[Tide Bites]: River Otters in a Land Without Rivers

“Tide Bites” is the monthly newsletter of UW Friday Harbor Laboratories. This month, outgoing FHL Postdoctoral Fellow Dr. Brent Hughes discusses his research on river otters. Read a short excerpt below, or read the full story at: http://depts.washington.edu/fhl/tidebites/Vol61/index.html. Dr. Hughes talks about his work with three undergraduates working under ‘Doris Duke Conservation Fellowships’. Undergraduates from UW or any school are invited to learn more about this summer opportunity at http://uwconservationscholars.org/.

“The FHL docks provide a unique opportunity to observe river otters, who frequent the docks and leave little “surprises.”  These droppings (scat) provide a glimpse into the river otter’s diet, and when combined with camera trap data can allow us to determine the timing of their foraging bouts and even the size of the animals. “

– Dr. Brent Hughes, FHL Postdoctoral Fellow

3 swimming river otters
A group of river otters hunting in the fully-marine waters of Drakes Estero, CA.

We live in an interesting time with respect to earth’s ecology.  Several centuries of extreme overhunting by humans – first by European colonials and later with commercial overexploitation and human population expansion – have resulted in animals at the top of most food webs being removed.  Top predators can influence entire food webs by keeping other consumers in check and stabilizing ecosystems, but we have little understanding of historical food web structure because predator loss (known as trophic downgrading) began so long ago.  Conservation research has found that the loss of top predators comes with a heavy cost, and groups such as the International Union for the Conservation of Nature (www.iucnredlist.org) have recognized some of these key species are under threat from extinction, mobilizing efforts to prevent further loss of biodiversity.

In the United States, legislation such as the Endangered Species Act and Marine Mammal Protection Act has helped protect vulnerable species from the risk of extinction by establishing laws to protect them and their habitats.  As their populations rebound, the return of these animals to their historical ecosystems will require us to rethink our underlying theories of their true breadth of habitats.  For example, we are finding that sea otters can be successful outside of the ocean by using tidal salt marshes for food, rest and pupping.  Alligators were once thought to lack the ability to process excessive salt, and therefore avoid marine environments.  However, my colleagues from Duke University (Drs. Brian Silliman and James Nifong) have found that not only do alligators use marine environments, but they can successfully hunt crabs and sharks.  These recolonization events also present a challenge to conservation, as managers adapt to novel food webs.

One species that has benefitted from conservation efforts over the last century is the North American river otter (Lontra canadensis).  Like many animals prized for their pelts, the river otter was under threat from overhunting, and by the early 19th century it was at risk for extinction.  However, primarily local-scale conservation measures and stricter water quality and pollution standards have allowed the river otter to rebound, and it now inhabits most of North America.  River otters are semi-aquatic mustelids (the weasel family), and are traditionally thought to be freshwater animals.  However, across both coasts of North America, river otters are expanding into coastal environments.  Certain populations along the west coast rely entirely on marine food sources because they do not live within proximity to major freshwater sources, such as the river otters in Drakes Estero in California.

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