size: 5036KB - Crocodile Specialist Group

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a maximum of 12 locations for an individual'
1.1) Mark-resight results
ri" ,oi"trtins iat" trable 1), an index which reflects the proportion of tagged animals in the
;;ffi;,;.a.;d *i*rui"a This is broken down bv time in months after release and
iorrected for samplitrg effort.
Table 1. Resighting rate each month since release, calculated from the number of tagged
animals seen, corrected for sampling effort'
Month
Km
Sampled
Number
Seen
Correction
Factor
Resighting
Rate
Comments
MARCH 29.'75 l5 1.43 lst batch
APRIL 26.50 49 1.60
MAY 40.25 60 1.06
JUNE 42.50 53 r .00
JULY 18.75 19 2.21
The decline in the resighting Iate seen in Table 1 rcflects the combined loss of tagged
animals from mortality, emigration and tag loss Emigration is-discounted.as considerable
efforts have been made to locate tagged animals outside the study area' wlthorlt success'
Tag loss is the biggest source of bias. Three means of estimating tag loss were built inlo the
deien - all animals carry both permanent marks (cut scutes) and temporary marks (head
l*tit-", *.fl sighting th; condilion and presence/absqnce of both lead- tags is specifically
Jt i; utotig tnJradio tagged animals, half have head tags and half have not' allowing
iot "na ill"n these animals are recaPtured for measuremenl. Lost ta€s are rcplaced
wheneverananimalishandledandmodifiedtagsarenowbgingappliedwhichalelessprone
"orputiton
to working loose.
It is estimated flom sighting that tag loss in the first 3 months after release was around 10 %'
it e ttti. loss on the pool of tagged animals available for sighting does
"umututiue"feciof
not alone explain the decline seen in Table l'
A sepamte analysis also indicates that the numbers available for resighting are decreasing
inroriet time. ihe ratio of firsr sighrings of a tag to second or repeat sightings has droPped
markedly each month since the release (Table 2).