The effect of seismic shooting on the courtship behaviour of cod (Gadus morhua)

Anthropogenic noise is a well-recognized stressor in the marine environment. Seismic airguns, used to locate oil and gas deposits in the seabed, are among the loudest sources of anthropogenic noise in the North Sea. Their low-frequency sounds overlap with the hearing and vocalisations range of many teleost fishes. Cod (Gadus morhua) produce sounds both during courtship and male-male aggression, and seismic surveys may therefore interfere spawning behaviour. In large spawning pens, we exposed spawning groups of wild caught cod to three hours of daily seismic shooting at varying distances to mimic what fish would be exposed to during a real seismic survey. We examined both short-term (minutes before and after individual air gun shots)) and long-term responses (hours to days, before, during and after the full exposure period) on spawning behaviour. Short-term effects included startle responses, reduction in courtship behaviours, and increased activity in female fish, but no significant effect on vocalisation. The only long-term effect was a significant reduction of flaunting behaviour, while all other reproductive behaviours were resumed quickly after exposure. In conclusion, our study shows that seismic shooting, at levels up to ~165 dB re 1μPa2s (similar to levels found about 5-35 km from a conventional survey) may affect cod courtship behaviour at each onset, within a time frame of minutes from the first close by shot, but not over subsequent hours or days.