Exposure to solar radiation may increase ocular UV-filtering in the juvenile scalloped hammerhead shark, Sphyrna lewini

Light energy is necessary for vision, but ocular tissues are subject to photodamage, and many vertebrates sequester UV-absorbant pigments in their preretinal ocular tissues, in part to minimize such damage. In this study (21 May–1 July 2001), juvenile scalloped hammerhead sharks, Sphyrna lewini (Griffith and Smith, 1834), were exposed to higher levels of solar radiation than they had previously experienced in the source habitat in the turbid waters of Kane’ohe Bay, Hawai’i, USA. Light transmission through the ocular media was measured in two individuals shortly after capture and in other individuals after 7, 14, 20, 27, and 41 days exposure to high light levels in a shallow, outdoor pen. Sharks from their usual habitat filtered a small proportion of the UV spectrum, but sharks exposed to greater solar radiation showed increased UV blocking in their corneal tissues, particularly at wavelengths below 310 nm. The proportion of UV blocked was relative to the duration of exposure. There were no changes attributable to exposure duration in transmission through the whole eye or lens, nor was there any clear pattern to variation in transmission through dorsal, ventral, anterior, and posterior quadrants of the cornea. Further experiments will be needed to confirm that this apparently rapid corneal adaptation to high light was due to the increased UV exposure.