319
9 Studying and Monitoring Aggregating Species
Once migration pathways have been documented, it is possible to evaluate or
experimentally manipulate them to learn more of migration dynamics. This is
applicable for resident aggregators, whose regular (often daily) movements allow
undertaking work on a regular and extended basis. For example, Mazeroll and
Montgomery ( 1998 ) experimentally tested a number of possible methods of migration
navigation for brown surgeonfi sh, Acanthurus nigrofuscus , and found landmarks
were important in determining the path, but that magnetic fi eld and sun compass
migration were not. Kifl awi and Mazeroll ( 2006 ) captured migrating surgeonfi sh,
determined their sex, tagged and released them. By observing migration behaviour
of tagged individuals of known sex over subsequent days they determined females
most often lead migrating groups.
9.6.11 Physical Parameter Considerations
The instrumentation of aggregation sites for physical parameters (temperature,
currents, tide, light), is of critical importance for understanding the dynamics of
aggregations and allowing comparison of conditions across numbers of sites. Colin
and Clavijo ( 1988 ) , Colin ( 1992 ) , Heyman et al. ( 2005 ) , Nemeth et al. ( 2007 ) and
Whaylen et al. ( 2006 ) provide examples of instrumented sites that have provided
new insights into aggregation dynamics (see Chap. 5 ). Annual physical data from an
aggregation site allow correlation of biological activity (timing of aggregations,
spawning) within the physical framework. Measuring water movement at and near
sites is important for documenting whether conditions might promote use of a certain site over others and dispersal of propagules after spawning. It is also important to instrument beyond aggregation sites if the intention is to examine
differences (if any) between sites and between known aggregation sites and sites
where no aggregations form.
The locations of instruments at an aggregation site depend on the parameters
being measured. A current meter deployed to record currents at the actual spawning
site needs to be located where the fi sh are spawning. Thermographs need to be
located close to the aggregation site, but unless there is thermal stratifi cation, anywhere near the aggregation (a few tens of meters) should be acceptable. The same
applies to salinity measurements. Light sensors could be bottom-mounted or put on
moorings at distances above the bottom.
The further removed an instrument is from the aggregation site, the less representative the data. Bolden ( 2000 ) used temperatures measured at Lee Stocking
Island, Bahamas (a tidally dominated bank habitat) as representing those at a shelf
edge Nassau grouper aggregation site more than 120 km south. In this case data
taken far distant from the aggregation site confuse the question of water temperature regimes at the aggregation site. When the intention is to clarify the relationship of physical environment to aggregation and spawning, data must be measured
at the site.
9 Studying and Monitoring Aggregating Species
Once migration pathways have been documented, it is possible to evaluate or
experimentally manipulate them to learn more of migration dynamics. This is
applicable for resident aggregators, whose regular (often daily) movements allow
undertaking work on a regular and extended basis. For example, Mazeroll and
Montgomery ( 1998 ) experimentally tested a number of possible methods of migration
navigation for brown surgeonfi sh, Acanthurus nigrofuscus , and found landmarks
were important in determining the path, but that magnetic fi eld and sun compass
migration were not. Kifl awi and Mazeroll ( 2006 ) captured migrating surgeonfi sh,
determined their sex, tagged and released them. By observing migration behaviour
of tagged individuals of known sex over subsequent days they determined females
most often lead migrating groups.
9.6.11 Physical Parameter Considerations
The instrumentation of aggregation sites for physical parameters (temperature,
currents, tide, light), is of critical importance for understanding the dynamics of
aggregations and allowing comparison of conditions across numbers of sites. Colin
and Clavijo ( 1988 ) , Colin ( 1992 ) , Heyman et al. ( 2005 ) , Nemeth et al. ( 2007 ) and
Whaylen et al. ( 2006 ) provide examples of instrumented sites that have provided
new insights into aggregation dynamics (see Chap. 5 ). Annual physical data from an
aggregation site allow correlation of biological activity (timing of aggregations,
spawning) within the physical framework. Measuring water movement at and near
sites is important for documenting whether conditions might promote use of a certain site over others and dispersal of propagules after spawning. It is also important to instrument beyond aggregation sites if the intention is to examine
differences (if any) between sites and between known aggregation sites and sites
where no aggregations form.
The locations of instruments at an aggregation site depend on the parameters
being measured. A current meter deployed to record currents at the actual spawning
site needs to be located where the fi sh are spawning. Thermographs need to be
located close to the aggregation site, but unless there is thermal stratifi cation, anywhere near the aggregation (a few tens of meters) should be acceptable. The same
applies to salinity measurements. Light sensors could be bottom-mounted or put on
moorings at distances above the bottom.
The further removed an instrument is from the aggregation site, the less representative the data. Bolden ( 2000 ) used temperatures measured at Lee Stocking
Island, Bahamas (a tidally dominated bank habitat) as representing those at a shelf
edge Nassau grouper aggregation site more than 120 km south. In this case data
taken far distant from the aggregation site confuse the question of water temperature regimes at the aggregation site. When the intention is to clarify the relationship of physical environment to aggregation and spawning, data must be measured
at the site.