291
9 Studying and Monitoring Aggregating Species
designs positioned at the depth of water to be tracked plus a marker fl oat, usually
with electronics for locating the drifter or recording its track. Deployment times
range from a few minutes to months and years with costs increasing as the tracking
and electronics involved become more sophisticated. The ability of drifters to mimic
the movement of eggs and larvae is probably reasonably good for a few hours to a
day or more, however once larvae develop the ability to change depth and swim
horizontally this changes. Physical factors, such as wind shear, waves and windage
of the drifter fl oat, also introduce errors in tracking that increase over time.
DY – Dye Release and Water Tagging
Parcels of water can be tagged with dye for short term tracking (a few hours) of
water which may contain eggs or larvae. This allows an estimate of where spawned
eggs might go in the fi rst few hours after spawning, and whether they would tend to
be retained locally or dispersed into distant waters. Fluorescein, which produces a
fl uorescent green colour in the water, is most commonly used. An observer can
mark a parcel of water where eggs are released by a squirt of dye (mixed with
seawater) from a small fl ip-top plastic bottle. Party balloons fi lled with dye and
water can be stationed underwater at a desired location and punctured by a pin
releasing a sizeable dye cloud instantly (Appeldoorn et al. 1994 ) . The relative
strength and direction of currents can be determined by observers by releasing a
small amount of dye and following its movement or tracking the dye stream emanating
from a pinhole in a plastic bottle moored above the reef (Atkinson 1987 ) . Large dye
releases can be used to assess movement of large water masses with eggs (Carter
1994 ) . However, dye usually disperses quickly to the point it is not easily visible.
Fluorometry can be used to track the movement at low dye concentrations.
Alternative means of “tagging” or tracking water with eggs have been suggested or
tried, using “egg surrogates” such as fl uorescent particles, wax particles and fatty
globules (Appeldoorn et al. 1988 ) . Drift vials (Domeier 2004 ) and drift cards are
other possible means of tracking water moving away from an aggregation site.
EC – Egg Collection
To collect relatively small numbers of eggs from a gamete cloud (to describe the
characters of the egg or examine fertilization rates) a fi ne mesh hand net can be used
by a diver to sweep the water where eggs are released. If larger numbers of eggs are
needed for rearing attempts, then they can be gathered using larger hand or plankton
nets. The eggs should be collected after a wait of up to 1 min after release, since
premature collection of eggs results in low fertilization rates (Petersen et al. 1992 ;
Colin et al. 2003 ) . Release of a small quantity of dye in the area of gamete cloud is
often useful for tracking the eggs for that time. For large scale rearing attempts, it is
usually necessary to strip gametes from ripe fi sh or otherwise artifi cially fertilize
eggs obtained from broodstock (Watanabe et al. 1995 ) .
EM – Experimental Manipulation
Experimental manipulations are relatively uncommon in aggregation studies.
Mazeroll and Montgomery ( 1998 ) manipulated potential cues for migration pathways
9 Studying and Monitoring Aggregating Species
designs positioned at the depth of water to be tracked plus a marker fl oat, usually
with electronics for locating the drifter or recording its track. Deployment times
range from a few minutes to months and years with costs increasing as the tracking
and electronics involved become more sophisticated. The ability of drifters to mimic
the movement of eggs and larvae is probably reasonably good for a few hours to a
day or more, however once larvae develop the ability to change depth and swim
horizontally this changes. Physical factors, such as wind shear, waves and windage
of the drifter fl oat, also introduce errors in tracking that increase over time.
DY – Dye Release and Water Tagging
Parcels of water can be tagged with dye for short term tracking (a few hours) of
water which may contain eggs or larvae. This allows an estimate of where spawned
eggs might go in the fi rst few hours after spawning, and whether they would tend to
be retained locally or dispersed into distant waters. Fluorescein, which produces a
fl uorescent green colour in the water, is most commonly used. An observer can
mark a parcel of water where eggs are released by a squirt of dye (mixed with
seawater) from a small fl ip-top plastic bottle. Party balloons fi lled with dye and
water can be stationed underwater at a desired location and punctured by a pin
releasing a sizeable dye cloud instantly (Appeldoorn et al. 1994 ) . The relative
strength and direction of currents can be determined by observers by releasing a
small amount of dye and following its movement or tracking the dye stream emanating
from a pinhole in a plastic bottle moored above the reef (Atkinson 1987 ) . Large dye
releases can be used to assess movement of large water masses with eggs (Carter
1994 ) . However, dye usually disperses quickly to the point it is not easily visible.
Fluorometry can be used to track the movement at low dye concentrations.
Alternative means of “tagging” or tracking water with eggs have been suggested or
tried, using “egg surrogates” such as fl uorescent particles, wax particles and fatty
globules (Appeldoorn et al. 1988 ) . Drift vials (Domeier 2004 ) and drift cards are
other possible means of tracking water moving away from an aggregation site.
EC – Egg Collection
To collect relatively small numbers of eggs from a gamete cloud (to describe the
characters of the egg or examine fertilization rates) a fi ne mesh hand net can be used
by a diver to sweep the water where eggs are released. If larger numbers of eggs are
needed for rearing attempts, then they can be gathered using larger hand or plankton
nets. The eggs should be collected after a wait of up to 1 min after release, since
premature collection of eggs results in low fertilization rates (Petersen et al. 1992 ;
Colin et al. 2003 ) . Release of a small quantity of dye in the area of gamete cloud is
often useful for tracking the eggs for that time. For large scale rearing attempts, it is
usually necessary to strip gametes from ripe fi sh or otherwise artifi cially fertilize
eggs obtained from broodstock (Watanabe et al. 1995 ) .
EM – Experimental Manipulation
Experimental manipulations are relatively uncommon in aggregation studies.
Mazeroll and Montgomery ( 1998 ) manipulated potential cues for migration pathways