Cue the Jaws Theme Song Please

May 12, 2017: The Horning Lab spent a fabulous day on Resurrection Bay testing a special type of satellite telemetry equipment, the Life History (LHX) tag. From 2005-2014, 45 LHX tags were surgically placed in juvenile Steller sea lions off the southcentral coast of Alaska. These individuals are from the Western distinct population segment (animals that reside in the central and western Gulf of Alaska, Aleutian Islands, and coastal waters off Japan and Russia). This population segment is currently listed as endangered under the Endangered Species Act.

LHX tags can monitor animals for several years, recording valuable information like how deep they dive and their body temperatures. After an animal dies, the LHX tag floats to the ocean surface and transmits all the stored data to a ground station. This initial location can give researchers information about when, where and why they die. Investigating predation patterns is important to predict the recovery and management of Steller sea lion populations in the future.

test_1
Getting read to simulate a predation event (aka throwing the tag overboard while shouting “PREDATION EVENT!”)

However, the accuracy of the predation location is currently unknown. After a tag hits the surface, varying amounts of time may elapse between the onset of satellite transmissions and the first successful uplinks to the Argos satellite system. The amount of delay may also vary with sea state (e.g., wind and waves).

lhx_2
After the tag surfaces from a predation event (real or simulated) it communicates with satellites to determine its position.

Over the next month, we are simulating predation events from known locations in Resurrection Bay and Prince William Sound. A “predation event” is not as scary as it sounds. Before deployment, we take accurate GPS coordinates from the boat and then dramatically throw the tags overboard while somebody hums the Jaws theme song. We will use modeling techniques to backtrack where the event occurred in space and time. Additionally, we will know more about the accuracy of the tags as well as their operating limitations. This tags will ultimately provide important information about the role of predation on Steller sea lions in our study area.

Written by: Dr. Casey Brown

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