Abstract

Harbor Porpoises (Phocoena phocoena) are protected under the European Habitats Directive as a migrating species within their entire range. International agreements like ASCOBANS (Agreement on the Conservation of Small Cetaceans of the Baltic, North East Atlantic, Irish and North Seas) add to the protective status under the auspices of the Convention of Migratory Species (CMS, Bonn convention). At the same time they are exposed to a large number of human activities in their marine ecosystem including fishery, vessel traffic, military and seismic activities, offshore constructions, chemical pollution and marine litter.

There are many types of anthropogenic sound in the world's oceans. The highest amplitude are impulsive sounds from undersea explosions, pile-driving, and airguns, but anthropogenic noise also includes continuous wave noise from military and commercial sonars and ship traffic. At the moment, impact pile-driving with hydraulic hammers is considered to be a cost-efficient way of building foundations for offshore wind farms. German offshore wind energy is supposed to expand to a nominal capacity of 25 GW by 2030. This ambitious goal means that, if the rated power of wind turbines remains at 5 MW, 5000 turbines will need to be erected over the course of 17 years, resulting in nearly 300 new turbines per year in the North and Baltic Seas combined. The construction of these turbines and their operation will potentially result in significant increases in regional ocean noise.

Systematic pathological investigations on harbor porpoises over the past 20 years showed that harbor porpoises are suffering more frequently from severe infectious diseases when compared to harbor porpoises from the arctic region. Furthermore, indications for an impaired immune and endocrine system were found and histopathological studies of the middle and inner ear showed that lesions occurred more often than expected.

As human activities associated with the construction of Offshore-wind parks increases, more knowledge about the hearing abilities of harbour porpoises is needed. The present investigation uses a non-invasive method for measuring auditory evoked potentials (AEP) to determine the frequency range of hearing and hearing thresholds in porpoises. Porpoises were were investigated when reported from Danish fishermen when incidentally caught in pound nets additionally trials were performed with animals under human care at the SOS Dolfinarium in Harderwijk, the Netherlands, and Fjord and Baelt Center, Denmark. Audiograms were measured on four free-ranging harbour porpoises and six audiograms were measured on harbour porpoises in human care. Audiograms showed good agreement with one another although differences of up to 30 dB were registered within the range of best hearing from 20 to 140 kHz. Additionally, measurements on stress hormones and cytokine profiles were conducted to develop indicators of the effects of anthropogenic stressors on the endocrine and immune systems of the animals. The study will continue with the ultimate goal to test harbor porpoises for the presence of temporary threshold shift (hearing loss) following exposure to a seismic airgun. The results are urgently needed to manage the protection of harbor porpoises utilizing habitat in the presence of human activities.

* Presenting author