Transcript: The Case of the Dead Dolphin
Welcome to "On the Line", a NOAA Fisheries podcast.
Kerri Danil: We are going to necropsy a long-beaked common dolphin that stranded in La Jolla this past weekend and try to learn a little bit about it, learn about its life history, and hopefully why it died.
Host: That’s Kerri Danil, a marine biologist with NOAA Fisheries. A few days before I spoke with her, a dolphin turned up dead on a nearby beach on La Jolla, California. It was a long-beaked common dolphin, male, a calf about six to eight months of age. Danil was about to begin a necropsy. That’s what you call an autopsy of an animal, and there were a bunch of graduate students on hand to observe. Danil narrated the procedure step by step for them, and that’s lucky for us because we can listen in.
Kerri Danil: It will get a full necropsy, which will include the blubber, which we save for contaminants. We’ll take histopathology of all the organs to look at disease. We’ll take liver and kidney for heavy metals. We look at the stomach for food habits, and we’ll take blood and spin it down and save the serum.
Host: Danil begins with an external examination of the animal’s body. What she’s looking for is signs that it died due to human activity, like did it get entangled in fishing nets or hit by a boat. But there was no signs of anything like that here, so Danil got out her scalpel and proceeded with the necropsy.
Kerri Danil: We always cut from the left side just to keep our orientation. So we’ll take a cut along here and then sweep up and then do a ventral cut along here.
Host: After the first incision is made, Danil examines the blubber.
Kerri Danil: Is it a nice creamy white color? Is there any kind of hemorrhaging? Are there parasites? Blubber is creamy white in color.
Host: The thickness of the blubber indicates whether or not the animal is well nourished. Also, environmental contaminants like heavy metals and industrial chemicals accumulate in the fatty tissue, so Danil removes several matchstick-sized samples of blubber and puts them in plastic specimen containers.
Kerri Danil: The kidneys are here. Our intestines are here. We’ll get a better look at them as soon as we get some of this off. The liver is sticking out here, the stomach here, the spleen here.
Host: Danil continues just like they do on TV. She takes out the organs and weighs them. Then she puts them on a board and slices them—she called it bread-loafing—so that she can check the color and consistency of the tissues. We’ll come back to Danil in a bit and see if her investigation turns up any definitive cause of death. In the meantime, Susan Chivers, another NOAA marine biologist, talked to me about the Marine Mammal Health and Stranding Network.
Susan Chivers: So there are stranding networks throughout the U.S. Those networks were established in 1972 with passage of the Marine Mammal Protection Act to monitor why animals are dying, who’s dying, where animals are, and just learn more about them.
Host: I asked Chivers, “Why bother with the necropsy? I mean, the animal’s already dead, right?”
Susan Chivers: Lots of reasons to bother. One is, for most species it’s really hard to study them because they’re free-swimming, deep-diving, pelagic species. So it gives us some insight into their life history, how big they are, how old they are, their age-length growth parameters, how many calves they have, when they reached sexual maturity. We get sort of basic natural history information about each of the species that we collect.
But not only that, it gives us a sense of what’s going on through time. So we have a really long record of cetacean strandings. Officially started in 1972 and we’ve had very consistent efforts since then, but we have records dating back to the 1850s. So we get an idea of who’s who in the neighborhood and what they’re dying of.
Host: Remember that blubber sample that Danil took from the dolphin during necropsy? Those samples go into a tissue bank dating back to 1972.
Susan Chivers: So we do collect tissues and we send them out for immediate review. Then we keep a set of tissues so that if there’s some question about some results and we need to repeat them, we have the material to send out again. We also have the ability to do retrospective studies. Like if something all of a sudden becomes of interest, then we can collect tissues over some time period to send out and look for trends over time.
Nick Kellar: Thirty years ago we were seeing what we call now, legacy compounds, things like PCBs and pesticides like DDT, which we knew for a long time were harmful for wildlife.
Host: That’s Nick Kellar. Dr. Kellar is also a biologist at NOAA Fisheries, but he’s a population biologist. You can think of him as like a public health expert but for marine mammals instead of for people.
Nick Kellar: And in the last 10 years, 15 years, what we see is an increase in novel chemicals like PBDEs as their use has increased.
Host: What are PBDEs?
Nick Kellar: They’re flame-retardants.
Host: These chemicals come from the human environment on land, but marine mammals are exposed to much higher levels of them than humans are because of biomagnification. That’s the process that causes contaminants to become more concentrated as they move up the food chain. Because marine mammals eat high on the food chain, they get large doses of these contaminants. One of the reasons to necropsy these animals when they wash up dead on the beach is because it allows us to see not only what chemicals they’ve been exposed to and how much, but also what diseases and other health issues they’ve been living with.
Nick Kellar: Many of the contaminants we’re worried about are endocrine disruptors, so they disrupt the normal hormone pathway. And so one of the things that we do, one of the many things we can do, is correlate contaminant levels that we see in the blubber with hormone levels that we see in the blubber. Do we see high levels of pregnancy in populations with lower levels of these contaminants and vice versa? And that would be suggestive then that the contaminant itself was having an adverse effect on pregnancy.
Host: What Kellar is talking about here is a correlation. He’s not proving cause and effect. But if he sees a correlation between a contaminant and a health problem, that may be a sign that chemical deserves a closer look to see how safe it is, and not just how safe it is for marine mammals but also how safe it is for humans. After all, marine mammals are mammals like us. We need to pay attention to what’s happening with them because their health has important implications for our own.
But let’s not get too wrapped up in our own human self-interest. We started out wondering what happened to that poor dolphin calf that washed up dead on the beach at La Jolla Shores. Let’s give Kerri Danil a call and see if she’s gotten results back yet from the histopathologist.
Kerri Danil: Hello.This is Kerri.
Host: Hello, Kerri. This is Rich Press calling from Silver Spring.
Kerri Danil: Hey, Rich. How are you doing?
Host: Good. How are you?
Kerri Danil: I’m doing well. Thanks.
Host: So I’m finishing up that podcast that I started making when I was out at your science center and you had that case of the baby dolphin calf that washed up on La Jolla Shores.
Kerri Danil: Yeah.
Host: And I promised my listeners that I would double back with you at the end of the podcast and find out what you learned about that case after you got the results back from the histopathologist.
Kerri Danil: Sure, sure. I can go over the report just a little bit. What she found was some bacteria in the brain and the lungs. And then the microbiology results which we submitted to them were swabs of the larynx and the area around the ears and the nasal sacs. And what came back on those were a variety of bacteria, but what was common among all of them was a bacteria called Pseudomonas. And so what she believes happened is that the immediate cause of death was drowning, but the cause is likely the ear infection and disorientation imbalance. So, what likely happened is this animal had an ear infection, which caused it to be disoriented, which would have made it perhaps inhale water, causing it to drown and die.
Host: You know, until I made this podcast, I don’t think I used the word necropsy so many times in one day before, and it got me thinking. We say autopsy when it’s a human being we’re looking at, but if it’s some other type of animal we say necropsy. I looked into it, and it turns out that the word autopsy comes from the Greek and it means to see one’s self. "Auto" means the self and "opsis", that comes from the same root as the word optics, means to see. And this makes sense because during an autopsy we see literally what we’re made of.
But the word necropsy just means to see death. The fact that two words for this procedure, one if it’s done on a human and another if it’s done on an animal, kind of sets us apart from the rest of the animal kingdom. But as this story about the dolphin calf that washed up dead on the beach demonstrates, often when we look at animals what we see is a reflection of ourselves.
Host: Thanks for listening. Join us again next time for more stories about ocean life and ocean science. I’m Rich Press, and you’re listening to "On the Line".
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"On the Line" is a production of the NOAA Fisheries Office of Communications.