New milestones in southern sea otter conservation

First in a series of new milestones in support of southern sea otter conservation, The Marine Mammal Center in Sausalito, California has significantly expanded its ability to care for and rehabilitate southern sea otters. Specifically, the Center has retrofitted its veterinary hospital to safely house and treat sea otters.

This will immediately benefit two sea otters recently admitted into the Center. Both animals were diagnosed with domoic acid toxicosis – aka amnesic shellfish poisoning – caused by a potent neurotoxin produced by diatoms (a major group of algae) and accumulated through the food chain. The toxin is produced by diatoms of the genus Pseudo-nitzschia, and accumulates in marine animals that feed on these phytoplankton, such as sardines, anchovies, and many species of crab and mussels. Domoic acid (DA) poisoning can lead to many symptoms, including disorientation and seizures. Therefore, rehabilitation centers have a keen interested in determining how DA patients fare after they are released back into the wild.

Eight-year-old southern sea otter Otto rests in a pool during rehabilitation at The Marine Mammal Center in Sausalito, CA. The male otter was rescued by trained responders from the Center’s San Luis Obispo Operations in Morro Bay, CA. An MRI of Otto’s brain revealed that he had a shrunken hippocampus, the area of the brain known to play a role in memory and navigation, which is common in animals with domoic acid toxicosis. Photo Credit Dana Angus © The Marine Mammal Center.

2. This leads to another milestone: these two sea otters will be the first to be released back into the wild with Life History Transmitters – or LHX tags.

LHX tags are a satellite-linked transmitter that is surgically implanted into the abdominal cavity of warm-bodied host animals. They function like a black box on aircraft: throughout the life of the host, they monitor multiple sensors (temperature, light, motion) to determine the state of the host. The tags do not transmit while their host is alive and well – from inside of a body, the signal would be far too weak to reach a satellite. Instead, all this data is stored in memory, and only transmitted to orbiting satellites post-mortem, after the tag has been liberated from the decomposing, dismembered or digested host body.

Dr. Abby McClain (R), Koret Intern Veterinarian at The Marine Mammal Center, and Dr. Mike Murray (L), Aquarium Director of Veterinary Services at Monterey Bay Aquarium, implant a Life History Transmitter (LHX) tag into a southern sea otter. Developed by Dr. Markus Horning, Science Director at the Alaska SeaLife Center, in collaboration with Wildlife Computers Inc. (Redmond, WA), this is the first application of LHX tags in rehabilitated southern sea otters, and will be an important way to track the success of the rehabilitation efforts. Photo Credit Elena Graham © The Marine Mammal Center

If all goes well, we will not hear from the LHX tags of these two otters for a long time.

If however any lingering after-effects of the DA poisoning lead to seizures or other potentially fatal complications, we will receive data from LHX tags that tell us exactly when and where the host animal died, and maybe even why. For example, elevated temperatures on their own could indicate a fever, and in combination with increased movement sensor output could indicate a seizure.

The surgical LHX tag implantation is done under standard aseptic conditions and full gas anesthesia.

We have successfully used LHX tags in California and Steller sea lions, and in harbor seals. Even so, any use of such tags in a new species of wild animals has to be preceded by careful trials under close observation, leading us to the third recent milestone: at the Monterey Bay Aquarium, veterinarian Dr. Mike Murray completed trials of LHX tags – either on their own or paired with short-range VHF tracking beacons – in four sea otters. These deployments over 6-8 weeks revealed no significant morbidity related to LHX tags, paving the way for their application in the two rehabilitated sea otters at the Marine Mammal Center.


Through these milestones our three organizations, the Monterey Bay AquariumThe Marine Mammal Center and the Alaska SeaLife Center are collaborating toward enhancing the conservation of sea otters in the North Pacific Ocean. All work described here was conducted under all required federal and institutional stranding response, research and animal care permits.

To read up on LHX tags, check out, as well as these recent blog entries on 60 North Science: “how we get research ideas“, and “paper in a nutshell” (summarizing a recent scientific paper on the initial LHX tag trials in harbor seal pups). You can read more about Otto the sea otter here, and here you can find a related the TMMC media advisory.

UPDATE: Check out this podcast about the sea otter LHX story!!

And keep checking back on 60 North Science for future entries on these two otters, LHX tags and their applications, and more science at the cutting edge of tomorrow.

Written by: Dr. Markus Horning

Featured Photo Credit: Bill Hunnewell © The Marine Mammal Center

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