47
2 Ecosystem Aspects of Species That Aggregate to Spawn
tropical fi sheries. Many aggregating fi shes include top carnivorous and numerous
herbivorous species with high commercial and ecological value, and may play an
important role in ecosystem function and fi sheries economics. The general concepts
behind EBM are to (1) maintain environmental quality and ecosystem productivity
while achieving long-term socioeconomic benefi ts, (2) minimize the effects of human
activities which may cause irreversible change to habitat structure, species assemblages and ecosystem processes, (3) gather information on key ecological components and processes that are relevant to maintaining ecosystem integrity and resilience,
and (4) adopt a precautionary approach to fi sheries management when data are limited that favour conservation and sustainability principles rather than maximizing
catch (Garcia et al. 2003 ; Pikitch et al. 2004 ; Appeldoorn 2008 ) . Each of these concepts is directly relevant to the management and maintenance of species which form
spawning aggregations and the aggregation sites utilized by these species.
Guidelines for EBM are meaningful for managing aggregating species so long as
the relevant spatial scales of management are identifi ed. EBM usually operates at
intermediate geographic scales of a few to 1,000’s of km
2 (Garcia et al. 2003 ) , which
encompasses most of the relevant biological processes and habitats used by aggregating species. The spatial parameters defi ned in Sect. 2.1 above may therefore provide an appropriate guide for EBM. In Fig. 2.3 the catchment area of a spawning
aggregation includes the home ranges of all mature adults spawning at a single site
but the trophic linkages associated with fi sh movements probably occur at smaller
spatial scales. The area and specifi c habitats occupied by the greater majority of the
spawning population defi ne the Functional Migration Area whereas the long-distance
migrants defi ne the catchment area. In some locations a species may have multiple
spawning aggregation sites and overlapping catchment areas whereas on small isolated islands they may have a single spawning aggregation site. In either case,
replenishment of the spawning population will come from a variable supply of larvae from self-recruitment and/or larvae spawned elsewhere. Since some species are
known to display strong site fi delity (Sadovy et al. 1992, 1994b ; Luckhurst 1998 ;
Zeller 1998 ) , persistence of an aggregation under heavy fi shing pressure may be
related to the relative proportion of larvae from upstream sources. To increase population resilience to fi shing and environmental change, EBM will need to take these
factors into consideration and be applied at spatial scales appropriate to aggregating
species and local geophysical constraints (i.e. island shelf areas).
Other management considerations include evaluating the role of aggregating
species in ecosystem stability, inclusion of shelf edge reefs, promontories of fringing reefs and reef pass channels in MPA design and analyzing the structure of food
webs and trophic linkages within functional migration areas to determine the reciprocal infl uence of aggregating species on ecosystem processes (Cury et al. 2003 ) .
Given the many gaps in ecological data of aggregating species, their vulnerability to
overfi shing and their possible inability to recover from extirpation, managers should
take a precautionary approach and carefully monitor, limit or prohibit fi shing on all
spawning aggregation sites to minimize the risk of stock collapse (Pikitch et al.
2004 ; Sadovy and Domeier 2005 ; Sadovy de Mitcheson et al. 2008 ) . FSA’s are
likely to be essential to the persistence of many fi sh populations and their maintenance important for managing sustainable fi sheries (Nemeth 2005 ) (Chap. 11 ).
2 Ecosystem Aspects of Species That Aggregate to Spawn
tropical fi sheries. Many aggregating fi shes include top carnivorous and numerous
herbivorous species with high commercial and ecological value, and may play an
important role in ecosystem function and fi sheries economics. The general concepts
behind EBM are to (1) maintain environmental quality and ecosystem productivity
while achieving long-term socioeconomic benefi ts, (2) minimize the effects of human
activities which may cause irreversible change to habitat structure, species assemblages and ecosystem processes, (3) gather information on key ecological components and processes that are relevant to maintaining ecosystem integrity and resilience,
and (4) adopt a precautionary approach to fi sheries management when data are limited that favour conservation and sustainability principles rather than maximizing
catch (Garcia et al. 2003 ; Pikitch et al. 2004 ; Appeldoorn 2008 ) . Each of these concepts is directly relevant to the management and maintenance of species which form
spawning aggregations and the aggregation sites utilized by these species.
Guidelines for EBM are meaningful for managing aggregating species so long as
the relevant spatial scales of management are identifi ed. EBM usually operates at
intermediate geographic scales of a few to 1,000’s of km
2 (Garcia et al. 2003 ) , which
encompasses most of the relevant biological processes and habitats used by aggregating species. The spatial parameters defi ned in Sect. 2.1 above may therefore provide an appropriate guide for EBM. In Fig. 2.3 the catchment area of a spawning
aggregation includes the home ranges of all mature adults spawning at a single site
but the trophic linkages associated with fi sh movements probably occur at smaller
spatial scales. The area and specifi c habitats occupied by the greater majority of the
spawning population defi ne the Functional Migration Area whereas the long-distance
migrants defi ne the catchment area. In some locations a species may have multiple
spawning aggregation sites and overlapping catchment areas whereas on small isolated islands they may have a single spawning aggregation site. In either case,
replenishment of the spawning population will come from a variable supply of larvae from self-recruitment and/or larvae spawned elsewhere. Since some species are
known to display strong site fi delity (Sadovy et al. 1992, 1994b ; Luckhurst 1998 ;
Zeller 1998 ) , persistence of an aggregation under heavy fi shing pressure may be
related to the relative proportion of larvae from upstream sources. To increase population resilience to fi shing and environmental change, EBM will need to take these
factors into consideration and be applied at spatial scales appropriate to aggregating
species and local geophysical constraints (i.e. island shelf areas).
Other management considerations include evaluating the role of aggregating
species in ecosystem stability, inclusion of shelf edge reefs, promontories of fringing reefs and reef pass channels in MPA design and analyzing the structure of food
webs and trophic linkages within functional migration areas to determine the reciprocal infl uence of aggregating species on ecosystem processes (Cury et al. 2003 ) .
Given the many gaps in ecological data of aggregating species, their vulnerability to
overfi shing and their possible inability to recover from extirpation, managers should
take a precautionary approach and carefully monitor, limit or prohibit fi shing on all
spawning aggregation sites to minimize the risk of stock collapse (Pikitch et al.
2004 ; Sadovy and Domeier 2005 ; Sadovy de Mitcheson et al. 2008 ) . FSA’s are
likely to be essential to the persistence of many fi sh populations and their maintenance important for managing sustainable fi sheries (Nemeth 2005 ) (Chap. 11 ).