Moreover, at least some of these ailments are age-related in otters (e.g., dental disease, Kenyon, 1969); thus, it is not surprising that they were more common in the WPWS sample, where 22% were old-age (9 + years) (31% of the Knight Island sample), than the sample from the Alaska Peninsula, where only 8% were old. Likewise, studies of other species have shown NVP-BKM120 supplier that gene expression can change dramatically in older age; in particular, inflammation/immune

response genes become overexpressed as the body becomes more frail (Ershler and Keller, 2000 and de Magalhães et al., 2009). This aging process may be speeded up from the stresses of a harsh environment. Additionally, facial wounds from mating and fighting have been shown to be a major contribution to infection (and subsequent mortality) in wild sea otters (Kreuder et al., 2003). In these respects, the captive otters were probably not a fair

reference group for free-ranging WPWS otters. Maybe the most interesting result of Miles et al.’s (2012) study was that the purportedly unusual gene signatures were considered sub-lethal, as none of the captured otters appeared to be fatally ill. Similarly, the radio-instrumented individuals studied by Bodkin et al. (2012), some of which were estimated to have encountered residual patches of submerged oil up to 24 times per year, all survived. If the NKI population is suffering long-term BYL719 demographic consequences from continued exposure to oil, then reproduction or survival

must be affected, yet in these studies, the individuals exhibiting the most extreme levels of exposure were not found to have reduced survival or declining fecundity. Bodkin et al. (2012) asserted that two elements are required to attribute delayed recovery to the spill: evidence of some demographic anomaly, and evidence of continuing exposure to oil. They claimed that “this exposure pathway provides a logical [our emphasis] explanation for why the northern-Knight Island sub-population PIK3C2G … had such a protracted recovery [if indeed that occurred]” ( Bodkin et al., 2012, p. 284). We argue that to attribute causation, one must observe a linkage between the exposure pathway and the effect, or at least a dose adequate to cause an effect; the mere existence of the exposure pathway is not sufficient, given that there is no evidence that otters could have been exposed to enough oil to have produced toxicological effects. Ecological risk assessment, as adopted by the U.S. Federal Government, demands much more than demonstrating the existence of an exposure pathway ( U.S. Environmental Protection Agency, 1998). Sea otters were also exposed to various other factors that could have affected their demography at NKI (discussed next).