During the last two hundred years many wetlands and streams in Sweden have been lowered to provide land for agriculture and forestry. Some of the coastal wetlands and streams probably served as spawning sites for certain species of fish in the Baltic Sea, but the present situation is not well known. As standardized methods to monitor fish in running waters are carried out during late summer or autumn, there is a need for methods to sample spring-spawning fish in these streams. The aim of this study was to survey the lower kilometer stretch of Hammerstaån in Stockholm, to investigate the extent to which the stream is used by spring-spawning fish. Furthermore, the study aims to evaluate a new type of survey fishing gill net called strömöversiktsnät (SÖN). This was done by comparing the catch of fish by SÖN with that of fyke nets. The comparison of the types of gear included number of fish caught, on a catch per unit effort (CPUE) basis, number of species and the size distributions. The study included 14 days with one gill net and one fyke net at two sites, in total 28 net-days. The inventory yielded in total seventeen species among which only trout (Salmo trutta), perch (Perca fluvitalis), roach (Rutilus rutilus), burbot (Lota lota), eel (Anguilla anguilla) and pike (Esox lucius) were previously known to occur. Six spawning species, smelt (Osmerus eperlanus), vimba bream (Vimba vimba), perch (Perca fluvitalis), roach (Rutilus rutilus), bream (Abramis brama) and white bream (Blicka bjoerkna) were caught in more than 60 individuals, which was set as a limit for comparisons of size distributions. There was no significant difference in CPUE between SÖN and fyke nets. Also length distribution did not differ between SÖN and fyke nets except for the species perch and white bream were the nets caught significant smaller perch and bigger white bream than the fyke nets. The results show that investigations with SÖN or fyke nets during springtime can be of great importance to increase our knowledge about spring-spawning fish in Swedish streams and the coastal areas of the Baltic Sea.

The need for more sustainable protein sources is growing globally due to the significant climate impact from the food system and the estimated population growth. Although vegetarian protein sources have been proven to be sustainable alternatives, there may exist additional resources that currently are not utilized but potentially could contribute as sustainable protein sources. Life Cycle Assessment (LCA) is an internationally standardized tool used to assess the potential environmental impacts of a product or service throughout its entire life cycle. The results from a recently conducted LCA for Swedish carp species showed that the average potential climate impact was 0.77 kg CO2-eq per kg of edible product, which is significantly lower than more commonly consumed protein sources. The bream is a carp fish that previously was consumed in Sweden, but now is caught only as a by-catch that is released back.  This study aims to assess the potential environmental impacts of minced bream produced in Stockholm and utilizing bream caught as by-catch to wild capture fishery in Mälaren. The study also investigates how the potential environmental impacts may change in alternative systems and how the potential climate impact compares to the potential climate impact of other protein sources consumed in Sweden. The results of the study confirm many of the conclusions made in reviewed literature, such as the wild capture fishery and transports being identified hotspots. The results also show a low potential environmental impact of the minced bream in the current system but significant increases in the potential environmental impacts if the minced bream was produced in the alternative systems. In comparison to other protein sources, the minced bream shows great potential, both now and in the future when the carbon budget may be limited to 0.5 kg CO2-eq per meal if we are to limit global warming to 1.5°Cabove pre-industrial levels.  Further studies are encouraged to collect more data and provide a better understanding of the environmental impacts of fish products. However, the results could function as an important benchmark that also highlights the potential of currently underutilized species of fish. / Behovet av mer hållbara proteinkällor ökar globalt till följd av matproduktionens stora klimatavtryck samt uppskattningar om en snabbt växande befolkning. Även om vegetariska proteinkällor har visats vara hållbara alternativ, finns en möjlighet att även andra resurser som i dagsläget inte utnyttjas har potential att bidra som hållbara proteinkällor. Livscykelanalys (LCA) är ett internationellt standardiserat verktyg som används för att utvärdera den potentiella miljöpåverkan från en produkt eller tjänst under hela livscykeln. En nyligen genomförd LCA visar att svenska karpfiskar har ett genomsnittligt potentiellt klimatavtryck på 0.77 kg CO2- ekvivalenter per kg ätlig produkt, vilket är avsevärt mycket lägre den potentiella klimatpåverkan hos många av de proteinkällor som idag konsumeras i större utsträckning. Braxen är en karpfisk som tidigare konsumerats i Sverige men som numera fångas enbart som en bifångst som släpps tillbaka.  Denna studie syftar till att utvärdera den potentiella miljöpåverkan av braxenfärs som produceras i Stockholm på braxen fångad som bifångst till gösfiske i Mälaren. Studien undersöker också hur den potentiella miljöpåverkan kan förändras i alternativa system och hur den potentiella klimatpåverkan kan jämföras med den potentiella klimatpåverkan från andra proteinkällor som konsumeras i Sverige. Resultaten från studien bekräftar många av slutsatserna i litteraturen som granskats, som att fisket och transporter identifierats som hotspots. Resultatet visar också en låg potentiell miljöpåverkan från braxenfärsen i det nuvarande systemet men en betydande ökning av den potentiella miljöpåverkan om braxenfärsen produceras i de alternativa systemen. Jämfört med andra proteinkällor visar braxenfärsen stor potential både nu och i framtiden när koldioxidbudgeten kan begränsas till 0.5 kg CO2-ekvivalenter per huvudmåltid om den globala uppvärmningen ska begränsas till 1.5 °Cöver förindustriella nivåer.  Ytterligare studier uppmuntras för att samla in mer data och ge en bättre förståelse för fiskprodukters miljöpåverkan. Resultatet kan dock fungera som ett viktigt riktmärke som också belyser potentialen hos för närvarande underutnyttjade fiskarter.