This report presents the results of twelve monthly ichthyoplankton surveys carried out from April 2010 until March 2011 in the southern North Sea. The aim of this study was to collect data on the temporal and spatial distribution of fish eggs and larvae on the Dutch Continental Shelf (NCP). However, since fish eggs and larvae are transported with the currents onto the NCP a larger area covering the majority of the southern North Sea was sampled during the surveys. Despite technical problems or bad weather conditions preventing the sampling of all planned stations during each survey, the coverage was good and the general trends in ichthyoplankton abundance became apparent. Fish eggs were found in all months but species and numbers varied per month across the southern North Sea. The highest abundance of fish eggs was found from January until May with fish eggs being found at all stations from April until July. Very few eggs were found between August and November. From December onwards abundance of eggs increased again. The pattern was the same on the NCP. In total 35 different species of fish eggs were found. Fish larvae were found in all months but species and numbers varied in a similar pattern to the fish eggs, except the highest abundance of larvae was found in December and January in the English Channel (mostly herring). Numbers of larvae in the southern North Sea increased from April until June and afterwards then gradually declined until November. After this the abundances increased again. Larvae were found at almost all stations from May until September. In October and November larvae were found at half of all the stations both in the whole sampling area and on the NCP. The patterns was the same on the NCP. In total 74 different species of fish larvae were found. Based on the results of a modelling study, a mitigating measure was issued by the Dutch authorities forbidding pile driving of offshore wind farm foundations from January to June, in order to ensure that negative effects on prey availability for birds and marine mammals within Natura 2000 areas are minimised. The results of the year-round monthly surveys show that from April until September fish larvae were found throughout the survey area, including the NCP, in varying numbers and varying species. Still in October and November larvae were found at half of the stations although at lower abundances. Even in December larvae were still found at a quarter of the stations on the NCP. Whilst the abundance of larvae was low in October and November, there are a few species with larvae present that are absent at other times of the year. These results on ichthyoplankton abundance and results of the experimental study on the effect of pile driving on fish larvae need to be combined. Ideally they should also be assessed with subsequent studies of ichthyoplankton transport and impact on the Natura 2000 sites. This unique study is the first to comprehensively sample and analyse the ichthyoplankton with monthly resolution in the southern North Sea. These data on spatial and temporal distribution of fish eggs and larvae can be used in modelling studies to assess the effects of human activities in the southern North Sea, on different fish stocks.
|Place of Publication||IJmuiden|
|Number of pages||433|
|Publication status||Published - 2011|
|Name||Report / IMARES Wageningen UR|
- fish eggs
- north sea