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(With Plate I and Text- fig. 1) 445 Apart from the extensive egg surveys carried out by Norwegian workers (Runnstrom, 1941) most of the investigations on the spawning of the Atlantic Herring have depended on studies of the distribution of the spawning fish, on captures of newly hatched larvae, and on records of the occurrence of herring eggs in the stomachs of predatory fish species (principally haddock). With the exception of recent observations by Bolster and Bridger (1957), attempts to sample egg concentrations quantitatively in the North Sea and neighbouring areas have usually proved abortive. In consequence little is known of the distribution and density of eggs on the spawning grounds, their percentage fertilization, mortality during the egg stage, hatching rate, and the relationship between the distribution of eggs and the nature of the sea-bed.To study these items, and also the subsequent production, dispersal, and mortality of larvae, and the relationship of these to subsequent year-class strength, it was decided to concentrate effort on the spring spawning in the Firth of Clyde (see Fig. 1). This area had been studied much earlier by Cossor Ewart (1884), and it was considered very suitable for intensive study for the following reasons: (i) spawning occurs in a relatively small, well defined, area of shallow depth (13-24 m); (ii) the spawning season is short, extending over a period of about one month; (iii) the main spawning ground is the scene of a small commercial fishery from which detailed information on the distribution and composition of the spawning shoals can be readily obtained; (iv) the dispersal of the larvae can be followed more closely than in the much more extensive regions of the northern North Sea; (v) the region is one in which accurate fixing of position by Decca and land bearings is possible.The general features of the biology of the herring in the Clyde have been described by Marshall,

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