Editing Mälaren (section)

=== Crayfish ===
Crayfish are of large cultural and economic importance in Sweden, with [[Crayfish party|crayfish parties]] being a longtime annual tradition for many Swedes.

Lake Mälaren was the first lake in Sweden to be affected by the [[crayfish plague]] (''A. astaci'' Schicora'')'' when infected crayfish imported from Finland were introduced to the lake with the intention of human consumption. The plague spread quickly through the lake, exacerbated by boat traffic, which decimated the indigenous [[Astacus astacus|noble crayfish]] (''A. astacus'') population and caused severe economic losses to the local fishing industry. From Mälaren, the plague spread rapidly to all freshwater bodies in Sweden.

After multiple recurrent outbreaks and failed attempts to restore populations of the noble crayfish, Swedish authorities introduced the North American [[signal crayfish]] (''P. leniusculus)'' to L. Mälaren, a species that is resistant to the plague. Since 1969, Mälaren has been continuously stocked with signal crayfish.<ref name=":0" /> However, it was later discovered that signal crayfish were often carriers of crayfish plague. In addition, while populations of noble crayfish and signal crayfish have been known coexist, their larger size, faster growth rate, and aggressiveness often allows them to dominate populations of noble crayfish. This, in addition to habitat degradation,<ref>{{Cite journal |last1=Capinha |first1=César |last2=Larson |first2=Eric R. |last3=Tricarico |first3=Elena |last4=Olden |first4=Julian D. |last5=Gherardi |first5=Francesca |date=August 2013 |title=Effects of climate change, invasive species, and disease on the distribution of native European crayfishes |url=https://pubmed.ncbi.nlm.nih.gov/23531056 |journal=Conservation Biology |volume=27 |issue=4 |pages=731–740 |doi=10.1111/cobi.12043 |issn=1523-1739 |pmid=23531056 |s2cid=25775481 |access-date=2022-10-13 |archive-date=2022-10-13 |archive-url=https://web.archive.org/web/20221013231552/https://pubmed.ncbi.nlm.nih.gov/23531056/ |url-status=live }}</ref> has led to a significant decrease in noble crayfish populations in L. Mälaren.

Signal crayfish have been largely successful in Sweden and rapidly expanded as a replacement population to noble crayfish. Stocking this species is now prohibited within multiple lakes in Sweden in order to protect noble crayfish population. In the Stockholm municipality, which includes L. Mälaren, signal crayfish are now illegal to import, move, or farm.<ref>{{Cite web |title=Kräftfiske - Stockholms stad |url=https://parker.stockholm/fiske/kraftfiske/ |access-date=2022-10-13 |website=parker.stockholm |language=sv |archive-date=2022-10-13 |archive-url=https://web.archive.org/web/20221013114441/https://parker.stockholm/fiske/kraftfiske/ |url-status=dead }}</ref> There have been efforts to encourage farming of noble crayfish populations instead.<ref>{{Cite web |title=Noble Crayfish farming in Sweden |url=https://www.slu.se/en/Collaborative-Centres-and-Projects/slu-aquaculture/education/noble-crayfish-farming-in-sweden/ |access-date=2022-10-13 |website=SLU.SE |language=en |archive-date=2022-10-13 |archive-url=https://web.archive.org/web/20221013114433/https://www.slu.se/en/Collaborative-Centres-and-Projects/slu-aquaculture/education/noble-crayfish-farming-in-sweden/ |url-status=live }}</ref> However, illegal farming of signal crayfish continues to be a problem due to greater public demand for the larger signal crayfish.<ref>{{Cite journal |last1=Bohman |first1=P. |last2=Degerman |first2=E. |last3=Edsman |first3=L. |last4=Sers |first4=B. |date=2011 |title=Exponential increase of signal crayfish in running waters in Sweden – due to illegal introductions? |url=https://www.kmae-journal.org/articles/kmae/abs/2011/02/kmae110017/kmae110017.html |journal=Knowledge and Management of Aquatic Ecosystems |language=en |issue=401 |pages=23 |doi=10.1051/kmae/2011040 |issn=1961-9502 |doi-access=free |access-date=2022-10-13 |archive-date=2022-10-13 |archive-url=https://web.archive.org/web/20221013114431/https://www.kmae-journal.org/articles/kmae/abs/2011/02/kmae110017/kmae110017.html |url-status=live }}</ref>