144 
Fishery Bulletin 1 10(2) 
et al., 2005), and by genetics (Barrett-Lennard et al., 
2000 ). 
Because of the lack of conclusive studies of genetic 
divergence across their range, the Gulf of Alaska- 
Aleutian Islands-Bering Sea transient stock includes 
all transient killer whales found in Alaskan waters 
west of southeastern Alaska other than the ATI stock 
(Allen and Angliss, 2010). However, photographic 
mark-recapture analyses indicate little apparent 
overlap between the Gulf of Alaska whales and the 
western segment of the stock (Matkin et al., 2007a; 
Durban et al., 2010). In this article we will refer to 
the non-ATI transients in the study area only as 
the Gulf of Alaska (GOA) transient population and 
consider their range to be the Gulf of Alaska and 
north gulf coast, which stretches from southeast- 
ern Alaska west through the Kodiak Island region. 
Although the full range and offshore distribution 
of the GOA transients is poorly defined, they have 
been photographed irregularly to the southwest of 
Prince William Sound-Kenai Fjords study area in 
Kachemak Bay, lower Cook Inlet, and Kodiak Island 
waters (Maniscalco et al., 2007; Matkin et al., 1999; 
C. Matkin, unpubl. data). 
The ATI transients are considered a separate stock, 
are classified as depleted under the Marine Mammal 
Protection Act, and currently number only seven in- 
dividuals (Allen and Angliss, 2010). The home range 
of the ATI transient population appears much more 
restricted than that of the sympatric GOA transients 
(Matkin et al., 1999; Scheel et al., 2001) or the para- 
patric west coast transients of southeastern Alaska, 
British Columbia, and Washington State coastal wa- 
ters (Ford and Ellis, 1999). ATI individuals have not 
been identified outside of the coastal waters of Prince 
William Sound and the Kenai Fjords (Matkin et al., 
1999; Saulitis et al., 2005). Because of its limited 
range, small population size, and the consistent re- 
sightings of subgroups and individuals, the population 
dynamics of the ATI population have been monitored 
directly from annual photographic data (Matkin et al., 
2008). However, for the GOA transients, the infrequent 
resightings of individuals, fluidity in group structure, 
and larger population size have made it impossible to 
directly track births and deaths and require a mark- 
recapture sampling approach to estimate abundance 
and assess population changes. 
In this article we fit mark-recapture models to 
long-term photographic identification data (1984 to 
2010) to examine abundance trends, site fidelity, and 
demography for the ATI and GOA transients in the 
coastal waters of Prince William Sound and the Ke- 
nai Fjords. We compare our results with previously 
described changes in the ATI population (Matkin et 
al., 2008) and contrast these results with our paral- 
lel analysis of the GOA transient population. We use 
photographic resighting data and satellite telemetry 
data to further differentiate the range of the two 
populations and provide a context for their differing 
abundance trends. 
Materials and methods 
Photographic mark-recapture 
Identification photographs of killer whales were 
obtained from the waters of Prince William Sound, 
Kenai Fjords National Park, and the adjacent coastal 
waters of the northern Gulf of Alaska (Fig. 1A). The 
entire region was not surveyed in any given year; how- 
ever, survey effort was focused towards Prince William 
Sound in the earlier years of the study (1980s) and was 
more evenly balanced across the region in later years. 
Photographic surveys were conducted between April 
and September over the 27-year period between 1984 
and 2010. In order to increase capture probabilities, 
survey effort was focused in areas known to be used by 
killer whales, or in response to sighting reports. Data 
were collected from a variety of platforms; all were 
small vessels less than 15 meters in length powered 
by either gasoline-outboard or diesel-inboard engines. 
During an encounter, whales were approached at a 
distance of 15 to 45 m and photographs were taken of 
the left side of each whale present, showing details of 
the dorsal fin and saddle patch (Matkin et al., 1999). 
Photographs were obtained with either 1) a Nikon 
F-100 SLR camera 1 with fixed 300-mm lens and Fuji 
Neopan 1600 black and white film, or 2) Nikon D70 
and D200 digital cameras with 80-200 mm zoom or 
300-mm fixed lenses. Individual whales were distin- 
guished by the shape and pattern of natural markings 
on their dorsal fins and adjacent saddle patch (Matkin 
et al., 1999) and were subsequently matched to cata- 
logs of photographs from previous years. Individual 
matches were corroborated by using co-occurrence 
with consistent associates because transient killer 
whales have been shown to travel in stable (and often 
life-long) matrilineal groupings (Ford and Ellis 1999; 
Matkin et al., 1999). Photographs were evaluated for 
quality, and only photographs resulting in reliable 
identifications were used. Typically, the entire group 
was photographed. Membership in the ATI or GOA 
transient population was determined either by genetic 
sampling, acoustic analysis, or observation of repeated 
association with other members of the population. 
We treated these photographic identifications and 
re-identifications as “captures” and “recaptures” to 
which analytical mark-recapture techniques could be 
applied for estimation of abundance and demographic 
parameters (Hammond, 1986, 1987, 1990). 
Individual whales were not seen in every year that 
they were known to be alive, likely in part because of 
the movement patterns of whales relative to the geo- 
graphical boundaries of the study area. This factor 
highlighted the need to allow for temporary emigration 
in the capture-recapture modeling. The popular Cor- 
mack Jolly Seber (CJS) model for estimating survival 
1 Mention of trade names or commercial companies is for 
identification purposes only and does not imply endorsement 
by the National Marine Fisheries Service, NOAA. 
