Monitoring of marine mammals in the framework of the construction and exploitation of offshore wind farms in Belgian marine water
Haelters, J. (2009). Monitoring of marine mammals in the framework of the construction and exploitation of offshore wind farms in Belgian marine water, in: Degraer, S. et al. Offshore wind farms in the Belgian part of the North Sea: State of the art after two years of environmental monitoring. pp. 237-266
In: Degraer, S.; Brabant, R. (2009). Offshore wind farms in the Belgian part of the North Sea: State of the art after two years of environmental monitoring. Management Unit of the North Sea Mathematical Models, Marine Ecosystem Management Unit/Royal Belgian Institute of Natural Sciences: Brussel. 287 + annexes pp., meer
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| Abstract |
For assessing the possible effects of the construction and exploitation of offshore windfarms on marine mammals, a monitoring plan was developed. This plan aims to both assess short-term and long-term effects, and requires a combination of different research methods. The monitoring results for 2008 can evidently not conclude about possible effects. Rather, 2008 was a year in which the monitoring programme was developed into detail, and in which methods were tested in the field. Given that the most abundant marine mammal in Belgian waters is the harbour porpoise Phocoena phocoena, research was focused at this species, although possible effects on other species are and will be assessed. The monitoring plan follows a BACI design: assessing the situation before, during and after the construction, and in both the impact zone as a control zone. The monitoring consists of the following disciplines: (1) aerial monitoring of porpoises to estimate ad hoc densities and distribution, using an internationally agreed methodology (line transect sampling); (2) use of static acoustic devices (PoDs) to determine presence of porpoises and dolphins at selected locations over a longer period of time; (3) assessment of other relevant data becoming available, such as originating from other monitoring activities around the windfarm areas (such as bird censuses) or from stranding schemes; (4) assessment of the possible impact of increased levels of underwater noise on marine mammals. The aerial surveys performed in 2008 yielded an estimation of 4,341 (2,630 – 7,167) porpoises present in Belgian waters at the beginning of April 2008, or a density of 1,21 (0.73-1.99) animals per km². A limited survey in May yielded lower numbers. The estimates are consistent with the data obtained from a large survey in 2005 (SCANS II). They confirm that at least up to 2008, fairly high densities of porpoises occurred in Belgian waters in spring until April. One of the conclusions of the analysis was that more surveys should be undertaken to be able to have more reliable estimates, and to be able to produce density surface models. At the end of 2008 four C-PoDs (porpoise detectors) were obtained. These static acoustic devices capable of demonstrating the presence of small cetaceans in the vicinity could not yet be deployed during 2008. Instead, a costefficient mooring system was designed, and mooring locations were selected. An analysis of strandings data indicated that during 2008, a lower number of porpoises had washed ashore than in previous years. Also sightings from the coast have declined. Reasons for this are unknown, but it is clear porpoises remained further away from the coast, while still being present in large numbers further offshore in Belgian waters. The results of the underwater noise measurements during construction works on the Thornton Bank indicated levels similar those produced by merchant shipping. While it was possible that porpoises would avoid the area around the construction site, in a similar way as they usually avoid motorised vessels, this noise level was of little concern, given its level and duration. However, due to several circumstances the noise level of certain more relevant and specific protection, could not be investigated during 2008. |
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