November 22, 2010

Otters and Trout in Sierran Lakes: Which Came First?

Despite having spent the last couple of decades hiking around the Sierra Nevada to conduct my research I'd never seen a river otter nor heard much about their presence in the mountains.That all changed a few years ago when a colleague observed a family of five otters swimming across a lake in northwestern Yosemite National Park. The following winter he observed otter tracks along a stream while doing snow surveys in the Park. And then this past summer I found evidence of otters at a lake in northern Yosemite. My curiosity was definitely piqued and I had to learn more. 

Otters are typically described as feeding mainly on fish, and trout are a favorite prey item. So were river otters found historically in the Sierra despite the absence of fish in most water bodies? Or did they expand their range into the Sierra following the introduction of trout into many lakes and streams starting in the mid-1800s? And if they were found in the mountains prior to fish introductions what did they eat? 

Several of us are still trying to answer these questions but the otter sign I found this past summer and some additional information sources we've turned up have provided some intriguing details. First, otters have been reported in the High Sierra for many decades, suggesting that their presence predated trout introductions. Second, some notes recorded by a Yosemite wilderness ranger in the 1970s suggested that otters were eating Sierra Nevada yellow-legged frogs (Rana sierrae). He reported seeing otters in a lake in the Vogelsang area and also found numerous pairs of discarded frog legs around the lake shore. Given how abundant R. sierrae were historically it certainly seems possible that otters could have subsisted on them. And finally, the otter sign that I found this summer was several otter scats atop a lakeshore boulder. I collected the scats and dissected them back in my lab. What I found amazed me. The scats contained dozens of bones of a size and structure that likely makes them those of Rana sierrae adults and juveniles. But the dominant remains in the scats were from aquatic invertebrates, including giant water bugs (Lethocerus americanus), backswimmers (Notonecta sp.), and dragonfly and damselfly larvae (Aeshna and Enallagma, respectively)! Given the relatively large size of frogs their inclusion in otter diets isn't particularly surprising. But invertebrates?? Notonecta are barely an inch long and yet otters were eating them by the dozens.

To return to the questions I posed at the beginning of this story, I'm guessing that otters utilized Sierran lakes prior to the introduction of trout and subsisted on a diet of amphibians, aquatic reptiles, and invertebrates. With the introduction of trout, otters had another food item on their menu. But did this new food item allow otters to increase in numbers? If so, could their elevated numbers be negatively impacting the few frog populations remaining today? I wish I knew. I'd sure love to be able to radio track some of these guys around Yosemite and figure out what habitats they use and get a more complete picture of their diets. 

If any of you readers have observations of river otters in the Sierra Nevada, I'd love to hear about them.

Back to The Mountain Yellow-legged Frog Site.

14 comments:

  1. Hi Roland,

    I saw you in your yard the other day and wanted to stop to chat with you about this a bit, but my lovely wife told me to leave you alone and let you enjoy your weekend. The last otters we have recollection of, was about four years ago on 385, crossing the highway along where the Little Walker confluences with the West Walker River. Other reports (Don Banta) indicate otters existed in Little Walker Reservoir at one point, but I haven’t seen them or heard of them since historic times. Also, rumor has it there is a population in the Lane and Roosevelt Lake watershed. The interesting thing about the rumored Roosevelt otters (via Leavitt Meadows pack guides) is the population drastically decreased with fish management however have recently became more robust due to the lakes crayfish infestation? Keep in mind this is merely word of mouth, but does hold merit in my opinion. Ive seen sign of otter or mink although I’m not sure which in the Dorothy Lake watershed. So, I think they have always existed in the Sierra Nevada. Probably making a living on anything they could get their teeth around, and coexisting along the same niche as maybe a mink which also is native to the Sierra Nevada. I however do not think there is an “increase in numbers” of otters or any other critter in the Sierra Nevada for that matter. Seems like every critter out there is having a hard time now days. When was the last time you saw a porcupine in the Mono Basin?

    Roland, respectfully how they impact frogs is your ball of wax, but I feel what few of them are left make a living eating fish and not frogs. Likewise with the few minks left. I wonder what the impacts of fish management would be on the otter/mink population in the Sierra Nevada if they have adapted to depend on introduced fish. Would fish removal adversely impact the small populations of these species such that we force them into a bottleneck or even worse, complete extinction from the Sierra Nevada? I don’t have a definitive answer but, I do know species evolve to depend on other food sources depending on what mother nature throws their way.

    Cheers,
    Matt Banta -

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  2. Hi Matt. Thanks for the comments. I too wonder how trout removals might affect otters, especially now that the formerly abundant frogs are largely gone. Given that trout will always be widespread in the Sierra I suspect that trout removals from a relatively small number of lakes would have little effect on otters. But to know with a greater degree of certainty being able to document what parts of the landscape otters currently use would sure be useful.

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  3. My mother and I were standing out on the patio and saw a river otter swimming down the Carson river(Mexican Dam area). I had never seen one before and had to Google it and your bolg came up.
    Sierra Udey

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  4. Interesting. Thanks for the post.

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  5. I had the opportunity to observe a group of 3 otters 9-2-12 on the Rubicon Res. in Desolation Wilderness. I was quietly flyfishing on a eastern point when I noticed a group of dark animals swimming (and diving)straight towards me, making a cough type of noise. When they got closer, I saw they were otters and the sound they were making appeared to be from clearing their nose of water after a dive. They came to within 15 feet of me, diving over and under my flyline. They were not concerned about my presence (I was sitting still, wearing green and khaki), tho the lead otter would look at me occasionally and growl. They spent several minutes in front of me before continuing on to a rock in the lake. They got up on the rock and laid still for a while. Then they played a while, and then laid still again, this time grouped together. I observed them on the rock about a half hour, until I needed to leave.
    Sincerely,
    Ellie Beals

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  6. Great sighting! Thanks for posting it.

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  7. I was amazed to see a river otter floating down the headwaters of Coyote Creek (Silver King/East Carson watershed) as the creek is about a foot deep and two feet across at that point. I got my dog on his leash and we sat quietly but the otter snorted and growled at us, peering from beneath some overhanging willows. I think it was surprised to see us too.

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    1. It is remarkable that this otter was in such a small creek. What was the date for this observation?

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  8. I am fairy certain I saw a river otter in the Owens River just south of Mazourka Canyon Rd. on Saturday, 8/22/15. It swam across the small pond within several feet of me, then into the cattails. About 30 minutes later it swam back across the pond, downstream and into the tules. Not having a camera, I can't verify it was an otter. However, the tail was too long for a mink, and it was definitely not a beaver. There is a open area where saltgrass is packed down from the top of the hill and to the water edge, though no single track. It is not typical of deer or cattle bedding. I cannot find any literature about river otters in the Owens River before or after European contact.

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  9. Hi April. Thanks for the post. I don't know of any verified otter sightings on the Owens River, so this is an interesting observation. Hopefully you'll get another sighting of this animal in the future. Bring your camera :-)

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  10. My colleague Justin Garwood dug through some literature and found two Inyo County records of otters in the Owens River near Independence. The observations are described in Schemp and White (1977, page 37). Both observations were made by R. Patterson, a "qualified observer", one in 1968 and one in 1973. So, maybe your observations point to otters that once inhabited the lower Owens area still being there. We definitely need a photograph of an animal or a track! I hope you can get one.

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  11. I was going down to a section of the north fork of the Yuba River in Sierra Co. approximately 2 miles south of Goodyear's Bar where I saw a river otter. I know it was an otter because I got fairly close to it and of course he disappeared under the water. I was there about 4 hours but never saw him again. I have been having fun researching them and I am wondering how common they are in my area.

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  12. We saw four river otters on the Merced River in Yosemite NP today. I had no idea they could be found in the Sierra. Spectacular sighting! On Hwy 140, between 120 and 41

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  13. Great sighting! Do you have a photograph that you could share? I'd like to add your sighting to a database of Sierran otter sightings and a photograph would provide a high level of confidence in the observation.

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