The “Crime”: Steller sea lions are disappearing: there are only about 1/5th as many sea lions in the Gulf of Alaska and the Aleutian Islands today as there were 40 years ago. Researchers are looking for clues using telemetry tags to discover how Steller sea lions are dying.
The Science Solution: Imagine a super-sleuth that can be at the scene of the crime (the death event) just as it happens. The high-tech implanted Life History Transmitter tag stays deep inside the Steller sea lion throughout its life measuring its body temperature, waiting until the animal dies.
The Death Event: Once the tag measures a drop in temperature inside of the warm-blooded animal, the tag‘s computer notes that the animal has died and continues to record temperatures at specific intervals as the body cools. The rate of cooling, either slow or quick, tells researchers how the Steller sea lion might have died.
Clues about the Cause of Death
The Big Chill: A dead body is a cold body. Steller sea lions, like humans, are homeotherms and have to produce heat by burning calories to maintain their body temperature of about 37 degrees Celsius (98 degrees Fahrenheit). When they die, heat production stops and their body begins to cool. If the body with the tags remains intact, it will cool gradually over a period of time from 37 degrees to the temperature of surrounding air or water. This can take a matter of hours or even days since sea lions are well insulated with fat or blubber.
The Quick Chill: Just how quickly a body cools is related to ambient (surrounding) temperature, and the mass (weight) of the body. A small body cools much quicker than a larger body. Researchers examine how the body cools over time, which is its cooling rate, to determine how the sea lion died and its mass at death (see Slow or Quick). An unusually low weight might suggest that a sea lion may have starved to death. Temperatures just before death may shed more light on events. Hyperthermia (elevated temperature called a fever) or hypothermia (very low temperature in a live animal that cannot burn enough calories to stay warm) might suggest health problems.
Massive Trauma: In some cases, the body breaks or is torn apart. The tags then cool much more quickly inside a smaller part of the body or they will fly out of the body and cool almost instantly. Most likely this will happen if a sea lion is attacked, killed and torn apart by a predator such as a shark or a killer whale.
Slow or Quick: Calculating Cooling Rates and Mass
Plotting the body temperatures just before and after death on a graph will generate a cooling rate profile for the animal. Researchers compare the actual cooling curve to what they would expect for an animal of its size based on its age and gender. They calculate the cooling rates based on a model (equation) that accounts for the sea lion’s mass and the surrounding temperature in air or water. Since they know the actual body temperatures from the tag, scientists can use the model to determine the animal’s mass at the time of death. In fact, coroners who investigate human deaths use the same types of cooling curves to tell when a person died.
Temperature Profiles: Look at the examples of different types of temperature profiles and the types of death they indicate. Use these to look at Stella, the Steller sea lion’s temperature graph and determine her cause of death.
CSI Records: Get to know the animals and places involved, and how the Life History Transmitter is helping scientists solve the case.
Profile: Stella, the Steller sea lion (PDF)>>
Profile: Sam, the sea otter (PDF)>>
Profile: Ozzy, the Orca (PDF)>>
Crime Scene: Ushagat Island, western Gulf of Alaska, United States (PDF)>>
Telemetry Device: Life History Transmitter (PDF)>>
Data: Temperature Profiles (PDF)>>