Matkin et al.: Abundance and residency patterns of two sympatric populations of Orcinus orca in the northern Gulf of Alaska 
153 
I50°W 140°W I30°W 
I — r~| — i — i — i — i 
0 37.5 75 150 Kilometers 
Figure 7 
Map of filtered movement tracks of (A) Gulf of Alaska (GOA) (4) and (B) 
ATI (1) transient killer whales (Orcinus orca) tagged with a low impact 
minimally percutaneous external-electronics transmitter (LIMPET) 
and subsequently tracked in 2007-10 as summarized in Table 3. 
2007). Maniscalco et al. (2007) found 
Steller sea lions to be the dominant 
prey, at least during the non-winter 
periods in the Kenai Fjords region. Re- 
cent observations of GOA transients in 
southeastern Alaska, described in this 
article, indicate increased use of that 
region where, perhaps not coinciden- 
tally, Steller sea lion and harbor seal 
numbers have increased substantially 
in recent decades (Allen and Angliss, 
2010 ). 
The combined numbers of both GOA 
and ATI transients that used Prince 
William Sound and Kenai Fjords over 
the course of a season was very low 
(currently estimated at -16 whales in 
2010) when compared with adjacent 
areas. In contrast, the parapatric west 
coast transient population in the coast- 
al waters of southeastern Alaska, Brit- 
ish Columbia, and Washington State 
numbers more than 200 individuals 
(Ford et al., 1999). Also, an annual ag- 
gregation of 80-100 transient whales 
has been reported in the Unimak Is- 
land region of the eastern Aleutian Is- 
lands in May and June (Matkin et ah, 
2007; Barrett-Lennard et al., 2011), 
and more than 300 transients use the 
coastal waters of a broader region of 
the Gulf of Alaska and Aleutian Is- 
lands (Durban et ah, 2010). These 
differences likely reflect lower prey 
availability for mammal-eating killer 
whales in the northern Gulf of Alaska 
compared with adjacent regions. 
Nuclear genetic diversity (Barrett- 
Lennard, 2000) indicates that the ATI 
transients were once a much larger 
population. This, coupled with their 
more recent sharp decline, makes 
it unlikely that predation by these 
whales was a significant factor in dra- 
matic decline of harbor seals in Prince 
William Sound in recent decades. Al- 
though it is conceivable that ATI pre- 
dation may have slowed harbor seal 
recovery, it is possible that the recent 
rebound in harbor seal numbers in 
Prince William Sound benefited from the ATI decline. 
In the ten-year period 1997-2006, harbor seal numbers 
increased an average of 1.66% per year (95% confidence 
interval=0.34% , 2.98% per year) (Small 3 ). 
Maniscalco et al. (2007) suggested that Steller sea 
lions were a primary prey for GOA transients in Kenai 
Fjords, at least seasonally, and that the small number 
3 Small, R. 2010. Personal commun. Alaska Department 
of Fish and Game, Juneau, Alaska 99802. 
of transients that used the area was not likely to have 
caused a decline in Steller sea lions. The consistent 
low numbers and lack of apparent increase in use of 
the area by GOA transients found in our study argue 
for a relatively even predation pressure on Steller sea 
lions in recent decades and support the conclusions of 
Maniscalco et al. (2007). In our population analysis 
we find little support for the hypothesis that declines 
in harbor seals or Steller sea lions in Prince William 
Sound and Kenai Fjords were a direct result of pre- 
