| Abstract |
Synchrony in population fluctuations have commonly been observed among a variety of species. They are generally attributed to the effect of common environmental forcings on population dynamics. Here, we investigate long term synchrony in the recruitment variations of the North East Atlantic fish populations. A PCA (principal component analysis) was performed to extract the main patterns of variation. The most significant one reflects the synchronous decrease of the recruitment for the majority of gadoids populations, in the Baltic Sea, Kattegat, North Sea, Irish Sea and West of Scotland. The inverse pattern was observed for half of the herring populations. Plaice populations also exhibit synchronous recruitment trends, characterised by strong year classes during the 80's. Recruitment variations of saithe and sole populations never correlate with these general patterns. The analysis suggests that a regime shift occurred between 1982 and 1998 in the North East Atlantic. Actually, a step-like change was detected for most of the time series of recruitment and sea temperature at the end of the 80's. These changes in recruitment are concurrent with the regime shift observed in the North Sea and with the large scale changes reported for the plankton, which were both related to climate change. However, the analysis of the recruitment, stock biomass and fishing mortality time series indicates that the trends in recruitment for some populations could also result of the exploitation. We conclude that the variations of recruitment may reflect a regime shift in some areas of the North Eastern Atlantic, in response to climate change, but that exploitation is also responsible of a great part of the recruitment variations. |
