Having finished the aquaria experiment at Lunds University (see former blog posts) some three weeks ago, Laura and I started to focus on the third LIFE action: re-introduction of Unio crassus in the Rivers Klingavälsån and Fyleån. Therefore, a fish cage design was established and material was bought in hardware stores. The cage construction was carried out in Hemmerstorps Möllas’ garden during one and a half weeks of sunshine.
The purpose of the fish cages is to fit them with artificially infested fishes with mussel glochidia to finally hatch young mussels. Only fish species known as potentially good host fishes from literature and from own experience gained during the aquaria experiment this year are used therefore. For collecting mussel larvae (glochidia), the Rivers Bråån and Tommarpsån were checked for gravid mussels at the end of July. Unfortunately, none of the 200 checked Unio crassus individuals were gravid anymore. Therefore, I found a greatly deformed living Unio crassus in Bråån, which probably got its different shape due to a unknown physical impact.
Together with Niklas, who is very experienced in mussel gravidity physiology further mussels were checked after the sunny and warm time of period one week ago. But, the results did not change: Probably, the gravidity season of Unio crassus is over for this year. Anyway, we decided to build up the net cages to generally evaluate the method of fish cages in flowing water, together with fish survival. Gained knowledge from this experiment can be used for the re-introduction action in the following years.
Finally, last week was the week of many actions. On Monday Niklas traveled to Skåne while Laura and I started to span plastic nets on fish-cage-frames. On Tuesday and Wednesday a third electrofishing of this year was carried out in Bråån and Tommarpsån which serves the host fish mapping action under natural conditions. Thanks to Delphine’s help, we could realize this LIFE action again.
The evenings were spent with finishing the fish cages. On Thursday, the first fish cages could be transported to the Nature 2000 site “Fyledalen” and settled up in its rivers. Additionally, fishes were caught, measured and placed in the cages. The same for Klingavälsån on Friday.
Over the week-end I started to feed the fishes and to monitor fish survival plus physico-chemical parameters. Yesterday evening I found one cage lying on its side next to the mil in Klingavälsån. All fishes escaped :(. In contrast, one cage already proved great stability since it’s protection shield kept away heavy water plants :).