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Why Are Sea Otters So Furry?

As Sea Otter Awareness Week comes to a close, we wanted to highlight one of our explorers, Lily Maxine Tarjan or “Max”, who received a grant from National Geographic in August of this year to conduct the first in-depth analysis of the sea otter mating system. What are your favorite and least favorite things about...

As Sea Otter Awareness Week comes to a close, we wanted to highlight one of our explorers, Lily Maxine Tarjan or “Max”, who received a grant from National Geographic in August of this year to conduct the first in-depth analysis of the sea otter mating system.

What are your favorite and least favorite things about otters?

From a field biologist perspective, otters are amazing because they are so observable. They stay close to the coastline, and they eat all of their food at the surface of the water. These behaviors continue to help scientists gain knowledge about the near shore ecosystem.

History also makes sea otters interesting. They are the most recently evolved marine mammal (excluding polar bears) and come from a family of weasels. Their closest relatives are not adapted to the marine environment, which explains why they are so furry rather than fat.

I don’t like the craftiness of sea otters. Sea otters are so agile in the water that they can only be captured when they’re asleep. If they sense a diver, they take off and we’ve missed our shot at capturing them. This means that getting samples for a project is time and labor intensive. Once a sea otter is tagged, however, we get so much information that it is all worth it. I have little to complain about with this study species.

What is a typical day in the field like for you?

I start my fieldwork in Monterey, California at 8 A.M. At that time, it is foggy! I search for otters along a 25-mile stretch of coastline, which is the intensive study area for the Monterey Bay Aquarium. On any given day, I can only cover half of the range. The north side is more developed and ends in downtown Monterey, CA. The south side is gorgeous, but the otters are farther offshore and much more difficult to find. I set out in one direction with a telescope, a radio receiver, a pack of tracking equipment, and my cocker spaniel, Natasha. I work my way along the coastline, stopping my car anywhere with a good vantage point of the ocean. At each stop, I use a radio receiver with a large antenna that picks up a signal from any nearby otter that has a radio transmitter. If I hear the receiver beeping, I know to look for a certain otter. I scan the ocean for otters. If I find one (or a whole group!), I look for colored plastic tags on their hind flippers. Study otters can be identified individually based on the colors of their tags. Once I have located an otter, I record the otter’s location, behavior, the weather conditions, etc. My lab collects a lot of data; you never know what will be useful. I will use the locations of individual otters to map male territories and to determine how many females are generally found within each territory. After I am satisfied that I have found all of the otters at one site, I drive along the coastline to a new location. I repeat this procedure for a half or a full day. Then I head back to Santa Cruz for classes and data analysis.

Tarjan scans the Monterey Bay for sea otters. Photograph by Gena Bentall
Tarjan scans the Monterey Bay for sea otters. Photograph by Gena Bentall

What did the grant from National Geographic help you accomplish?

The National Geographic Grant funds my genetic analyses at a lab at UC Davis and my travel to otter sites in central California. My project objective is to rigorously describe the sea otter mating system. I aim to identify the resources—such as kelp canopy and invertebrate prey availability—that male sea otters defend in territories. Traveling to my field sites has allowed me to begin mapping the territories of individual males and to record the resources available within each territory. Ultimately, I want to identify the males that sire the most pups and contribute the most to population growth. Funding for genetics and paternity analysis is essential for determining the fathers of the pups. Overall, this information will allow me to identify the territory resources that contribute to reproductive success in this species.

Have you ever had something unusual happen while you were out in the field?

I think anyone who does observational fieldwork or wildlife photography can sympathize with this experience. A colleague and I were doing a six-hour energy budget on a male sea otter in Big Sur, CA. That means that we watch the same otter for six hours and record whatever he does. We were hoping to get some foraging data from this otter (information about what he eats). What did he do during those six hours? He slept. He slept the entire time. Then, ten minutes before the sun set, our delightful otter rolled out of his bed of kelp and started foraging. I guess he wanted to watch the sunset as he ate his dinner, because he swam out straight towards the setting sun. The result of his chosen direction was the blinding reflection of the sun in our telescopes. Our hard-earned foraging data looked something like, “Prey type: Unknown, unknown, unknown.”

What is the biggest threat for sea otters today?

There is no single “biggest threat”, but rather a multitude of threats to sea otters in California. The relative importance of individual threats varies by region and changes over time. Data collected by my colleagues from USGS and CDFG indicates that shark-bite mortality has increased greatly over the last ten years in a few locations, particularly at the northern and southern ends of the sea otter’s distribution in California. That may be the factor having the greatest impact on population growth at the moment. Other sources of mortality include nutritional stress, harmful algal blooms (HABS), bacterial infections and infectious diseases, and mating wounds inflicted by males. It is likely that pollution from land (including nutrients and pathogen pollution) contributes to the high incidence of HAB mortality and also infectious diseases, many of which originate from terrestrial animals. Another equally important consideration, however, are the synergistic effects of multiple threats. For example, there has been some suggestion that certain diseases may increase an otter’s likelihood of getting bitten by a shark. These connections between threats are a major challenge for conservation in general.

Have you ever gotten attached to a certain sea otter in particular?

My favorite otter so far is Jack. Jack is a territorial male who lives just north of the Monterey Bay Aquarium. He has two pink tags on his flippers, and he consistently sleeps in one patch of kelp that is only a stone’s throw offshore. He was the first otter that I got to know by name, and he certainly makes my job of finding him easy.

Are you working on a new project?

Studies of the sea otter mating system up to this point are descriptive and inferred based on behavioral observations. I plan to quantify the reproductive success of males that hold reproductive territories using genetic analyses. I would like to rigorously determine whether the sea otter mating system resembles that of elephant seals, where 3% of the males sire 92% of the pups, or resembles that of harbor seals, where males each have a nearly equal number of pups. I also want to identify the features that make a high quality territory, and how they relate to male reproductive success. I am considering features such as kelp canopy availability for resting, foraging opportunities, shelter from wind and waves, and territory size. I am excited to gain more definitive insight into the mating system and to identify resources that are important to reproduction in a threatened species.

If you had an endless supply of funds, what would your next project be?

Phew, can I tell you after I finish my PhD? There are a number of questions that arose during my current project. For example, are females attracted to resources or to the males themselves? What makes a charismatic male sea otter, and how could you measure it? I suspect that hormones relate to male personalities, particularly with respect to aggression. The challenge is that sea otter hormone levels go haywire when an animal is captured. A colleague at a conference told me about Katherine Ayres, who trained a dog to track whale scat to measure whale hormone levels. A solution like that to measuring hormone levels would offer many answers about sea otters, not just for my project.

How would you suggest we celebrate sea otter week?

This week is about awareness, so the most important way to celebrate is to spread the word! Find a fun fact and tell your friends. Sea otters are great for that. Did you know that they eat a third of their body weight every day? Can you imagine how many quarter pounders that would be for you?

Another piece of awareness is respecting wildlife. The most frustrating aspect of my fieldwork is watching kayakers get too close and disturb wild sea otters. Fleeing is a waste of the otter’s valuable energy. I would encourage people to admire and respect wildlife more.

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Meet the Author

Amy Bucci
Amy Bucci is a web producer for National Geographic. Her projects mainly cover National Geographic explorers, grantees and initiatives.