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This
year the
Seychelles
whale shark monitoring programme will be expanding to
include a broad range of environmental monitoring during
the whale shark season due to support from the Save Our
Seas Foundation. The expansion comes after the analysis of
data from the last six years which has shown that the
distribution of sharks is localised and changes over the
course of the ‘season’.
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A
sea-bed mounted ADCP unit of the type to be used
in Seychelles . Image courtesy Sontek Inc.
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Currently
the environmental monitoring component consists of sea
temperature probes set at three stations in coastal waters
off Mahe along with a programme of weekly plankton tows
which are carried out off Matoopa Point by volunteers from
Global Vision International on behalf of MCSS. This season
will see some significant additions to this regime;
firstly an Acoustic Doppler Current Profiler (ADCP) is
being set up on the sea-bed off the south of Mahe; this
instrument measures particle size and movement across
three beams allowing a minute by minute analysis of
plankton size, the depth at which it is found and the
direction and speed of the current. This is a valuable
addition to the MCSS programme as it will help provide
information on the behaviour of the whale sharks’ food
source.
The
next additional monitoring component will be the capture
of Conductivity, Temperature and Depth profiles in the
areas where sharks are found; this had been done
occasionally in the past using a CTD loaned from the
D’Arros research station. The CTD data allows a two
dimensional ‘slice’ of the water column to be analysed
to show any variations of temperature or salinity with
depth which can also affect the distribution of plankton
and the diving behaviour of whale sharks. The arrival of
our own CTD unit will allow the regular capture of this
information.
The
third component will be the implementation of daily
plankton tows at three set depths along the same
‘slice’ as the CTD measurements; combined with the CTD
information and whale shark sighting records, this data
will help show how the plankton distribution is affected
by the temperature and salinity and how these
environmental variables affect whale shark numbers and
distribution.
This
major increase in environmental monitoring would not have
been possible without the support of the Save Our Seas
Foundation or the team of six interns and two team leaders
in the whale shark monitoring programme this season. The
data from the programme will be fed into the national
environmental databases and will also be used by an MSc
student for her Masters thesis.
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