April 01, 2013

 

 Uncharted waters

Marine mammal medicine still full of many unknowns

Posted on March 20, 2013 

 

The U.S. Navy Marine Mammal Program started more than 50 years ago as a means to improve torpedo and ship designs. Today, research continues, but the focus has shifted toward discovering how to improve the health of the program’s California sea lions and bottle-nosed dolphins. By extension, the marine mammal and zoo communities have benefited, and there’s potential for results to translate to the greater veterinary and human medical fields as well.

From the beginning

The Navy started using animals because its scientists were interested in learning how they could swim so fast and silently, how their sonar worked, how deep they could dive, and more. The answers, they figured, might be useful to humans trying to live and work under the sea.

“The Navy mainly wanted to figure out secrets from dolphins and then go on with their business. It wasn’t viewed as some long-term thing,” said Dr. Sam Ridgway, who joined the Navy program in 1962, two years after it was started at Point Mugu, a missile base on the California coast.

It costs $25 million to $28 million a year to run the Navy Marine
Mammal Program, which goes through 800,000 pounds of fish a year.
 
In Dr. Ridgway’s book, “Dolphin Doctor,” he wrote: “Our small laboratory at Point Mugu was to become a focal point of dolphin research in the 1960s. Many scientists from major universities came there to study our dolphins. As the first veterinarian to work full-time with dolphins, I faced unique problems in my job of keeping these mammals healthy for the scientists. Little was known about dolphin medical care or physiology. We did not know how to anesthetize a dolphin for surgery or even how to take a blood sample for diagnostic tests, let alone how to interpret the test results.”

Researchers learned more about the dolphins, particularly that they would cooperate with people in the open ocean. In 1965, a dolphin named Tuffy participated in a Navy program called SEALAB II, an undersea station where people lived more than 200 feet below the surface for a month. Tuffy assisted Navy divers by taking them objects and transporting messages.

Hearing test

Dr. Ridgway was encouraged to create a veterinary research component for the Navy program. Early on, most studies were supported by the Office of Naval Research. They explored everything from diving to water balance to kidney physiology to hearing, echolocation, and the effects of sound on marine mammals.

“Usually, with the Office of Naval Research, we had to come up with something new every few years. So, rather than being a physiologist forever, you had to be a behaviorist or psychologist or something else. You had to learn something new, but that’s kind of a lot of fun to explore new things,” Dr. Ridgway said.

With that approach, program veterinarians made big breakthroughs, such as discovering how to safely administer anesthesia to dolphins, how to study their physiology in the open sea, and how to apply medical technology to marine mammals.

More recently, the Navy needed to know how close its animals could be to Navy sonar and still be safe. That’s when Dr. Ridgway and others including Dr. James J. Finneran hit on the notion of using the temporary threshold shift (TTS), a well-established parameter in human audiology, as a metric to identify how much sound is tolerable for animals.

So, they trained Navy dolphins and sea lions to undergo hearing tests similar to those given to people who are seated in a booth and told to push a button when they hear a sound. The animals are taught to vocalize when they hear a sound played, and such training has become a routine part of animal care, said Mark Xitco, PhD, head of the scientific and veterinary support branch of the Navy program .

While this was happening, the impact of anthropogenic sound on wild marine mammals became a hot topic.

“Lawyers from each side were arguing, and we were the only ones who could inject any data into the discussion. And much of the current mitigation measures the (National Marine Fisheries Service) imposes on the wider Navy, oil and gas industry, and other activities they regulate about producing sound in the ocean, those safe sound limits are based largely on TTS data that was derived here at our program,” Dr. Xitco said. Dr. Finneran has taken the work further, he said, by developing a noninvasive hearing test involving electrophysiological techniques, with surface electrodes measuring small electrical changes in the brain associated with sound. This advancement enables the use of hearing tests in wild marine mammals.

The latest developments 

Despite publication of more than 1,000 papers since the program’s inception, much remains unknown about marine mammals. One reasons is that the sample size is smaller compared with that of domestic animals, said Capt. Kamala Rapp-Santos, an attending veterinarian with the program. Plus, marine mammals are not as easy to work with as domestic animals are, and most research has been limited to the past 50 years or so.
 
A procedure still in research is the pulmonary function test. The program’s physiologists and clinicians have been working to define the functional parameters of dolphin and sea lion lungs. They hope to learn what the animals’ normal pulmonary capabilities are so they can be better ventilated during anesthesia.
 
The Navy Marine Mammal Program has a breeding program for dolphins and a research program. Most, if not all, the research is noninvasive. Many of the dolphins and sea lions participate in research projects, be it as simple as providing a blood sample or as complicated as participating in a study on echolocation full time. In all, the program has come out with more than 1,000 publications since its inception.
 
Dr. Cynthia R. Smith, executive director of the National Marine Mammal Foundation, is investigating ammonium urate uroliths, which are commonly found in managed-collection dolphins.
 
The project started with a single animal that had a ureteral obstruction. The process of unblocking the ureter brought together an entire network of specialists and experts in marine mammal medicine.
 
“We learned the best way to diagnose the disease, the prevalence of the disease in wild and managed dolphins, and now we’re working on the prevention and treatment,” Dr. Smith said.
 
Dr. Rapp-Santos is working with the Naval Medical Center to develop an extended-release antibiotic hydra gel. She said dolphins can form abscesses in the body, including their lymph nodes.
 
“With dogs, you could easily put them under anesthesia to flush and drain the abscess. With dolphins, anesthesia is more complicated and is avoided except in cases where it is absolutely essential. They don’t tolerate anesthesia well, and putting them in the ocean with an open and draining wound is not a good idea, so we are working on advanced methods, including the gel,” she said.
 
The gel would allow veterinarians to treat the abscess without pulling the dolphin from the water.
 
Additional areas that program researchers are working on include using adipose stem cells to heal skin wounds and defining diabetes in dolphins, which have a type 2–like syndrome that they can turn on and off (see page 873).

Marine mammal veterinarians are also trying to determine whether there’s a probiotic for dolphins, but first, they must figure out what bugs dolphins have in their gastrointestinal tract. They are developing a product to enhance dolphins’ GI health, said Capt. Lara S. Cotte, officer in charge of clinical veterinary services.