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P.L. Colin
AT – Acoustic Tagging
Implantation or external application of an acoustic transmitter to a fi sh or other
marine animal allows tracking of its movements either by directional hydrophone or
passive acoustic receivers positioned in the area of interest (Domeier 2005 ) . Surgical
implantation is now commonplace (Zeller 1997, 1998a ; Nemeth et al. 2007 ) . Fishes
can be tagged while dispersed (outside of aggregations) or during aggregation.
Internal tags used for fi shes larger than about 50–60 cm SL transmit for a year or
more. They also can provide information on temperature, depth and other parameters.
The receiving stations gather data for many months, but need to be recovered for
download at intervals and battery replacement. Acoustic tagging is expensive compared to conventional tagging, with a cost of US$100–200 per implanted tag, as well
as US$2,000–3,000 per receiver. Sample sizes are usually constrained by costs, but
should be maximized when possible. Arrays of over 50 receivers have been deployed
for single studies, as well as hundreds of fi sh being tagged (Domeier 2005 ) .
BM – Bathymetric Mapping
Electronic depth sounders with an integral Global Positioning System (GPS) unit
allow recording of latitude – longitude – depth (y, x, z) data at sea, an essential part
of any spatial examination of aggregation sites. A survey pattern run from a boat
over an aggregation site and nearby areas is used to produce customized bathymetric
maps (Colin et al. 2003 ) . Multibeam surveys are expensive and equipment intensive, but are the ultimate in bathymetric mapping (Weaver et al. 2005 ; Nemeth et al.
2008 ). More information is provided below.
DO – Direct Observation by Snorkelling or Diving
Direct observation of aggregations is usually done by swimmers (snorkelling or
SCUBA) at the aggregation site. The observer is equipped with suitable diving
equipment depending on conditions. An underwater watch, preferably digital, and a
recording slate are essential. Care should be taken that the presence of one or more
observers in the water does not alter the behaviour of aggregated fi sh. Fish may be
skittish, and often it is diffi cult to observe spawning. Observers try to get as close as
possible to the fi sh, to see details that would be missed at a distance, but fi sh are
often disturbed by this close approach. Many areas with aggregations also have high
levels of spearfi shing, so many fi shes are already wary of humans. Possibly using
red underwater lights at night would allow observation of fi sh behaviour for species
suspected of spawning after dark; most reef fi shes can see red light, but its penetration is limited in water, perhaps reducing its disturbance effect compared to white
light. More information on snorkelling and diving with aggregations is included in
Colin et al. ( 2003 ) .
DR – Drifter Release
Current-following (Lagrangian) drifters can track water movement over time, and
assuming that eggs are incorporated into the same water mass, can be used with
certain caveats to track eggs and larvae. Most drifters have a drogue of various
P.L. Colin
AT – Acoustic Tagging
Implantation or external application of an acoustic transmitter to a fi sh or other
marine animal allows tracking of its movements either by directional hydrophone or
passive acoustic receivers positioned in the area of interest (Domeier 2005 ) . Surgical
implantation is now commonplace (Zeller 1997, 1998a ; Nemeth et al. 2007 ) . Fishes
can be tagged while dispersed (outside of aggregations) or during aggregation.
Internal tags used for fi shes larger than about 50–60 cm SL transmit for a year or
more. They also can provide information on temperature, depth and other parameters.
The receiving stations gather data for many months, but need to be recovered for
download at intervals and battery replacement. Acoustic tagging is expensive compared to conventional tagging, with a cost of US$100–200 per implanted tag, as well
as US$2,000–3,000 per receiver. Sample sizes are usually constrained by costs, but
should be maximized when possible. Arrays of over 50 receivers have been deployed
for single studies, as well as hundreds of fi sh being tagged (Domeier 2005 ) .
BM – Bathymetric Mapping
Electronic depth sounders with an integral Global Positioning System (GPS) unit
allow recording of latitude – longitude – depth (y, x, z) data at sea, an essential part
of any spatial examination of aggregation sites. A survey pattern run from a boat
over an aggregation site and nearby areas is used to produce customized bathymetric
maps (Colin et al. 2003 ) . Multibeam surveys are expensive and equipment intensive, but are the ultimate in bathymetric mapping (Weaver et al. 2005 ; Nemeth et al.
2008 ). More information is provided below.
DO – Direct Observation by Snorkelling or Diving
Direct observation of aggregations is usually done by swimmers (snorkelling or
SCUBA) at the aggregation site. The observer is equipped with suitable diving
equipment depending on conditions. An underwater watch, preferably digital, and a
recording slate are essential. Care should be taken that the presence of one or more
observers in the water does not alter the behaviour of aggregated fi sh. Fish may be
skittish, and often it is diffi cult to observe spawning. Observers try to get as close as
possible to the fi sh, to see details that would be missed at a distance, but fi sh are
often disturbed by this close approach. Many areas with aggregations also have high
levels of spearfi shing, so many fi shes are already wary of humans. Possibly using
red underwater lights at night would allow observation of fi sh behaviour for species
suspected of spawning after dark; most reef fi shes can see red light, but its penetration is limited in water, perhaps reducing its disturbance effect compared to white
light. More information on snorkelling and diving with aggregations is included in
Colin et al. ( 2003 ) .
DR – Drifter Release
Current-following (Lagrangian) drifters can track water movement over time, and
assuming that eggs are incorporated into the same water mass, can be used with
certain caveats to track eggs and larvae. Most drifters have a drogue of various