The age distribution of stocks is usually considered as an indication of how healthy a stock may be. In general stocks which are lightly exploited will contain a much larger proportion of older fish than a stock which is heavily exploited. A stock which is heavily exploited will probably be dependent on one year class which will recruit to the fishery and which will immediately be subjected to fishing effort. Obviously in such a fishery failure of recruitment or poor recruitment will have drastic effect on the catches. Herrings can be aged accurately until are about 10 years old and generally recruit to the adult stocks during their third year. During this year, the majority of fish will spawn for the first time.

For some time past studies have been performed on herring fecundities by various scientists. Farren (1938) was the first to suggest that stocks could be separated by studying the different fecundity/length relationship of winter and autumn spawing populations from the Irish coast. Burd and Howlett (1974) calculated a fecundity index by length cubed and as a result clearly separated the spawning populations of Banks and Downs herring in the North Sea. Molloy (1979) regressed fecundity on length cubed for Celtic sea samples and was able to distinguish between the autumn spawning component and the winter spawning component in the Celtic Sea. This paper describes fecundity studies carried out on autumn spawning herring from the newly established management unit (V1a Lower and V11b) off the North west of Ireland. The results are compared with fecundity data from other Irish stocks and with the results obtained by Farran on the same stock over 40 years ago. It may be possible to use these results to calculate the spawning potential of the herring and those spawning off the Scottish coast. The spawning grounds from which these herring were taken are situated a few miles off the North West coast.

The herring fishery which takes place every spring and early summer off the North Coast of Donegal is one of the most regular and uniform on the coast of Ireland, and, as it has been under close observation from a scientific point of view since 1921, a short account of it will serve to illustrate the aims of modern methods of research and the extent to which these methods can lead to results of practical value.

Surveys for herring larvae in the Celtic Sea were conducted for the sixth ~ successive season between October 1983 and February 1984. The modifications made to the survey grid in the previous season to take account of the amalgamation of the Celtic Sea and Division VIIj for assessment purposes and to ascertain if larvae drift into the Irish Sea were also adopted for the 1983/84 surveys. A drift of larvae towards the Irish Sea was apparent in 1983/84. The larval abundance index for 1983/84 based on a standard survey area was almost three times higher than any previous value. A continuous increase in larval indices since 1978/79 indicates a recovery of the spawning stock.

Corrected proof

It is well known to herring fishermen that, in order to get the best returns, the mesh of their nets must correspond to the size of the fish on the grounds, but that this correspondence must take into account of both the length and the weight or condition of the fish has not, I think, been clearly pointed out. I have tried in this paper to express in definite figures a relationship between the size of the mesh and the condition and length of the fish taken together.

Einarsson (1951) has shown that it is possible to separate in a mixed fishery the winter/spring spawned fish from summer/autumn spawned fish on the basis of the appearance of the nuclei of the otoliths. In general, the winter/spring spawned fish have small hyaline and opaque nuclei, whereas the summer/autumn spawned fish have large hyaline nuclei. Otoliths from herrings taken at Dunmore East in the period 1960 to 1964 were examined and classified using Einarsson's method.