Comparative growth and development of autumn and spring spawned Atlantic herring larvae reared in large enclosed ecosystems

Populations of Atlantic herring larvae Clupea harengus harengus L. were reared in 300 m3 in situ plastic enclosures for about 60 d in Sep to Nov 1978 and for about 90 d in Apr to Jul 1980.The addition of soluble organic effluent from North Sea oil production had little direct effect on the larvae in 1980 and, in 1978, it was difficult to discern effects due to the inadvertent trapping of juvenile fish predators.Developmental progression of the enclosed populations of larvae, as defined by morphological staging, differed between seasons.While developmental rate was undoubtedly correlated with growth rate, initial size of larvae (0.067 mg in autumn 1978 and 0.138 m g in spring 1980) had a significant effect on early development.It is suggested that the small egg size of the Minch autumn spawned herring serves to delay the developmental rate of the larva at a time when temperature and food conditions could stimulate rapid growth.This mechanism helps to ensure that larvae which hatch in September do not metamorphose before the onset of winter.In contrast the large egg and hatching larva of the Clyde spring spawner favours rapid progression through the developmental stages to early metamorphosis.