Lunacy in Atlantic cod: assessing the timing of spawning in Atlantic cod using ocean models and electronic data storage tags

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Understanding the environmental processes determining the timing and success of reproduction is of critical importance to developing effective management strategies for marine fish. Unfortunately, it has proven difficult to comprehensively study the reproductive behaviour of broadcast-spawning fish, such as Atlantic cod (Gadus morhua), in the wild. The combination of oceanographic models and electronic data storage tags (DSTs) has the potential to provide insights into the behaviour of fish, allowing for data collection over relatively large spatial and temporal scales that can be correlated to predicted environmental conditions and ultimately be used to refine predictions of year-class strength. In this paper we present data retrieved from DSTs demonstrating that Atlantic cod spawning in Iceland is tied to a lunar cycle with a pronounced semilunar cycle within it. Peak spawning activity occurs around the full and new moon with no evidence of relationship with diel tidal or day