Population assessment of western gray whales in 2006. Paper SC/59/BRG41 presented to the International Whaling Commission

• Main Authors: Justin G. Cooke, David W. Weller, A L. Bradford, Er M. Burdin, Robert L. Brownell
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Published: 2007
• Subjects: Pacific; Reeves; Sakhalin
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.551.6994; http://cmsdata.iucn.org/downloads/updated_population_assessment.pdf

A population assessment of the western gray whale (Eschrichtius robustus) was conducted using photo-identification data collected off Sakhalin Island under the joint Russia-U.S. programme from 1994 to 2007. This is an update of the assessments by Reeves et al (2005) and Cooke et al. (2006) which used data up to 2003 and 2005 respectively, fitted to the same, individually-based population model. New median estimates of key population parameters (with 90 % Bayesian confidence intervals) are 0.978 (0.967- 0.987) for the non-calf annual survival rate; 0.78 (0.69- 0.86) for the survival rate from “calf “(~6 mo age) to “yearling ” (~18 mo age); 2.5 % per annum (1.6 % – 3.5%) for the average annual rate of population increase over 1994-2007; 0.45 (0.39- 0.52) for the female sex ratio and 130 whales (120- 142) for the 1+ (non-calf) population size in 2008. The updated assessment is more optimistic than Reeves et al (2005) mainly because of the reduced calving intervals observed in recent years, implying a higher reproductive rate. The modal calving interval has shortened from 3 years up to 2002 to 2 years post-2002. Forward projections of the population model to 2050, assuming no additional mortality or disturbance to reproduction, indicate a high probability (>99%) of population increase. Five whales (all female) have been caught or found dead on the Pacific coast of Japan