Fishers' Observations and Experiences of the Changing Lake Muddusjärvi
Manuscript submitted to newspaper Inarilainen
Minna Turunen, Helena Syrjänen, Hannah Strauss-Mazzullo
University of Lapland, Arctic Centre
In the winter of 2026, fishers on Lake Muddusjärvi were interviewed as part of the multidisciplinary and international FROST project (2025–2029), funded by NordForsk. The primary goal of the interviews with fishers is to increase understanding of how environmental and climate changes affect fishing in Arctic lakes and how fishers are adapting to changing conditions.
The FROST project involves researchers from Finland and other Nordic countries, Canada, and the United States. Researchers from the University of Lapland are responsible for interviewing fishers, while Professor Kimmo Kahilainen of the University of Helsinki is in charge of hydrological, fish and food web research. The project combines natural and social science research with local knowledge from fishers to form as holistic a picture as possible of the conditions in Arctic lakes and how they are changing. The project includes 12 research areas across the Arctic region. In Finland, the research sites are Lakes Muddusjärvi and Kilpisjärvi.
Changing Fish Populations
Based on fishers’ observations, the fish populations in Lake Muddusjärvi have undergone various changes over the decades. Large whitefish (Coregonus lavaretus) have been observed to have declined, while the dwarf form of whitefish—known as “reeska”—is now more abundant than before. Brown trout (Salmo trutta) and Arctic char (Salvelinus alpinus) populations are also estimated to have declined. Meanwhile, the reproduction of autumn-spawning fish may be hindered by rising water temperatures. At the same time, there has been a marked increase in the abundance of spring-spawning perch (Perca fluviatilis) and pike (Esox lucius).
Fishers believe that several factors may be behind these changes, such as natural fluctuations in fish stocks, past stocking events, and low fishing pressure. In particular, eutrophication of the aquatic environment and climate change are believed to have a significant impact on the lake’s fish stocks. Changes in fish stocks are therefore unlikely to be explained by a single factor but are rather the result of the combined effects of several factors. However, the interplay between these factors is not yet fully understood.
According to fishers, the fish in Lake Muddusjärvi have remained virtually free of parasites. There are few parasites in whitefish, and they have no significant impact on the use of the fish. There are some parasites in brown trout. According to a commercial fisher interviewed :
“The brown trout and grayling in Lake Muddusjärvi are top-quality, parasite-free, and it has a pleasure to sell them for customers.”
Measures are taken to prevent the spread of parasites: fish guts are not discarded in the lake so that fish feeding birds such as gulls do not eat them and continue the parasite life cycle.
Changes in the Whitefish Population and Underfishing
“You can’t get this lake to a whitefish lake again”
According to the commercial fisher interviewed, the number of large whitefish in Lake Muddusjärvi has declined to such an extent that he has been forced to switch fishing to a different lake. Lake Muddusjärvi is full of small fish, especially dwarf whitefish form “reeska”. The fisher describes his relationship with the lake as a process of learning and adaptation, in which he has had to adjust his fishing methods to the lake’s changing conditions:
“If you set an 18-millimeter mesh size net there at the right time, and every other mesh has a dwarf whitefish “reeska” in it, then you know you’ve got quite a cleaning task to perform. The lake teaches me—I don’t teach the lake… but we’re now already on informal terms. No need to be formal anymore.”
According to fishers, the main problem with the whitefish population in Lake Muddusjärvi is not unsustainable overfishing, but rather, on the contrary, underfishing. The lake is currently underfished. As seine fishing has declined, the total number of fish has increased, resulting in a decrease in their average size and a deterioration in their condition.
According to fish surveys conducted in Lake Muddusjärvi over the past few decades, the lake is home to two forms of whitefish that grow to a large size—the bottom dwelling whitefish, “pohjasiika” and the open-water dwelling “riika”—as well as two dwarf whitefish forms, the open-water form “reeska” and deep-water form “rääpys”, says Professor Kimmo Kahilainen. These whitefish forms differ in terms of habitat and feeding habits. Reeska, in particular, is thought to compete with larger whitefish for the same food resources.
The problem at Lake Muddusjärvi appears to be the excessive abundance of fish stocks relative to the lake’s available food resources. Whitefish forms have very different diets, but as populations become denser, competition for food within a form is often intense. For example, small sized whitefish form “reeska” feed on zooplankton throughout their lives, whereas the larger growing forms shift to larger sized prey items along increasing size. Competition between whitefish forms is most intense during the juvenile stage, when all forms feed on zooplankton.
According to fishers, the abundant but small-sized whitefish stock should be reduced through more intensive fishing to change population structure and improve fish growth. One proposed solution was a multi-year fishing campaign that would be more effective than current methods and could even be commercial fishing in nature and potentially supported by the European Union. Fishing could be carried out, for example, using traps, nets, and seine. Although many fishers still have seine gear in storage, there appears to be little interest in joint seine fishing. According to the fishers interviewed, seine fishing is labor-intensive, and the viability of the effort depends on whether there are fish buyers and functioning markets for the catch.
The Sustainability of Brown trout and Grayling fishing Is Put to the Test
The fishers interviewed seem to fish responsibly:
“When we run out of frozen fish, that’s when we have to head out. That’s how we live.”
However, there is great concern about the decline in fish stocks. The inflowing rivers to Lake Muddusjärvi, as well as small forest lakes, are considered particularly vulnerable to fishing pressure, and, in the fishers’ view, cannot withstand heavy fishing. The decline in the brown trout population is considered particularly alarming, and it is believed to be largely due to recreational fishing in spawning areas. Tourism operators also fish for brown trout in the Rivers Kaamasjoki and Kielajoki. Many fishers view nets set in rivers as a significant threat to fish populations, particularly brown trout. Net fishing is also perceived to have a detrimental effect on brown trout migration routes and access to spawning grounds. According to fishers, net fishing in rivers may partly explain why brown trout populations in some lakes are currently surprisingly low given the environmental conditions of Lapland.
For this reason, many fishers support increasing restrictions on brown trout fishing in rivers, particularly during the spawning season. Some of the fishers interviewed also propose broader restrictions on the fishing. One suggestion is to impose a complete ban on brown trout fishing for five years to allow population to recover.
According to Kimmo Kahilainen, the brown trout population in Lake Muddusjärvi has a long life cycle, as the fish juveniles spend an average of five years in the river before moving to the lake to grow. For example, changes that occur during the juvenile stage—such as a poor year class—are not visible in the lake until years later. Unfortunately, there is no comprehensive monitoring data on juvenile densities in the River Kaamasjoki and its tributaries, making it difficult to assess potential changes.
The interviewed fishers regard the depletion of grayling (Thymallus thymallus) populations a result of overly intensive ice fishing or hook-and-line fishing, particularly in forest lakes:
“It’s definitely a sustainability issue when you see, say, a hundred holes drilled with a battery-powered ice auger, and there’s a hook in every single one. It’s absolutely incomprehensible to do that for grayling.”
According to many fishers, the Arctic char population in Lake Muddusjärvi has declined. One fisher interviewed said that his 90-year-old neighbor had already noted about ten years ago that the Arctic char had moved to deeper waters to spawn. Fishers attribute the decline in Arctic char to factors such as global warming and summer boating. On the other hand, according to one fisher, the Arctic char population in Lake Muddusjärvi was heavily fished in the 1960s and 1970s, once it was realized that it was a valuable fish. However, according to the fisher, the Arctic char population in Lake Muddusjärvi is now recovering. According to a fish survey covering large subarctic lakes, the Arctic char population in Lake Muddusjärvi was relatively low compared to that of Lakes Inarijärvi and Kilpisjärvi. However, based on winter and summer test fishing, Arctic char are still present in Lake Muddusjärvi, and the test fishing also showed signs of young fish.
A Critical View of Catch-and-Release Fishing
Fishers took a critical view towards catch-and-release fishing, i.e. releasing caught fish back into the water, which is practiced in recreational and fishing tourism. In their view, caught fish should primarily be used as food rather than caught and released. The fishers also raised concerns about the impact of warming surface waters on the survival of released fish. They noted that in warm water, fish may have a reduced tolerance for stress, leading to increased mortality following release. This observation is also supported by research data, as mortality rates increase significantly at high water temperatures. Fishers considered this particularly concerning for fall-spawning fish, as warm water conditions can impair their chances of survival as the spawning season approaches.
Perch and Pike Have Become More Abundant
According to fishers’ observations, Lake Muddusjärvi has experienced a marked “perchification of Arctic lakes”: the perch population has increased, and the fish have grown larger. Fishers attribute the increase in perch populations specifically to warm summers, which improve the survival of juveniles during their first year of life. These observations by fishers were also confirmed by test fishing in Lake Muddusjärvi. Spring-spawning fish, such as perch and pike, clearly benefit from the longer open-water season and rising temperatures. Today, cold summers—which used to decimate entire perch year classes—are almost entirely absent, and this is increasing perch populations.
The pike population is also perceived to have grown significantly. As recently as about 15 years ago, pike and perch were considered scarce in the study lakes, whereas today large pike—even those measuring up to one meter—are abundant. At the same time, brown trout catches have declined significantly. Long-term fishing observations support this change: a person who fished in the same spots with the same lures caught almost exclusively brown trout when he was young, but about 50 years later, perch and pike have become the main catches. The fisher felt that the lures that had previously been effective for catching brown trout and Arctic charr are now useless.
Eutrophication is a concern for fishers
According to fishers’ observations, Lake Muddusjärvi has become eutrophic, particularly at river mouths and in shallow bays, over the past ten years. Brown trout, grayling, and Arctic charr are especially vulnerable to eutrophication. One possible cause of eutrophication mentioned by fishers may be humus washed out from the watershed, which warming and higher rainfall may exacerbate. Humus darkens the water and clogs fishing gear. According to fishers, it would be possible to keep nets in Lake Muddusjärvi for a long time in early spring, but the rivers flowing into the lake—such as the River Kaamasjoki—begin to carry so much humus from the catchment area’s peatlands that the nets become clogged. Earlier spring arrival increases runoff and, at the same time, darkens the water. The effect of humus is already visible after winter, on the warmest days of April—this usually marks the end of winter netting.
In Sikovuono, a bay of Lake Muddusjärvi, there are signs of severe siltation and overgrowth. The bay used to have clear water and a rocky bottom, but today the bottom is covered by a thick layer of peat and mud. Eutrophication is also evident in the increase in aquatic vegetation, the darkening of the water, and the rapid fouling of fishing nets. With the rains and spring floods, dark, humus-rich water spreads from Sikovuono toward Lake Muddusjärvi. The fjord has been dredged earlier, but the problem persists, and many fishers consider suction dredging necessary.
Fishers cited winter feeding of reindeer on the ice of small, barren mountain lakes as a particular cause of eutrophication. This is perceived to increase nutrient loading and litter accumulation, and the practice is reported to continue despite bans. It was also estimated that flocks of swans arriving in the spring may contribute to nutrient loading. According to the fishers interviewed, the barren and nutrient-poor nature of the mountain lakes makes them particularly susceptible to eutrophication.
Net fishing is on the decline
As the older generation of fishers passes away, the traditional fishing culture is fading. The number of people who fish with nets has decreased and continues to decline. Net fishing in the winter is labor-intensive, and freezing temperatures limit it. Young people no longer fish with nets:
“They go ice fishing in the winter and trolling in the summer, and they buy Atlantic salmon fillets at the store.”
Many fishers believe that if there were more brown trout in Lake Muddusjärvi, there would also be more fishers there.
Winter fishing on Lake Muddusjärvi is not very extensive due to the lake’s large size and the cold, windy winter conditions. Based on the experiences of the fishers interviewed, winds have become both more frequent and stronger in recent years, which has made winter fishing more difficult. For this reason, winter fishing also takes place in smaller and more sheltered bodies of water, such as Lake Paatari and the River Kettujoki that flows into it, as well as Lake Inarijärvi. Another factor driving winter fishing on Lake Inarijärvi is the area’s more abundant fish stocks.
Many fishers have noticed that ice now forms later and melts earlier on Lake Muddusjärvi. On the other hand, according to some of those interviewed, no clear change is noticeable, as ice conditions vary greatly from year to year. Last winter on Lake Muddusjärvi was typical in terms of when the ice set in, but the ice melted earlier than expected.
In the fall, as the lake freezes over, snowfall often begins before the ice has had time to harden properly. A layer of snow insulating the ice slows down the hardening process, resulting in less black ice forming than before. The fall thaw may therefore last a long time and delay anglers’ access to the lake:
“Sometimes it feels like it’s not even worth setting them [brown trout nets] at all if freezing of lake goes into December.”
Adapting to Change
According to experienced fishers, the environment is changing so rapidly these days that old guidelines and fishing methods no longer always apply. Some fishers rely on their own judgement when adapting to these changes, while others draw on traditional knowledge passed down from one generation to the next. Fishers who rely heavily on traditional knowledge may find it more difficult to adapt to rapidly changing environmental conditions.
Commercial fishing has traditionally focused on whitefish, but with the sharp increase in perch stocks, fishers could have shifted their efforts more toward perch. However, not all fishers have responded to this change. According to one commercial fisher, there is little competition among commercial fishers during the summer perch fishing season, as perch are so abundant in many lakes and catching them does not require significant investment in equipment.
The fisher’s view is that flexibility and the large number of waterways help him adapt to changing conditions:
“So the [future] outlook is good when there’s flexibility and opportunities, and plenty of waters. If something needs to be changed, there’s a chance for it.”
He also emphasized that part-time paid work and hunting provide a financial buffer for the household.
Adapting to changes in fish stocks and the aquatic environment may mean switching to a different fishing lake. It may be particularly difficult for local subsistence fishers to adapt to a situation where Lake Muddusjärvi would primarily contain pike and perch in the future, as they are accustomed to catching whitefish in forested lakes. For fishers coming from elsewhere—especially from the south—the change may be easier if they are already familiar with fishing for pike and perch.
Research Needs in Lake Muddusjärvi
Some fishers highlighted several research needs related to the fish community structure and food web in Lake Muddusjärvi. It would be interesting to determine whether changes in the size structure and abundance of whitefish are related to the feeding patterns of other fish species and the functioning of the lake’s entire food web. It would be important to study the following topics, for example:
Size structure of the whitefish population: What is the current size structure of the whitefish population in Lake Muddusjärvi?
Sexual maturity of whitefish: At what size and age do whitefish reach sexual maturity?
Whitefish stock density and causes of stunted growth: How dense is the whitefish stock in Lake Muddusjärvi today? Could previous whitefish stocking efforts be linked to the current stock density and the stunted growth of the whitefish? Is the small size of the whitefish possibly a characteristic of the lake’s original whitefish stock?
The diet of the whitefish: Has the decline in large whitefish affected the diet of dwarf whitefish form “reeska”? Does “reeska” currently rely more on food resources that larger whitefish previously consumed?
Changes in perch diet: Have perch diet changed? Do perch now feed more on whitefish than on three-spined sticklebacks? What might be the cause of a possible diet change?
The test fishing data collected from Lake Muddusjärvi in 2026 will allow for a comparison with similar results from previous decades. At the same time, the data provides insights into potential changes in the size structure of the whitefish population, as well as in sexual maturity and the proportions of different forms. Regarding fish diet, the study will focus particularly on the food competition between different forms of whitefish and perch. Large perch feed on smaller whitefish, and as perch grow larger, they may increasingly feed on reeska and small benthic whitefish. The most recent test fishing period ended recently, and we will return to the detailed results at a later date.
