Avoidance of solar ultraviolet radiation by juvenile coho salmon (Oncorhynchus kisutch)

Abstract

Shade-seeking behavior and avoidance of solar ultraviolet radiation (UVR) by newly emerged coho salmon (Oncorhynchus kisutch) alevins and two-month-old coho juveniles was documented in experimental trials in the Little Qualicum River, British Columbia, using outdoor chambers that provided the fish with a binary choice of photo environments. Under high solar intensities (i.e., midsummer, cloudless skies) coho of both age classes strongly preferred 50% neutral density shaded conditions to unattenuated full-spectrum (280–700 nm) sunlight (t test, p < 0.025). In addition, coho alevins and juveniles showed a high selective avoidance of UVR (280–400 nm) (t test, p < 0.05). Within the UVR spectrum, coho responded significantly to UVA (320–400 nm) (t test, p = 0.028). Evidence of UVB (280–320 nm) avoidance was confounded by higher visible and UVA irradiance levels under screens exposing coho to UVB. Under lower solar intensities (i.e., cloudy skies) coho showed no spectral preference and did not seek neutral density shade. Behavioral avoidance of high intensity UVR, particularly UVA, suggests that shade-seeking behavior of juvenile coho may be linked to avoiding potentially harmful UVR exposure.