The effect of pile driving noise on mating behavior in squid (Doryteuthis pealeii)

As the United States invests in wind energy development, it is essential to evaluate how pile driving will affect commercially and ecologically valuable species. Hammering piles into the seafloor during construction of offshore windfarms produces high intensity sound that can alter marine animal behavior and is considered a threat to many protected species. However, the effects of pile driving are poorly understood with respect to many ecologically vital taxa. We examined the effects of pile driving noise on mating behavior in the semelparous longfin squid, Doryteuthis pealeii, a keystone and commercially important species whose habitat range overlaps with projected windfarm locations. Males of this species utilize two mating tactics and alternate between them according to mating conditions. Generally, large males are consorts and pair with females, whereas small males attempt sneak copulations. We exposed squid to up to three 5-min playbacks of either pile driving or silent controls in groups consisting of a large male, a small male, and a female. We then evaluated changes in alarm responses and mate-guarding wherein one male guards a female from copulation attempts by the smaller sneaker male. Responses were compared to baseline behaviors and analyzed across time. While reactions to pile driving have been observed in individual squid, we found robust mate guarding that was not significantly disrupted by playbacks. Squid spent significantly more time mate-guarding as the trial progressed and particularly in the 5-min period prior to the third playback. Squid tested with pile driving indicated alarm on the first pulse of the first playback but subsequently habituated to the sound. These data suggest that groups of squid respond differently to pile driving noise compared to individual squid tested in previous work. The context in which squid are exposed to pile driving, including group size and behavioral state, is therefore vital for determining noise impacts. These semelparous squid engaged in mating behavior may deviate from expected responses due in part to the biological relevance of mating.