The structure of coastal ichthyoplankton in the area of the Dudinka River confluence (Eastern Sakhalin)

Abstract

The structure of ichthyoplankton complex and features of early fish ontogeny were analyzed in the coastal area off the Eastern Sakhalin. The study area is characterized by strong variations of temperature and salinity in May–July. Minimum temperature (+0.4 °C) was registered at a depth of 20 m in May, and maximum one (+15.7 °C) was recorded at a depth of 3 m in September. During the entire study period, salinity varied from 3.5 PSU in littoral zone close to the Dudinka River mouth to 31 PSU at a depth of 13–20 m. Eggs and larvae of 17 fish species from 5 families, typical for the Eastern Sakhalin, were identified in ichthyoplankton. Pleuronectidae species prevailed in taxonomic list with ratio of 71%. Gadus chalcogrammus eggs and larvae (71% of total value) prevailed in the second decade of May; Clupea pallasii bottom eggs (70%), in the third decade of May; and Pleuronectidae eggs and larvae (91–100%), in June–September. Mean ichthyoplankton abundance decreased from 52 ind.·m−3 in littoral zone to 21–22 ind.·m−3 above depths of 5–10 m and 13 ind.·m−3 above 20 m. The proportion of dead G. chalcogrammus eggs and Pleuronectidae eggs did not exceed the values obtained for the Northeastern Sakhalin and was lower than in Aniva Bay. In May, the proportion of G. chalcogrammus and Hippoglossoides robustus prelarvae with pathologies increased. It could be caused by the development of eggs at late stages in adverse conditions. Maximum species diversity was observed in June. Seventy-seven percent of cumulative abundance was composed by eggs of four species, G. chalcogrammus, H. robustus, Myzopsetta punctatissima, and Limanda aspera.

Keywords

• fish eggs
• fish larvae
• ichthyoplankton
• abundance
• species diversity
• Eastern Sakhalin