TIMING OF HATCHING IN AMMODYTES MARINUS FROM SHETLAND WATERS AND ITS SIGNIFICANCE TO EARLY GROWTH AND SURVIVORSHIP

The significance of hatch date for the growth and survival of the sand eel, Ammodytes marinus, was investigated using otolith microstructure. Hatch dates of 2 to 6 mo-old juvenile A. marinus caught near Shetland were compared between 1990 and 1992, during which period year-class s trength varied by more than an order of magnitude. The hatch-date dist ribution of juveniles in the 1992 year-class was compared with that es timated directly from the abundance of newly emerged larvae on the spa wning grounds. The extent of larval hatching periods in 1990 and 1991 was also estimated from continuous plankton-recorder data. There were significant differences in hatching periods between all three years, h atching in 1990 and 1992 being markedly earlier than the long-term mea n peak in hatching indicated from archival data. Most individuals from the 1991 year-class attained a larger size by July than those in othe r year-classes, despite hatching later. Variation in individual growth rates both within and between year-classes indicated that there was a seasonal cycle of growth opportunity in all years investigated. The s tudy suggests that the degree of coupling between hatching and the ons et of spring secondary production may be an important contributory fac tor to year-class variability in this species.