SOLAR ULTRAVIOLET RADIATION AND THE SPAWNING HABITAT OF YELLOW PERCH,PERCA FLAVESCENS

Abstract

Dissolved organic carbon (DOC) strongly influences the underwater levels of potentially damaging solar ultraviolet radiation (UVR) in freshwater lakes. Even so, little is known about how DOC-related variation in UVR may influence natural populations and communities in lakes. Past studies of fish recruitment have emphasized the importance of temperature, food limitation, and predation in controlling year-class strength in fish. Here we report that high UVR levels in low-DOC lakes also may modify the spawning depth, hatching success, and thus recruitment of certain freshwater fishes. We examined how UVR influences the spawning habitat and hatching success of yellow perch (Perca flavescens) eggs in two lakes with different DOC levels and thus different UVR environments. Yellow perch eggs were incubated at the same depth (0.8 m) in quartz tubes (with mesh ends for water exchange) in both lakes in a modified reciprocal transplant experiment. Solar radiation was manipulated to provide three treatments that included exposure to full solar radiation (quartz alone), shielding from UV-B with wavelength selective filters (Mylar D), and dark controls that removed all wavelengths of solar radiation. All eggs in the light treatments in the high-UVR lake perished, whereas survival to hatching of eggs in all treatments in the low-UVR lake and in the dark controls in the high-UVR lake were ≥96%. Survival time in the high-UVR lake was longer in UV-B-shielded than in fully exposed (quartz) treatments, and eggs collected from the high-UVR lake survived longer than those collected from the low-UVR lake in identical UVR treatments. A survey of natural spawning depths in the two lakes revealed a much deeper spawning depth in the high-UVR lake (median = 3.2 m) than in the low-UVR lake (median = 0.4 m). Deeper spawning depths in the high-UVR lake suggest that yellow perch can avoid direct UVR damage in low-DOC lakes. DOC and hence UVR in lakes may be altered by both anthropogenic and natural disturbances in the surrounding watershed, suggesting that these disturbances may have consequences for the spawning habitat of fish.