On the Biology of Calanus finmarchicus, I. Reproduction and Seasonal Distribution in the Clyde Sea-Area during 1932

Abstract

1. Fortnightly samples were taken with a fine-meshed net in single vertical hauls at different positions in the Clyde Sea-Area.2. Each stage of Calanus present, from ovum to adult, was counted, and charts were constructed expressing these results for one year as total numbers and as percentage composition.3. Calanus passes the autumn and early winter mainly in its Stage V copepodite form.4. In general, total numbers were high in September, 1931, and fell steadily to a minimum in March; in Loch Fyne the minimum occurred i n April.5. A sudden increase was observed in May and numbers rose to maximal values; the decline also was sudden.6. Reproduction began in February and three plainly marked breeding periods were observed between February and July.7. The time taken by the egg in developing into the adult was four weeks.8. The total life of a Calanus during the summer was estimated to be about two and a half months; in winter it is five to six months.9. In Loch Fyne a noticeable lag occurred during the winter and early spring.10. The number of Calanus present in the autumn of 1932 was considerably less than.at the same time in 1931. This may have been due to a shortage of food.