Environmental management of Antarctic cruise tourism: Does ship presence affect marine mammal acoustic behavior? A multi-year case study on the acoustic occurrence of Ross and leopard seals in relation to the presence of the German research icebreaker Polarstern

Tourism in Antarctica is increasing, with visitors mostly choosing ship cruises often advertised as “Last chance tourism” taking advantage of increasing climate change awareness. While the existing guidelines for tourist operators are designed to protect this fragile region, many aspects of the local fauna, such as animal distribution and behavior, are still largely unknown due to difficulties studying these species. Without supporting data, it is challenging to design effective measures that minimize negative impacts of cruise ships on the Antarctic environment. A potential negative impact is the anthropogenic underwater noise generated by the vessels visiting the areas. Marine mammals rely on sound for many purposes such as foraging, orientation and reproduction. Ship noise can therefore potentially affect critical life phases of these species. Here we present a case study investigating how vessel acoustic presence affects the vocal behavior and timing of acoustic presence of leopard seals (Hydrurga leptonyx, LS) and Ross seals (Ommatophoca rossii, RS). RS are one of the least studied Antarctic species. Both pinniped spe cies are known to mainly produce underwater sounds during the mating season, presumably to attract mating partners in pack-ice areas. The German research icebreaker Polarstern (PS) annually resupplies Neumayer Station III (NS) - the German Antarctic Research Facility. Its arrival at the pier where cargo is unloaded has been noted to coincide with the onset of pinniped vocal activity in this area. Here, we use passive acoustic data that were recorded close to the pier over a 5-year period to investigate and compare how seal vocal behavior and vocal activity relate to the timing of ship arrival, presence and departure. The seals’ behavior over the relatively short analysis period of 5 years was complex due to their natural calling variation within life phases (before, during and after mating season). Thus, interpretation was not always straightforward. The arrival timing of the PS had an effect on RS, which delayed their appearance in 2010 and 2011 coinciding with the anticipated arrival of the ice-breaker. However, once arrived, both species showed no avoidance behavior and calling times remained unchanged despite PS. LS and RS calling activity decreased significantly during PS presence, but tended to recover instantly post PS departure. It is therefore unlikely that the animals left the area completely and decrease in calling may instead be related to masking. However, further research is needed to further explore what caused the decrease in calling. Both LS and RS seemed to use higher frequency call types during PS presence. The seals’ arrival times are also affected by prevailing ice conditions and associated food distribution. LS arrival time differed within the 5 years, whereas the RS arrived slightly earlier each year. The marine soundscape planning approach was applied to explore how ship arrivals can be timed to minimize potential disturbances. Ship quietening techniques and reduced ship speeds can also contribute to reduced underwater noise levels. Lastly, stricter legislative measures are needed to regulate which regions during which periods can be used for tourism.