2009a. Quantifying the effects of prey abundance on killer whale reproduction

• Main Authors: Eric J. Ward, Elizabeth E. Holmes, Ken C. Balcomb
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: Killer Whale; Orca; Orcinus orca; Killer whale
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.220.5028; http://alaskafisheries.noaa.gov/protectedresources/whales/killerwhales/articles/ward_holmes_balcomb_preyabundance09.pdf

1. Management decisions for threatened and endangered species require risks to be identified and prioritized, based on the degree to which they influence population dynamics. The potential for recovery of small populations at risk may be determined by multiple factors, including intrinsic population characteristics (inbreeding, sex ratios) and extrinsic variables (prey availability, disease, human disturbance). Using Bayesian statistical methods, the impact of each of these risk factors on demographic rates can be quantified and assigned probabilities to express uncertainty. 2. We assessed the impact of a wide range of factors on the fecundity of two threatened populations of killer whales Orcinus orca, specifically whether killer whale production is limited by availability of Chinook salmon Oncorhynchus tshawytscha. Additional variables included anthropogenic factors, climate variables, temporal effects, and population variables (population size, number of males, female age). 3. Our results indicate that killer whale fecundity is highly correlated with the abundance of Chinook salmon. For example, the probability of a female calving differed by 50 % between years of low salmon abundance and high salmon abundance. Weak evidence exists for linking fecundity to other variables, such as sea surface temperature.