Archipelago Research Institute

Field station full of stories

Tag: environmental monitoring

New paper! Influence of environmental conditions, population density, and prey type on the lipid content in the northern Baltic Herring

Our new paper, where we investigated the effects of different environmental stressors on the lipid content of the northern Baltic Herring (Clupea harengus membras) was recently accepted for publication in the Canadian Journal of Fisheries and Aquatic Sciences.

In this study we collected herring samples from local trap net fishermen during 1987-2006 and 2013-2014 and analysed their lipid content and fatty acid composition. We discovered that the average lipid content of herring muscle has decreased on average from 5-6% wet weight (w.wt) to 1.5% w.wt. The decrease in sea water salinity and increased size of the herring stock explained best the declining lipid content. Also,  sea water temperature during January-April also had a significant effect in our modelling. We estimated that the amount of the lipid storage incorporated in the spawning stock decreased by approximately 45% during the study, with respective energy content decreases. Fatty acid composition analysis revealed that herring lipids contained a high proportion of essential fatty acids EPA (20:5n-3) and DHA (22:6n-3), which likely originated from its main summertime prey, the freshwater calanoid copepod Limnocalanus macrurus – a zooplankton species that has become highly abundant in the Bothnian Sea.

Global climate change can affect the energy content of fish by altering their lipid physiology and consumption.The results of this study illustrate that various climate change induced processes are leading to changes in the lipid content of the Baltic Herring and, consequently, to changes in the energy flows of the northern Baltic ecosystem.


Herring from the Archipelago Sea. Photo: Johannes Sahlsten

Rajasilta, M., Hänninen, J., Laaksonen, L., Laine, P., Suomela, J.-P., Vuorinen, I. & Mäkinen, K. 2018. Influence of environmental conditions, population density, and prey type on the lipid content in Baltic Herring (Clupea harengus membras) from the northern Baltic Sea. Canadian Journal of Fisheries and Aquatic Sciences (accepted for publication)

Read more about the project:

The Baltic herring project


New research project investigates parasites found in the Baltic herring

In the Archipelago Research Institute, the reproductive biology of the Baltic herring (Clupea harengus membras) has been studied for over 30 years, since 1984. During the last few years we have discovered large amounts of parasitic worms in the body cavity of herring, collected from the Airisto Inlet. The phenomenon is new as no worms have been previously discovered in our samples. Dna-analyses conducted by the University of Eastern Finland showed that the parasitic worms are in fact two species (Corynosoma strumosum ja C. semerme), belonging to the phylum Acanthocephala. A new research project, studying the distribution and occurrence of these worms in the local herring, seal and great cormorant populations will begin next summer. 

Acanthocephala, also called thorny- or spiny headed worms, are commonly found in fish and seals. In Finland, 11 species are known to occur. The parasitic worms don’t infect humans. The Baltic herring is a safe and nutritious food fish and no cold treatment is required when preparing the fish.


According to our preliminary studies, in 2014-2015, approximately 15% of herring in the Airisto Inlet were infected by the parasitic worms.

Corynosoma-worms use herring as an intermediate host. The grey seal (Halichoerus grypus) and/or ringed seal  (Pusa hispida) are definitive hosts for the Corynosomaspecies. Of the two seal species, the grey seal is common in the Bothnian Sea and nowadays also in the Archipelago Sea. The steady increase of the grey seal population and its spread to the middle- and inner archipelago might have caused the parasitic infection in herring. The species C. strumosum has also been discovered in  Great Cormorants (Phalacrocorax carbo). Therefore, it is possible that the bird species is also a definitive host as the increase of the cormorant population coincides with the timing of our findings.


Parasitic worms may cause negative effects for commercial herring fishery. Therefore, it is important to understand the extent of the phenomenon and the causes behind it.

The two-year study is funded by the Archipelago Sea Fisheries Action Group (officially Saaristomeren kalatalouden toimintaryhmä in Finnish). The research is carried out together with the Joensuu Molecular Ecology Group of the University of Eastern Finland. The project’s field work begins next summer. The aim is to chart the distribution and occurrence of the parasitic worm species in the local herring population. We will also investigate whether the Great Cormorant is a definitive host in addition to the grey seal.

Stay tuned for updates from the field!

Keep calm and keep monitoring – on the importance of environmental monitoring

Last week, the mainstream media in Finland and abroad (e.g., here and here) reported of a research, published in the journal Plos One, where three-quarters of flying insects in nature reserves across Germany were observed to have vanished in 27 years. The results are alarming as insects are an integral part of life on Earth as both pollinators and prey for other wildlife. Thus, the scale of the losses to all insects will have profound impacts on human society.

After reading the article, in addition to the consequences of these results, I started to think about long-term environmental monitoring and its significance. Monitoring programs are often criticized as “costing too much while delivering too little” and most funding is granted to short-term research projects. So, what is so important about environmental monitoring? How do we benefit from these long data sets?

Field course students  examining insect samples, collected in Seili. In the back of the photo is a Malaise-trap similar to the ones used in the German study. Photo from ARI’s archive.

Environmental monitoring can be described as a programme of recurring, systematic studies that reveals the state of the environment and separates anthropocentric effects from natural processes. Monitoring can be conducted for a number of purposes, for example to establish environmental baselines or identify trends. Environmental monitoring programs also vary significantly in the scale of their spatial and temporal boundaries, and scope. Ecosystems in general require long-term monitoring because they are complex and sensitive, and most key changes in the environment take place over prolonged periods.

In zooplankton research, even a 20-year-long data set is sometimes not considered long enough to reveal underlying trends. Decades worth of data contain a lot of sample bottles. In the photo are some monitoring zooplankton samples, collected from the Airisto Inlet, Archipelago Sea. Photo from ARI’s archive.

The participation by amateur naturalists and other collaborators can be invaluable to the monitoring program because of  funding shortfalls and the large amount of work that goes into the collection and analysis of samples. For example, the data used in the German study, was largely collected and analyzed by amateur entomologists (Krefeld Entomological Society).

Environmental monitoring is a central part of many field station’s work. The location, infrastructure and trained staff make it possible to sample year round.  In Seili, the abundance of ticks have been monitored since 2012. The aim is to eventually have a long time series of tick abundances. Photo by Esko Keski-Oja.

The condition of the spawning herring population has been monitored in Seili for over 30 years and this cooperative effort has resulted in data sets that are unique in even in the Baltic Sea scale. Local fishermen have been an important part of this project as without their help, the collection of fish samples would have been difficult. Photo by Juha Kääriä.

What is good quality monitoring? For one, systematic sampling is key in order to get trustworthy and comparable results, and neglecting this step might make the whole data series completely useless. In the German study, this meant for example that the size, shape,color, location and placement of the trap had to be similar in each of the 63 sampling locations. Also, the way the insects were preserved, handled and analysed had to be the same. Thus, quality assurance certainly isn’t easy, and systematic work is required in each step of the way as more often than not, several people participate in the collection and handling of the time series.

Systematic sampling is key in environmental monitoring in order to get trustworthy and comparable results. In the photo, the species composition from a sample, collected with a light trap in Seili, is under analysis. Photo by Katja Mäkinen.

Monitoring programs are often criticized as “costing too much while delivering too little” and the lack of funding has often forced officials to curtail monitoring and data collection. However, environmental monitoring serves a vital scientific role by revealing long-term trends that can lead to new knowledge and understanding. For example, Charles David Keeling’s long-term measurements of atmospheric carbon dioxide at Mauna Loa island, Hawaii, provided the first unmistakable evidence that carbon dioxide emissions from human activities were warming the Earth (the famous Keeling’s Curve). As a result of this careful and consistent work, global climate change is now widely accepted as a scientific fact!

The results of monitoring are also of fundamental importance for evaluating environmental planning and policy as it is only through such careful observation that we can evaluate the health of our natural resources and make science-based management decisions. Also, the drafting and prioritization of environmental policies is based on the findings of environmental monitoring.

Cost-efficiency requires that monitoring programs  adapt new methods. Environmental monitoring is becoming increasingly automated. The ODAS buoy of Seili (in the photo) measures seawater parameters from a water column 4 times a day and sends the data automatically to the ARI’s administered website. In 2015, also a weather station, measuring e.g. air temperature, wind speed and direction was added to the assembly. 

See also: The long tradition of environmental monitoring in Seili (an English translation at the end of the post)

Text: Katja Mäkinen, research technician and PhD researcher, working with long-term environmental data and monitoring.