Journey Across the Gulf of Alaska
Tracking Tag Found on Remote Beach, Yields Valuable Dive Data

In early November 2003, scientists Mary-Anne Lea and Ben Wilson attached a special floating dive tag (see first report) to a juvenile Steller sea lion near Little Island in Southeast Alaska (blue star on map below). The male sea lion, marked as =425 for visual re-sighting purposes, was captured and released under the Behavior@Sea Project at the University of British Columbia.

As part of this unique project, Lea and Wilson sought to track the winter movements of juvenile sea lions to better understand their interactions with their habitat — specifically, their fine-scale interactions with prey in the vast winter prey fields of Southeast Alaska. To accomplish this, they attached floating time-depth recorder tags to ten juvenile Steller sea lions aged 1.5–2.5 years. The tags were designed to record dive information and detach and float to the surface for retrieval during the next summer molt.

Remarkable Journey
Wilson and Lea successfully tracked =425 from a research vessel until late March 2004, when he was last sighted at Benjamin Island while still suckling and dependent on his mother. He then disappeared until 18 May 2006, when scientists from the NOAA National Marine Mammal Laboratory sighted him at Shakun Rock in the Gulf of Alaska (red star on map) – an impressive 700 miles (1,125 km) from Little Island. The dive tag had molted off some time earlier and was nowhere to be found.

On 21 June 2006, almost four years after =425 was tagged, Mr Frank O’Donnell of the Wildman Lake Lodge found the missing satellite tag on a beach 43 miles (70 km) south of Port Heiden (yellow star on map), on the opposite side of the Bering Sea. A small label on the tag provided Mr O’Donnell with a phone number to report his find, which had traveled at least 1,400 miles (2,260 km) from Little Island and 700 miles (1,250 km) from the Gulf of Alaska.

“In over 30 years I have seen very few sea lions near the Lodge,” Mr O’Donnell says, which suggests that =425 carried the tag only part of the distance to Bristol Bay before molting. It is likely the tag drifted the rest of the way along the Alaskan Current (orange arrow). Regardless of its ultimate method of arrival, Mr O’Donnell’s fortuitous recovery of the tag revealed a remarkable journey.

Valuable Data
Behavior@Sea scientists were very excited to access the dive data stored on the tag carried by =425, and they were not disappointed. The tag had recorded nine months of fine-scale dive data before molting off on 9 August 2004. During that time, the young sea lion made at least 41,290 dives to a depth of 26 feet (8m) or more, reaching an average depth of 101.1 feet (30.8m) and a maximum depth of 825.1 feet (251.5m). There was also a marked change in his surface/haul-out time between March and April 2004, suggesting that =425 was probably weaned around this time.

What does all this mean? The data supports the belief that, among sea lion populations in Southeast Alaska, juvenile males appear to be the primary ‘emigrators’ or explorers (as is the case in most mammalian populations). Juvenile male sea lions are also capable of large-scale movements that see them mixing with sea lions from western populations at a relatively young age.

The remarkable recovery of the tag and its important data highlights the importance of collaborative research. The Consortium funded the Behavior@Sea Project and the Alaska Department of Fish and Game assisted in capture and tag deployment. Scientists from the NOAA National Marine Mammal Laboratory could identify =425 by his permanent markings thanks to a shared tracking and re-sighting database, made possible by the Alaska Department of Fish and Game and Lauri Jemison. Mike Sigler’s phone number at the NOAA Auke Bay Laboratories provided Mr. O’Donnell with valuable contact information to report the retrieved tag.

9 January 2008