Effect of trophic conditions on the growth and abundance of larvae of herring Clupea pallasii marisalbi in areas of their mass aggregations in Kandalaksha and Onega bays of the White Sea

On the basis of materials collected during June 18–26, 2012, in three polygons in Onega (Ukhta Inlet) and Kandalaksha (Chupa and Knyazhaya inlets) bays of the White Sea, the effect of concentration and size-species structure of the zooplankton and of the amount of potential predators on the numbers and growth rate of larvae of the White Sea herring Clupea pallasii marisalbi are considered. The total numbers of zooplankton in Ukhta, Chupa, and Knyazhaya inlets (25041, 39162–76555, and 18459–33870 ind/m³, respectively) noticeably exceeds minimal values necessary for the growth and development of larvae. Correlation analysis of the size composition of larval herring and size-species composition of net mesoplankton indicates that food preferences of larvae of different size groups significantly differ. The growth rate of larvae in Kandalaksha Bay is 0.20–0.25 mm/day. A feedback between the numbers of larvae of the White Sea herring and hydromedusas was revealed: in Chupa Inlet at a greater concentration of jelly-bodied zooplankton, the numbers of larvae were considerably lower, and their reduction at 5 days turned out to be more significant than at a relatively low concentration of medusas in Knyazhaya Inlet. This indicates that food conditions are not always a single and decisive factor responsible for the formation of strong or weak-year classes of herring.