A preliminary study of microstructure in otoliths of seacaught mackerel (Scomber scombrus L.) larvae
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Mackerel larvae have been sampled during two cruises south of lrland, in May and June 1989 and preserved in ethanol. The microstructure of the otoliths (sagittae) from the mackerel larvae have been examined. There is a linear relationship between length (3.6 - 11.6 mm) of the larvae and the radius of the otolith and there is an exponential relationship between the dry weight of the same larvae and the radius of the otolith. Although the mackerel larvae initially have a high specific growth rate (~ 12 % d^-1), the corresponding otolith increment size is rather small (< 1 µm). From an estimated age of 20 days till an age of 35 days the specific growth rate increased three times (~ 30 % d^-1 ), while the increment size doubled (~ 1.5 µm). The average hatching date for the sampled mackerel larvae in May were estimated to 16. April 1989, and the average spawning date was calculated to 10. April 1989. For the larvae sampled in June the average hatching date were estimated to 21. May 1989, and the average spawning date was calculated to 16. May 1989.