Growth rates and age distributions of capelin (Mallotus villosus) larvae in the Barents Sea investigated by otolith increment analysis

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In order to investigate age distributions and growth rates, otoliths from capelin larvae collected from the Barents Sea during the summers 2001-2003 were analysed using otolith microstructure analysis. Stations were selected to represent areas with different water masses and temperature regimes. One hundred forty larvae from two stations in 2001 and 2002 and three stations in 2003 were analysed. Water temperature in the upper 50 m differed by up to 1.5o C between stations within years. Before the otolith increment analysis, the otoliths were coded and analysed together with otoliths from larvae of known age from bag rearing experiments. The average change in body length was 0.33 mm per increment. Except for 2002, there were no differences between stations within years with respect to increment number distributions and body length distributions. Average increment width differed between years. The larvae collected in 2002 had on average far fewer increments (average 14) than those collected in 2003 (average 24) at the same time of year. The average change in body length per increment (0.33 mm) corresponds to bag-reared larvae that deposit about one zone per day in the otoliths. This suggests that otolith increment analysis of capelin larvae may provide valuable information about age distributions and growth rates in capelin larvae. The implications of the results for assessment of factors affecting mortality rates and drift patterns of capelin larvae will be discussed.