The structure of coastal ichthyoplankton and features of early fish ontogeny in the area of the Dudinka river confluence (Eastern Sakhalin)

Abstract

The structure of ichthyoplankton complex and features of early fish ontogeny were studied in coastal area off the Eastern Sakhalin. Strong variations of temperature and salinity in May–July characterized study area. Minimal temperature (0.4°С) was registered at a depth of 20 m in May. Maximal temperature (15.7°С) was recorded at a depth of 3 m in September. During total study period salinity varied from 3.5 psu in littoral zone close to the mouth of Dudinka River to 31 psu at a depth of 13–20 m. Eggs and larvae of 17 fish species from 5 families, typical for East Sakhalin, were identified in ichthyoplankton. Pleuronectidae species prevailed in taxonomic list with ratio of 71%. Gadus chalcogrammus eggs and larvae (71% of total value) were dominant in the 2^nd decade of May, bottom Clupea pallasii (70%) – in the 3^rd decade of May, Pleuronectidae eggs and larvae (91–100%) – from June to September. Average concentrations of ichthyoplankton decreased from 52 ind.·m³ in littoral zone to 21–22 ind.·m³ above depths of 5–10 m and up to 13 ind.·m³ above 20 m. The proportion of dead G. chalcogrammus eggs and Pleuronectidae eggs didn’t exceed the values, which were obtained for the area of northeastern Sakhalin and was lower than in Aniva Bay. In May proportion of G. chalcogrammus and H. robustus dead prelarvae and prelarvae with pathologies increased. It could be caused by development of eggs at late stages in adverse conditions. Maximal species diversity was observed in June. Eggs of four species: G. chalcogrammus, H. robustus, Limanda punctatissima, L. aspera, composed 77% of cumulative abundance. Dominance-diversity curve was typical for native community of Eastern Sakhalin.

Keywords: fish eggs, fish larvae, ichthyoplankton, abundance, species diversity, Eastern Sakhalin