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

Abstract

Anthropogenic noise, such as e.g., seismic shooting used to locate oil and gas in the seabed, is recognized as a significant pollutant in the oceans. The sounds produced by the seismic airguns is of a low frequency, overlapping with the hearing and vocalisation range of many teleost fish, such as cod (Gadus morhua). During the spawning season cod produce sounds and perform a series of different courtship behaviours some in correlation with vocalisations. Seismic therefore, have the potential to disrupt the communication and hence the spawning behaviour. For my master thesis I am investigating what the short- and long-term effects of seismic shooting are on cod spawning behaviour by studying videos of captured cod exposed to seismic sound. The short-term analysis consisted of comparing the behaviour in ten minutes videos of right before seismic exposure to the first ten minutes into seismic exposure. To study the long-term effects the behaviour in the days before, during (but not at time of exposure) and after exposure was analysed and compared. In this thesis I found that cod were affected by the disturbance and showed clear startle behaviour and reduced their courtship during seismic exposure. The behaviours flaunting, fin display, follow and chase all decreased during the exposure while startle behaviour and jerk increased. In addition, female cod who were less active than the males, became more active during seismic shooting. The long-term study found that the behaviour flaunting was significantly reduced in the exposure days. However, this effect was not seen in the other behaviours and it thus, appear that cod habituated to noise. As a result of this type of analysis cod behaviour was intently studied and behaviour that has not previously been properly documented were observed and discussed. This includes the meaning of jerk behaviour, female performing courtship behaviours, and homosexual behaviours.