Fourth International Orca Symposium and Workshop - CEBC - CNRS

− film produces the highest-resolution images and is recommended over digital
photography (although with technical improvements digital will likely take over as the
medium of choice in the future)
− images from video stills are almost worthless for killer whale photo-identification
− when the film is analysed, it is recommended that every identifiable individual in
every image be entered in a long-term database
In British Columbia, identification photographs have been extremely useful for analyses
of association patterns. In these analyses the frequency with which any two individuals are
either identified together in the same image or appear in consecutive images is used to
calculate an objective index of the strength of their social affiliation. A general discussion of
the application of photo-identification to association analysis ensued. van Ginneken
questioned the utility of association indices based on the number of photographic events,
rather than the total time spent together. Olesiuk agreed, and noted that if the study were
starting again, he would want to see proximity and time spent together measured, rather than
simple presence in the same encounter/ consecutive image. He said that the method worked
well in the BC study largely because of the enormous database: more than 50,000 frames—it
would not work as well in smaller studies. Barrett-Lennard pointed out that in the first 15
years of research in BC, researchers attempted to photograph groups of killer whales in single
images, but in recent years there has been more emphasis on full-frame photographs as
individuals--making association analysis by this method more difficult. According to the
methods used to date, this will indicate a weakening of the strength of association for many
pairs. Olesiuk agreed and noted that field researchers would do well to identify photographic
sampling criteria and stick to them. Several researchers noted that 1) regardless of the criteria
used regarding the number of whales per image, it is best to work systematically through
each group of killer whales in every encounter and 2) although the models established in the
early British Columbia studies are general helpful, researchers should establish photographic
sampling protocols based on the objectives of their own studies.
In addition to association analysis, identification photographs are used to estimate
abundance. A discovery curve is a useful way of generating a rough abundance estimate. In
this approach, one simply plots the total number of identified whales that have been
catalogued in each year of an study. When the total number of identified whales levels off
despite ongoing photo-identification work, it is assumed that most of the individuals in the
population have been identified. A second approach is sight / re-sight analysis. Here, a
researcher photographs as many whales as possible in the study area over a defined sighting
period. At a later point, he or she repeats the exercise, and then analyses the photographs to
determine how many of the individuals were sighted twice. In the method’s simplest form,
the ratio of the number sighted twice to the total number sighted is assumed to be equal to the
ratio of the total number sighted to the total population. Many sophisticated variants of this
basic relationship are described in the literature. Care must be taken when using photoidentification
data in sight / re-sight analysis because abundance estimates are strongly
influenced by photo-quality and animal distinctiveness. A powerful way of eliminating the
bias is to split the process into three stages: one observer or group of observers scores photoquality,
another scores animal distinctiveness, and the most experienced observer scores
matches between samples.
Acoustic Analysis
John Ford’s study of killer whale calls in late 1980’s and early 1990’s showed that
British Columbian killer whales use group-specific call repertoires. Furthermore, he showed
FOURTH INTERNATIONAL ORCA SYMPOSIUM AND WORKSHOPS
SEPTEMBER 23-28 2002, CEBC-CNRS, France
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