Comparative aerial and underwater visual acuity of the mink, Mustela vison schreber, as a function of discrimination distance and stimulus luminance.

The aerial threshold visual angle of mink rose from 15.4 min at 10 cm stimulus distance to 19.1 min at 90 cm and the underwater angle varied from 32.7 min at 10 cm to 46.6 min at 90 cm, all at 34 mL luminance. At constant 30 cm stimulus distance, the aerial angle rose from 15 min at 34 mL to 51.7 min at 0.012 mL, the underwater angle from 31.4 min at 34 mL to 95 min at 0.012 mL, the aerial and underwater data forming similar curves. If mink hunt in water at somewhat higher light levels than in air they can obtain equal acuities in the two media.