489
12 Species Case Studies
period. Individual females mate nearly every day, and these females tend to be
highly faithful to particular mating sites (Warner 1986 ) .
Because the eggs produced by females are pelagic and there is no parental care,
the eggs themselves immediately become part of the plankton. Mating and egg
release occur at the down-current ends of reefs, and individual females must migrate
from the up-current feeding areas to the down-current spawning sites. In many
cases, this is only a short distance and takes just a few minutes; however, certain reef
confi gurations result in daily spawning migrations that can comprise more than
10% of the daily activity (Warner 1995 ) .
Down-current mating sites consist of upward projections from the edge of a reef,
and serve to minimize the distance a female must travel up into open water to release
her pelagic eggs near the surface (Warner 1988 ) . Tagging studies have shown that
once a mating site is chosen by a female, she migrates to that particular site, migrating to spawn at it by the same specifi c route on a regular basis (Warner 1986, 1995 ) .
Wholesale removals and replacements of populations demonstrated that mating site
location itself is determined by tradition, involving social learning passed on through
females; the same mating sites are used over many successive generations based on
sites selected by females (Warner 1988 ) . Successive whole-population replacements
showed that females are in fact capable of mating site resource assessment, but
under normal circumstances they avoid individual assessment and only copy other
females (Warner 1990a ) . Females do not engage in intensive mate assessment or
searches for mates. Experiments that shifted males from one mating site to another
indicate that sites, rather than males, are the objects of female choice (Warner 1987 ) .
Finally, by replacing only males or females on a reef it was shown that females
determine mating site location without reference to male behaviour (Warner 1990b ) .
Thus female mating behaviour appears to operate without much reference to males
(Warner and Schultz 1992 ) .
The mating system is polymorphic. Large males can control all the mating sites
on small reefs when fi sh densities are low. However, on larger reefs with many fi sh
the most successful mating sites are economically undefendable by large territorial
males (Warner and Hoffman 1980a ) , and most of the matings go to IP males in
group-spawning aggregations (Warner and Hoffman 1980b ; Warner 1984b ) . The
group spawning aggregations on large reefs with many blueheads can range up to
many thousands of individuals, taking place every day of the year (Warner 1995 )
(Fig. 12.39 ). Spawning aggregations are not the only means of reproduction in this
species, and individual females can opt to group-spawn on 1 day and pair-spawn
with a large territorial male on another. Aggregations are only found on larger reefs
where large numbers of fi shes exist.
12.14.3 Commercial and Research Value
The bluehead wrasse is not fi shed for food, other than incidentally, although it is
taken occasionally for the marine aquarium trade. The daily spawning aggregations
can be easily observed and have been the object of sport diving.
12 Species Case Studies
period. Individual females mate nearly every day, and these females tend to be
highly faithful to particular mating sites (Warner 1986 ) .
Because the eggs produced by females are pelagic and there is no parental care,
the eggs themselves immediately become part of the plankton. Mating and egg
release occur at the down-current ends of reefs, and individual females must migrate
from the up-current feeding areas to the down-current spawning sites. In many
cases, this is only a short distance and takes just a few minutes; however, certain reef
confi gurations result in daily spawning migrations that can comprise more than
10% of the daily activity (Warner 1995 ) .
Down-current mating sites consist of upward projections from the edge of a reef,
and serve to minimize the distance a female must travel up into open water to release
her pelagic eggs near the surface (Warner 1988 ) . Tagging studies have shown that
once a mating site is chosen by a female, she migrates to that particular site, migrating to spawn at it by the same specifi c route on a regular basis (Warner 1986, 1995 ) .
Wholesale removals and replacements of populations demonstrated that mating site
location itself is determined by tradition, involving social learning passed on through
females; the same mating sites are used over many successive generations based on
sites selected by females (Warner 1988 ) . Successive whole-population replacements
showed that females are in fact capable of mating site resource assessment, but
under normal circumstances they avoid individual assessment and only copy other
females (Warner 1990a ) . Females do not engage in intensive mate assessment or
searches for mates. Experiments that shifted males from one mating site to another
indicate that sites, rather than males, are the objects of female choice (Warner 1987 ) .
Finally, by replacing only males or females on a reef it was shown that females
determine mating site location without reference to male behaviour (Warner 1990b ) .
Thus female mating behaviour appears to operate without much reference to males
(Warner and Schultz 1992 ) .
The mating system is polymorphic. Large males can control all the mating sites
on small reefs when fi sh densities are low. However, on larger reefs with many fi sh
the most successful mating sites are economically undefendable by large territorial
males (Warner and Hoffman 1980a ) , and most of the matings go to IP males in
group-spawning aggregations (Warner and Hoffman 1980b ; Warner 1984b ) . The
group spawning aggregations on large reefs with many blueheads can range up to
many thousands of individuals, taking place every day of the year (Warner 1995 )
(Fig. 12.39 ). Spawning aggregations are not the only means of reproduction in this
species, and individual females can opt to group-spawn on 1 day and pair-spawn
with a large territorial male on another. Aggregations are only found on larger reefs
where large numbers of fi shes exist.
12.14.3 Commercial and Research Value
The bluehead wrasse is not fi shed for food, other than incidentally, although it is
taken occasionally for the marine aquarium trade. The daily spawning aggregations
can be easily observed and have been the object of sport diving.