What did you study?
I mapped the reproduction areas of sea-spawning whitefish and vendace along the Finnish and Swedish coasts of the Gulf of Bothnia, as well as the reproduction areas of perch and pikeperch along the Finnish coast. The study used datasets that had previously been collected as part of research conducted at the Natural Resources Institute Finland. The aim was to determine where the important reproduction areas of these species are located and what kinds of environmental conditions define their distribution.
The spawning, egg development and first life stages of autumn-spawning whitefish and vendace, and spring- and summer-spawning perch and pikeperch, often take place in geographically restricted areas and are sensitive to environmental conditions. I combined extensive fish larval datasets with spatial data and statistical modelling to identify reproduction areas and describe them on maps. The dissertation also examined how these map-based models should be interpreted.
What were the main results?
The study showed that observations of fish larvae, together with spatial datasets describing the environment, can be used to identify key reproduction areas of fish species even across extensive coastal areas. However, the conditions favourable for reproduction were clearly species-specific.
The larval production of perch and pikeperch was concentrated in shallow, sheltered coastal areas that warm up rapidly in spring. For pikeperch, water turbidity was also an important environmental factor. Whitefish larvae, in turn, were concentrated along shallow and often sandy shores. Vendace reproduction was particularly limited by salinity, which is why its most important coastal reproduction areas are located in the nearly freshwater conditions of the Bothnian Bay.
From the perspective of fish reproduction, not all coastal areas are of equal importance. Relatively small areas may produce a large share of the fish larvae in a region, making reproduction areas especially important.
How can the results be applied? What new knowledge did the study provide?
The methods and map datasets developed in the study can be used, for example, in fisheries regulation, marine spatial planning, environmental impact assessment, the design of monitoring programmes and the restoration of coastal areas. Maps describing fish reproduction areas are available in the VELMU map service.
The study evaluates the factors affecting the performance and accuracy of map-based models. When interpreting and using map-based models of fish reproduction areas, the accuracy of sampling and modelling variables should be taken into account. The dissertation also emphasizes that the location of a reproduction area alone does not guarantee successful fish reproduction. Temperature, salinity, bottom quality, shelter, ice conditions and water quality, together with biological factors, form a complex whole. The variability typical of northern areas, which can at times be substantial, as well as longer-term changes caused by climate warming or human activities, may either strengthen or weaken the importance of an area for fish reproduction.
M.Sc. Lari Veneranta defends their doctoral dissertation "Spatial identification of reproduction areas of whitefish, vendace, perch and pikeperch in the coastal areas of the northern Baltic Sea: environmental drivers and early life-stage constraints of reproduction” on August 31st at Agora, Auditorio 2.
Opponent is Associate Professor Ulf Bergström (Swedish University of Agricultural Sciences) and custos is Professor Juha Karjalainen (University of Jyväskylä). The language of the event is English.
Further information: Lari Veneranta, lari.veneranta@luke.fi
