Matkin et al Abundance and residency patterns of two sympatric populations of Orcinus orca in the northern Gulf of Alaska 
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Figure 6 
(A) Estimates of abundance for Gulf of Alaska (GOA) transient killer whales 
(Orcinus orca) in the Prince William Sound-Kenai Fjords study area. The 
broken horizontal line represents the trend given by a change-point model. 
(B) Posterior probability of a change in the abundance level in each year, 
characterising the trend model. 
Discussion 
Although approximately the same number of individu- 
als was identified annually in the two transient killer 
whale populations we monitored in the coastal waters 
of Prince William Sound and the Kenai Fjords, the 
population parameters estimated by our mark recap- 
ture model were notably different. The ATI transients 
exhibited high site fidelity and high capture probability, 
indicating that essentially every member of this small 
population was photographed annually in our coastal 
study area. In contrast, we estimated higher rates of 
turnover and lower capture probabilities in the study 
area for GOA transients. The most likely explanation 
for the latter pattern is that these whales were part 
of a significantly larger population with a more exten- 
sive range. The distribution of sightings was heavily 
weighted toward the ocean entrances and outer coast 
