590
Glossary
Typically group spawns appear to comprise a single, possibly a few, females, and
a larger number of following males with the production of pelagic eggs. Sperm
competition is likely to be involved and group-spawning males typically have
higher ripe GSI than pair-spawning males
Gyre a ring-like system of ocean currents normally rotating in an anti-cyclonic
(clockwise) direction in the northern hemisphere
Haremic spawning a mating system that consists of a male that spawns exclusively
with a group of females that he defends directly from other males or which utilize
territory, such as feeding territory, that he defends. Spawning is in pairs
Hermaphroditism refers to individuals who have both unequivocal ovarian tissue
and testicular elements that are reproductively active either simultaneously or
sequentially. This is considered to be functional hermaphroditism. Sequential
hermaphroditism can take two forms; protandry in which an organism is born
as a male, and then changes sex to a female, and protogyny in which the organism
starts as a female, and then changes sex to a male. In protogynous species, there
are sometimes two male forms; an initial phase male and a terminal phase male.
Initial phase males tend to resemble females and spawn in groups with other
females and are not territorial. Terminal phase males are territorial and have a
distinctively bright colouration. Individuals are born as males or females, but if
they are born males, they are not born as terminal phase males. Females and initial
phase males can become terminal phase males. Usually, the most dominant
female or initial phase male replaces a terminal phase male by sex change, when
those males die or abandon the group
Hyperstability a phenomenon in which an observed index of stock abundance (e.g.
catch per unit of effort , or CPUE) remains stable while the abundance (population size) of the stock in question is actually declining (Fig. 8.6)
Income breeding reliance on concurrent intake: whereby daily reproduction is
directly subsidized by continued feeding as would be expected for many resident
spawning species (Warner 1995 )
Indicators of spawning (direct and indirect) three criteria can verify directly that
fi sh are gathering for the purpose of spawning; (1) undisputed spawning observations, (2) females with hydrated eggs and (3) presence of post-ovulatory follicles
in the ovaries of aggregating females. A fourth means of directly documenting
the presence of a spawning aggregation is added in Chap. 1 : (4) identifi cation
of very early stage eggs and larvae, collected for example by plankton tows,
that can be positively associated with the aggregating species. Indirect signs can
be used for documenting new aggregations for species already known to form
spawning aggregations. Indirect signs can include behaviours or colour patterns,
if these are demonstrably known to be associated only with spawning, as well
as gonadosomatic index (see GSI) data or the presence of swollen abdomens
(indicating the presence of hydrated eggs) in a large percentage of the aggregated
individuals. In the absence of witnessing the spawning event, it is not realistically
possible to gather enough information to document spawning without sampling
ovaries or larvae (Colin et al. 2003 , Chap. 1 )
Initial phase see Hermaphroditism
Glossary
Typically group spawns appear to comprise a single, possibly a few, females, and
a larger number of following males with the production of pelagic eggs. Sperm
competition is likely to be involved and group-spawning males typically have
higher ripe GSI than pair-spawning males
Gyre a ring-like system of ocean currents normally rotating in an anti-cyclonic
(clockwise) direction in the northern hemisphere
Haremic spawning a mating system that consists of a male that spawns exclusively
with a group of females that he defends directly from other males or which utilize
territory, such as feeding territory, that he defends. Spawning is in pairs
Hermaphroditism refers to individuals who have both unequivocal ovarian tissue
and testicular elements that are reproductively active either simultaneously or
sequentially. This is considered to be functional hermaphroditism. Sequential
hermaphroditism can take two forms; protandry in which an organism is born
as a male, and then changes sex to a female, and protogyny in which the organism
starts as a female, and then changes sex to a male. In protogynous species, there
are sometimes two male forms; an initial phase male and a terminal phase male.
Initial phase males tend to resemble females and spawn in groups with other
females and are not territorial. Terminal phase males are territorial and have a
distinctively bright colouration. Individuals are born as males or females, but if
they are born males, they are not born as terminal phase males. Females and initial
phase males can become terminal phase males. Usually, the most dominant
female or initial phase male replaces a terminal phase male by sex change, when
those males die or abandon the group
Hyperstability a phenomenon in which an observed index of stock abundance (e.g.
catch per unit of effort , or CPUE) remains stable while the abundance (population size) of the stock in question is actually declining (Fig. 8.6)
Income breeding reliance on concurrent intake: whereby daily reproduction is
directly subsidized by continued feeding as would be expected for many resident
spawning species (Warner 1995 )
Indicators of spawning (direct and indirect) three criteria can verify directly that
fi sh are gathering for the purpose of spawning; (1) undisputed spawning observations, (2) females with hydrated eggs and (3) presence of post-ovulatory follicles
in the ovaries of aggregating females. A fourth means of directly documenting
the presence of a spawning aggregation is added in Chap. 1 : (4) identifi cation
of very early stage eggs and larvae, collected for example by plankton tows,
that can be positively associated with the aggregating species. Indirect signs can
be used for documenting new aggregations for species already known to form
spawning aggregations. Indirect signs can include behaviours or colour patterns,
if these are demonstrably known to be associated only with spawning, as well
as gonadosomatic index (see GSI) data or the presence of swollen abdomens
(indicating the presence of hydrated eggs) in a large percentage of the aggregated
individuals. In the absence of witnessing the spawning event, it is not realistically
possible to gather enough information to document spawning without sampling
ovaries or larvae (Colin et al. 2003 , Chap. 1 )
Initial phase see Hermaphroditism