267
8 Fishery and Biological Implications of Fishing Spawning Aggregations…
At the national level, examples of fi sher responses to aggregation protection are
instructive. In the Gulf of Mexico, USA, fi shers for gag grouper, in response to
protection from fi shing during its peak aggregation month, changed their behaviour
and intensifi ed activity prior to and after protection; note that, initially, only one
spawning month was protected with all spawning months protected subsequently.
Economic analyses show that gag aggregation protection did not result in reduced
fi shing pressure on the target stock, or in increases in biomass, probably because of
this behaviour (Smith et al. 2008 ) . In other words, fi sher response was so marked
that it evidently offset the biological benefi ts from the temporary fi shing restriction.
The study indicates that seasonal restrictions cannot necessarily operate alone to
reduce fi shing pressure in an open-access fi shery and highlights the importance of
factoring in fi sher behaviour and economics to biological models for management.
In Pohnpei, during the closed season for grouper aggregations, the pressure on other
reef fi shes increased, in particular for parrotfi shes (Scaridae), goatfi shes and emperors, (Lethrinidae), to maintain overall sales (Rhodes and Tupper 2007 ; Rhodes et al.
2008 ) . Loss of Nassau grouper stocks in the USVI and elsewhere due to lack of
management and overfi shing in the late 1970s led to fi shers targeting smaller, less
frequently marketed, groupers (e.g. Munro and Blok 2005 ; Karras and Agar 2009 ) .
8.5.2 Costs and Benefi ts of Aggregation
vs. Non-aggregation Fishing
Large and predictable fi sh gatherings are an obvious target for fi shing, but long-term
sustainability in the absence of suffi cient controls may only apply for subsistence,
or occasional cultural, uses. When commercial pressures come into play, without
effective management (Sect. 8.5.1 ) this activity is considerably less appealing as a
long-term good use of natural resources. A summary of the costs and benefi ts of
aggregation exploitation versus total protection, highlights areas where further analyses are warranted to determine best overall and long-term monetary value from
aggregating species (Table 8.2 ). The middle ground of managed aggregation fi shing
is also a possibility, with elements of both benefi ts and costs from the more extreme
examples presented (see also Chap. 11 ).
While aggregation closures may greatly benefi t stocks, associated costs and other
implications can have serious detrimental effects on communities that may depend
signifi cantly on aggregations for their livelihood, and all possible management
options should be considered. For example, the Colorado River Delta region located
in the northernmost section of the Gulf of California is one of the most productive
fi shery regions in Mexico. A major source of this productivity is the seasonal occurrence of several commercially important fi shes such as Gulf corvina, totoaba, Gulf
croaker, Micropogonias megalops , sierra mackerel, Scomberomorus sierra , and
several species of sharks and rays that migrate there to feed on sardines and shrimp
and to spawn within massive aggregations (Cudney and Turk 1998 ; RodriguezQuiroz 2010 ) . The local communities that surround the Delta rely on these seasonally plentiful resources as their main source of revenue, and the closure of their
8 Fishery and Biological Implications of Fishing Spawning Aggregations…
At the national level, examples of fi sher responses to aggregation protection are
instructive. In the Gulf of Mexico, USA, fi shers for gag grouper, in response to
protection from fi shing during its peak aggregation month, changed their behaviour
and intensifi ed activity prior to and after protection; note that, initially, only one
spawning month was protected with all spawning months protected subsequently.
Economic analyses show that gag aggregation protection did not result in reduced
fi shing pressure on the target stock, or in increases in biomass, probably because of
this behaviour (Smith et al. 2008 ) . In other words, fi sher response was so marked
that it evidently offset the biological benefi ts from the temporary fi shing restriction.
The study indicates that seasonal restrictions cannot necessarily operate alone to
reduce fi shing pressure in an open-access fi shery and highlights the importance of
factoring in fi sher behaviour and economics to biological models for management.
In Pohnpei, during the closed season for grouper aggregations, the pressure on other
reef fi shes increased, in particular for parrotfi shes (Scaridae), goatfi shes and emperors, (Lethrinidae), to maintain overall sales (Rhodes and Tupper 2007 ; Rhodes et al.
2008 ) . Loss of Nassau grouper stocks in the USVI and elsewhere due to lack of
management and overfi shing in the late 1970s led to fi shers targeting smaller, less
frequently marketed, groupers (e.g. Munro and Blok 2005 ; Karras and Agar 2009 ) .
8.5.2 Costs and Benefi ts of Aggregation
vs. Non-aggregation Fishing
Large and predictable fi sh gatherings are an obvious target for fi shing, but long-term
sustainability in the absence of suffi cient controls may only apply for subsistence,
or occasional cultural, uses. When commercial pressures come into play, without
effective management (Sect. 8.5.1 ) this activity is considerably less appealing as a
long-term good use of natural resources. A summary of the costs and benefi ts of
aggregation exploitation versus total protection, highlights areas where further analyses are warranted to determine best overall and long-term monetary value from
aggregating species (Table 8.2 ). The middle ground of managed aggregation fi shing
is also a possibility, with elements of both benefi ts and costs from the more extreme
examples presented (see also Chap. 11 ).
While aggregation closures may greatly benefi t stocks, associated costs and other
implications can have serious detrimental effects on communities that may depend
signifi cantly on aggregations for their livelihood, and all possible management
options should be considered. For example, the Colorado River Delta region located
in the northernmost section of the Gulf of California is one of the most productive
fi shery regions in Mexico. A major source of this productivity is the seasonal occurrence of several commercially important fi shes such as Gulf corvina, totoaba, Gulf
croaker, Micropogonias megalops , sierra mackerel, Scomberomorus sierra , and
several species of sharks and rays that migrate there to feed on sardines and shrimp
and to spawn within massive aggregations (Cudney and Turk 1998 ; RodriguezQuiroz 2010 ) . The local communities that surround the Delta rely on these seasonally plentiful resources as their main source of revenue, and the closure of their