Latvia and Estonia need to improve knowledge on food webs in their lakes. Therefore, during Summer 2020 Estonian post-doctorate Katrit Karus from the Institute for Environmental Solutions (IES) together with researchers from Estonian University of Life Sciences have carried out lake fieldwork campaigns in Estonia and Latvia.
IES researchers study food webs in comprehensive manner. This will help to understand how food webs function. Moreover, the study results will describe the mechanisms that determine the mortality of larval fish in water bodies, which is crucial for fish stock management – fish farming, aquaculture.
IES post-doctorate Katrit Karus showcased the latest conclusions and described further steps of the research.
IES: We know that in the previous research periods (April – June 2020) you analysed data gathered during 2019 fieldwork campaigns. What did you focus on during Summer and Autumn research seasons of 2020?
Katrit Karus (K.K.): During summer of 2020 we carried out fieldwork campaigns in 8 study lakes. During mid-June, we carried 4 campaigns in Estonia (Akste, Nohipalo Valgjärv, Kaiavere, Prossa). Afterwards, during mid-July, 4 campaigns took place in Latvia (Riebinu, Auciema, Laukezers, Varzgune). Most important tasks were to estimate the development of natural fish resources, to collect data about general characterization of the studied lakes, as well as the measuring of physico-chemical data and collection of fish community samples.
IES: Why it was necessary to repeat fieldwork campaigns in 2020?
K.K.: The mortality of newly hatched fish larvae is extremely high, eliminating up to 99% within a few days after fish first feeding. Fish larvae may die for many reasons, beside predation. The starvation because of the shortage of suitable food objects (size, morphology) could be one of the main factors of high mortality during the early life stages. To assess larval fish abundances quantitatively we repeat fish community studies after 1 year. That helps to measure the development of the young fish. We focus on 0+ fish (hatched in 2019) year class strength – fish survival and stock development after 1 year
IES: How the development of natural fish resources was estimated?
K.K.: Fish communities were studied by using Nordic gillnets for sample collection from costal and open-water areas of the lakes. Floating and bottom-set gillnets were used in all 8 lakes: 2 gillnets were put into costal and 2 gillnets into open-water areas. Fish sampling was successful, and gillnets were full of fish individuals, especially in Lake Kaiavere in Estonia. Fish samples will be analysed by the middle of October 2020 and data will be compared with results from 2019 fieldwork campaigns. Thus, allowing us to assess how much young fish are left and how strong they are comparing to their year-class.
IES: What kind of innovative technologies and methods you used during fieldwork campaigns?
K.K.: Lake Kaiavere in Estonia is known to have a very rich fish community. Thus, this lake was chosen to test and elaborate a novel fieldwork technique to assess larval fish abundance in coastal areas of the lake. For these tests flying drone equipped with a camera were used in combination with white plate method. The white plate method is an actual white plate labelled with horizontal and vertical gridlines with fixed dimensions that is placed under the surface layer of the water. This method allows to count larval fish individuals in a fixed area. Drone captures an image, then larval fish abundance in the image is measured and finally the number of fish larvae in a certain area or the whole lake can be calculated.
IES: What locals think about your activites in the researched lakes?
K.K.: During fieldworks we met several locals near the lakes and many of them are very interested in our research activities. It is nice to meet the locals that are interested and take care of the treasures of nature they live next to. Some of the locals were so interested in our research that they joined to see how to perform standard fish community studies and other measurements on the lakes.
The research is a part of the project „Fish feeding conditions in lakes with different planktonic food web structure and microvegetation “(MICROFISH), No.220.127.116.11/VIAA/1/18/301. Agreement with State Education Development Agency of the Republic of Latvia No. Programme number 18.104.22.168/16/I/001. The project is financed by the European Regional Development Fund, the State budget of the Republic of Latvia and the foundation „Institute for Environmental Solutions”.
Find out more about the project here.