May 9, 2017
Our remote camera images give us insights about sea lion behavior onshore, but where do they go when they’re at sea? To better understand why their numbers are declining in parts of the Aleutian Islands, we need to know where Steller sea lions forage (or hunt) for their prey that consists of fish and squid. Due to our concern with declining pup births, we are focusing on monitoring adult females’ hunting patterns while they are pregnant, and may also be nursing a pup.
The best way to track an individual sea lion’s movements and dive behavior is by using satellite-linked transmitters, also known as satellite tags. The tags are slightly larger than a deck of cards and allow us to see where sea lions go, how deep they dive, and when they come to shore. This information is saved to the tag, then up-linked to satellites (via the Argos satellite location and data collection system) so we can download the data later when we’re back at the office.
The best time to attach tags on females is complicated by their biology and the weather in the Aleutians. Sea lions shed their fur from August through November. That means if we attach a tag before she has molted, the tag will fall off with her shed fur. Unfortunately, large storms and typhoons tend to kick up after September, and the high seas and strong winds can keep us from being able to work. By November the storms intensify through winter. So, we schedule our trips during October when many of the females have already molted and storm activity is just beginning.
Attaching the tags onto the animals is a coordinated effort to minimize any impacts on the sea lions and any risks to the researchers who must get close to adult females that weighs more than 800 pounds.
Attaching the tags onto the animals is a coordinated effort to minimize any impacts on the sea lions and any risks to the researchers who must get close to adult females that weigh more than 800 pounds. We work with colleagues from Alaska Department of Fish and Game, University of Alaska Fairbanks, and the Vancouver Aquarium to safely capture and handle the adult female sea lions. It can take up to 12 scientists to have the expertise necessary to safely capture, sample, and attach a satellite tag.
Similar to our summer research cruises to look for marked animals, we visit known sea lion sites and take the inflatable skiff to shore to drop off the team and heavy gear. The problem with finding animals during October is that they are a lot harder to locate than they are during the summer breeding season when they gather on land in larger numbers. But your work classifying remote camera images on Steller Watch, helps us pinpoint the most popular sites.
Once we arrive near a site with a good number of females, we find a safe place to land, which can sometimes be up to a mile away. The whole team hikes and climbs to a staging location and the scouting begins. A few people, including a skilled darter, will sneak up to get a closer look, searching to maximize our chances for a successful capture. When all the conditions are just right, sedatives are loaded into a dart that will be delivered from C02-powered rifle.
It takes a lot of stealth and patience to slowly sneak in for the perfect line-up. Steller sea lions have great sensory capabilities. That means if they smell, see, or hear you, they will head into the ocean. Once in position and a female is in a good location, the skilled darter will take the shot and the dart—essentially a flying syringe—launches and hits, the sedative is delivered immediately and the dart falls out.
The rest of the team hears the good news on the radio call and waits about 10-minutes for the sedative to kick in. The veterinarian and a few others are the first to approach the adult female. The veterinarian administers gas anesthesia and as soon as she is assured that the animal is doing well, she gives the OK. Suddenly the team erupts into hurried and quiet movements and a lot happens very quickly and efficiently to ensure safety of the sea lion and keep the handling time as short as possible.
I immediately get to work on attaching the satellite tag on top of her head—the best body location to maximize satellite up-links. First, I clean and brush the fur to remove dirt and loose fur, then I align the tag for good fit, and finally I use quick-setting epoxy to glue the tag to the fur. In the meantime other biologists are taking measurements and samples for laboratory analysis that will allow us to assess her physical condition, health, and whether she has any diseases or contaminants. She is marked for future identification, just the like the animals you see in the remote camera images. When everyone is done, we clear away and the veterinarian administers the reversal agents to counteract the sedatives, and removes the gas anesthesia device. The female starts to wake and rather quickly is up and on her way, usually to the water, as we all watch, hidden from her view.
Between 2011 and 2015, 13 adult females have been captured and tracked in the Aleutian Islands; you’ll see them in the remote camera images marked with an equal sign (“=”) and numbers, from 25 to 36. We’ve had great success with the satellite tag data—we even tracked one female up to 254 days! This information offers insights into their behavior leading up to when they give birth in the following summer breeding season. Adult female Steller sea lions in the Aleutian Islands have shown a diversity of foraging behaviors, from remaining exclusively nearshore on short trips, to trips of over 260 miles (420 km) offshore and lasting six days.
I am a research wildlife biologist with NOAA Fisheries Alaska Fisheries Science Center in Seattle, in the Alaska Ecosystems Program where I’ve studied Steller sea lions and northern fur seals since 2000. My primary research interest is vertebrate physiological ecology, which at NOAA Fisheries translates into studying sea lion foraging behavior, health status, and body condition to help address conservation questions and wildlife management issues.