A decade ago, we set out to unravel deep ocean crime scenes we weren't even sure existed. The crime? Endangered Steller sea lions were rapidly disappearing in parts of Alaska. Their numbers dropped by 80% in three decades, yet only rarely did anyone see or sample dead sea lions. Live sea lions studied in the summer when they haul out to breed seemed healthy and had healthy pups.
We wanted to know when, where, and why sea lions die. To unravel the mystery, we needed information from those animals that we don't see, those that might not breed, those that might never come back ashore. So we developed a special monitoring tag that could send us data about the sea lions we can't directly observe.
This so-called Life History Transmitter or LHX tag is a small electronic monitor surgically implanted into the gut cavity of young sea lions under anesthesia. Don't worry, we checked that this does not alter the behavior or survival of the animals. After all, we don't want to influence the data we need!
Since 2005, we've placed tags in 45 young sea lions in the Prince William Sound area of the Gulf of Alaska. So far, 17 of these sea lions have died. That's actually about how many deaths we expected. Young sea lions have a tough life and most don't even reach the age of reproduction.