Southern Sea Otters: Part 2

*** Our next Eyes on Conservation project comes from Sarah Chinn, a Wild Lens collaborator from The Maasai Giraffe and The Lost Migration videos. Sarah is currently a USGS Western Ecological Research Center biologist studying Southern sea otters in San Luis Obispo County, California. This is the second half of a two part series on sea otters. Read part one here. ***

Radio tracking Sea Otters from shore. Photograph by Sean Bogle.

SEA OTTER FAST FACTS:

• For thermoregulation they depend on a clean, water resistant, and well-groomed coat that has about 650,000 hairs per square inch – more in a sq. inch than a human has on its entire head.
• Sea otters do not have blubber like other marine mammals (i.e. whales and seals), in order to stay warm they need to spend a significant time foraging and eat about 25% of their body weight each day.
• Female give birth once a year and pups can be born any time of the year, but the peak is spring and a smaller peak in fall. Females care for their pups for approximately 6 months.

Sea otter population numbers are slow to increase due to several factors, many of which are anthropogenic, or caused by humans. Causes of death include but are not limited to: white shark bites, infectious diseases that cause encephalitis (Toxoplasma gondii transmitted by felid feces and Sarcocystis neurona transmitted by opossum feces), acanthocephalan worms, bacterial and viral infections, domoic acid toxicity, microcystin poisoning. Other factors that surely influence mortality are limited food resources and exposure to chemical contaminants.

Sea Otter habitat: the Kelp Forest. Photograph by Beth Hoffman.

Sea otters are indicators of the health of the nearshore ecosystem. When population numbers are abundant, sea otters are a keystone species in the nearshore community, meaning they directly limit (via predation) numbers of herbivorous species such as urchins and thereby promote the growth of kelp forests that then leads to higher primary productivity (i.e. photosynthesis) and species diversity.

However, in parts of California as well as southwest Alaska, sea otter populations have been so decimated that they are not effective in this keystone role. Population monitoring is important to understand the many factors that are limiting the recovery of populations.

Our study otters are monitored every day. The main method we use is telemetry. Each study animal is assigned a unique VHF radio frequency, and we can hear that frequency when we are near the otter. We can also tell certain behaviors just from hearing the signal, i.e. if the otter is foraging if we hear the signal for a small length of time (surface time eating) and then do not hear it for 1-3 minutes (diving), then hear it again (back on surface with prey item)…repeatedly. When the otter is diving or under the water we cannot hear the transmitted signal.

Southern Sea Otters. Photograph by Sean Bogle.

Once we hear a signal we can judge the approximate distance (far or very close) and obtain a bearing of where that otter is approximately located. When we get a visual of the otter with our telescope, we can confirm its identity by its uniquely colored flipper tags. From there we can observe behavior, foraging, interactions and where it is i.e. resting in a Macrocystis kelp bed with 4 other sea otters.

We also conduct 12-hour activity budgets on single otters. The purpose of this is to obtain a “snapshot” of that otter’s daily life. During these bouts we take behavioral data on that otter every 10 minutes and do our best to determine what prey items it is eating, how many, success rate, dive duration, surface times, and how much of the day is spent resting, foraging, etc.

– Sarah Chinn