Abundance and distribution of larval herring, Clupea harengus (Actinopterygii: Clupeiformes: Clupeidae) in the pomeranian bay, baltic sea as an indicator of spawning sites

Abstract

Background. The Pomeranian Bay is one of the most important spawning areas of herring, Clupea harengus Linnaeus, 1758, at the Polish coast. The distribution of spawning grounds in the region has only been discussed in one paper, published two decades ago. The identification of the exact locations of the spawning grounds in the bay is of key importance, among others for the evaluation of possible consequences of construction projects in coastal areas, such as that of the gas terminal in Świnoujście. Materials and methods. Herring larvae (6-29.1 mm standard length, SL) were collected between March and July at six (1992-1996, 1998) and 10 (2007-2011) stations located in the Pomeranian Bay, Baltic Sea, by means of BONGO-nets with 505 μm mesh. The abundance of herring larvae at each of the stations (related to 100 m3) was measured for specimens smaller than 10mmSL. Such abundances were used as indicators of spawning site locations. Results. The presence of spring-spawned herring larvae <10 mm in the Pomeranian Bay was recorded from mid-April to the end of June, with the highest numbers from late April to early June. The maximum abundance observed on single day varied from 50 to 667 ind. per 100 m3 in the years 1992-1998, except one day in 1993, when the values reached 2239 ind. per 100 m3 and from 54 to 482 ind. per 100 m3 in 2007-2011. Spawning grounds were identified throughout the study area. In the period of 1992-1998, more intense spawning was observed in the western part of the Pomeranian Bay than in its eastern part. Results regarding the potential impact of the gas terminal construction site provided no indication of its effect on herring spawning intensity and success in the area. Conclusion. The entire study area in the Pomeranian Bay serves as a spawning ground for spring-spawning herring. Higher intensity of spawning in western part of the bay in the years 1992-1998 was probably a result of more intensive spawning migrations to the Greifswalder Bodden. No effect of the gas terminal construction in Świnoujście (2010 and 2011) on herring spawning or survival of eggs and yolk-sac larvae was observed.