Impact of high marine traffic on harbor porpoise: Effect on abundance and distribution
Nehls, G.; Zydelis, R.; Matuschek, R.; Brandt, M.; Diederichs, A.; Hoeschle, C.; Thomsen, F. (2024). Impact of high marine traffic on harbor porpoise: Effect on abundance and distribution, in: Popper, A.N. et al. The effects of noise on aquatic life: Principles and practical considerations. pp. 1077-1103. https://dx.doi.org/10.1007/978-3-031-50256-9_118 |
| Authors | | Top | - Nehls, G.
- Zydelis, R.
- Matuschek, R.
- Brandt, M.
| - Diederichs, A.
- Hoeschle, C.
- Thomsen, F.
| |
| Abstract | Increasing evidence documents effects of impulsive underwater noise on hearing and behavior of marine mammals, but knowledge about the impacts of extensive or chronic exposure of cetaceans to continuous noise from shipping is still scarce. The distribution of harbor porpoises (Phocoena phocoena) was analyzed in relation to shipping noise and other environmental variables in an area with intense marine traffic, the Fehmarnbelt in the Baltic Sea. Autonomous noise recorders were deployed at 19 positions within the Fehmarnbelt between September 2009 and November 2010 (bandwidth = 16 Hz–16 kHz). Harbor porpoises were surveyed from March 2009 to October 2010 using aerial visual line transect surveys (altitude = 76 m and 250 m). The acoustic data were analyzed using 10 s intervals (CI = L5, L50 and L95). Noise maps were derived using AIS data for each month in 2010 in a grid of 750 × 750 m cells and applying an empirical geometrical spreading loss model. Ambient noise in the Fehmarnbelt was dominated by shipping noise (median SPL: 109–132 dB re 1μPa), and noise levels found are typical for busy waterways. Distribution modelling was used for analyzing correlations between environmental variables and porpoise densities. The best fitting distribution model included variables characterizing water temperature at the bottom, water depth, and underwater noise; plus, temporal variable as survey year and season were also important. The model shows porpoise densities declining with increasing median sound levels to about 130 dB re 1 μPa. Thus, median shipping noise levels significantly affected the distribution of harbor porpoises in the study area, but little habitat displacement appeared as a result. This finding might reflect habituation and a trade-off, where the benefits for the porpoises to stay in the study area outweigh the disruptions of disturbance due to underwater noise exposure. |
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