Annual variation in gobiid larval density in the northern Baltic Sea

The highest densities of gobiid larvae along the Finnish Baltic coast from 1974 to 1996 were found in the Aland Islands and the Archipelago Sea. The annual variation in gobiid densities was three-fold (from 1.1 to 3.3 larvae m ^-2) with peak densities in the years 1977 and 1992 and the lowest density in 1987. No long-term trends in the density were found. The earliest gobiids were caught in the first half of May and the occurrence of larvae peaked at the end of June to early July. Within breeding seasons there was a positive correlation between water temperature at a depth of 1 m and the density of larvae. The density of larvae, however, did not correlate with mean summer temperature or the mean temperature of the previous summer. Instead larvae production was negatively affected by the severity of the previous winter as indicated by the maximum ice cover in the Baltic. The density of larvae was independent of larval density of the previous year suggesting that gobiid production primarily depends on the spawning stock size and may hence be regulated by density-independent factors.