| dc.description.abstract | This study investigated the impact of shipping activity and environmental conditions on the Northeast Pacific blue (Balaenoptera musculus) and fin whale (B. physalus) calling activity in the Santa Barbara Channel. Passive acoustic data were collected and analyzed from late November through late March for two consecutive years: 2019/20 and 2020/21, covering the beginning of the global Covid-19 pandemic, which reduced shipping activity worldwide. Presence of three blue whale call types and two fin whale call types in 15-minute windows was manually marked and number of daily ship passages was counted in the total 2892 hours of data. Additionally, remotely sensed environmental data from the study site, including measurements of sea surface height (SSH), sea surface temperature (SST), and chlorophyll a (Chl a), covering October 25 – March 25 during both 2019/20 and 2020/21 were extracted from the European Union Copernicus Marine Service Information (CMEMS) and used as a proxy for primary productivity and prey abundance. Overall, significantly fewer blue whale calls were detected in 2019/20, as well as fin whale 20 Hz-calls. Fin whale 40 Hz-calls were continuously present throughout both years, with significantly higher activity in 2019/20. There was no clear difference in shipping activity between the two years, hence no effect of reduced shipping activity as a result of Covid-19 was observed in these data. However, shipping activity was still negatively affecting the presence of blue whale B- and D-calls, as well as fin whale 20 Hz-calls. Significantly lower SST and higher Chl a values in 2020/21 compared to 2019/20 suggest higher productivity in the second year, which was characterized by a La Niña event. The significant positive relationship between Chl a and all blue whale call-types, as well as fin whale 20 Hz-calls likely explains the higher calling activity of all these call-types in 2020/21, and lower activity during the less-productive winter of 2019/20. The persistent presence of fin whale 40 Hz-calls confirms the continuous presence of some fin whale populations in the Santa Barbara Channel, whereas the annual variability of blue whale calls suggests that the timing of their occurrence could be driven by favorable environmental circumstances as they seek high densities of prey over a broad area during the foraging season. In conclusion, these findings contribute to the growing understanding of blue and fin whale acoustic activity and their response to anthropogenic noise. The results of this study raise concerns for these whale populations that seek prey-abundant areas amidst the high noise levels in the Santa Barbara Channel. Continuing research efforts to explore the impact of anthropogenic sound sources on marine fauna is essential for enabling the conservation of the underwater soundscape on which these animals depend. | |
