Abundance of harbour porpoises (Phocoena phocoena) on the Dutch Continental Shelf, aerial surveys in July 2010 - March 2011

De bruinvis (Phocoena phocoena) is de algemeenste zeezoogdiersoort in Nederlandse wateren. Desondanks waren er tot 2010 geen aantalsschattingen beschikbaar voor het Nederlands Continentaal Plat

Local Birds in and around the Offshore Wind Park Egmond aan Zee (OWEZ) (T-0 & T-1)

The Dutch consortium "NoordzeeWind" operates the first offshore wind farm in Dutch North Sea waters. The park, consisting of 36 turbines on monopiles, is located NW of IJmuiden harbour, some 8 NM off the Dutch mainland coast. Named after the nearest town ashore, the park will be known as "Offshore Wind farm Egmond aan Zee" (OWEZ). A second offshore wind farm has also become operational, the Princess Amalia Windfarm (PAWF). This report deals with distribution patterns of local seabirds in an area of approximately 885 km2 around the OWEZ and PAWF park

Harbour porpoises (Phocoena phocoena) in the Marsdiep area, the Netherlands: new investigations in a historical study area

Na de terugkeer van bruinvissen in de Nederlandse kustwateren is er in 2010 een haalbaarheidsonderzoek uitgevoerd om na te gaan of het opnieuw de moeite waard zou kunnen zijn om bruinvissen in het Marsdiep te bestuderen. De aantallen bruinvissen die in het voorjaar van 2011 werden gezien waren groot, maar weken niet wezenlijk af van wat er, op basis van zeetrektellingen bij Huisduinen, aan aantallen bruinvissen in de afgelopen vier seizoenen werd gezien. De door Verwey waargenomen verplaatsing van bruinvissen "met het getijde mee" kon tijdens ons onderzoek niet worden bevestigd

Shortlist Masterplan wind Aerial surveys of harbour popoises on the Dutch Continental Shelf

In het kader van het Shortlist Masterplan Wind programma zijn in 2010-2011 vliegtuigtellingen uitgevoerd om het seizoensgebonden voorkomen en de verspreiding van bruinvissen Phocoena phocoena op het Nederlands Continentaal Plat (NCP) in kaart te brengen. Dergelijke informatie is essentieel om het effect van menselijke activiteiten, i.c. offshore windparken op bruinvissen te begrijpen, te kwantificeren en uiteindelijk te minimaliseren

Assessment of the Effects of the Offshore wind Farm Egmond aan Zee (OWEZ) for Harbour Porpoise (comparison T0 and T1)

The aim of this study was to investigate whether the Offshore Wind farm Egmond aan Zee (OWEZ) has influenced the occurrence of harbour porpoises

Using aerial surveys to estimate density and distribution of harbour porpoises in Dutch waters

To investigate harbour porpoise density and distribution in Dutch waters, dedicated line transect distance sampling aerial surveys were conducted from May 2008 to March 2010. In total 10,557 km were covered on survey effort during 16 survey days in February to May, August, November and December. Using line-transect distance sampling techniques, porpoise density and abundance were estimated for each sub-area and survey season. The density estimate for harbour porpoises during the March 2010 survey (study areas B, C and D) is 1.33 porpoises per km² (95% C.I. 0.665–2.566, CV 0.34), which amounts to a total abundance of 66328 porpoises (95% C.I. 32745–125220, CV 0.34). The density shows strong seasonal variability, with the highest densities in winter and spring and the lowest densities in summer. All on effort survey data collected in March 2010 were analysed using a Generalized Additive Mixed Model (GAMM), to quantify the distribution of sightings in space and time. The GAMM reveals a strong effect of hour of day and cloud cover; most porpoises are sighted around noon and at intermediate cloud-cover. It is hypothesized this is either an effect of light conditions affecting sighting probability or within-day variation in behaviour influencing the proportion of time spent at surface. Finally, we discuss why such baseline information on absolute density and distribution is necessary to assess the current and future impact of anthropogenic activities on porpoises, and how it may be used to design the appropriate mitigation measure

Generalized functional responses for species distributions

Researchers employing resource selection functions (RSFs) and other related methods aim to detect correlates of space-use and mitigate against detrimental environmental change. However, an empirical model fit to data from one place or time is unlikely to capture species responses under different conditions because organisms respond nonlinearly to changes in habitat availability. This phenomenon, known as a functional response in resource selection, has been debated extensively in the RSF literature but continues to be ignored by practitioners for lack of a practical treatment. We therefore extend the RSF approach to enable it to estimate generalized functional responses (GFRs) from spatial data. GFRs employ data from several sampling instances characterized by diverse profiles of habitat availability. By modeling the regression coefficients of the underlying RSF as functions of availability, GFRs can account for environmental change and thus predict population distributions in new environments. We formulate the approach as a mixed-effects model so that it is estimable by readily available statistical software. We illustrate its application using (1) simulation and (2) wolf home-range telemetry. Our results indicate that GFRs can offer considerable improvements in estimation speed and predictive ability over existing mixed-effects approaches

Distribution of marine mammals in the North Sea for the generic appropriate assessment of future offshore wind farms

The Dutch government has formulated the ambition to increase the generation of renewable energy, among others by increased exploitation of offshore wind farms in the North Sea. To compose the generic appropriate assessment, Deltares has asked IMARES to provide an overview of the current knowledge on the spatial and temporal use of the North Sea by marine mammals that are protected under the Habitat Directive Annex II: common seal (Phoca vitulina), grey seal (Halichoerus grypus), harbour porpoise (Phocoena phocoena), bottlenose dolphin (Tursiops truncatus) . In addition, white beaked dolphin (Lagenorhynchus albirostris) and minke whale (Baleanoptera acutorostrata) are treated (Annex IV)