Length and age at maturity of Norwegian spring-spawning herring for the year-classes 1959 -61 and 1973 -78
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http://hdl.handle.net/11250/103967Utgivelsesdato
1986Metadata
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The age and length at maturity is calculated for the six year-classes,
1973-78. The age at maturity is also calculated for the
year-classes 1959-61. The two periods are caracterized by great
differences in stock abundance and recruitment. The proportion of
mature herring in an age group is estimated as it's proportion
in the spawning stock while maturing (at 3, 4 and 5 years) relative to
it's proportion of mature fish in the spawning stock when
fully recruited (mean proportion at 6, 7 and 8 years). The length at
maturity for an age group is calculated as follows. The
length distributions of the recruiting yearclasses while still
maturing is back calculated from the length distribution of the
fully recruited age group (at 6, 7 or 8 years). To find the length at
maturity, the relative proportions of mature fish in the early age
groups are used directly in these length distributions assuming the
maturation to be length dependent. According to the growth rates of
the different year-classes, the age at maturity vary from 3 to 5
years in the investigated period. However, the length at
maturity is found to be fairly constant.