We need a better understanding of northern pike ecology. This requires robust and cost efficient monitoring methods so that managers can make informed decisions on resource use and conservation. In the research project ePIKE, we develop and evaluate eDNA as a non-invasive method for pike monitoring. The project consists of laboratory trials, mesocosm experiments and sampling of natural habitats.
In the research project ePIKE we investigate if eDNA can be efficiently used as a non-invasive monitoring method for Swedish pike stocks. eDNA is a relatively new methodology and in a first step we will compare and test existing techniques. This will be followed by small scale experiments in aquaria under controlled environmental conditions and in semi-natural tanks and ponds. Field campaigns investigating the relationship between eDNA and pike biomass under natural conditions are also included.
We hope that the project will contribute to better, less invasive and more cost efficient estimates of pike stocks in both coastal and freshwater environments.
Improved monitoring methods as a means to aid management
The development of eDNA-methods for the monitoring of fish is particularly important for species that lack standardized monitoring methods. Pike is one of the most important recreational fish species in Sweden. Being a predator, the pike plays a vital role in aquatic food-webs. Despite it’s socioeconomical and ecological importance, the pike has been neglected in biological monitoring, partly because pike seldom are caught by standard monitoring methods. As a consequence, there is no adequate data to guide authorities in appropriate management strategies for this species. To better understand the ecology of the pike and to be able to make informed decision there is a need for new monitoring methods.
ePIKE and the research team
ePIKE is divided into three complementary work packages. The research team consists of Anti Vasemägi, Martin Ogonowski, Göran Sundblad, Patrik Bohman, Josefin Sundin, and Erik Karlsson at the Department of Aquatic Resources, SLU.
Work package 1 – Evaluation and development of molecular methods
eDNA-methods have recently been applied successfully to detect pike in the environment using qPCR. The PCR-method is able to amplify DNA-molecules which allows very small amounts of DNA to be detected in the water. However, questions remain regarding which extraction methods to use and what the limit of quantification is. Therefore, we will test the efficiency of different filter types and optimize extraction methods to develop suitable lab protocols for qPCR.
Work package 2 – Determination of an eDNA-biomass relationship
The amount of eDNA is expected to differ between different life stages of pike. It is therefore important to determine how the eDNA-signal varies in relation to fish size. In this work package we will investigate how the eDNA-biomass relationship differs between juvenile and adult pike under semi-natural conditions. It is also important to determine when it is most favourable to sample eDNA. Therefore we will study how the eDNA-signal fluctuates over the season as temperature and water quality change.
Work package 3 – Field-based evaluation of the eDNA methodology
Our overarching aim is to evaluate the applicability of eDNA for monitoring of pike populations in the wild. Based on the results obtained from work packages 1 and 2, we will develop a series of protocols and sampling strategies appropriate for this type of monitoring. In conjunction, we will also compare the eDNA-based methods to other sampling methods aimed at specific life stages of pike. By these comparative studies we will be able to systematically evaluate the appropriateness of eDNA as a monitoring method for pike.
Experiments with pike 2019
Laboratory experiment with juvenile pike
The objective of this experiment was to:
- Obtain eDNA-samples from pike to identify suitable primers (mtDNA, COI and 5S rDNA ITS)
- Estimate DNA shedding and degradation rates
- Determine the DNA-biomass relationship under controlled and nearly optimal conditions
Juvenile pike where caught in collaboration with the Swedish Angling Association “Sportfiskarna” in a nearby wetland in June 2019 and transported to aquaria at the institute of freshwater research, SLU, Drottningholm. After an acclimation period, we conducted a small scale experiment where different densities of juvenile pike (0, 1, 3, 9 individuals, 3 replicates each) were incubated in aquaria containing 15L filtered lake water. Water temperature and other environmental variables were monitored continuously. eDNA samples were collected by filtration through a 1.2 µm nitrocellulose filter at seven time points (before the addition of pike, during the incubation and after removal of pike).
Preliminary results from the experiment
Juvenile pike collected from the wild were successfully kept under laboratory conditions (in accordance with ethical permits). Individual isolation in Whitman-Vibert-boxes proved to be an effective method to prevent injuries and cannibalism when several individuals were kept together. The preliminary studies have provided valuable information and practical experience in stress-mitigation and survival of juvenile pike under laboratory conditions. Work analysing eDNA samples from the experiment and design of new 5S rDNA primer pairs is ongoing in collaboration with the Estonian University of Life Sciences in Tartu. .
During 2019 we have conducted a comprehensive literature review which will be useful in the development of laboratory protocols and experimental designs.
Experiments with pike 2020
We conducted a comprehensive collection of eDNA samples from the Stockholm Archipelago during spring. We collected water samples for eDNA analysis from 22 shallow bays during the pike spawning period (March-May). The collection of eDNA was synchronized with the hook-and-line fish survey within the ReFisk project. This will enable the comparison of different sampling methods. All eDNA samples are frozen and will be analysed during 2021.
During 2020, our team was reinforced by a new Master’s student – Ofír Svensson. At the experimental facility in Drottningholm we conducted a series of outdoor mesocosm experiments where pike of different sizes, ranging a few kg to approximately 10 kg were incubated in natural lake water to determine the DNA-biomass relationship in adult pike. We also studied the effect of pike densities on eDNA shedding and different combinations of filtration setups in order to optimize the sampling and DNA recovery.
During autumn, we have moved into the lab where we are testing different DNA extraction methods with the aim to find a cost efficient, reliable and effective protocol which will be used to analyze the accumulated samples from mescosm experiments and the field. The winter months will therefore be primarily dedicated to analysis of collected samples, but also to planning!
During 2021 we will conduct yet another field study where we aim to study how the eDNA-signal fluctuates seasonally. More info to come!
On March 17th we installed a fish counter in the wetland Hemmesta sjöäng east of Stockholm. The counter is mounted at the entrance of the wetland where it will count, measure length and film all fishes that moves in and out of the wetland. Link to the counter
During spring, as pike spawn we will besides monitoring the counter also take water samples for eDNA analyses continuously over the entire spring season. By doing so we can investigate if the amount of eDNA in the outflow from the wetland can be used to successfully describe the patterns of the spawning migration. Sampling is done in accordance with techniques we have developed in earlier parts of the project.
The study at Hemmesta is done in collaboration with the Swedish Angler Association and Värmdö county, whom also involve school students to manage the wetland within the project Skolbäcken. We are very happy about these collaborations and the synergistic effects at the local level. We are also grateful to the volunteers that have contributed in different ways. The fish counter comes from TiVA and the management of the website is operated by Fiskevårdsteknik.
ePIKe is financed by the Swedish Environmental Protection Agency (SEPA) in collaboration with the Swedish Agency of Marine and Water Management (SwAM).