Merav Ben-David grew up on a small family farm in Israel. As a child, she rode horses and cared for abandoned baby birds and small animals found in the fields. Her fascination with animals eventually led to studies in biology, earning Bachelor’s and Master’s Degrees at Tel-Aviv University and a Ph.D. at the University of Alaska. As a young woman during her undergraduate years, she began researching otters in 1982 around the Sea of Galilee. She floated the small streams from the Golan Heights to the Sea of Galilee on inner tubes to survey Eurasian otters.
Merav is now a professor at the University of Wyoming in the Department of Zoology and Physiology, but her decades studying otters have taken her many places around the world. She focuses on river otters. Most river otters actually live near the ocean in the marine environment.
“I have studied river otters that have probably never seen a river in their lives. If you do a global abundance survey, the highest numbers are in coastal environments. In the Rocky Mountains, you’d be hard pressed to find enough fish to support a large otter population. Otters used to live all over North America before trapping and water pollution reduced their numbers. But inland otters have low densities, while coastal otters occur at high densities.”
In the U.S. in the 19th and 20th centuries, otters were hunted for their thick fur and had become a rare sight by the 1900s. The last confirmed river otter in Colorado was taken by trapper Nat Galloway in the lower canyon of the Yampa River in 1906 or 1909. Reintroductions of river otters in the 20th century have brought them back to many different environments including rivers, lakes, ponds and marshes.
Otters are natural swimmers with short legs, webbed feet, a long flexible body and strong tail. Their eyes, nose and ears are on the top of their head so they can observe what is happening out of the water while most of their body stays underwater. On long dives, they can actually close their nostrils and ears, and their dense fur keeps them warm in cold water.
In the Rocky Mountains, otters are usually solitary except for mothers raising their young, or small groups that form where there is plenty of prey. According to Merav, “Otters are very flexible socially. They will form groups where there is more food to share. Otters are amazing. If one is injured and a healthy otter in the same group catches a fish, it will give it to the injured animal. The injured otter makes squeaky ‘pup noises,’ and other otters will feed it. But in most river systems in the Rocky Mountains, there are too few otters, and they are solitary because there isn’t enough food to share. If you do see a large group, 3 or 4 adults together, those will be all males. Usually the groups are male and the females are more solitary. That’s opposite of most mammals.”
River Otters, linocut by Jill Bergman
Pups are born in the spring in dens near the water. Otters don’t dig their own dens, but use empty hollows, abandoned burrows of other animals, or even beaver lodges. There are usually one or two pups per litter born in the mountains, but otters can have up to five pups in areas with more abundant food sources. Pups are born furry, blind and toothless. They are entirely reliant on their mother at first. As they grow, she teaches them to swim and hunt until they are ready to be on their own after about a year.
Otters communicate with squeaks, whistles, yelps, growls and body posture. Other important communication tools they use are scent marking and urinating or defecating in certain areas called latrines. Soon after a mother gives birth, she starts scent marking to announce herself to attract a new mate. Otters will breed shortly after the female gives birth, but embryo implantation is delayed for about 10 months while the mother raises her newborn pups.
River otters eat a variety of aquatic animals including fish, crayfish, frogs, reptiles and birds. They have a high metabolism and eat about 10% of their body mass per day. Mothers have to work extra hard to feed their pups and themselves. According to Merav, “Otters eat everything aquatic, occasionally birds, especially ducks. I’ve seen an otter and a bald eagle coordinate hunting ducklings. The otter rose from beneath and the eagle bombed them from above. Sometimes the otter won, sometimes the eagle won. The ducks always lost. When there is an abundance of food, otters coordinate with each other, too. They bunch up the fish schools and each grab a mouthful.”
As a top predator in their ecosystems, otters can have an effect on populations of their prey. In the Rocky Mountains, they don’t have many predators of their own. Merav and her colleagues have seen eagles or coyotes try to catch otter pups. But otters are versatile and can escape through the water where other animals don’t want to follow.
One of the things Merav studies is how river otters link aquatic and terrestrial ecosystems. “They forage and rely on aquatic systems, but they do all other activities on land. Sea otters live nearly exclusively in the marine environment and are good indicators of the health of that environment. But river otters can tell you what’s happening in both water and on land. They eat fish from aquatic environments, but they scent mark, defecate and urinate on land. Otters eat fish and then bring all those nutrients like phosphorus and nitrogen to the land which fertilizes the plants, including trees. Along the coast in Alaska, we found that Sitka spruce and western hemlock trees that grow on otter latrines are healthier and have more needles. Otters act as little pumps to bring nutrients from aquatic to terrestrial environments. In the Rocky Mountains we don’t see much fertilization because a single otter won’t bring enough nutrients to be noticeable. In Yellowstone where they were protected by the National Park and never disappeared, they do occasionally form groups and we find effects of their fertilization on vegetation there.”
Otters are an important piece of a complete ecosystem and a good indicator of water pollution. Where otters thrive, the water system is clean. When otters disappear from a waterway, it is worth checking for pollution. Merav and her colleagues did a study on the New Fork, a tributary of the Green River, in Wyoming. The New Fork flows through the Jonah Field and the Pinedale Anticline, areas with extensive natural gas drilling.
Fracking Drill Sites in the Pinedale Anticline and Jonah Field, photo by Bruce Gordon, EcoFlight
“There are otters above the Jonah Field, and up the Green River, and below the Fontanelle Dam, but there are no otters in the fracking area. We put in monitors that continuously sampled water quality and we found surges of pollution. If you do a grab sample, you would never detect the pollution because it had already moved downriver. They release polluted water to the river, and 2 days later it is all the way down at the reservoir. There is high salinity, or salt content, from the fracking fluid. We put sensors above and below the fracking sites and found high salinity below the site. Fish died because they put marine level salinity in fresh water.”
Otters usually move away when a waterway isn’t healthy, but sometimes they stay in an area with certain pollutants. In areas with elevated levels of contaminants like PCBs, DDT, cadmium, and mercury, it is found in the organic material and sediment of the river. The poisons are eaten by snails and insects which are eaten by fish and frogs, and then those are eaten by otters. This means the otters end up with high levels of contaminants. One study where otters live on the polluted Duwamish River through Seattle is collecting otter poop to test for levels of chemicals and heavy metals. Over the 17 years of planned cleanup of the river, otter latrines will be analyzed and hopefully show reduced pollutants over time.
To understand the movements of otters, they have to be tracked. Over the years, Merav has noticed, “Otters are very smart and difficult to live-capture. They quickly learn what a trap is and how to avoid it. We have to use leg hold traps, but they figure those out quickly too. If you catch an otter once, you can’t recapture it. Of hundreds of otter captures, we’ve only recaptured 6 individuals. Only one of those we caught 3 times. The only reason we caught her the 3rd time was because she was so old. She didn’t have any teeth left. She was so old, I think she was a little demented.”
To track otters, scientists have tried a variety of techniques. They can’t carry transmitters around their necks like many land mammals because they frequently dive or slide through narrow areas. The collars could easily be caught and trap the otter. Instead, they have been implanted with radio transmitters under the skin in the past. But these days, scientists use noninvasive genetic sampling, supplemented with camera traps. Fecal samples can easily be collected at latrines, where otters repeatedly visit to scent mark.
Merav describes another way of collecting genetic samples using hair snares. “They don’t seem to mind hair snares, they realize they can get out, so the same otters will pass through more than once, unlike box traps or leg hold traps. That’s how we identify individuals from their genetic fingerprint and monitor their movements. The otters have to go through the hair snare and it cinches around them as if it was a regular snare. We cut the strands into little barbs so it grabs hair as the otter passes through. Instead of the locking mechanism on a regular snare, we replace it with a paper clip. The snare is anchored to the ground, so when the otter struggles, the paper clip opens and the otter walks away. It doesn’t take very long for them to pull out of it, but it grabs some hair. I believe they enjoy it because it’s like brushing themselves. We set up cameras, so we have videos of some otters pushing the snares out of the way and walking past. But a lot of the time they go through when we put them where they slide to the river.”
Photos of hair snares provided by Merav Ben-David
It is a pleasure to see river otters playing and fishing in the wild along a river or mountain lake. Their presence indicates clean water, a balanced ecosystem and a successful reintroduction in the Rocky Mountain region.