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Understanding and modelling the environmental control of fish recruitment has been a central question in fish population ecology for the last century. Most environment-recruitment models have primarily been developed to model mean recruitment using conventional regression techniques which assume that all environmental parameters are included and that the residual unexplained variability is unstructured. However, the complexity of environmental controls and the empirical evidence that many relationships have failed when retested suggest that these assumptions are generally not met. Most environmental controls may be considered as limiting factors to recruit- ment and act in interaction with other factors (often not measured or not known). We used quantile regression modelling, which is specifically designed to model limiting relationships, to reanalyse environment-recruitment relationships that have been published for 4 fish stocks: (1) Northeast Arctic cod (Barents Sea), (2) Atlanto-Scandian herring, (3) Bay of Biscay anchovy and (4) Pacific sar- dine. The method was adapted to the specific case of autocorrelated time series, a common feature of most environmental signals. The results from quantile regression were not straightforward exten- sions of conventional regressions. For Northeast Arctic cod and Pacific sardine, the original relation- ships with temperature were not statistically significant in the quantile model. For Atlanto-Scandian herring the relationship was confirmed and temperature clearly appeared as a limiting factor to recruitment. The published relationship for the Bay of Biscay anchovy with upwelling was not con- firmed, but the previously undetected relationship with river runoff was established. In this specific case, it was only by using a quantile model that the relationship could be detected as statistically sig- nificant. These results confirm the ability of quantile regression models to provide robust interpreta- tion of environment-recruitment relationships and to produce environmentally based advance warning when recruitment is expected to be low.

International audience; Spatial patterns in pelagic biodiversity are the result of factors acting from a global to a local scale. The global patterns have been studied intensively using taxa such as foraminifera and euphausiids. However, these studies do not allow direct comparisons of neritic and oceanic regions or examination of relationships between local and regional patterns of pelagic diversity. Here we present a map of the diversity of calanoid copepods, a key planktonic group, summarising 40 yr of continuous monthly investigations in the North Atlantic and North Sea. The high number of samples (168162) allowed mesoscale patterns in diversity to be detected for the first time at an ocean-basin level. Our results demonstrate pronounced local spatial variability in planktonic diversity and refine previous global studies at a lower resolution. They form a baseline at which long-term changes in planktonic diversity can be better assessed and ecosystem management plans implemented.

A short review shows that in cold, arctic regions of the North Atlantic positive relationships are generally observed between cod recruitment and water temperatures whilst negative relationships are observed in warm-temperate regions. According to this relationship, cod recruitment in the Irish Sea should be negat~vely related to sea temperature. Using 3 ~ndependent sources of longterm temperature records we test this hypothesis and show a highly significant connection between the recruitment of cod and temperature signals. We suggest that this relationship should be taken into account, in addition to spawning stock biornass, in any future attempt at understanding cod recruitment in this area.

Journal home page: http://www.int-res.com/journals/meps/ We tested whether the long-term fluctuations in abundance of 0-group cod Gadus morhua and pollack Pollachius pollachius sampled from 1919 to 1994 at 38 stations along the Norwegian Skagerrak coast might be related to the North Atlantic Oscillation (NAO). The short- and long-term fluctuations of both species exhibited different spatial structures and were probably of different origins. The former, which were previously shown to be related to biotic interactions, displayed signifcant highest similarities across the smallest scales (0t o 21 km). In contrast, the long-term fluctuations were similar at a larger scale (equal to or larger than the Norwegian Skagerrak coast) and were probably due to extrinsic factors. We have shown that the climatic conditions along the Norwegian Skagerrak coast and the fluctuations of Calanus finmarchicus in the Skagerrak were closely associated with the NAO. Long-term fluctuations of cod and pollack were, however, not associated linearly or non-linearly with the NAO or C. finmarchicus. Trends of cod and pollack appeared to be related to the long-term fluctuations in the bottom sea grass coverage, mainly constituted by Zostera marina, and it cannot be dismissed that fishing has contributed to the recent decline of these fish populations. We also conclude that the postsettlement period is crucial for these populations because of competition for space.

The influence of the North Atlantic Oscillation (NAO) on 2 major zooplankton species of the eastern North Atlantic and the North Sea, Calanus finmarchicus and C. helgolandicus (Copepoda, Calanoida), was investigated. Our results confirm that from December to April, west wind stress (WWS) intensity and temperature are strongly related to the NAO. If these results were expected, more striking were the close relationships between NAO and Calanus species abundance. Fluctuations in abundance of C. finmarchicus mainly result from the combination of 2 factors, both driven by the NAO: WWS effects on spring primary production and temperature. The case of C. helgolandicus is more complicated, as the links between this species and the NAO result from the combination of several factors. Two of these factors, spatial heterogeneity of WWS strength over the area and temperature, are directly driven by the NAO. The third one, competition between the 2 Calanus species, is indirectly influenced by the NAO. Biogeographical boundaries of the 2 copepods are also modified by the NAO. Thus, in a comparable way to the El Nifio Southern Oscillation in the Pacific, the NAO impacts the pelagic ecosystem of the eastern Atlantic and the North Sea.

Spatial and temporal patterns of Calanusfinmarchicus and C. helgolandicus (Copepoda, Calanoida) were investigated in the northeast Atlantic and the North Sea from 1962 to 1992. The seasonal cycle of C.finmarchicus is characterised by a single peak of abundance in spring, whereas the seasonal cycle of C. helgolandicus shows 2 abundance maxima, one in spring and one in autumn. The former species mainly occurs in northern regions (limited by the 55*N parallel in the North Sea and by the 50*N parallel in the open ocean). The latter species shows 2 types of spatial patterns, occurring in the Celtic Sea during spring and in the Celtic Sea plus the North Sea in autumn. Differences in seasonal spatial patterns of Calanus species may result from different responses to the environment, ultimately due to different life cycle strategies, different vertical distributions, opposite temperature affinities and interspecific competition. Futhermore, results reveal that annual means of abundance are closely related to annual maxima and to spatial extensions of the species. It also appears that the long-term trends of the 2 Calanus species are opposite: C. finmarchicus shows a clear downward trend in abundance, while C. helgolandicus presents an upward one.