Introduction

An ICES Symposium on The Influence of Climate Change on North Atlantic Fish Stocks was held in Bergen, Norway, from 11 to 14 May 2004. The Symposium, sponsored by the ICES/GLOBEC Working Group on Cod and Climate Change (WGCCC) as part of their synthesis activities, was convened to address the issue of climate variability and its impact on cod and other fish stocks in the North Atlantic. It followed 11 years after the first WGCCC-sponsored ICES Symposium on Cod and Climate (ICES, 1994) in Reykjavík, Iceland, which was convened to gather together the then current knowledge of the influence of climate variability on cod. The 2004 Symposium was timely because of the recent declines and collapses of some important commercial fish stocks in the North Atlantic, declines in which environmental influences are believed to have played a role. In addition, there has been growing concern about the effects of anthropogenically induced climate change on fish populations, especially in light of the general warming throughout the North Atlantic during the later 1990s (see Turrell et al., 2003) and into the present decade. The Symposium was held to provide a forum to further document environmental effects on fish, to investigate the mechanisms through which climate influences fish populations, to determine better ways by which environmental effects could be incorporated into fisheries assessment and management decisions, and finally to investigate how fish stocks could be influenced by future climate scenarios. A scientific steering committee, under the chairmanship of Harald Loeng (Norway), was established to help the co-conveners, and consisted of Keith Brander (ICES), Bob Dickson (United Kingdom), Steingrimur Jonsson (Iceland), Brian Rothschild (USA), Mike Sinclair (Canada), Nils Christian Stenseth (Norway), and Øyvind Ulltang (Norway). The Symposium was attended by 146 participants from 19 countries. It was organized along five major themes: Climate–Zooplankton–Fish Linkages, Distributional Shifts in Fish Stocks, Changes in Fish Production, Impacts of Future Climate Change, and Fisheries Management under a Changing Climate. The Production Session was divided into three subsessions (Ecosystems and Trophic Interactions; Growth, Condition, Reproduction, and Mortality; and Recruitment and Abundance) because of the large number of submitted papers under this topic. Invited papers were presented at the beginning of each session, and Jim Hurrell (USA) set the stage for the Symposium in a presentation entitled Climate variability in the North Atlantic: past, present, and future, with special emphasis on the response of the oceanography to the climate, most notably the North Atlantic Oscillation (NAO). While variability in the NAO up to the 1950s can be accounted for by internal atmospheric dynamics, changes in the NAO since that time are consistent with anthropogenic forcing. In addition, understanding climate variability in the North Atlantic is complicated by recent links connecting NAO variability to that in the equatorial Indian Ocean. These new findings underscore the global scale of the problem. Ultimately, there were 62 oral and 35 poster presentations, of which 33 appear in this volume. At the time of publication, most of the presentations and posters could be viewed at http://www.imr.no/2004symposium/web/. Results presented at the Symposium and in this volume show evidence of climate-induced variations in zooplankton production and distribution, including jellyfish, as well as documented evidence of increased survival of fish larvae with higher prey abundance. Recent warming trends have resulted in northward shifts in both the distribution and spawning sites of several species of fish, consistent with observations during earlier warm periods such as the 1920s and 1930s. Coherent fluctuations in fish abundance with changes in ocean temperatures were documented not only for recent times but also by analysing historical data collected as far back as the 17th and 18th centuries. These and other studies linking climate variability and fish responses were used, together with climate change scenarios, to predict likely impacts on fish stocks in future. The challenges for incorporating environmental effects into fisheries assessment methodology were much discussed, and several possibilities were presented. Long-term declines in North Sea cod are due primarily to heavy exploitation, but recent evidence of the role played by changing climate in reducing recruitment, plus evidence for a warmer future climate, all suggest that the public and politicians are looking to scientists to resolve this challenge sooner rather than later. In the ICES meeting on the impact of climate variability on the marine ecosystem held more than 50 years ago (ICES, 1949) Gunnar Rollefsen in his Preface stated, “The causes of fluctuations in the behaviour, occurrence, and abundance of fish stocks have been attributed to widely different conditions in nature, and practically no progress has been made on some of these problems for a very long time”. While we still have a long way to go in understanding these same causes, results from the latest Symposium indicate that steady progress is indeed being made. The latter is largely a result of the formulation of improved biophysical models, with more accurate and precise parameterizations of important biological processes, increased use of comparative studies to gain insight into processes and mechanisms, and utilization of higher level statistical methods. Most of these techniques are based upon information gathered from long-term data sets, and maintaining these through future monitoring efforts is essential for unravelling the impacts of climate variability on fish populations. The Symposium would not have been the success it was without the untiring efforts of several people. We therefore thank the scientific steering committee, the local organizing committee (Ingunn Bakketeig, Vibeke Kristiansen, Geir Ottersen, Jan Erik Stiansen, Kari Østervold Toft, and especially Lennart Edstrøm, Signe Solbakken, and the late Vigdis Eriksen), and the co-sponsors (ICES, GLOBEC, the Institute of Marine Research in Bergen, and the City of Bergen) for their help in making the Symposium a success. The ICES Journal of Marine Science Editor, Bernard A. Megrey, advised us on policy and performed the important stylistic edit. Final acceptance of each revised, edited paper was Bernard's prerogative. Bill Anthony, ICES, carried out a thorough copy-editing of all manuscripts accepted for publication. Søren Lund at ICES and others at the Publisher, Elsevier, saw the papers through to timely publication. It was a pleasure to work with them all. Finally, we wholeheartedly thank those who provided or supported the content of this issue of the ICES Journal of Marine Science. The editors, authors, and publisher are particularly indebted to the referees for generously giving of their time and, more importantly, through their prompt and comprehensive reviews, providing an even broader perspective of viewpoints than were represented at the meeting. The referees are listed at the back of this volume. Thanks are also extended to all the authors who made the required revisions of their manuscripts within tight deadlines.

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