The effect of organohalogen contaminants on western Steller sea lion survival and movement in the Russian Far East

The western stock of Steller sea lions (Eumetopias jubatus) have experienced dramatic declines since the 1960s, particularly in the western Alaskan and Asian portions, which have continued to decline or stabilized at low levels. Multiple causes for this decline have been proposed and may include anthropogenic contamination from organohalogen contaminants (OCs). These include polychlorinated biphenyls (PCBs) and dichlorodiphenyltrichloroethane (DDT), which have not been ruled out as a potential cause for the lack of recovery. The objective of this study was to determine the effects of OCs on survival and movement probabilities estimated in program MARK using resighting data collected from 2003 to 2009. PCBs and DDTs were measured in whole blood from 136 (74 males and 62 females) individually marked, free-ranging pups from four Russian Far East rookeries. The mean concentration of ∑ PCB and ∑ DDT was 4.25 ± 5.12 and 3.22 ± 4.28 ng g− 1 ww (n = 136), respectively, and the average ∑ PCB and ∑ DDT concentration for those above the aggregate mean (n = 44) was 9.25 ± 6.55 and 7.65 ± 5.21 ng g− 1 ww, and those below the aggregate mean (n = 92) the concentration was 1.86 ± 0.89 and 1.11 ± 0.65 ng g− 1 ww, respectively. The lowest estimated probabilities of survival occurred in the first year, ranging from 38% to 74%, but increased for ages 1-9, ranging from 82% to 94%. The greatest movement occurred from Medny Island west toward the Kamchatka Peninsula (33%) and to Bering Island (18%), and low movement estimates for other natal rookeries was largely due to minimal resighting effort. The estimated probabilities of resighting varied by location (48%-87%), but had greater precision than survival or movement parameters. Survival and movement were most affected by age and location rather than OCs.