The following information is part of the text from the report "Status of killer whales in Canada", by R.W. Baird.
Population Size and Trends
No world-wide population estimates are available. Regional population estimates, where available, have been derived through photo-identification surveys and/or line-transect surveys. Line-transect surveys have generally been used in areas where more intensive photo-identification studies are impractical (e.g., the Southern Ocean), but are also accompanied by large confidence limits (see e.g., Matkin and Saulitis 1994). Furthermore line-transect surveys do not allow for discrimination of individuals from sympatric populations.
In B.C., four separate populations must be considered, transients, "northern" and "southern" residents, and "offshore" killer whales (which should probably be considered "offshore" residents, see discussion above). The most detailed information is available for northern and southern residents, as all of the southern resident pods and many of the northern resident pods are censused each year. As all individuals are recognizable, the census provides an actual count of the number of individuals in the population. As of 1998, the southern resident population numbered 89 individuals (van Ginneken and Ellifrit 1998). While the population has grown since the cessation of the live-capture fishery in 1973, the current population is smaller than the population near the start of that fishery (Figure 5), and has declined for the last three years (1996-1998). Such a decline is not unprecedented (Olesiuk et al. 1990; Figure 5); since the cessation of the live-capture fishery the population showed a similar decline from 1980 through 1984. As discussed under Limiting Factors (below), this earlier decline was likely due in part to the removal of animals in the live-capture fishery (Olesiuk et al. 1990). The most recent decline appears to have resulted from an increased death rate. Using data presented by van Ginneken and Ellifrit (1998), the average per capita death rate between the years 1995 to 1998 (mean of 0.052) is significantly higher (Mann-Whitney U-test, p = 0.0084) than the average for the preceding 19 years (mean of 0.021 from 1976 through 1994). The per capita birth rate for this same period (mean of 0.034) is similar to the average for the previous 19 years (mean of 0.038). In the period from 1995 to 1998, age-specific mortality rates for mature females between 35 and 65 years of age are four to five times higher than reported by Olesiuk et al. (1990; see Table 2). It is unclear however whether this current population decline may be due to demographic stochasticity, or even perhaps delayed effects of the removal of animals in the live-capture fishery, and a study modeling the probability of such effects occurring by chance or due to selective removals is warranted.
As of 1993 the number of northern residents thought to occupy British Columbia waters (if only seasonally) numbered approximately 200 individuals (Ford et al. 1994a). More recent surveys have been undertaken, but the Department of Fisheries and Oceans, Pacific Region, which undertakes these surveys, has not released current data. This "population" has been growing at a relatively stable rate since the 1960s (Oleisuk et al. 1990; Ford et al. 1994a). Because of the associations and shared mtDNA haplotypes with residents in Alaska, the effective population size for northern residents should probably be considered larger than the absolute number recorded within B.C. waters, and the overall trend in the larger population is unknown (since less complete information is available for Alaskan residents). Population estimates for several regions of Alaska are available and are summarized by Matkin and Saulitis (1994). Taking into account only those whales documented in B.C., there was no evidence of density-dependent effects as of the late 1980s (Meyers 1990), but data collected since then have not yet been examined. Brault and Caswell (1993) examined pod-specific demography of residents, and concluded that most of the variance in individual pod growth rates was due to variance in adult reproductive output, rather than effects of pod size or structure.
Population size is not known for "offshore" killer whales. The first "offshore" killer whales groups were encountered in the mid-1980s, and about 200 "offshore" killer whales had been documented as of 1993 (Ford et al. 1994a). These whales have been identified over a relatively short period of time, thus while natural mortality should only have accounted for a few deaths, new individuals are being regularly documented (Walters et al. 1992; Ford et al. 1994a). Of 56 "offshore"-type whales documented off California, 23 were direct matches with "offshore" killer whales recorded off Oregon, Washington, British Columbia and southeast Alaska (Black et al. 1997). No trend information is available for this population.
For transient killer whales, the total population size is unknown but probably numbers in the low hundreds. Seventy-nine transients had been photo-identified in B.C. and Washington up to 1986 (Bigg et al. 1987), and a further 90 or more have been documented in the 10 years since (Ford et al. 1994a). Considering their wide-ranging movements, known associations, and shared genetic haplotypes, transients from bordering areas should be considered part of the same population which uses B.C. waters (Black et al. 1997). Of 79 transients documented in southeast Alaska, 69 have been observed in British Columbia (Dahlheim et al. 1997; Ford and Ellis 1999). One hundred and five transients have been documented off California, and at least 10 of those have been documented in B.C., Washington, or further north in Alaska (Black et al. 1997). New individuals are occasionally being recorded in some areas (e.g., van Ginneken et al. 1998). Because of the long-resighting interval for some transients, it is not possible to determine deaths in the same way as for residents, thus some of the whales already documented are probably no longer living. The use of mark-recapture models for estimating transient population size is not appropriate, as the probability of encountering transients in any particular area differs between groups (see Baird and Dill 1995, and differences between regional catalogues, e.g., Black et al. 1997; Palm 1997; van Ginneken et al. 1998). Population trend information is unavailable.
No population estimates are available for the Canadian Arctic or Atlantic waters, though compilations of records have been presented by Lien et al. (1988), Mitchell and Reeves (1988), Reeves and Mitchell (1988a) and Wenzel and Sears (1988). Some anecdotal evidence suggests that the number of whales which utilize the St. Lawrence has declined in the last 60 years; Vladykov (1944) reports that large numbers of killer whales (including groups up to 40 individuals) were found in the area in spring and fall, feeding on belugas. It is clear that numbers which utilize the area today are much smaller (Mitchell and Reeves 1988; Wenzel and Sears 1988). The largest group reported off eastern and Arctic Canada in the last 20 years appears to be of 22 individuals (Finley 1990). Mitchell and Reeves (1988) note that killer whales appear to be "uncommon in the western North Atlantic relative to other medium-sized and large cetaceans, and that they may be numerically few" (this view is supported by data presented by Lien et al. 1988). As noted above, a review of western North Atlantic records subsequent to those mentioned above is warranted. Regional estimates for some portions of the eastern North Atlantic suggest relatively large populations (Anonymous 1993). Off West Greenland, considerable survey efforts have been undertaken since 1984, yet few killer whales have been recorded, suggesting that killer whales are not abundant in that area (Anonymous 1993).