263
8 Fishery and Biological Implications of Fishing Spawning Aggregations…
which fi shes may be stressed in exploited or disturbed spawning aggregations is
not known.
Reductions in aggregation numbers could affect social cues that stimulate short or
long-term changes in reproductive condition or are otherwise associated with mating. In many aggregating species, males show temporary courtship colour changes
(Colin et al. 2003 ) . In some groupers, courtship activity and colour pattern changes
associated with spawning are less intense (qualitative observations include less activity by males in female pursuit and less frequent courtship) at sites with smaller,
dispersed aggregations when compared to sites with large, dense aggregations
(Nassau grouper Colin 1992 , leopard grouper Erisman et al. 2007 ) . Several groupers
and the Atlantic cod form dominance hierarchies with male defence of breeding territories (e.g. scamp and gag grouper Gilmore and Jones 1992 , tiger grouper Sadovy
et al. 1994a, b , Atlantic cod Hutchings et al. 1999 ) . Removal of fi sh during aggregation and breeding periods could affect these hierarchies, with unknown impacts on
reproductive output. Since ovulation periods of aggregating species are often highly
synchronized to coincide with short courtship and spawning periods, delayed or
disrupted courtship could potentially cause eggs to over-ripen, thereby reducing egg
viability or developmental success of eggs and larvae (Rowe and Hutchings 2003 ) .
The possible importance of aggregations for social cues in relation to sex change was
addressed in Sect. 8.4 .
One of the few specifi c examples of clear evidence that fi shing on spawning
aggregations can directly and negatively impact reproductive potential comes from
the Atlantic cod (Rose et al. 2008 ) . A spawning ground in Bar Haven, Placentia
Bay, Newfoundland, was opened in 1997 and from 1998 to 2000 was heavily fi shed
at spawning time. Between 33% and 40% of the total annual catch came from this
area followed by a stock decline and less recovery in spawning biomass than predicted by fi shery models. The data from the resulting model suggest not only that
there was weak compensation in survival at low stock size, but that the mortality
rate of the Bar Haven spawning fi sh was considerably higher than that in the general
population, and that a decline in egg production and then recruitment were the
results of aggregation-fi shing.
Some aggregating species show high site fi delity, whereby fi sh return each year
to spawn at the same sites; disruption of factors enabling such returns could potentially infl uence reproduction. Aggregations can persist at the same sites for many
years, even decades, suggesting a degree of traditionality (Colin 1996 ; Domeier and
Colin 1997 ) . Examples of site fi delity across years exist for a range of species
( Epinephelus alexandrinus = Mycteroperca fusca Waschkewitz and Wirtz 1990 ,
groupers and wrasses Domeier and Colin 1997 , Nassau grouper Starr et al. 2007 ,
European plaice Hunter et al. 2003 , camoufl age grouper Rhodes and Tupper 2008 ) .
There is also good evidence in several species that social learning and tradition play
a role in the repeated formation of aggregations at specifi c sites, and that younger
fi sh learn to use and fi nd sites from older, experienced fi sh (bluehead wrasse Warner
1988, 1990 , Atlantic cod Rose 1993 , European plaice Arnold and Metcalfe 1995 ,
brown surgeonfi sh Acanthurus nigrofuscus Mazeroll and Montgomery 1998 ) .
Indeed, the learning component of fi sh migratory behaviour may be particularly
8 Fishery and Biological Implications of Fishing Spawning Aggregations…
which fi shes may be stressed in exploited or disturbed spawning aggregations is
not known.
Reductions in aggregation numbers could affect social cues that stimulate short or
long-term changes in reproductive condition or are otherwise associated with mating. In many aggregating species, males show temporary courtship colour changes
(Colin et al. 2003 ) . In some groupers, courtship activity and colour pattern changes
associated with spawning are less intense (qualitative observations include less activity by males in female pursuit and less frequent courtship) at sites with smaller,
dispersed aggregations when compared to sites with large, dense aggregations
(Nassau grouper Colin 1992 , leopard grouper Erisman et al. 2007 ) . Several groupers
and the Atlantic cod form dominance hierarchies with male defence of breeding territories (e.g. scamp and gag grouper Gilmore and Jones 1992 , tiger grouper Sadovy
et al. 1994a, b , Atlantic cod Hutchings et al. 1999 ) . Removal of fi sh during aggregation and breeding periods could affect these hierarchies, with unknown impacts on
reproductive output. Since ovulation periods of aggregating species are often highly
synchronized to coincide with short courtship and spawning periods, delayed or
disrupted courtship could potentially cause eggs to over-ripen, thereby reducing egg
viability or developmental success of eggs and larvae (Rowe and Hutchings 2003 ) .
The possible importance of aggregations for social cues in relation to sex change was
addressed in Sect. 8.4 .
One of the few specifi c examples of clear evidence that fi shing on spawning
aggregations can directly and negatively impact reproductive potential comes from
the Atlantic cod (Rose et al. 2008 ) . A spawning ground in Bar Haven, Placentia
Bay, Newfoundland, was opened in 1997 and from 1998 to 2000 was heavily fi shed
at spawning time. Between 33% and 40% of the total annual catch came from this
area followed by a stock decline and less recovery in spawning biomass than predicted by fi shery models. The data from the resulting model suggest not only that
there was weak compensation in survival at low stock size, but that the mortality
rate of the Bar Haven spawning fi sh was considerably higher than that in the general
population, and that a decline in egg production and then recruitment were the
results of aggregation-fi shing.
Some aggregating species show high site fi delity, whereby fi sh return each year
to spawn at the same sites; disruption of factors enabling such returns could potentially infl uence reproduction. Aggregations can persist at the same sites for many
years, even decades, suggesting a degree of traditionality (Colin 1996 ; Domeier and
Colin 1997 ) . Examples of site fi delity across years exist for a range of species
( Epinephelus alexandrinus = Mycteroperca fusca Waschkewitz and Wirtz 1990 ,
groupers and wrasses Domeier and Colin 1997 , Nassau grouper Starr et al. 2007 ,
European plaice Hunter et al. 2003 , camoufl age grouper Rhodes and Tupper 2008 ) .
There is also good evidence in several species that social learning and tradition play
a role in the repeated formation of aggregations at specifi c sites, and that younger
fi sh learn to use and fi nd sites from older, experienced fi sh (bluehead wrasse Warner
1988, 1990 , Atlantic cod Rose 1993 , European plaice Arnold and Metcalfe 1995 ,
brown surgeonfi sh Acanthurus nigrofuscus Mazeroll and Montgomery 1998 ) .
Indeed, the learning component of fi sh migratory behaviour may be particularly