Effects of temperature and salinity on the abundance of larval herring in the Pomeranian Bay during 1992-98 and 2007-10

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Previous research indicates that despite the high variability of the Pomeranian Bay basin, it is a convenient place for the reproduction of many fish species, including herring. The goal of this work was to evaluate the possible effect of hydrological conditions (temperature and salinity) on the abundance of herring larvae in the Pomeranian Bay. Two sets of data were analysed: recently obtained (2007–2010) and historical (1992–1998). In both periods the herring larvae samples were collected between April and July at about ten stations located in the same area. The mean density for different years varied from 18 to 557 individuals 100 m–3, with the maximum numbers observed usually in the second half of May. High abundance years were positively correlated with low temperature and high salinity. In addition, salinity was correlated with the timing of peak hatch, higher salinity leading to earlier hatching. The mechanism of those relationships is probably a mixture of several factors related to development and survival of eggs and early stages of larvae, as well as to timing and intensity of herring reproduction. In addition, this work allowed us to verify where the spawning places in the Pomeranian Bay are distributed.