Fig. 3. Penguin diving behavior.

Typical krill-feeding dives recorded in (A) January 2013, when sea ice was extensive, and (B) December 2016, when sea ice was nearly absent. In ice-covered seasons, penguins slowed ascending speeds down at the end of each dive to search for cracks in the ice for breathing [red arrows in (A)]. (C to G) Relationships between dive depth and dive duration of krill-feeding dives for each season, with the ordinary least-squares regression lines (2010/11, Y = 1.30 × X + 66.6, R² = 0.57, N = 531; 2011/12, Y = 1.36 × X + 69.7, R² = 0.20, N = 485; 2012/13, Y = 1.19 × X + 77.3, R² = 0.49, N = 1119; 2016/17, Y = 1.01 × X + 55.7, R² = 0.60, N = 2275).