There are numerous harbor seals (Phoca vitulina) living in tidewater glacier fjords in Alaska. Harbor seals are covered with short, stiff, bristle-like hair. They reach five to six feet (1.7-1.9 m) in length and weigh up to 300 pounds (140 kg). Tidewater glaciers calve icebergs into the marine environment, which then serve as pupping and molting habitat for harbor seals in Alaska. Although tidewater glaciers are naturally dynamic, advancing and retreating in response to local climatic and fjord conditions, most of the ice sheets that feed tidewater glaciers in Alaska are thinning. As a result, many of the tidewater glaciers are retreating. Scientists are studying the glacier ice and distribution of harbor seals to understand how future changes in tidewater glaciers may impact the harbor seals. Jamie Womble, a marine ecologist based in Alaska, is one of them.
As Womble put in her recently published paper in PLOS One, “The availability and spatial distribution of glacier ice in the fjords is likely a key environmental variable that influences the abundance and distribution of selected marine mammals; however, the amount of ice and the fine-scale characteristics of ice in fjords have not been systematically quantified. Given the predicted changes in glacier habitat, there is a need for the development of methods that could be broadly applied to quantify changes in available ice habitat in tidewater glacier fjords.”
To conduct her research, Womble has used a variety of analytical tools including geospatial modeling (GIS), multivariate statistics, and animal movement models to integrate behavioral and diet data with remotely-sensed oceanographic data. Most recently, she has worked with object-based image analysis (OBIA).
“OBIA is a powerful image classification tool. Many people studying forests and urban areas use it,” Anupma Prakash, a colleague of Womble and professor of geophysics at the University of Alaska, told GlacierHub. “In our case, we could not use the satellite images because the satellite images did not have the details we required. We flew our aircraft quite low so we saw a lot of detail and could identify individual icebergs.”
OBIA offers an enhanced ability to quantify the morphological properties of habitat. Satellite imagery, on the other hand, is not a viable method in Alaska as there are few cloud free days.
“We wanted to classify our images into water, iceberg, and brash-ice (small pieces of ice and water all smushed together),” Prakash added. “The color and smoothness of water helped us isolate it. For icebergs the color, shape, and angular nature helped us isolate it, and the rest was bash-ice.” So it is now feasible to quantify fine-scale features of habitats in order to understand the relationships between wildlife and the habitats they use.
Thanks to the work of scientists like Womble and Prakash, OBIA can now be applied to quantify changes in available ice habitat in tidewater glacier fjords. The method can also introduced in other geographic areas, according to professor Prakash. Now that there is a more advanced method to study the harbor seals in Alaska, the hope is that other researchers will use the OBIA method to make further discoveries about key ocean habitats.