298
P.L. Colin
spear. Line and trap caught fi shes are usually alive when brought up and can be
measured and tagged, then released. Swim bladders may need to be defl ated; the gas
can be released by hypodermic needle. If surgical procedures are used, such as
implantation of acoustic tags, anaesthetics can reduce stress on the fi sh (Zeller 1997,
1998a ) . When returned to the water, fi sh are disoriented, stressed and easy prey for
predators. A remote release trap (Nemeth 2005 ) or a weighted line which releases
the fi sh have been used for returning tagged fi sh to the bottom and potentially reduce
predator mortality.
SP – Still Photography
Still photography is used to document fi sh abundance, colouration and behaviour,
among other things. Good photos can convey to others the magnitude of an impressive aggregation (Smith 1972 ) or provide evidence of new aggregations (Erisman
et al. 2009 ) . More recently, digital photography has revolutionized documentation
of aggregations and opened new possibilities for gathering data. More information
is found in the following section.
SS – Stationary (Tether) Survey
Many aggregations are reasonably stable in their location allowing an observer to
make a series of observations, such as frequency of spawning, from a single point
relative to the aggregation. The presence of an observer, particularly a SCUBA diver
producing noise and bubbles could disturb aggregations and can be minimized by
having the observer stationary and quieter. An observer can be tethered above the
bottom by a line secured to the bottom; hovering like an infl ated balloon over a fi eld.
The line, secured to the bottom, is clipped to the diver by a quick release fi tting. The
observer is made positively buoyant by slightly infl ating the buoyancy control
device normally worn while diving. There is no need to swim to maintain position,
so the diver produces less noise and bubbles (as breathing is slowed and air consumption reduced) and the position provides an excellent fi eld of view. Diver depth
is reduced (compared to being on the bottom) allowing longer dive times and less
chance of decompression sickness. Tethering was useful in observing surgeonfi sh
aggregations in Puerto Rico (Colin and Clavijo 1988 ) .
TC – Transect Count
A variety of different transect type counts are used to estimate numbers of fi sh
present in aggregations and how they change over time. Counting fi sh on a consistent
and standardized basis in short-lived, often large, groups that might change in number
during the course of the day is of interest to a wide range of workers and managers.
The diffi culties and costs of doing so should not be underestimated. These are
discussed more fully in the following section.
TG – Tagging
Conventional tagging, where an externally visible marker or branding with identifying
information is attached to the fi sh, is still extremely valuable and when used with
acoustic (sonic) tagging, the two are mutually advantageous. A number of studies
P.L. Colin
spear. Line and trap caught fi shes are usually alive when brought up and can be
measured and tagged, then released. Swim bladders may need to be defl ated; the gas
can be released by hypodermic needle. If surgical procedures are used, such as
implantation of acoustic tags, anaesthetics can reduce stress on the fi sh (Zeller 1997,
1998a ) . When returned to the water, fi sh are disoriented, stressed and easy prey for
predators. A remote release trap (Nemeth 2005 ) or a weighted line which releases
the fi sh have been used for returning tagged fi sh to the bottom and potentially reduce
predator mortality.
SP – Still Photography
Still photography is used to document fi sh abundance, colouration and behaviour,
among other things. Good photos can convey to others the magnitude of an impressive aggregation (Smith 1972 ) or provide evidence of new aggregations (Erisman
et al. 2009 ) . More recently, digital photography has revolutionized documentation
of aggregations and opened new possibilities for gathering data. More information
is found in the following section.
SS – Stationary (Tether) Survey
Many aggregations are reasonably stable in their location allowing an observer to
make a series of observations, such as frequency of spawning, from a single point
relative to the aggregation. The presence of an observer, particularly a SCUBA diver
producing noise and bubbles could disturb aggregations and can be minimized by
having the observer stationary and quieter. An observer can be tethered above the
bottom by a line secured to the bottom; hovering like an infl ated balloon over a fi eld.
The line, secured to the bottom, is clipped to the diver by a quick release fi tting. The
observer is made positively buoyant by slightly infl ating the buoyancy control
device normally worn while diving. There is no need to swim to maintain position,
so the diver produces less noise and bubbles (as breathing is slowed and air consumption reduced) and the position provides an excellent fi eld of view. Diver depth
is reduced (compared to being on the bottom) allowing longer dive times and less
chance of decompression sickness. Tethering was useful in observing surgeonfi sh
aggregations in Puerto Rico (Colin and Clavijo 1988 ) .
TC – Transect Count
A variety of different transect type counts are used to estimate numbers of fi sh
present in aggregations and how they change over time. Counting fi sh on a consistent
and standardized basis in short-lived, often large, groups that might change in number
during the course of the day is of interest to a wide range of workers and managers.
The diffi culties and costs of doing so should not be underestimated. These are
discussed more fully in the following section.
TG – Tagging
Conventional tagging, where an externally visible marker or branding with identifying
information is attached to the fi sh, is still extremely valuable and when used with
acoustic (sonic) tagging, the two are mutually advantageous. A number of studies