The importance of egg and larval mortality in the determination of year-class strength was discussed at a colloquium at La Jolla, California in 1975 (see Hunter, 1976). In addition to the obvious effects of starvation, predation and disease, pollution by such substances as copper is an important factor affecting viability. The copper concentration in sea water is generally about 1–2,µ/l. Chester & Stoner (1974), in a comprehensive survey, found an average copper concentration of 0.8µ/l in the open ocean and 0.9 µg/l nearer the shore. In British waters Preston et al. (1974) reported a range of 1.1–1.6 µg/l and Portmann (1972a) found a range of 1–20 µg/l with the possibility of 1000 µg/l near sea-bed copper deposits.