Abstract
Offshore petroleum platforms in the northern Gulf of Mexico provide a unique environment for many reef-associated and pelagic fish species; however, the factors that contribute to increased localized fish abundance remain poorly quantified. All manned platforms possess large floodlights for nighttime operations and these also illuminate the surrounding waters. Two platforms (MC582 and ST151), located off the Louisiana coast, were examined to quantify this artificial light field. A multi-spectral radiometer instrument package was used to record subsurface irradiance along a regularly spaced grid around each platform. Spectral patterns indicated that the predominant source of underwater light near MC582 was the natural gas flare, while floodlights predominated in the water beneath ST151. Irradiance profiles (log10 photosynthetically active radiation) indicated that 10 to 1000 times more light was present near the platforms compared to open water control sites and that light levels decreased with increasing depth. Irradiance values were interpolated to estimate the 3-dimensional underwater light field and volumes were constructed based on published visual thresholds for 3 larval/juvenile fish taxa. Results suggest that platforms provide an enhanced foraging environment for larval, juvenile and adult fishes by providing sufficient light to locate and capture prey, as well as by attracting and concentrating positively phototaxic prey taxa.