Long-lining is a frequently used method in marine fisheries. Similarly to trawling and nets, also long-lining is associated with bycatch which may have negative impacts on the ecosystems. However, different methods of long-lining may vary in the amount and ratio of bycatch but methods have rarely been compared directly. This study investigates whether the fishing method of floated demersal longlining baited with live Pacific Anchoveta (Cetengraulis mysticetus) has a lower bycatch ratio or bycatch amount than using demersal long lines baited with filet pieces of dead fish. The study was carried out in collaboration with artisanal small-scale fishermen in the Paquera area of the Gulf of Nicoya in Costa Rica. Six efforts were made in February of 2023, and were then compared to dead bait data from the same area from 2015 and 2016 collected by Universidad Nacional de Costa Rica. This comparison showed no significant difference between the two methods in bycatch ratio but showed that live bait longlining captures significantly more total fish and bycatch per catch per unit effort (CPUE). There are also ethical issues and issues with bait fish acquirement that points against live bait fishing. However, there are certain arguments in support of the method, such as broadening the exploitation strain across more species and not hindering financially struggling artisanal fishermen further.

Aquaculture is of growing importance in the global seafood production. The environmental impact of aquaculture will largely depend on the type of environment in which the aquaculture system is placed. Sometimes, due to the abiotic or biotic conditions of the seascape, certain aquaculture systems tend to be placed within or near specific ecosystems, a phenomenon that in this thesis is referred to as aquaculture system - ecosystem links. The exposed ecosystems can be more or less sensitive to the system specific impacts. Some links are known to be widespread and especially hazardous for the subjected ecosystem such as the one between the shrimp aquaculture and the mangrove forest ecosystem. The aim of this thesis was to identify and investigate causes and consequences of other spatial links between aquaculture and ecosystems in the tropical seascape. Two different aquaculture system - ecosystem links were identified by using high resolution satellite maps and coastal habitat maps; the link between sea cage aquaculture and coral reefs, and the one between seaweed farms and seagrass beds. This was followed by interviews with the sea cage- and seaweed farmers to find the drivers behind the farm site selection. Many seaweed farmers actively choose to establish their farms on sea grass beds but sea cage farmers did not consider coral reefs when choosing location for their farms. The investigated environmental consequences of the spatial link between sea cage aquaculture and coral reefs were considerable both on the local coral reef structure, and coral associated bacterial community. Furthermore, coral reef associated fish are used as seedlings and feed on the farms, which likely alter the coral food web and lower the ecosystem resilience. Unregulated use of last resort antibiotics in both fish- and lobster farms were also found to be a wide spread practice within the sea cage aquaculture system, suggesting a high risk for development of antibiotic resistant bacteria. The effects of seaweed farms on seagrass beds were not studied in this thesis but have earlier been shown to be rather substantial within the borders of the farm but less so outside the farm. Further, a nomenclature is presented to facilitate the discussion about production system - ecosystem links, which may also be used to be able to incorporate the landscape level within eco-certifying schemes or environmental risk assessments. Finally - increased awareness of the mechanisms that link specific aquaculture to specific habitats, would improve management practices and increase sustainability of an important and still growing food producing sector - the marine aquaculture. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 2: Manuscript. Paper 3: Manuscript. Paper 4: Manuscript.</p>

The purpose of this study was to investigate whether it is possible to control fish that migrate during spawning season with the help of an electric barrier. The results aim to increase knowledge about electric barriers as the method so far is scarcely used in Sweden. Examples of situations where the method could be useful are when monitoring restoration measures of wetlands and when controlling fish at hydropower plants. This study was conducted in Harrbäcken, where fish migrate during spring to spawn. The fish migrate up through Harrbäcken, partly to spawn in the stream itself and partly to spawn in Sladaviken just upstream. Attempts to control the fish with an electric barrier were carried out and data were collected via recordings from three different fish counters. The results showed that the electric barrier did not impede fish spawning migration, although this result was not entirely convincing. Furthermore, the electric barrier influenced which fish counter the fish chose. Finally, the result show that the electric barrier influenced which fish counter larger roach (Rutilus rutilus) chose. Larger roach chose to swim beside the electric barrier when it was turned on and through the electric barrier when it was turned off. Although this study contributes to an increased understanding, more studies within the subject are desirable.

At present, it is focused either on aquaculture or agriculture. Those who focus on aquaculture or Recirculating Aquaponics System (RAS) receive a by-product of ammonia, which is then cleaned and the water either goes back to the fish or it is not cleaned at all and as they do in the salmon farms for example they let it sink to the bottom which creates eutrophication and major problems among the marine. Those who focus on agriculture use colossal amounts of land and outdoor areas for cultivation. Most of them use chicken manure and huge amounts of pesticides for the plants to be optimal. Another alternative is that you can use aquaponics, which is a kind of ecosystem where fish and plants live and thrive on each other's residual products. The fish produce ammonia in the fish tank which eventually makes the water uninhabitable and instead of having a cleaning pump in the fish tank, the water is sent to the cultivation bed where the plants pick up the nutrients and clean the water in turn so that the water can be pumped back to the fish tank. This system makes it possible to produce both fish and plants in an optimized and safe system. Aquaponics is advantageous in that it utilizes the by-product of the fish and gives it to the plants. Where ammonia is the fish’s residual product that turns into nitrite and then to nitrate and it is precisely nitrate that the plants use as nutrition, in turn, they purify the water that goes back into the fish tanks, which gives a closed cycle. At present, aquaponics has not been able to impact on a large scale more than in a few places, partly because there is ignorance of how it works and partly because it requires technical knowledge of how to build a functioning system together. The project goal that we strive for is to get a PlugNPlay solution that enables people who want to invest in aquaponics, but do not have the technical knowledge to compile a functioning optimal system. The project group will also compare different farming methods and make measurements on which medium is the best to grow in, but also what kind of food that works to grow in an efficient way. / I dagsläget fokuseras det antingen på vattenbruk eller på jordbruk. De som fokuserar på vattenbruk eller Recirkulerande Akvaponiska System (RAS) får en biprodukt bestående av ammoniak, som sedan rengörs och vattnet går antingen tillbaka till fiskarna eller så rengörs det inte alls och som de gör i till exempel laxodlingarna, de låter det sjunka till bottnen vilket skapar övergödning och stora problem bland det marina. De som fokuserar på jordbruk använder kolossala mängder av jord och ytor utomhus för att kunna odla. De flesta använder sig av hönsgödsel och enorma mängder bekämpningsmedel för att plantorna ska bli optimala. Ett annat alternativ är att man kan använda sig av akvaponik som är ett sorts ekosystem där fiskar och växter lever och frodas på varandras restprodukter. Fiskarna producerar ammoniak i fisktanken som gör så att vattnet till slut blir obeboeligt och istället för att ha en rengöringspump i fisktanken så skickas vattnet över till odlingsbädden där växterna plockar upp näringen och rengör vattnet i sin tur så att vattnet sedan kan pumpas tillbaka till fisktanken. Detta system gör det möjligt att producera både fisk och växter i ett optimerat och säkert system. Akvaponik är fördelaktigt i den mån att den utnyttjar biprodukten ifrån fiskarna och ger denna till växterna. Där ammoniak är fiskens restprodukt som blir till nitrit och sedan till nitrat och det är just nitrat som växterna använder som näring, i sin tur så renar de vattnet som går tillbaka in till fisktankarna vilket ger ett slutet kretslopp. Akvaponiken har i dagsläget inte slagit igenom storskaligt mer än på ett fåtal platser, dels för att det finns okunskap om hur det fungerar dels för att det krävs teknisk kunskap om hur man bygger ihop ett fungerande system. Projektmålet som vi strävar efter är att få till en PlugNPlay lösning som gör det möjligt för människor som vill satsa på akvaponik men inte har den tekniska kunskapen att sammanställa ett fungerande optimalt system. Projektgruppen kommer även att jämföra olika odlingssätt och göra mätningar på vilket medium som är bäst att odla i men även vilken sorts mat som fungerar att odla på ett effektivt sätt.

An optimal method for stunning animals before slaughter should result in instantaneous and irreversible insensibility. Today, there are various stunning and slaughter practices used around the world for farmed fish. With aquaculture being a growing food sector, the welfare of the animals used has become increasingly important in the consciousness of consumers, researchers and regulatory bodies. With growing research into the subject matter, an overview to summarize and examine how these practices impact on the welfare of the fish, and how well they conform to animal welfare legislation, is warranted to minimize the suffering of farmed fish. Stunning practices used in aquaculture include methods such as electrical and percussive stunning, carbon dioxide and asphyxiation. Each with its own level of effectiveness in terms of how fast the method results in loss of consciousness, whether or not the effect is reversible and how the welfare of the fish is affected as determined by behavioural and physiological stress responses. It was concluded that there is no unambiguous answer as to which stunning method is optimal in regard to animal welfare in modern day aquaculture. The optimal method for a given facility is influenced by factors like practicalities relating to each individual method as well as legislation on EU and national level. Suggestions were made for future research.

Migration occurs among many animal species for the purpose of, among other things, finding food or to reproduce. Spawning migration is a form of migration that occurs among many fish species where they move to another site for reproduction. The movement can be obstructed by migration barriers like road culverts. Barriers to migration pose one of the greatest threats to biodiversity and ecosystem functions in freshwater. They impair the connectivity of watercourses and may prevent fish from improving reproductive success or completing their life histories altogether. There are both benefits and costs with migration, benefits such as increased survival for the adults and offspring, and costs such as increased energy consumption and increased mortality. The costs are often dependent on the morphological traits of the individual, like body shape and size. In this study, the spawning migration of two species of fish of the family Cyprinidae, ide (Leuciscus idus) and roach (Rutilus rutilus) was investigated. Few studies have been made on ide or on roach compared to other cyprinids and salmonids. This study might therefore enhance the overall knowledge of these two species. The overall aims of this project are to study and compare phenotypic correlates of spawning migration behaviour of ide and roach. The field studies were performed in Oknebäcken, Mönsterås (SE632310-152985), Sweden in March and April 2020. To describe the watercourse and define the location and characteristics of different potential migration barriers, a simplified biotope mapping method was used. The fish were caught in a hoop net and then measured, weighted, sexed, and injected with passive integrated transponder using the bevel down method. In order to register in stream movement of fish, reading stations with antennas were placed, at two locations upstream from the marking station and one downstream at the estuary. The sex ratio differed from the expected 1:1 with a majority of females for both species. This might be a result of fluctuations in survival of spawn coupled with different age-at-maturity between sexes. We found that individuals that arrived early to the stream were larger for both study species, as other studies also reported. Also, male ide was both larger and arrived before female ide. There might be an energy cost associated with early arrival to the stream and therefore, larger individuals arrive first. For roach, there was no difference in arrival time between the sexes although female roach were larger. There was no difference in the time spent in the stream between the species. For ide, females stayed for a longer period of time in the stream than males. However, the opposite was true for roach. This may be because male roach might benefit from more fertilization events when staying longer. There might therefore be a trade-off between the energy cost in staying in the stream and the increased fitness advantage in fertilization events. We found no correlation between any of the morphological traits and migration distance. However, since very few individuals were registered at the upstream reading stations, there might be an effect of migration barriers on the spawning migration. The mortality after spawning was higher for roach than for ide. For ide, a larger proportion of females than males died. For roach, individuals that arrived early was classified as alive to a greater extent than those who arrived late. Both similarities and differences between the species were discovered in this study which concludes that even closely related species might differ substantially from each other.

The global population is expected to increase and the greatest challenge for the world’s food-producing sector is to secure food and nutrition through sustainable production methods and reduced waste. Aquaculture is the cultivation of aquatic organisms including fish, molluscs, crustaceans and algae, and has a significant role in providing food and employment as the demand for food is increasing. In this study, conventional open-net pen farming was compared to semi-closed aquaculture systems (S-CCS), as well as the possibility of implementing integrated multi-trophic aquaculture (IMTA) in Sweden. Open-net pens are cost-effective and well-proven methods, but due to environmental impacts, the opportunities are limited. Cultivation in S-CCS reduces the environmental impact by strengthening the barrier between the cultivated organism and the surroundings. Implementing IMTA offers the potential for diversification of aquaculture production and economic yield. Sweden has major potential to develop competitive aquaculture through sustainable technological solutions and by diversifying productivity. / Den globala befolkningen förväntas öka och den största utmaningen för världens livsmedelsproducerande sektor är att säkra tillgången på mat och näring genom hållbara produktionsmetoder och minskat avfall. Vattenbruk är odling av vattenlevande organismer inklusive fisk, blötdjur, kräftdjur och alger, och har en betydande roll för att tillhandahålla mat och sysselsättning när efterfrågan på mat ökar. I denna studie jämfördes konventionell kassodling med semi-slutna vattenbrukssystem (S-CCS), samt möjligheten att implementera integrerat multitrofisk vattenbruk (IMTA) i Sverige. Kassodling är kostnadseffektivt och en välbeprövad metod, men på grund av miljöpåverkan är möjligheterna begränsade. Odling i S-CCS minskar miljöpåverkan genom att stärka barriären mellan den odlade organismen och omgivningen. Implementering av IMTA erbjuder potential för diversifiering av vattenbruksproduktionen och ekonomisk avkastning. Sverige har stor potential att utveckla konkurrenskraftigt vattenbruk genom hållbara tekniska lösningar och genom att diversifiera produktiviteten.

Seaweed has been hit hard by climate change around the world. The island of Zanzibar, which is the world’s third biggest exporter of seaweed, is one of the places where seaweed is affected. 80 percent of the seaweed farmers on Zanzibar are women who are directly affected by climate change since they are making a living from seaweed farming. New efforts to tackle the impact of climate change on seaweed has been made on Zanzibar through the SEA PoWer project which is a new technique of growing seaweed and enables twenty-four female seaweed farmers to grow in deep and cooler waters instead of the more traditional way which is in shallow waters. The aim of this study is to, from a livelihood perspective, examine women’s experiences and perceptions of the old versus the new techniques of farming seaweed on Zanzibar, Tanzania.  The research questions for this study focus on finding out the women’s experiences and perceptions of the changes in the techniques in relation to opportunities for livelihoods through seaweed farming. Furthermore, this study investigates if women experience conflicts of interest with men regarding the use of ocean space. Semi-structured interviews with eleven women who have used the new technique of growing seaweed were conducted and the results was analyzed in the light of previous research, through the definitions of livelihood and gender, and the theoretical concept of feminist political ecology. The result has shown that all women experienced improvements in their livelihoods through the new technique of seaweed farming. One clear improvement was that there were no negative health effects when using the new technique. The study also found that there are no conflicts of interest between men and women regarding the use of ocean space when using the new technique of seaweed farming. The women had a positive view on the future and had high expectations, they had already noticed positive effects on their livelihoods in form of social, human, physical capital and health.

Marine salmon farming is a new and fast-growing industry in Iceland after decades of uncertainties within aquaculture development in the country. While growing at a tremendous speed in the last few years, the development has been challenged by different social groups in regard to its socio-economic and environmental effects. Research has shown that there is a lack of knowledge on the perceptions on different stakeholders involved in the farming. This study aims to investigate how different stakeholders perceive the marine salmon farming industry being established in Bíldudalur, in the Westfjords of Iceland, by conducting a case study. Semi structured interviews were carried out with different stakeholders as well as an online survey was distributed to the residents of Bíldudalur, following a focus groupdiscussion. Analysis of the responses demonstrated that current aquaculture regulations have not held up with the expanding industry which has created tension amongst stakeholders. The results show that many worry about the wild salmon stock and that with current regulations, it is hard to predict how much marine farmed salmon will be bred in Iceland, due to weak regulations. Simultaneously, the local community of Bíldudalur has experienced a lot of positive changes in their rural community following the establishment of fish farming in their community. On this basis, further research is needed to compare the findings to other rural communities involved in fish farming in Iceland as well as further research on Iceland´s current changes in regulation and policies and how aquaculture development is promoted in Iceland.