4b), apparently due to a lower proportion of click here adult females in this area (Bodkin et al., 2002). Although many otters from NKI have been radio-tagged since the spill, no studies have reported unusually high mortality there, and since the months after the spill, no dead otters have been recovered for which mortality was attributed directly or indirectly to oil contamination. Secondly, SKI and NKI showed parallel population dynamics despite dramatically different oiling levels (Fig. 4a). Thirdly, instead of slowly recovering over time, otter numbers at NKI dropped sharply after

2001 (Fig. 3b), coinciding with an abrupt decline in numbers at unoiled Montague Island (Fig. 3a). That same year investigators discovered more buried oil persisting on shorelines of WPWS than was previously thought (Short et al., 2004), suggesting a possible pathway for continued contamination of otters digging in the intertidal zone, but no explanation for why otter numbers would decline so suddenly (along both oiled and unoiled shorelines) 12 years

after the spill. Short et al. (2006, p. 3728), who investigated the distribution of subsurface oil residues on shorelines at NKI, suggested that otters digging for clams in this region would “encounter lingering Exxon Valdez oil repeatedly during the course of a year,” perhaps at least once every 2 months, and concluded that this frequency of encounter would be sufficient to affect their health and thus hamper population growth. Z-VAD-FMK in vitro Neff et al. (2011) pointed out, however, that Short’s estimate assumed that otters dig for clams everywhere along the shoreline and that oil residues occur evenly across all shoreline substrates – neither of which is correct. Otters dig for clams in perpetually-wet sandy or gravel beaches in the lower intertidal zone, whereas remaining Histidine ammonia-lyase oil residues are sequestered in small pockets in mid- and upper tide zones behind boulders or under cobble, protected from wave and storm action ( Neff et al., 2011). Indeed, the protection afforded by this substrate is the very reason that some oil remained in the environment.

Clams are generally not found in this type of habitat, and otters do not (and cannot) dig there. When otters dig for clams, they leave pits in the substrate, which may last for many months and are readily visible along shorelines at low tide. Boehm et al., 2007 and Boehm et al., 2011 and Neff et al. (2011) found that foraging pits along NKI shorelines in 2006 were distinctly separated by habitat and tidal zone from pockets of subsurface oil residues that existed within the intertidal zone, suggesting that foraging otters would rarely encounter oil. These results spurred a further investigation by Bodkin et al. (2012), who searched soft-sediment beaches in 2008 and found more otter pits in the mid-intertidal zone than Boehm et al. did along all shoreline types in NKI. Bodkin et al. also found traces of oil in or near some otter pits.