a unique spawning site, or time, that ensures a relatively high recruitment success for the offspring may be the single most important
driving force behind the evolution of the phenomenon (although there are many
competing hypotheses, Chaps. 4 , 6 , and 7 ). Aggregations that occur solely for the
purpose of copulating in the absence of releasing offspring (e.g. elasmobranchs)
are therefore not considered spawning aggregations in this defi nition, but singlesex gatherings for the purpose of releasing offspring (e.g. female decapods) are
considered spawning aggregations since they meet all criteria (Fig. 1.2a ).
Nonetheless, from a management perspective, some non-spawning gatherings may
also require action because the concentration of adults may attract excessive fi shing pressure, as in the case of nurse shark, Ginglymostoma cirratum (Pratt and
Carrier 2001 ) .
Fisheries management plans are beginning to focus on spawning aggregations
and MPA planning is beginning to incorporate them. This fact underscores the
importance of creating a defi nition that both adequately describes a unique biological
phenomenon, while also strengthening the phrase “spawning aggregation” from a
fi sheries perspective. A less restrictive defi nition fails to distinguish a phenomenon
where a species is particularly vulnerable to intense fi shing pressure from other
general gathering behaviours, thereby losing its value in fi sheries discussions while
relinquishing its power to examine the proximal and ultimate factors that might be
involved in its evolution.
1 Revisiting Spawning Aggregations: Defi nitions and Challenges
is actually a list of species that were believed or observed to spawn at the same
aggregation site as the aggregating leopard coralgrouper, Plectropomus leopardus .
However, many of these species had never been documented to form a spawning
aggregation (Melita Samoilys personal communication). The unfortunate use of
this informal list from the GBRMPA report has erroneously perpetuated a large
number of species as examples of aggregate spawners. If these species, and those
from another anecdotal source (Johannes 1981 ) , are removed from Claydon’s
review, approximately two thirds of the species now drop off his list of species
that aggregate to spawn. This is an important example of why great care need be
taken when discussing and identifying species that aggregate to spawn and why the
primary literature needs to be referred to and evaluated in such cases.
The defi nition of a spawning aggregation proposed in this chapter is more
restrictive than Claydon’s ( 2004 ) defi nition and clarifi es the original intent of
Domeier and Colin ( 1997 ) ; however, the substitution of the word ‘animal’ for ‘fi sh’
is much less restrictive than previous defi nitions and allows the consideration of
additional phyla. When considering new phyla, the word ‘spawn’ may appear too
restrictive since it is generally used to describe the release of eggs and sperm or a
large number of offspring; this would exclude mating/breeding aggregations that
may only involve copulation. From strictly a management perspective, a periodic,
predictable mass gathering of economically valuable marine organisms presents
similar challenges, regardless of the function of the aggregation, but it is the mass
gathering of adults, release and subsequent dispersal of large numbers of offspring
that make this phenomenon biologically unique and distinct from other types of
aggregations. The selection of a unique spawning site, or time, that ensures a relatively high recruitment success for the offspring may be the single most important
driving force behind the evolution of the phenomenon (although there are many
competing hypotheses, Chaps. 4 , 6 , and 7 ). Aggregations that occur solely for the
purpose of copulating in the absence of releasing offspring (e.g. elasmobranchs)
are therefore not considered spawning aggregations in this defi nition, but singlesex gatherings for the purpose of releasing offspring (e.g. female decapods) are
considered spawning aggregations since they meet all criteria (Fig. 1.2a ).
Nonetheless, from a management perspective, some non-spawning gatherings may
also require action because the concentration of adults may attract excessive fi shing pressure, as in the case of nurse shark, Ginglymostoma cirratum (Pratt and
Carrier 2001 ) .
Fisheries management plans are beginning to focus on spawning aggregations
and MPA planning is beginning to incorporate them. This fact underscores the
importance of creating a defi nition that both adequately describes a unique biological
phenomenon, while also strengthening the phrase “spawning aggregation” from a
fi sheries perspective. A less restrictive defi nition fails to distinguish a phenomenon
where a species is particularly vulnerable to intense fi shing pressure from other
general gathering behaviours, thereby losing its value in fi sheries discussions while
relinquishing its power to examine the proximal and ultimate factors that might be
involved in its evolution.