Introduced alien signal crayfish (Pacifastacus leniusculus) in Finland : uncontrollable expansion despite numerous crayfisheries strategies

In Finland, massive signal crayfish introductions started towards the end of 1980s, with an estimated total of 2.2 million signal crayfish been stocked before year 2016. During that period, Finnish fisheries authorities have implemented three national management strategies setting guidelines for the crayfish introductions. The main aims of the strategies have been conservation of native noble crayfish stocks and a controlled spreading of the alien signal crayfish within a designated region. In this study, we report the current distribution of signal crayfish in Finland in comparison to the guidelines set in these three national strategies. The present distribution area of the signal crayfis…

Rysäkalastussaaliiden rakenne ja kalastuksen kestävyys

Nostetta särkikaloista -hankkeen kevään 2019 pilottikohteiden (Pieni Raudanvesi, Haukivesi, Puruvesi, Ruokojärvi) rysäsaalista ja kalaston rakennetta arviointiin särjen, ahvenen ja lahnan osalta ja samalla arvioitiin kalastuksen kestävyyttä olemassa olevien aineistojen ja vasta valmistuneen vajaasti hyödynnettyjen kalalajien saalispotentiaaliarvion (Ruokonen ym. 2019) pohjalta. Saaliin hyödynnettävyyttä elintarvikkeeksi selvitettiin kalalajeittain yhteistyössä kalajalostajien kanssa sekä teoriatasolla käyttäen vertailupohjana Suomen (2017) tekemää selvitystä jalostukseen kelpaavista kalalajeista ja kokoluokista. Lisäksi selvitettiin särkikalojen vaelluksia Pienen Raudanveden ja Haukiveden v…

Predation by signal crayfishPacifastacus leniusculuson fish eggs and its consequences for coregonid recruitment

The character and magnitude of predation by the invasive, ectothermic Pacifastacus leniusculus, a crayfish widely introduced to Europe and Japan from North America, on the eggs of coregonid fishes, vendace Coregonus albula and whitefish Coregonus lavaretus were examined by experimentation, modelling and field data. The present results showed that P. leniusculus has the potential to be very efficient predator of fish eggs under winter conditions, but the predation by P. leniusculus did not significantly decrease production of coregonid larvae during the years with a high P. leniusculus population in the study lake. Hence, the mortality caused by the novel invertebrate predator appeared to co…

Are the effects of an invasive crayfish on lake littoral macroinvertebrate communities consistent over time?

Management of invasive species requires assessment of their effects on recipient ecosystems. However, impact assessment of invasive species commonly lacks a long-term perspective which can potentially lead to false conclusions. We examined the effects of the invasive signal crayfish (Pacifastacus leniusculus Dana) on the stony littoral macroinvertebrate communities of a large boreal lake and assessed the extent to which the patterns observed in previous short-term studies were stable over time. We used temporal macroinvertebrate data collected in five consecutive years from a site with a well-established crayfish population, a site with no crayfish and a site where crayfish had been recentl…

Ecological impacts of invasive signal crayfish in large boreal lakes

Effects of an invasive crayfish on the littoral macroinvertebrates of large boreal lakes are habitat specific

Summary Invasive crayfish are widely acknowledged to have negative effects on benthic food webs in lakes, but few studies have investigated such effects at wider spatial scales and in varying habitats under natural conditions. We examined the effects of introduced signal crayfish (Pacifastacus leniusculus) on the macroinvertebrate assemblages of different habitats in two large boreal lakes. We evaluated whether the density, taxon richness and species composition are altered by the non-native crayfish and whether the responses are similar for stony and vegetated habitats and across a depth gradient. We also studied the influence of crayfish on periphyton biomass at stony sites, as a potentia…

The relationship between stocking eggs in boreal spawning rivers and the abundance of brown trout parr

Abstract Stocking with eggs has been widely used as a management measure to support degraded salmonid stocks. In Finland, Atlantic salmon and both sea-migrating and lake-migrating brown trout are stocked as eggs, alevins, fry, parr, and smolt, whereas trout are also stocked as mature fish. The aim of this stocking is to improve catches and to support collapsed spawning stocks. We assessed the success of stocking with brown trout eggs in a study of 17 Finnish boreal forest rivers, of which 9 were subject to egg stocking. All rivers contained some naturally spawning trout. In 16 rivers, including non-stocking years and unstocked rivers, egg stocking did not increase the total (wild and stocke…

Diet and trophic niche of the invasive signal crayfish in the first invaded Italian stream ecosystem.

The occurrence of the signal crayfsh Pacifastacus leniusculus in the Valla Stream was the frst established population of this invasive species recorded in an Italian stream ecosystem. We evaluated the seasonality of diet and trophic niche of invasive signal crayfsh in order to estimate the ecological role and efects on native communities of the stream ecosystem. We studied the diferences in food source use between sexes, life stages and seasons using carbon and nitrogen stable isotope analyses. To supplement stable isotope analyses, we evaluated food source usage using traditional stomach content analysis. We tested the hypothesis that juveniles have a diferent diet, showing diferent trophi…

Trophic role of marbled crayfish in a lentic freshwater ecosystem

Species’ introductions may cause severe adverse effects on freshwater ecosystems and their biota. The marbled crayfish, Procambarus virginalis Lyko, 2017, is an invasive parthenogenetically reproducing crayfish with rapid reproduction, maturation and tolerance to a wide range of environmental conditions, which was introduced to many sites across Europe during the last decade. Due to its recent speciation and limited number of field studies, the knowledge of trophic interactions of the marbled crayfish in freshwater food webs is scarce. An invaded area located in Central Europe was studied to identify the marbled crayfish food web interactions using analysis of carbon 13 C and nitrogen 15N i…

Indirect effects of invasive crayfish on native fish parasites

Interactions between invasive and native species are often modified by parasites. One little-studied scenario is that invasive species affect parasite transmission to native hosts by altering the relative abundance of hosts needed in parasite life cycles, for example by predation on these hosts. Here we show that presence of an invasive crayfish species, Pacifastacus leniusculus, decreases the mean abundance of native parasites transmitted from snails and aquatic isopods to perch, Perca fluviatilis, in two large boreal lakes in Finland. In contrast, parasites transmitted to the fish from planktonic copepods or mussels, hosts not readily preyed on by crayfish, were not affected by crayfish p…

Comparing the effects of introduced signal crayfish and native noble crayfish on the littoral invertebrate assemblages of boreal lakes

The introduced North American signal crayfish Pacifastacus leniusculus (Dana) has replaced the native noble crayfish (Astacus astacus) in many European freshwaters and can be considered a new component of these ecosystems. The 2 species are apparently similar in many respects, but their ecological equivalence is uncertain and has been little investigated, especially at the whole-lake scale. We compared the effects of the 2 species on the abundance, species richness, and composition of littoral macroinvertebrate assemblages in a set of small- and mediumsized boreal lakes, which included 8 lakes with noble crayfish, 8 lakes with signal crayfish, and 8 lakes without crayfish. We collected semi…

The introduced signal crayfish and native noble crayfish have different effects on sublittoral macroinvertebrate assemblages in boreal lakes

It takes time to see the menu from the body: an experiment on stable isotope composition in freshwater crayfishes

For many applications and ecological studies in which wild individuals are brought to laboratory it would be essential to know accurately how fast novel diet is reflected in composition of different tissues. To study the effects of two different diets on the stable isotope composition of freshwater crayfish muscle and hemolymph, we conducted a three month experiment on noble crayfish (Astacus astacus) and signal crayfish (Pacifastacus leniusculus) by feeding them sweet corn (Zea mays) or Baltic herring (Clupea harengus membras) as novel food. During the experiment, the crayfish were given 0.4 g of selected food daily and the amount consumed was recorded. The samples for the stable isotope a…

Migration strategies of brown trout (Salmo trutta) in a subarctic river system as revealed by stable isotope analysis

We estimated the proportions of anadromous and freshwater‐resident brown trout (Salmo trutta) in different parts of the subarctic River Näätämöjoki/Neidenelva system (Finland and Norway) using carbon, nitrogen and hydrogen stable isotope analyses of archived scales as identifiers of migration strategy. Our results showed that carbon stable isotope values were the best predictor of migration strategy. Most individuals fell into two clearly distinct groups representing anadromous (47%) or freshwater‐resident (42%) individuals, but some fish had intermediate carbon values suggesting repeated movement between freshwater and the sea. The proportion of anadromous individuals decreased steadily wi…

Invasive crayfish increase habitat connectivity

Several studies have shown that distinct compartments of lake ecosystems are coupled via transportation of organic matter, nutrients and energy across habitat boundaries. Here we evaluate the potential of the invasive signal crayfish (Pacifastacus leniusculus (Dana)) to modify energy pathways in large boreal lakes. Using a stable isotope mixing model and calculation of the isotopic niches we estimated the contribution of different food sources to the diets of crayfish captured from different habitats, and from that inferred their potential to transport energy across the littoral-profundal gradient. The crayfish caught from the littoral area utilized mainly littoral food sources, whereas the…

Invasive crayfish increase habitat connectivity: a case study in a large boreal lake

Several studies have shown that distinct compartments of lake ecosystems are coupled via transportation of organic matter, nutrients and energy across habitat boundaries. Here we evaluate the potential of the invasive signal crayfish (Pacifastacus leniusculus (Dana)) to modify energy pathways in large boreal lakes. Using a stable isotope mixing model and calculation of the isotopic niches we estimated the contribution of different food sources to the diets of crayfish captured from different habitats, and from that inferred their potential to transport energy across the littoral-profundal gradient. The crayfish caught from the littoral area utilized mainly littoral food sources, whereas the…

Tackling invasive alien species in Europe II: threats and opportunities until 2020

2nd Freshwater Invasives - Networking for Strategy II (FINS-II) Conference -- JUL 11-14, 2016 -- Zagreb, CROATIA Skora, Michal Edward/0000-0002-9121-1318; Groom, Quentin/0000-0002-0596-5376; Lukas, Juliane/0000-0003-3336-847X; Skora, Michal/0000-0002-9121-1318; Piria, Marina/0000-0001-6324-9282; Smith, Emily/0000-0003-2767-9933; Simonovic, Predrag/0000-0002-4819-4962; Pastorino, Paolo/0000-0002-0585-1168; Koutsikos, Nicholas/0000-0003-0680-4504; Vilizzi, Lorenzo/0000-0001-8103-885X; Dobrzycka-Krahel, Aldona/0000-0002-4252-895X; Tarkan, Ali Serhan/0000-0001-8628-0514 WOS: 000412582000002 Invasive alien species (IAS) are a significant and growing problem worldwide. In Europe, some aspects of …