292
P.L. Colin
in Red Sea surgeonfi sh, while Warner ( 1988, 1995 ) manipulated entire spawning
groups of bluehead wrasse, Thalassoma bifasciatum , to examine whether locations
of aggregation sites were learned or innate. The various disruptions to spawning
caused by the presence of humans around the aggregation and fi shing activities are
uncontrolled manipulations. In some regards their effects can be tested by comparing
with undisturbed populations (Johannes et al. 1999 ; Colin et al. 2003 ) . Knowing
these effects are perhaps most important in considering whether certain activities,
such as tourist SCUBA diving, should be permitted on aggregations, and if so, how
they are best conducted.
FM – Fecundity Measurements
For fi shes, fecundity is the number of eggs a female can produce and spawn and can
be expressed at the level of a single spawning event, annually or over a lifetime. It is
sometimes important information to know in any evaluation of the role aggregations
play in population maintenance but its estimation is diffi cult and is only relevant for
certain kinds of questions. Fecundity, for example, is sometimes used in standard
fi sh stock assessments, such as spawning stock biomass per recruit models. Given
the very high mortality rates between egg production and settlement, it is becoming
increasingly evident that fecundity per se is not often directly relevant in pelagic
spawning fi shes for assessing reproductive success. More important is the relevance
of body size to fecundity and egg quality, as well as the levels of natural mortality
associated with the egg and larval stages. The potential (total number of all oocytes)
and actual (total number of advanced oocytes) fecundity of females are typically
different values due to atresia and other factors (West 1990 ) and it is important to be
very clear in describing the methodology applied in fecundity studies (Sadovy
1996 ). The numbers of eggs for a given female is determined by fi rst measuring the
size of the ovaries, either their volume (usually by displacement of water in a graduated cylinder) or weight. Ovaries are then subsampled to determine numbers of eggs
per unit weight or volume and their state of readiness for spawning. Ultrasound
imaging has been used (Whiteman et al. 2005 ) to measure fecundity in living fi sh,
determining gonad size with imaging techniques, then using cannula samples for
oocytes per unit volume. Using hydrated eggs is one of the best approaches to measuring batch fecundity (i.e. number of eggs likely to be released in a spawning
event) and this is only possible close to spawning. For annual or lifetime fecundity
further methods have to be applied to determine spawning frequency, reproductive
longevity and size specifi c parameters in relation to egg production.
FS – Fishery Sampling from Fisher Catch
A fi shery on the aggregation may give access to data on length, weight, sex ratio,
gonad condition and abundance from fi shes caught by the fi shery. Such “hard data”
on fi sh numbers and size are useful for evaluating the accuracy of visually acquired
information and as part of an assessment of management outcomes. Researchers
can work with fi shers to sample their catch for information that ranges from catch
per unit of effort, catch volumes, gear selectivity, and sizes and sexes of fi sh taken
in the fi shery, to species identifi cation, etc. Sometimes fi shery capture data are not
P.L. Colin
in Red Sea surgeonfi sh, while Warner ( 1988, 1995 ) manipulated entire spawning
groups of bluehead wrasse, Thalassoma bifasciatum , to examine whether locations
of aggregation sites were learned or innate. The various disruptions to spawning
caused by the presence of humans around the aggregation and fi shing activities are
uncontrolled manipulations. In some regards their effects can be tested by comparing
with undisturbed populations (Johannes et al. 1999 ; Colin et al. 2003 ) . Knowing
these effects are perhaps most important in considering whether certain activities,
such as tourist SCUBA diving, should be permitted on aggregations, and if so, how
they are best conducted.
FM – Fecundity Measurements
For fi shes, fecundity is the number of eggs a female can produce and spawn and can
be expressed at the level of a single spawning event, annually or over a lifetime. It is
sometimes important information to know in any evaluation of the role aggregations
play in population maintenance but its estimation is diffi cult and is only relevant for
certain kinds of questions. Fecundity, for example, is sometimes used in standard
fi sh stock assessments, such as spawning stock biomass per recruit models. Given
the very high mortality rates between egg production and settlement, it is becoming
increasingly evident that fecundity per se is not often directly relevant in pelagic
spawning fi shes for assessing reproductive success. More important is the relevance
of body size to fecundity and egg quality, as well as the levels of natural mortality
associated with the egg and larval stages. The potential (total number of all oocytes)
and actual (total number of advanced oocytes) fecundity of females are typically
different values due to atresia and other factors (West 1990 ) and it is important to be
very clear in describing the methodology applied in fecundity studies (Sadovy
1996 ). The numbers of eggs for a given female is determined by fi rst measuring the
size of the ovaries, either their volume (usually by displacement of water in a graduated cylinder) or weight. Ovaries are then subsampled to determine numbers of eggs
per unit weight or volume and their state of readiness for spawning. Ultrasound
imaging has been used (Whiteman et al. 2005 ) to measure fecundity in living fi sh,
determining gonad size with imaging techniques, then using cannula samples for
oocytes per unit volume. Using hydrated eggs is one of the best approaches to measuring batch fecundity (i.e. number of eggs likely to be released in a spawning
event) and this is only possible close to spawning. For annual or lifetime fecundity
further methods have to be applied to determine spawning frequency, reproductive
longevity and size specifi c parameters in relation to egg production.
FS – Fishery Sampling from Fisher Catch
A fi shery on the aggregation may give access to data on length, weight, sex ratio,
gonad condition and abundance from fi shes caught by the fi shery. Such “hard data”
on fi sh numbers and size are useful for evaluating the accuracy of visually acquired
information and as part of an assessment of management outcomes. Researchers
can work with fi shers to sample their catch for information that ranges from catch
per unit of effort, catch volumes, gear selectivity, and sizes and sexes of fi sh taken
in the fi shery, to species identifi cation, etc. Sometimes fi shery capture data are not