File Entry: Comparative Demography and Viability of Northeastern Pacific Resident Killer Whale Populations at Risk file

Created: 2014-09-11 09:03:19
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Comparative Demography and Viability of Northeastern Pacific Resident Killer Whale Populations at Risk.

L.A. Vélez-Espino, J.K.B. Ford, H.A. Araujo, G. Ellis, C.K. Parken, and K.C. Balcomb
Fisheries and Oceans Canada
Science Branch, Pacific Region
Pacific Biological Station
Nanaimo, BC
V9T 6N7

Canadian Technical Report of
Fisheries and Aquatic Sciences 3084


Two distinct populations of resident killer whales (Orcinus orca) in the northeastern Pacific Ocean have been identified in Canada and the U.S. as being of conservation concern. In this paper we quantify the differences in demographic rates between southern residents (SRKW) and northern residents (NRKW) and merge perturbation and population viability analyses to study population responses to potential management actions targeting specific vital rates. The life cycles of these two populations were modeled as two-sex stage-structured models based on high-quality demographic data encompassing one killer whale generation (25 years; 1987-2011). Projection matrices were used to compute stochastic population growth and run stochastic simulations of extinction risk and recovery probabilities. Expected population growth rates are 0.91% annual decline (lambda = 0.9909; 95% CI: 0.9719-1.0081) for SRKW and 1.58% annual increase (lambda = 1.0158; 95% CI: 1.0027-1.0285) for NRKW. Conservatively, and under status-quo conditions, SRKW’s population size is expected to reach 75 individuals in a generation, with an extinction risk of 49% and an expected minimum abundance of 15 during a 100-year period, whereas NRKW’s population size could reach 400 individuals in a generation in the absence of density dependence, with an extinction risk of zero and an expected minimum abundance of 238 individuals during a 100-year period. SRKW’s lower realized and expected population growth as well as its lower viability relative to NRKW was mainly ascribed to SRKW’s lower production and survival of viable calves, lower proportion of juveniles transitioning into young reproductive females, and greater vital rate variances.

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