295
9 Studying and Monitoring Aggregating Species
GS – Genetic Sampling
Fin clips placed in a suitable vial with a high concentration of ethanol is the simplest
reliable technique for genetic sampling. Genetic samples are useful for looking at
population structure relative to whether a single aggregation represents a single
genetic stock, or whether there are multiple stocks at a single aggregation. Such
information, combined with other biological and oceanographic information, is
important for management decisions. If opportunity arises to collect tissues it might
be important to take samples, even if not for immediate use, especially in the case
of threatened species.
HA – Hydroacoustic Survey
This is a remote sensing method that combines the return sonar echoes from fi shes
with GPS positioning to map out the distribution and numbers of fi shes over an area.
It has been used for single species aggregations of commercially valuable fi sh like
Atlantic cod, Gadus morhua (Lawson and Rose 2000 ) and orange roughy,
Hyplostethus atlanticus (Bull et al. 2001 ) . For reef fi sh aggregations, however,
diffi culties arise in separating echoes from a variety of fi shes whose acoustic signals
have been poorly characterized and may co-occur in an aggregation area. The high
density of fi sh in some aggregations makes discrimination of individual fi sh
problematic. Their availability for detection may vary according to their height
above the substrate or their short-term movements in and out of detection range
(Taylor et al. 2006 ) . Such surveys should not be used without detailed validation
because of the tendency to overestimate reef fi sh numbers (see later).
IS – Instrumentation at Site
Instruments installed at the aggregation site measure physical data, such as temperature, current speed and direction, tide, salinity and light. To document conditions at
the aggregation site, they should be installed as close to the site as is reasonable.
Similar monitoring instruments can be installed at locations other than the
aggregation site to determine any differences between aggregation and nonaggregation sites.
Temperature loggers are inexpensive and should be deployed for any serious
study. Current meters are useful to deploy at aggregation sites (Fig. 9.2 ) and many
incorporate pressure (tide) and temperature sensors as well. A single instrument can
now provide a suite of data for a spawning site that was almost unimaginable not
very long ago. Information can either be extremely detailed (Fig. 9.3a ) or show the
overall picture of conditions at a site (Fig. 9.3b ). Tide sensors provide important
data because many aggregation areas are far from established tide stations and shelf
edge sites may have very different tides. Salinity may be relatively constant at sites,
but seasonal data would be useful if variation is likely. Recording light meters are
useful if observations are made on a number of days of the timing of courtship and
spawning activity, because day to day variation in the timing of spawning may be
related to the light intensity as infl uenced by cloud cover. At most aggregation sites
it is probably unnecessary to measure oxygen, as this is usually near saturation values
9 Studying and Monitoring Aggregating Species
GS – Genetic Sampling
Fin clips placed in a suitable vial with a high concentration of ethanol is the simplest
reliable technique for genetic sampling. Genetic samples are useful for looking at
population structure relative to whether a single aggregation represents a single
genetic stock, or whether there are multiple stocks at a single aggregation. Such
information, combined with other biological and oceanographic information, is
important for management decisions. If opportunity arises to collect tissues it might
be important to take samples, even if not for immediate use, especially in the case
of threatened species.
HA – Hydroacoustic Survey
This is a remote sensing method that combines the return sonar echoes from fi shes
with GPS positioning to map out the distribution and numbers of fi shes over an area.
It has been used for single species aggregations of commercially valuable fi sh like
Atlantic cod, Gadus morhua (Lawson and Rose 2000 ) and orange roughy,
Hyplostethus atlanticus (Bull et al. 2001 ) . For reef fi sh aggregations, however,
diffi culties arise in separating echoes from a variety of fi shes whose acoustic signals
have been poorly characterized and may co-occur in an aggregation area. The high
density of fi sh in some aggregations makes discrimination of individual fi sh
problematic. Their availability for detection may vary according to their height
above the substrate or their short-term movements in and out of detection range
(Taylor et al. 2006 ) . Such surveys should not be used without detailed validation
because of the tendency to overestimate reef fi sh numbers (see later).
IS – Instrumentation at Site
Instruments installed at the aggregation site measure physical data, such as temperature, current speed and direction, tide, salinity and light. To document conditions at
the aggregation site, they should be installed as close to the site as is reasonable.
Similar monitoring instruments can be installed at locations other than the
aggregation site to determine any differences between aggregation and nonaggregation sites.
Temperature loggers are inexpensive and should be deployed for any serious
study. Current meters are useful to deploy at aggregation sites (Fig. 9.2 ) and many
incorporate pressure (tide) and temperature sensors as well. A single instrument can
now provide a suite of data for a spawning site that was almost unimaginable not
very long ago. Information can either be extremely detailed (Fig. 9.3a ) or show the
overall picture of conditions at a site (Fig. 9.3b ). Tide sensors provide important
data because many aggregation areas are far from established tide stations and shelf
edge sites may have very different tides. Salinity may be relatively constant at sites,
but seasonal data would be useful if variation is likely. Recording light meters are
useful if observations are made on a number of days of the timing of courtship and
spawning activity, because day to day variation in the timing of spawning may be
related to the light intensity as infl uenced by cloud cover. At most aggregation sites
it is probably unnecessary to measure oxygen, as this is usually near saturation values