Northern elephant seal spleen volume during rest (min 0) and diving (min 1–7) was obtained by using MR imaging techniques (n = 5). Each animal had four dives. Splenic volume does not decrease significantly after min 2 (ANOVA, F(6,28) = 33.94, P < 0.0001). Error bars indicate 95% confidence interval (bootstrap analysis, 10,000 repeats).