POPULATION TRENDS OF SOUTHERN RESIDENT KILLER WHALES (ORCINUS ORCA) FROM 1960-1999 David E. Bain1 and Kenneth C. Balcomb III2 Six Flags Marine World Vallejo, Vallejo, CA 94589 Center For Whale Research, Friday Harbor, WA 98250

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BACKGROUND INFORMATION In the mid 1960’s, prior to live-capture collections for oceanariums, it is believed that about 100 individuals comprised the Southern Resident community of killer whales. A decline in population levels occurred as a result of collections for public display through the early 1970’s (Hoyt 1990), decreasing the number of whales to about 70 individuals. Beginning in 1974, the Southern Resident community of killer whales was censused annually using photo-identification methodology. Based on these studies, the Southern Resident killer whale population was shown to recover to nearly 100 individuals by the mid-1990’s. However, during the last few years (1995-1999), a significant decline in population levels has been observed. In May, 1995, the population count was 98 individuals. By October, 1999, this number had dropped to 83 whales, a decline of over 15%. This recent decline led Baird (1999) to recommend to the Committee on the Status of Endangered Wildlife in Canada that this population be listed as threatened (since this population inhabits both U.S. and Canadian waters its status needs to be considered by both governments). Southern Residents are genetically isolated from other killer whales with which they share their range (Hoelzel et al. 1998, Hoelzel and Dover 1989). Olesiuk et al. (1990) summarized the life history parameters of resident killer whales from 19731987 (their study included Northern Residents in addition to Southern Residents). They characterized the per capita birth rate as 5.1%, the per capita death rate as 2.2%, so population growth was 2.9% per year. Females continued to reproduce until about 40 years of age, and over 75% of viable calves reached adulthood. Olesiuk et al. (1990) realized the population would not continue to increase forever, and suggested mortality might increase, birth rates might decline, and approximately half of juveniles would die before reaching adulthood when the population stopped growing. Ford et al. (1994) published an update of the membership of the population through 1993, but did not recalculate population parameters.

METHODS Recent data on births and deaths were collected by the Center for Whale Research. Expected population trends were calculated based on population parameters in Olesiuk et al. (1990), which were based on a period of population growth from 1973-1987. Births of new population members and deaths of known individuals were determined as described by Olesiuk et al. (1990), Bigg et al. (1990), and Bain (1990). The numbers presented here are based on population estimates for July 1 of each year. This was done to allow comparison of data from recent years, when data are available from most of the year, with data from earlier years, when data are available only from a short period during the summer (and thus counts reported here may differ slightly from other reports).

Mortality rates were calculated for each year. To smooth out random fluctuations, a five year moving average was also calculated. Removals for public display were treated as mortalities. In addition, natural mortality of 2.2% per year was assumed for the years prior to data collection (1960-1974). Fecundity was indexed as calves recruited per reproductive age female. A calf was counted as recruited if it was believed to be alive on July 1, typically corresponding to an age that would range from 3-9 months. Females were counted as reproductive if their age was estimated to be from 15 to 39. Expected calving was estimated at 20% of the number of reproductive females (Bain 1990). To allow testing for trends through time, data were pooled over periods corresponding to publication dates of prior research: 1974-1987 (Olesiuk et al. 1990); and 1974-1993 (Ford et al. 1994); and the time periods since (1987-1999 and 1993-1999). Expected rates in comparisons were based on the earlier period. Confidence intervals were based on a binomial distribution (Small and DeMaster 1995). Population estimates are shown in Figure 1. The population probably peaked at around 97 individuals prior to the start of extensive collections for public display in 1967. The population dropped to about 70 toward the end of collections in 1973. The population increased steadily through the 1980 census. The population then declined by 11% over the next four years. The population then resumed its increase through early 1995, when it reached its pre-capture levels. In the subsequent 4 years, the population declined by about 15%. Mortality remained near 2.2% for most of the census period. However, there was an increase in 3 of the 4 seasons from 1982-1985, and over the 6 seasons from 1994-1999 (Figure 2). Pooled mortality rates are shown in Table 1. Mortality rates from 1974 through 1993 did not differ from those reported by Olesiuk et al. (1990, p.4 for adult males and females, p.25 for juveniles) Adult male and female mortality was significantly higher in 1993-1999 than in 1974-1993 (p