Does the Lunar Cycle Affect Reef Fish Catch Rates?

The lunar cycle was examined as a potential source of variation in CPUE for the most common commercial reef fish species captured in the Gulf of Mexico. Using fishery observer data for species captured with bottom longline and vertical line gear types, the analyses modeled CPUE with two different approaches: (1) a generalized additive model with cyclic splines to explain nonlinear variations with the 29.5‐d lunar cycle; and (2) a generalized linear model using periodic regression with the sine and cosine functions to describe cyclic variations in CPUE. A lunar effect on catch rates was detected for Red Grouper Epinephelus morio and Tilefish Lopholatilus chamaeleonticeps ; however, no lunar effect was detected for Yellowedge Grouper Hyporthodus flavolimbatus , Red Snapper Lutjanus campechanus , or Vermilion Snapper Rhomboplites aurorubens based on either method. The lunar effect in the bottom longline fishery differed between species, with increased CPUE consistently predicted to occur near the new moon for Red Grouper and to take place proximal to the full moon for Tilefish. Red Grouper captured with vertical line gear had two CPUE increases predicted around the waxing and waning lunar phases. Inconsistencies in lunar effect between gear types for Red Grouper were present, possibly due to different mechanisms affecting CPUE. Results suggest that lunar cycles influence catch rates for some of the reef fish species examined and should be considered as potential environmental covariates for standardizing nominal CPUE. Received October 14, 2016; accepted February 2, 2017 Published online April 11, 2017