Saturday, August 9, 2014

A Marine Mammal Murder Mystery

* Please be aware: there are graphic images of blood and body parts in this post. *

A crowd gathers.

A crowd gathers down on the dock... What's going on?

The body bag.

It's a crime scene. The body is lifted out of the ocean and rolled onto the dock.
The victim.

Then the victim is revealed: a large male harbor seal. Our mission: to determine the cause of death.

Of course, what I'm witnessing isn't truly a crime scene -- it's a seal necropsy conducted by the NOAA Marine Mammal Stranding Network. Anyone who finds a dead marine mammal can call the Network, and a team of responders might be able to collect the animal for a research necropsy like this one.

Here on the dock we have a whole crew of Stranding Network members gathered: a local whale-watching boat guide, the Whale Museum Stranding Network Coordinator, a veterinarian named Dr. Joe, a couple of vet students from UC Davis, and a hoard of curious labbies (me included).

First, Dr. Joe observed the body for external signs and found...

Clue #1: a series of puncture wounds through the seal's backside.

A vet student examines the incision.

He made an incision next to the punctures, allowing us to discover...

Clue #2: a hemorrhage, visible as a block of frozen blood filling the space between the skin and the abdominal cavity. (The seal's body was frozen after it was collected to preserve it for this necropsy.)

For the next hour experts examined the body front and back, inside and out, looking for more clues. Everything looked normal until we cut into the chest around the lungs and heart and found...

Clue #3: another enormous hemorrhage filling the entire thoracic cavity.

Clearly, this seal had been badly injured. But what actually caused the death? Was it attacked by a Stellar's sea lion, then hit by a boat in its compromised state? Or did orcas bite it and smack it around with their tails before deciding they weren't hungry after all?

These two hypotheses seemed to be the most likely, though we'll never know for certain what happened. Dr. Joe took dozens of samples from all over the body to send to the lab for processing, so maybe the Stranding Network will have a better idea once the results come back.

One thing we did find out for sure is what the seal ate for his last meal...

Stomach contents.

A huge salmon! The fish was partially digested, but its head and skeleton were still intact. At least this seal ate well before it died.

After the seal necropsy, the Stranding Network had one more puzzle to solve, this time by examining a porpoise head.

A porpoise ear.

The main question was whether the porpoise had any damage to its ears. Porpoises use echolocation to navigate and find prey, and scientists are concerned that the noise from large ships might be harming porpoises' sensitive ears. The Network will have to wait for lab results to come back before they know the health of the ears.

Although we all would have preferred to watch this seal and porpoise leaping from the ocean, healthy and happy, we were grateful for the chance to learn from these animals' deaths. One day I will be as knowledgeable about anatomy and ecology as Dr. Joe so I too can solve marine mammal murder mysteries.

4 comments:

  1. Cool necropsy! Is it a known orca whale behavior to attack a seal but then not eat it even though they could? Or was that just speculation? I would think they'd attack only if hungry enough to eat their prey.

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  2. First (and probably the last) porpoise ear I've ever seen!

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  3. Jane -- orcas are known to beat around seals before eating them. This video has a weird soundtrack and some intense slow-mo... but it gets the idea across. https://www.youtube.com/watch?v=O0qMT2YBIcg
    I don't know if they are likely to beat a seal without being hungry enough to eat it, or if they were scared away from their meal by something.

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  4. Jane- Orca's also bring seals and other food to their young to help train them to hunt, similar to a mom cat, and sometimes the prey escapes the young. I also just read about two juvenal dolphins who 'kidnapped' a newborn harbor porpoise and 'played' with it roughly until it was rescued by a research vessel. I guess bullying is not just a human trait. Jeanette C

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