Spawning habitat and egg mortality in capelin, Mallotus villosus (Müller) - responses to extreme abiotic conditions

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The oceanic Barents Sea capelin spawns demersally in deeper waters along the Finnmark and Murman coasts in March and April. The spawning habitat contrasts that of many fjord populations – e.g. the Balsfjord capelin – which spawn intertidally on the beaches in April and May. Capelin eggs adhere to the substratum (coarse sand) and hatch after approximately 150 day-degrees. However, eggs which develop on the beaches are periodically exposed to air and extreme variations in both temperature and salinity. The abiotic challenges which meet the eggs of beach spawning capelin differ markedly from those spawned under relatively stable microclimatic conditions in deeper waters. In this study, we report on the abiotic in situ conditions which characterize the spawning beach of the Balsfjord capelin during an incubation period. Data provided from laboratory experiments show the effects of an extreme microclimate on the mortality and osmoregulatory capacity of eggs.