Daily growth rate and hatching-date distribution of Norwegian spring-spawning herring (Clupea harengus L.)

Abstract

Hatching-date distribution and daily growth rate were back-calculated from otoliths of 2-month-old Norwegian spring-spawned herring larvae of the 1985 and 1989 yearclasses. These hatching-date distributions were compared with the hatching-date distribution estimated directly from the larvae sampled on the spawning grounds. Herring hatched significantly earlier in 1985, with an average hatching-date of 27 March, compared to 2 April in 1989. In both years, however, the larvae were calculated to have been hatched in late March, indicating favourable survival conditions for the larvae that hatched in this period during both years. The back-calculated growth rate in the two years peaked (0.37–0.41 mm d⁻¹) between the ages of 30 and 40 days, and decreasing to between 0.24 and 0.29 mm d⁻¹ until the end of the observations (age 60 days). At 60 days the herring were at a size suitable for schooling. The average daily length increment of the sampled larvae was estimated at 0.32 mmd⁻¹