Fish populations in the Barents Sea fluctuate considerably. NTNU researcher Harald Yndestad has worked to identify the factors that influence oscillations in fish populations over time. He has discovered that there is a connection between fluctuations in fish populations and the position of the Moon in relation to Earth. The lunar orbit is not circular; the angle varies by 5 degrees over a span of 18 years. When the angle changes, the tides on Earth shift direction. As a result, there is an increased flow of temperate water from the Atlantic Ocean into the Barents Sea. Warmer waters contribute to an increase in plankton production, and therefore fish.