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The
introduction of the Interactive Individual Identification
System, IRIS as it was known, photo-identification
software to the Marine Conservations Society Seychelles
Whale Shark Programme during the last season has already
brought to light one or two surprises!
Prior
to 2005, images were scanned from photographs or slides
and as such were limited in number. Since 2005, with the
advent of affordable digital photography, the photo ID
project was viable and almost every whale shark
encountered by the programme was photographed.
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The IRIS
visual comparison of S208: original sighting in
2001 compared to an image taken on 23rd October
2006 showing the matched spot patterns on each
image.
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Project
leader, whale shark researcher David Rowat, has now
compiled all the identification photos of individual whale
shark encounters from 2001 through to the end of last
season, i.e. 2006. A total of 9,168 images!
These
were then sorted to select images of the left and right
sides, showing the area just behind the last gill slit,
which is regarded as having the most individual spot
patterning.
From
the selected images, digital fingerprints were created for
each image using IRIS and stored in a database for
comparison. 632 files were in the left-side database and
415 in the right-side series. One by one, each fingerprint
was compared to all the others of the same side and
matches were combined within each year group. For each
comparison the IRIS programme compares the fingerprints
and give a list of the top 50 best ranked matches. The
researcher then uses the ranking score (the lower the
better), a visual comparison and a tool called the spot
cloud, which shows the deviation of the matched spots from
each other, to confirm or decline the best matched images.
After
these comparisons were completed, the final count left a
total of 300 images in the left-side database and 215 in
the right.
Final
tallies for each of the years in ongoing but in the 2006
season 195 individual animals have been identified with
over 220 matches being made within the season. The
surprises have been in the number of animals that were
recorded in 2006 that were also matched to previous years.
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| The The
IRIS ‘spot cloud’ pattern showing the
difference in the position of marked spots from
the two images of whale shark S208, with 19 pairs
of spots being matched giving a score of 0.05,
which indicates an almost perfect match.
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Of
the 195 individuals 36 were also recorded in 2005, five
from 2004, two from 2002 and one from 2001. The 2001 shark
was in fact a tagged shark, S208, recorded on the 28th
August 2001 and was matched to three sightings in 2006 on
the 2nd, 23rd and 25th of October 2006. Similarly, in 2005
four sharks from 2001 were identified, two had been tagged
previously, S201 and S210, while the other two had not
been tagged but were photographed on the 27th of October
2001
While photo identification is extremely time consuming, it
does have the potential to provide some interesting
insights in the study of whale shark populations.
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