Temporal and spatial variation in the growth rates of Baltic herring (Clupea harengus membras L.) larvae during summer |
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Authors: | T. Hakala M. Viitasalo H. Rita E. Aro J. Flinkman I. Vuorinen |
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Affiliation: | 1.Department of Ecology and Systematics, Division of Hydrobiology, P.O. Box 17, University of Helsinki, 00014 Helsinki, Finland,;2.Finnish Institute of Marine Research, P.O. Box 33, 00931 Helsinki, Finland,;3.Department of Ecology and Systematics, Division of Population Biology, P.O. Box 17, University of Helsinki, 00014 Helsinki, Finland,;4.Finnish Game and Fisheries Institute, Fisheries Division, P.O. Box 6, 00721 Helsinki, Finland,;5.Archipelago Research Institute, University of Turku, 20014 Turku, Finland, |
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Abstract: | It has been suggested that larval survival determines the year-class strength in most marine fish species. During their growth and development, the ability of the larvae to catch prey and avoid predation will increase. However, the factors affecting short-term changes in the growth of Baltic Sea herring have been little studied in the field. We collected Baltic herring (Clupea harengus membras L.) larvae from five different towing areas in the Archipelago Sea (SW Finland) during May and June 1989, right after the main spawning season. Twenty thousand two hundred and ten larvae were analysed and the area-specific growth rate (i.e. increase in standard length) was estimated by tracing the larval cohorts from the length-frequency data. This represents the first Baltic herring study with daily sampling during a long study period. The growth rate was related to environmental factors, such as temperature, number of zooplankters, and wind speed and direction. Large variation in larval growth rate occurred between areas: lowest and highest growth rates were 0.18 and 0.52 mm·day-1. Temperature was an important variable controlling larval-fish growth rate. An increase of one 1°C in average water temperature corresponded to an increase in growth rate of 0.043 mm·day-1. This may have been caused either by a direct temperature effect (changes in metabolic rate) or by the indirect effect of changes in food availability. We also found the densest herring populations in the areas with highest average water temperature. However, temperature and larval growth rate both increased towards the inner archipelago. |
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