298 Monitoring Threatened Species and Ecological Communities
with caution. Estimates of apparent survival, which fell well below the expected
biological survival rates for similar species reported elsewhere (e.g. Wang et al.
2012), sometimes suggested quite high rates of permanent emigration. Nonetheless,
despite these high rates of permanent emigration, the abundance estimates
remained relatively stable indicating similar rates of permanent immigration.
Temporary emigration was observed only from Bynoe Harbour at rates that
varied between the transition between a wet season and the following dry season
and the corresponding transition from the dry to wet season, and were substantially
greater for the probability of returning following an absence (~57%) than for
emigrating following a presence (~17%). The movement of humpback dolphins was
estimated to be constant between primary samples and symmetric between pairs of
sites at around 9% per interval in both directions between Darwin Harbour and
Bynoe Harbour. The estimated rates of movement between sites might have been
informative of movement out of Darwin Harbour and into Bynoe Harbour and
Shoal Bay after primary sample 4 (see Fig. 22.4) had the populations been larger and
more between-site movements observed. This result highlights the difficulties in
detecting movements in mark–recapture data when local populations are small.
The full potential of the MSCRD could not be exploited in this study, mainly
because of the small sizes of the dolphin populations using the three sites. This
situation meant that the MSCRD model could only be employed here for the
humpback dolphin data. Reasonably precise estimates of abundance were obtained
Fig. 22.5. Capricorn Cetaceans Project team taking photographs of Australian humpback and snubfin
dolphins in the Whitsundays region as part of a long-term photo-identification mark–recapture study. Photo:
Capricorn Cetaceans Project, Marine Ecology Research Centre, Southern Cross University.