Over the past century, advances in technology and historical events such as climate change have resulted in significant changes in the exploitation pattern, population sizes and the potential yield of fish stocks. These variations provide contrast in the data that improves our knowledge on population dynamics and our ability to develop management strategies for long-term sustainable exploitation. In this study, we use a standardized scientific trawl survey to obtain a historical time series of relative abundance, recruitment and size structure for plaice in the Kattegat-Skagerrak. Our work extends the available time series by more than 80 years so that the evaluation of trends is more informative than is possible from the current assessment. We show that the current adult biomass is approximately 40% of the maximum observed at the beginning of the century and during the 1960s. The average maximum individual length has been reduced by 10 cm over the studied time period. An analysis of trends in mean length indicates that fishing mortality was variable during the first half of the century and has increased steadily over the past 20 years. Recruitment has been the highest on record during recent years, suggesting that the alleged link between coastal environmental degradation and juvenile survival is of low importance. The overall findings of our work will provide managers with a historical perspective on the population dynamics of the stock, which will support the long-term management of plaice in the Kattegat-Skagerrak.

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Increased knowledge on the spatial distribution of marine resources is crucial for the implementation of a true ecosystem approach to management and the conservation of marine organisms. For exploited fish species characterized by aggregation behaviour during spawning time, the identification and tracking of spawning areas is essential for a correct assessment of their productivity and population abundance. To elucidate this concept, we reconstructed the spatio-temporal distribution of adult plaice (Pleuronectes platessa, Pleuronectidae) during spawning time along the 20 th century. Historical data reveal that not only the abundance but also the former population richness was much higher than previously estimated and has declined because of protracted over-exploitation during the last 30years. We conclude that forecast of stock recovery to former levels of abundance neglecting spatial reorganizations might be over-optimistic and shaded by a lost memory of the past population richness. These results reinforce the importance of managing exploited marine resources at a greater spatial resolution than has been carried out in the history of fishery management. © 2010 Blackwell Publishing Ltd

We analyze marine benthic communities at different sites in Skagerrak with the purpose of understanding the role of exogenous and endogenous factors in explaining the species’ temporal dynamics. The previous finding that the dynamics of these species communities are mainly driven and synchronized by environmental (temperature) forcing was only weakly supported when analyzing single‐species dynamics at five sites where four of the species were present every year. There was no consistent pattern in how the temperature affected the realized per capita growth rate, either across species at a given site, or among sites for a given species. Furthermore, there was no net‐interaction from the community on a given species strong enough to give rise to second‐order dynamics. However, when implementing a Multi Dimensional Scaling (MDS) analysis and incorporating all sampling sites and species ‐we found that the different communities clustered in relation to depth, hence, communities at the same depth were more “similar” than communities at different depth. Revealing the underlying interactions shaping these marine benthic communities is a challenge that calls for an array of various and complementary approaches.

Climatic variability is most likely to have an effect on marine populations and it is important to understand further the synchronicity between climatic oscillations and the life cycle of benthic species. This chapter presents a variety of studies on climate influence on marine benthos communities in the North Sea, Skagerrak, and Baltic. The main conclusion is that the NAO affects single species as well as whole communities and functional groups, and that the impact may differ geographically and depend on the species composition of the communities.