2016 JISAO Internship Program
A comparison of PCA and DFA for identifying regime shifts in the Gulf of Alaska
My name is Madisyn Frandsen. I am a senior Environmental Engineering student at Tarleton State University in Stephenville, Texas. I spent my summer working with the Resource Ecology and Fisheries Management Division (REFM) at NOAA with the goal of updating the regime shift indicators for the Eastern Bering Sea and Gulf of Alaska using a dynamic factor analysis (DFA), as well as automating the code for future use by NOAA. The initial project goal was to update the regime shift indicators using a principal component analysis (PCA), but the DFA was thought to be a more suitable method. Another branch of my research was comparing these two methods for the study of regime shifts. Both forms of analysis are used for dimension reduction of a large set of time series to find a common trend. What differs between the two is that a DFA is designed to handle time series data while a PCA is not. A regime shift is a decadal switch from one characteristic behavior of a naturally occurring phenomenon, to another. In marine ecology, a regime shift signifies a change in the suite of dominant species.
The study was conducted using 33 biological time series (1965-present), 16 for the Eastern Bering Sea and 17 for the Gulf of Alaska. The time series included recruitment and catch data for either region. The PCA was conducted in R using singular value decomposition, and the DFA was performed in the ‘MARSS’ package in R. The results of each method were then run through Regime Shift Detection Software (SRSD), to determine if and where possible regime shifts have occurred for either region. Through this, I developed a code that will be useful in future regime shift studies.
Another project I worked on over the course of the internship was developing indices of capelin and sand lance using “sampler” species. These “sampler” species included various predatory seabird and fish species. The study was also separated into two regions, the Eastern Bering Sea and Gulf of Alaska. A DFA was also conducted on these time series, and the results were run through the SRSD.
Although on weekdays I was busy with work, I had time on the weekends to go on lots of adventures with the other JISAO interns. We would do anything from exploring downtown, to camping in the rain forest. I went on lots of hiking trips and ferry rides to various islands. I was also able to improve my climbing skills at the University of Washington’s Crags climbing center. Over the course of the summer I have made many new friends who I will miss greatly when we all have to part to go back home.
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