Matkin et at: Abundance and residency patterns of two sympatric populations of Orcmus orca in the northern Gulf of Alaska 
149 
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Figure 4 
Annual estimates of the probability of survival <j> t , for both ATI and Gulf of 
Alaska (GOA) transient killer whales (Orcinus orca). Solid squares represent 
the posterior median, and bars represent the 95% probability intervals. 
trend model, revealed contrast- 
ing patterns (Figs. 5 and 6). The 
estimated number of GOA whales 
using the study area in each an- 
nual period, N t , showed relatively 
little variation from a low pos- 
terior median of six whales in 
1996 and 2005 to a high of 18 
in 1990. The ATI whales showed 
evidence of greater abundance 
changes, from an estimated high 
of around 22 in 1989 to a low of 
seven at the end of the series. As 
a result, there was strong evi- 
dence that the abundance of ATI 
whales declined over the study pe- 
riod and unequivocal support for 
inclusion of the trend model for 
abundance with p(gP= 1) = 1. The 
entire posterior distribution for 
the trend parameter, /3 lt fell be- 
low zero, indicating a probability 
of 1.00 of a downward trend. In 
contrast, the posterior distribu- 
tion for the trend parameter was 
evenly spread above and below 
zero for GOA whales, with 51% of 
the posterior density in favor of a 
negative trend. As a result, there 
was little support for including 
a model for trends in abundance 
with p(gP= 1) = 0.02. Correspond- 
ingly, the posterior density for 
the change-point was distributed 
evenly across all years for GOA 
whales and reflected no obvious 
changes in abundance. For ATI 
transients, in contrast, there 
was a distinct peak in the poste- 
rior probability distribution for a 
change-point, and 97% of the pos- 
terior density for an abundance 
change occurred in the five years 
after 1989. 
Emigration of GOA transients 
away from the study area was 
also supported by photographic 
resighting data from southeast- 
ern Alaska and British Columbia 
(Table 2). For 1995-2007 there 
were 16 encounters with GOA transient whales in 
these adjacent regions, including one (5 June 2001) 
with GOA transients in association with known mem- 
bers of the west coast transient population (Matkin 
et al., 2007b). There were no resighting data outside 
of Prince William Sound-Kenai Fjords for ATI tran- 
sients despite substantial survey effort in southeastern 
Alaska (Dahlheim and White, 2010) and in adjacent 
regions to the west of the study area (Matkin et al., 
1999, 2007a; Durban et al., 2010; senior author, un- 
publ. data). Additionally, the one tagged ATI transient 
did not travel out of the area. All these observations 
support the inference from the mark-recapture model 
of high fidelity to the study area. 
Satellite-monitored LIMPET tags were attached to 
GOA transients in Prince William Sound on four occa- 
sions for a total of 73 days of transmissions (Table 3). 
One individual (AT73) was tagged on two occasions 
in different years. Tagged whales traveled a total dis- 
tance of 7107 km during 73 days for an average move- 
