Killer whales and other ocean predators are targeting and killing the pups of a threatened northern sea lion species at an increasingly high rate, scientists warned this week.
Without a reduction in predators, the sea lion population will have difficulty recovering, the researchers added.
The researchers focused on the endangered western population of the Steller sea lions (Eumetopias jubatus), which is the largest member of the eared seals family. The population has declined by 80 percent from its peak about four decades ago.
They monitored 36 juveniles in the Kenai Fjords and Prince William Sound region of the Gulf of Alaska from 2005 to 2011. The pups had tags implanted in their abdomens to record body temperature, surrounding light levels and other conditions during the sea lions’ lives.
After each sea lion’s death, the tag data was transmitted to satellites and then analyzed by the researchers. This technology allowed scientists to determine the manner in which the sea lions died, because traumatic deaths and non-traumatic deaths left different “signatures” on the recorders.
“The transmitters are amazing recorders of the life history of the animals, and can tell us in most cases how they died,” study researcher Markus Horning, a marine mammal expert at Oregon State University’s Hatfield Marine Science Center in Newport, Ore., said in a statement.
Temperature and light can reveal how long it took the tags to become dislodged from the pup or reach the water’s surface; this information can then indicate the type of death suffered by the pup.
“Gradual cooling and delayed extrusion are signs of a non-traumatic death, say disease or starvation, or of entanglement, drowning or shooting,” Horning said. “When the sensors record precipitous drops in ambient temperature along with immediate sensing of light and the onset of data transmission, it is indicative of acute death by massive trauma