307
9 Studying and Monitoring Aggregating Species
9.6.4 Time Lapse Video and Still Photography
A stationary still or video camera positioned so it can see an aggregation site is a
very useful, but underutilized, tool for examining the changes in fi sh abundance and
behaviour over a period of time (Whaylen et al. 2006 ) . It can be especially useful for
wary fi sh, such as the humphead wrasse (Colin 2010 ) . The camera is mounted on a
tripod or other fi xed structure so it is steady and properly oriented. Such photo and
video monitoring sites should be carefully chosen, based on previous knowledge, as
a slight error in locating the camera system can mean no images of value are
recorded, while the activity of interest is occurring and visible just a short distance
away. There is always the factor that if the aggregation moves slightly between days
or years, the equipment, even with detailed prior knowledge, might not be positioned for optimal information gathering.
A modern digital camera can (at present) take thousands of high resolution photographs during a single deployment. If such a camera in an underwater housing
stationed on a tripod at an aggregation site takes a photo every few minutes, a
detailed record of the aggregation would be obtained over a period of days, assuming a strobe is used at night (Fig. 9.8 ). A simple system is limited to available light;
however, for night time use a strobe system could be utilized. Some cameras have a
connector for externally triggering the camera via an electrical switch and these
would be easier to use for a timed deployment using a simple timer circuit and relay
to trigger the camera. Other cameras, without a remote switch capability, might
need a small solenoid to trigger the camera, via the shutter release button, and this
would involve more battery power for such a circuit.
It might be useful to position the time lapse camera on a tripod pointed straight
up at the aggregation site. Using available light, any fi shes present above the camera
within the angle of view of the lens should be visible and since they are against a
lighter water surface, might be easily countable in each frame.
Video camera provide similar capabilities, some can be confi gured to take a short
sequence (a few sec or more) at some regular interval (Whaylen et al. 2006 ) .
Recording on hard drives, instead of video tape, allows even more time. Probably
with such equipment battery life becomes the limiting factor and can be extended
using external battery power.
9.6.5 Measurement of Numbers and Density of Fish
in an Aggregation
One of the most basic questions about any aggregation is how many fi sh are present;
a seemingly simple question which is often surprisingly challenging to properly
address. Seven different methods were suggested in Table 9.1 to approach this problem (and there are probably many others possible), however, none are truly accurate
and in some the results cannot be cross-checked or verifi ed. Ideally multiple
9 Studying and Monitoring Aggregating Species
9.6.4 Time Lapse Video and Still Photography
A stationary still or video camera positioned so it can see an aggregation site is a
very useful, but underutilized, tool for examining the changes in fi sh abundance and
behaviour over a period of time (Whaylen et al. 2006 ) . It can be especially useful for
wary fi sh, such as the humphead wrasse (Colin 2010 ) . The camera is mounted on a
tripod or other fi xed structure so it is steady and properly oriented. Such photo and
video monitoring sites should be carefully chosen, based on previous knowledge, as
a slight error in locating the camera system can mean no images of value are
recorded, while the activity of interest is occurring and visible just a short distance
away. There is always the factor that if the aggregation moves slightly between days
or years, the equipment, even with detailed prior knowledge, might not be positioned for optimal information gathering.
A modern digital camera can (at present) take thousands of high resolution photographs during a single deployment. If such a camera in an underwater housing
stationed on a tripod at an aggregation site takes a photo every few minutes, a
detailed record of the aggregation would be obtained over a period of days, assuming a strobe is used at night (Fig. 9.8 ). A simple system is limited to available light;
however, for night time use a strobe system could be utilized. Some cameras have a
connector for externally triggering the camera via an electrical switch and these
would be easier to use for a timed deployment using a simple timer circuit and relay
to trigger the camera. Other cameras, without a remote switch capability, might
need a small solenoid to trigger the camera, via the shutter release button, and this
would involve more battery power for such a circuit.
It might be useful to position the time lapse camera on a tripod pointed straight
up at the aggregation site. Using available light, any fi shes present above the camera
within the angle of view of the lens should be visible and since they are against a
lighter water surface, might be easily countable in each frame.
Video camera provide similar capabilities, some can be confi gured to take a short
sequence (a few sec or more) at some regular interval (Whaylen et al. 2006 ) .
Recording on hard drives, instead of video tape, allows even more time. Probably
with such equipment battery life becomes the limiting factor and can be extended
using external battery power.
9.6.5 Measurement of Numbers and Density of Fish
in an Aggregation
One of the most basic questions about any aggregation is how many fi sh are present;
a seemingly simple question which is often surprisingly challenging to properly
address. Seven different methods were suggested in Table 9.1 to approach this problem (and there are probably many others possible), however, none are truly accurate
and in some the results cannot be cross-checked or verifi ed. Ideally multiple