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Dispatches from the field

Investigating Steller sea lion declines on remote Aleutian Islands

Steller sea lions
Aerial view captured by a hexacopter showing a previously marked male, M539  Photo: NOAA Fisheries

Steller sea lions
Steller sea lion
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Busy week-two surveying western limit of the U.S.

July 5, 2016- This week has been jam-packed! And there still wasn’t enough time to get everything on our wish list done. Fear not, we have surveyed our top priority sea lion sites, had time to survey for whales, and have conducted almost 50 fish camera tows. Phew! Another tool the fish biologists are using is a CTD which stands for conductivity, temperature, and depth. This tool measures the depth, temperature, and salinity profile of the area. They have dropped the CTD 15 times at each of the areas they have towed the underwater fish camera.

We have had to work hard to fit in all of this work since we were approaching our deadline for reaching Dutch Harbor by July 5th so we could offload fish camera and whale survey gear, and have five of the eight of our scientific team disembark in time to catch their flights home on the 6th. The remaining three biologists are staying on to survey sea lion sites around Dutch Harbor, Alaska. The last few days have been filled with transiting east from the farthest west reaches of the United States, with intermittent stops for some surveys along the way.

As one of our top priorities, we have visited 35 sea lion sites. It’s important that we conduct counts of adult, juvenile, and newborn (or pup) sea lions at these sites in the Rat and Near Islands, some of which have not been visited for five years. Concurrent with our research cruise, a NOAA Corps flight crew is operating a Twin Otter aircraft with a team of three biologists to survey sites from the Delarof Islands and eastward. Ultimately, our goal for this year is to use all of our resources to conduct a survey of the Aleutian Islands and western Gulf of Alaska. Next year, our focus will be to conduct counts from southeast Alaska to the western Gulf of Alaska. This count information is used to estimate abundance and trends in order to monitor this endangered population. For more information on population count estimates and trends, please see our most recent technical memorandum.

Our typical day on the ship begins with underwater camera tows or a whale survey until about ten o’clock am (ADT). The best time to survey sea lions is from 10am to 9pm (ADT) during their peak haul-out time. As we approach a sea lion site, the Captain will navigate the Tiglax just offshore so as not to disturb the animals. From the ship, biologists use binoculars to survey for sea lions. If there are enough animals present, the ship’s crew will launch the skiff and biologists will approach the site to take a closer look. At many of these sites we can move around in the skiff and conduct counts and look for marked animals. This means three to four of us are juggling binoculars and a camera with a telephoto lens to capture images of marked animals. This process can usually take about an hour or more. It’s great to get an up close and personal look.

Hexacopter or drone
Holding a hexacopter (or drone) before it takes flight  Photo: Kristen Campbell, NOAA Fisheries


For the more abundant sites, sites with complex topography, or those sites with pups present, Van and I have been able to use the hexacopter to collect aerial images for the survey. So far we have flown the hexacopter at 10 sites in the Rat and Near Islands.

Another important task has been to visit all six sea lion sites where we have digital cameras stationed. These remote cameras are pointed at various sections of a site to capture images of marked sea lions hauled out on land. This is an important method for collecting sightings of marked animals since we are only able to survey this remote area once or twice a year.

There are four sites with cameras in the Near Islands, one in the Rat Islands, and one site in the Delarof Islands, on Ulak Island for a total of 20 cameras. Last summer, a camera was mounted and focused on the tidal waters at one rookery site to capture any killer whale activity. These cameras are programmed to capture images approximately every 20 minutes during daylight hours. In the last year, we have collected more than 375,000 images.


Remote camera
Brian Fadely (left) and Tom Gelatt (right) retrieve memory cards from two remote cameras at the rookery on Agattu Island, in the Near Islands  Photo: Paul Wade, NOAA Fisheries


It takes a lot of effort to go through and find marked animals from these images. These sightings, along with those we have conducted from the skiff or shore while on our cruise, are used to estimate survival and birth rates, and track movements. Since this part of the population has continued to decline, this information is important for assessing possible causes for the lack of recovery.

Last year, NMFS biologists marked a very small proportion (0.01%) of the pups born in the western stock of the U.S. These marks are permanent so individuals can be identified throughout their lifetime. In the western end of the Aleutian Islands, we mark animals only at two sites; one site is in the Near Islands on Agattu Island and the other is in the Delarof Islands, at Ulak Island. Sites where sea lion pups are marked have their own unique symbol associated. For example on Agattu, the leading symbol is “~”. When adult or juvenile animals are captured, since we don’t know where these animals were born, they are marked with an “=” symbol. The symbols are followed by numbers, increasing chronologically. Seeing these marked animals over time can tell quite a story.

Three marked individuals we have seen on this cruise are good examples.

An adult female marked =30 was captured on Kiska Island at Cape St. Stephens on October of 2014. She weighed 774 pounds and was almost 8.5 feet long! We saw her in the summer of 2015 during our research cruise in June with a new pup. During this year’s cruise, we saw her at the same site with another pup. Sea lion females can have one pup per year but sometimes, especially out here in the Aleutian Islands, we can see them having a pup every other year; sometimes we see them have a pup every two years. In those instances where they don’t have a pup every year, we typically see them with their offspring from the previous year or two—those juveniles can grow to almost be the same size as mom!

Another female we have seen was marked >61 as a pup on Ulak Island in June of 2015. She weighed about 69 pounds and was almost 3 and a half feet long. (These pups can be quite large. We once marked a male pup that weighed over 100 pounds and was just over 4 feet long.) This year was our first sighting of >61 since she was marked and she is looking great.

The combination of visual observations and the remote camera images occasionally allow us to document movement of animals from other parts of the population, including Russia. A male sea lion that was born on Medny Island, in the Commander Islands, Russia was seen at Attu Island in the Near Islands in 2011 and 2012 during our research cruises. We didn’t see him during our cruise in 2013 but our volunteers spotted him from the images collected from the remote cameras at the same site. He appears to be a sub-adult male, maybe 7 to 9 years old. In 2014 and this year, he was seen in the Rat Islands and during our cruise.

And we've observed adult females born on Medny that have given birth on Attu Island in the US. All without a passport.

Come back next week to hear about our success surveying sea lions sites around and east of Dutch Harbor. Also, I will tell you about our remote field camp efforts.

Post by: Katie Sweeney, NOAA Fisheries Biologist

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