151
5 Timing and Location of Aggregation and Spawning in Reef Fishes
5.8.7 The Spawning Stupor
The prime, and oft-cited, example of a “spawning stupor” is from the observation
that schooling mullets were easily dip-netted at night from the side of a ship tied
to a dock while numerous bright lights were directed at the water, while sharks
were also attacking the group (Helfrich and Allen 1975 ) . Johannes ( 1978 ) was
present at this site and dip-netted numbers of large fringelip mullet ( Crenimugil
crenilabris ), normally a diffi cult fi sh to approach, from what he considered a
spawning aggregation without signifi cantly disturbing the remaining fi sh. Black
tip reef sharks were reported to be feeding on the mullet also, the prey fish
making “only sluggish and ineffectual efforts to avoid” the sharks. It was
believed the fi sh were in a stupor-like condition allowing spawning (the fi sh
were ripe, but not actually spawning?) to proceed without interruption despite
the dangers from predators. However, “night lighting” is a common technique
used to dazzle and attract fi shes to a boat so they can easily be netted and the
infl uence of the bright lights and possibly other conditions present mean that
this should not be considered normal behaviour. Helfrich and Allen ( 1975 )
reported the shark attacks to occur early in their observations (after 20:30 h),
while spawning (at some distance from the vessel) was believed to occur only
after midnight, with no instances of shark predation noted during that probable
spawning event.
In support of spawning stupors, Johannes et al. ( 1999 ) cited the observation
by Robertson ( 1983 ) of a 1.3 m long carcharinid shark (not identifi ed) attacking
a single spawning pulse of several hundred brown surgeonfi sh at Lizard Island,
Australia. The outcome of the attack was uncertain, but probably unsuccessful
and did not disrupt the surgeonfi sh spawning. However, this can interpreted as
the spawning fi sh were suffi ciently aware during the attack that those individuals
close to the shark avoided being bitten, while the others continued spawning.
Several attacks on spawning brown surgeonfi sh in Palau failed to interrupt spawning behaviour for more than a few seconds (PLC unpublished data). In a fi nal
example Johannes et al. ( 1999 ) cited the fact that divers could swim among
spawning cubera snapper without disturbing them as indicative they were in a
stupor state. It is more reasonable to suppose that the fi sh were aware of events
around them but had no reason to fear or fl ee from divers, as divers regularly visit
these aggregations so fi sh become habituated to their non-threatening presence
(Heyman et al. 2001 , 2005 ).
There is no doubt the behaviour of many fi shes is altered when in spawning
aggregations, such as letting divers approach closer than normal (Hamilton 2005 ,
Kadison et al. 2007), but some reports have interpreted such changes as “spawning
stupors” (Burton et al. 2005 ; Gladstone 1996 ) . The existence of a “spawning stupor” which overwhelms all self-preservation behaviour, is at best an uncertain
(and in a sense unfortunate) concept, which like many appealing myths in biology
gains credence with each incorrect repetition, misapplication or misinterpretation.
5 Timing and Location of Aggregation and Spawning in Reef Fishes
5.8.7 The Spawning Stupor
The prime, and oft-cited, example of a “spawning stupor” is from the observation
that schooling mullets were easily dip-netted at night from the side of a ship tied
to a dock while numerous bright lights were directed at the water, while sharks
were also attacking the group (Helfrich and Allen 1975 ) . Johannes ( 1978 ) was
present at this site and dip-netted numbers of large fringelip mullet ( Crenimugil
crenilabris ), normally a diffi cult fi sh to approach, from what he considered a
spawning aggregation without signifi cantly disturbing the remaining fi sh. Black
tip reef sharks were reported to be feeding on the mullet also, the prey fish
making “only sluggish and ineffectual efforts to avoid” the sharks. It was
believed the fi sh were in a stupor-like condition allowing spawning (the fi sh
were ripe, but not actually spawning?) to proceed without interruption despite
the dangers from predators. However, “night lighting” is a common technique
used to dazzle and attract fi shes to a boat so they can easily be netted and the
infl uence of the bright lights and possibly other conditions present mean that
this should not be considered normal behaviour. Helfrich and Allen ( 1975 )
reported the shark attacks to occur early in their observations (after 20:30 h),
while spawning (at some distance from the vessel) was believed to occur only
after midnight, with no instances of shark predation noted during that probable
spawning event.
In support of spawning stupors, Johannes et al. ( 1999 ) cited the observation
by Robertson ( 1983 ) of a 1.3 m long carcharinid shark (not identifi ed) attacking
a single spawning pulse of several hundred brown surgeonfi sh at Lizard Island,
Australia. The outcome of the attack was uncertain, but probably unsuccessful
and did not disrupt the surgeonfi sh spawning. However, this can interpreted as
the spawning fi sh were suffi ciently aware during the attack that those individuals
close to the shark avoided being bitten, while the others continued spawning.
Several attacks on spawning brown surgeonfi sh in Palau failed to interrupt spawning behaviour for more than a few seconds (PLC unpublished data). In a fi nal
example Johannes et al. ( 1999 ) cited the fact that divers could swim among
spawning cubera snapper without disturbing them as indicative they were in a
stupor state. It is more reasonable to suppose that the fi sh were aware of events
around them but had no reason to fear or fl ee from divers, as divers regularly visit
these aggregations so fi sh become habituated to their non-threatening presence
(Heyman et al. 2001 , 2005 ).
There is no doubt the behaviour of many fi shes is altered when in spawning
aggregations, such as letting divers approach closer than normal (Hamilton 2005 ,
Kadison et al. 2007), but some reports have interpreted such changes as “spawning
stupors” (Burton et al. 2005 ; Gladstone 1996 ) . The existence of a “spawning stupor” which overwhelms all self-preservation behaviour, is at best an uncertain
(and in a sense unfortunate) concept, which like many appealing myths in biology
gains credence with each incorrect repetition, misapplication or misinterpretation.