LAUSR

Sea otters live dangerously. The smallest of marine mammals has dense fur but no blubber, and must take in an enormous number of calories each day to stay warm and balance metabolic costs (Morrison et al. 1974, Yeates et al. 2007). Along the open coast in places like Monterey Bay, California, near the center of the recovering southern sea otter (Enhydra lutris nereis) range, starvation is not uncommon, particularly for nursing mothers that must not only meet their own caloric needs but those of their pups (Thometz et al. 2014). Anything that can help tip the balance to keep an animal from going into the red, on a metabolic balance sheet, will help an otter survive. Hauling out, the act of leaving coastal waters to rest on the shore, can have a big benefit to sea otters. As any swimmer knows, one loses body heat much faster in water than in air. In Alaska, particularly on the Aleutian Islands, northern sea otters regularly haul out, sometimes in large groups (Riedman and Estes 1990). However in California, southern sea otters are only rarely observed hauling out, mostly in secluded spots during darkness (Faurot 1985), and there have been no extended observational studies of the behavior of hauled out otters in the wild. Indirect evidence of hauling out has been gleaned from temperature loggers attached to otters, since air temperatures are notably warmer than the cold waters along the California coast (Tinker et al. 2013). This indirect evidence suggests open coast otters haul out fairly rarely (4.1% of the time in Monterey, 0.4% of the time along the Big Sur coast). We have found that sea otters in Elkhorn Slough, the largest estuary within the range of the recovering southern subspecies, frequently haul out on protected salt marshes for extended periods (Fig. 1). They do this even in the middle of the day: the behavior seems to be driven more by tides than time of day, with the otters entering the flooded tidal creeks during high tides and resting on the marsh until the tide drops again. To our knowledge, this is the first report in the literature of sea otters using marshes to haul out anywhere in the range of the species. Our discovery of how extensively otters haul out on salt marshes was serendipitous, as are many ecological surprises (Doak et al. 2008). Indeed, the role of serendipity is highlighted in a recent memoir by a leading sea otter ecologist (Estes 2016). We began monitoring an expanse of salt marsh and tidal creeks to ensure there was no disturbance to marine mammals resulting from a nearby restoration project. Since we had to watch all day long, during construction hours, we found a nearby hill that provided a broad vantage point for observing the marsh, creeks, and restoration site (Fig. 2). It turned out this was a game changer in our common perception of sea otter behavior. If you approach otters in the salt marsh ecosystem by boat or on foot, they quickly scatter. However, looking from above, with telescopes from our hill, we were able to observe their undisturbed behavior. Following the completion of the restoration project, our team of citizen scientists has continued intensively monitoring this salt marsh ecosystem from the adjacent hill. What we observe is that otters spend about a third of the time spent in this tidal creek network hauled out on the marsh. Their haul out time mostly appears to consist of resting, with just a bit of grooming at the start and end of a haul out period. We sometimes observe