NORTH SEA FISH STOCKS-RECENT CHANGES AND THEIR CAUSES

RAPPORTS ET PROCÈS-VERBAUX DES RÉUNIONS VOLUME 172 NORTH SEA FISH STOCKS-RECENT CHANGES AND THEIR CAUSES A Symposium held in Aarhus 9-12 July 1975 Edited by G. HEMPEL CONSEIL INTERNATIONAL POUR L EXPLORATION DE LA MER CHARLOTTENLUND SLOT - DANEMARK Prix: c. d. 170.00 Août 1978

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T A B LE O F C O N T E N T S Page Introduction and historical background, by G. H em pel... 5 Map of the North Sea with ICES statistical divisions I Va, b, and c... 10 Long-term changes in landings of fish from the North Sea, by M. J. H o ld en... 11 The industrial fisheries in the North Sea, by K. Popp M ad sen... 27 Changes in the Norwegian mixed fisheries in the North Sea, by J. Lahn-Johannessen, S. H. Jakupsstovu, and T. Thomassen... 31 Changes in cod stocks and cod fisheries in the North Sea, by N. D a a n... 39 Changes in North Sea haddock and whiting, by R. Jones and J. R. G. H is lo p... 58 On fluctuations in the haddock population of the North Sea, by D. Sahrhage and G. W agner... 72 Changes in plaice stocks and plaice fisheries in the North Sea, by R. C. A. Bannister 86 The spawning of plaice (Pleuronectes platessa L.) in the southern North Sea and English Channel, by D. Harding, J. H. Nichols, and D. S. T u n g a te... 102 Changes in plaice larval dispersal in the last fifteen years, by J. W. Talbot... 114 Changes in North Sea sole stocks (Solea solea (L.)), by J. F. de V een... 124 Long-term changes in North Sea herring stocks, by A. C. B u rd... 137 Variations in growth rate and maturity of herring in the northern North Sea in the years 1955-1973, by G. H u b o ld... 154 The growth of herring in the northwestern North Sea, by A. Saville... 164 Some comments on herring larval distribution and abundance in the North Sea, by A. S aville... 172 Long-term variations in the Swedish herring fishery off Bohuslän and their relation to North Sea herring, by H. H ö g lu n d... 175 A century of observations on sprat in the Skagerrak and the Kattegat, by A. L indquist... 187 The effect of recent changes in the North Sea mackerel fishery on stock and yield, by J. Hamre... 197 Trends in Scottish research-vessel catches of various fish species in the North Sea, 1922 1971, by J. Richards, D. W. Armstrong, J. R. G. Hislop, A. S. Jermyn, and M. D. Nicholson... 211 Immigration of southern fish into the North Sea, by K. H. Postum a... 225 The German industrial fisheries in the North Sea and their by-catches, by K. Tiews 230 Changes in the stock of brown shrimp (Crangon crangon L.) in the coastal area of the Netherlands, by R. B oddeke... 239 The predator-prey relationship between fish populations and the stock of brown shrimp ('Crangon crangon L.) in German coastal waters, by K. T ie w s... 250 Non-commercial fish species in the German Bight: Records of by-catches of the brown shrimp fishery, by K. Tiews... 259 On the nursery-aspects of the Waddensea for some commercial fish species and possible long-term changes, by G. Rauck and J. J. Zijlstra... 266 Recent biological phenomena in the German Waddensea, by H. M ichaelis... 276 Changes in the seal populations of the North Sea, by C. F. Summers, W. N. Bonner, and J. van H aaften... 278 A multispecies analysis of the effects of variations of effort upon stock composition of eleven North Sea fish species, by K. P. Andersen and E. Ursin... 286

Page Competition and co-existence with particular reference to gadoid fish species, by R. Jones 292 On the disappearance of bluefin tuna in the North Sea and its ecological implications for herring and mackerel, by K. T iew s... 301 Long-term changes in North Sea hydrography, by H. W. Hill and R. R. D ickson 310 Long-term variations of temperature and salinity in the inner German Bight, by G. Becker and D. K ohnke... 335 Long-term hydrographic variations off southern Norway, by R. Ljøen and R. Sætre 345 The nutrient contents of North Sea water: Changes in recent years, particularly in the Southern Bight, by H. P o stm a... 350 Long-term observations on nutrient contents near Helgoland in relation to nutrient input of the River Elbe, by F. Lucht and M. G illbricht... 358 Variations in phytoplankton near Helgoland, by E. H agm eier... 361 Variations in bacteria in the German Bight, by W. Gunkel and M. G illbricht... 364 A model of the biological effects of eutrophication in the North Sea, by E. Ursin and K. P. A n d ersen... 366 A method of predicting the biological effects of synthetic pollutants in the North Sea, by H. Lassen... 378 Continuous Plankton Records : Large-scale changes in the abundance of phytoplankton in the North Sea from 1958 to 1973, by P. C. R e id... 384 Changes in the zooplankton of the North Sea, 1948 to 1973, by J. M. C olebrook... 390 The plankton in the northwestern North Sea, 1948 to 1974, by V. Bainbridge, D. C. T. Forsyth, and D. W. C anning... 397 The benthos of the western North Sea, by A. D. M cin ty re... 405 Changes of macrobenthos in a sublittoral sand area of the German Bight, 1967 to 1975, by E. Rachor and S. A. G e rla c h... 418 Macrobenthos investigations in the eastern part of the German Bight from 1950 to 1974, by E. Ziegelm eier... 432 Synopsis of the Symposium, by G. Hempel... 445 NOTE ON TH E SPECIES NAMES In this volume the common species of fish from the North Sea are usually referred to by English name only. Readers who may not be familiar with these names are referred to pp. 12-19 of the article by M. J. Holden where the English names appear in alphabetical order followed by the scientific names.

The first volume in this series was published in 1903, and all volumes, except Vols. 5 and 23, are still available. A list of titles with current prices may be obtained from the Secretariat of the International Council for the Exploration of the Sea, Charlottenlund Slot, DK-2920 Charlottenlund, Denmark. The latest volumes are as follows: Vol. 160: Symposium on the Biology of Early Stages and Recruitment Mechanisms of Herring, 1968 (1971) D.Kr. 60.00 Vol. 161 : Special Meeting on the Biochemical and Serological Identification of Fish Stocks, Dublin 1969 (1971) D.Kr. 55.00 Vol. 162: Physical Variability in the North Atlantic, Proceedings of a Symposium held in Dublin 25-27 September 1969 (1972) D.Kr. 90.00 Vol. 163: The ICES Diffusion Experiment RHENO 1965 (1973) D.Kr. 50.00 Vol. 164: Fish Stocks and Recruitment, Proceedings of a Symposium held in Aarhus, 7-10 July 1970 (1973) D.Kr. 110.00 Vol. 165: Seventy Years Agrowing, a History of the International Council for the Exploration of the Sea 1902-1972, by A. E. J. Went (1972) D.Kr. 70.00 Vol. 166: Cod and Herring in the Baltic. Proceedings of a Special Meeting held in Helsinki, 23-25 September 1971 (1974) D.Kr. 55.00 Vol. 167: Physical Processes Responsible for Dispersal of Pollutants in the Sea, Particularly in the Nearshore Zone. A Symposium held in Aarhus, Denmark, 4-7 July 1972 (1974) D.Kr. 90.00' Vol. 168: Measurement of Fishing Effort. A Special Meeting held in Charlottenlund, Denmark, 25-26 September 1970 (1973) D.Kr. 50.00 Vol. 169: The Biology of the Seal. A Symposium held at the University of Guelph, Ontario, Canada, 14-17 August 1972 (1975) D.Kr. 180.00 Vol. 170: Hydro-Acoustics in Fisheries Research. A Symposium held in Bergen, 19-22 June 1973 (1977) D.Kr. 110.00 Vol. 171: Petroleum Hydrocarbons in the Marine Environment. Proceedings from ICES Workshop held in Aberdeen, 9-12 September 1975 (1977) D.Kr. 95.00 Vol. 172: North Sea Fish Stocks - Recent Changes and their Causes. A Symposium held in Aarhus 9-12 July 1975 (1978) D.Kr. 170.00 Vol. 173: M arine Ecosystems and Fisheries Oceanography. Four Symposia of the Joint Oceanographic Assembly held in Edinburgh, 13-24 September 1976. In press. Vol. 174: Eel Research and Management. A Symposium held in Helsinki, 9-11 June 1976. In press. Vol. 175: Population Assessments of Shellfish Stocks. A Special Meeting held in Charlottenlund, 29 September-1 October 1976. In press. Subscriptions or standing orders should be placed with C. A. Reitzel s Forlag, Nørre Søgade 35, DK-1370 Copenhagen, Denmark. Single volumes or back-number sets may be ordered from C. A. Reitzel s Forlag or from the ICES Secretariat, Charlottenlund Slot, DK-2920 Charlottenlund, Denmark. Prices do not include mailing costs. IM PR IM ERIE BIANCO LUNO A /s C O PEN H A G U E