During the last decades marine aquaculture has steadily expanded and diversified to include a wider range of commercial species. Despite the intense effort towards understanding the biological requirements of farmed species, several issues remain to be addressed. Mariculture success is restricted by a number of production bottlenecks including limited seed supply, caused mainly through a combination of compromised productivity in broodstock paired with high mortalities during the early life stages. Productivity and survival success is often dependent on the successful recreation of natural environmental conditions. While in a commercial setting a concerted effort is generally made to simulate key environmental stimuli there remains a lack of understanding of the significance of many potential signals. The overarching aim of this thesis was to investigate the effects of some of the overlooked environmental stimuli on fish performance in enclosed facilities and where possible relate this to the natural setting from which the species have been removed. The studies contained in this text are focused on the effects of anthropogenic noise, light spectral composition and substrate on the performance of broodstock and juvenile development of two valuable commercial marine species Atlantic cod (Gadus morhua) and turbot (Scophthalmus maximus). The aim of Chapter 3 was to test if artificial sound can act as a stressor in Atlantic cod and thereafter to examine if chronic sound disturbances can compromise broodstock spawning performance in land-based facilities. Results showed that anthropogenic noises in a land-based marine farm are within the auditory thresholds of cod and other fish species. Juvenile cod exposed to 10 min of artificial noise (100-1,000 Hz) from 10 to 20 dB 1 re µPa above background sound levels presented a typical acute stress response with a 4 fold elevation of plasma cortisol levels within 20 min, with a return to basal levels after 40 min, while the intensity of the stress response (in terms of amplitude and return to normal levels) appeared to be correlated to the noise level applied. When a similar artificial noise of 35 dB 1 re µPa above background sound level was applied to a broodstock population daily on a random schedule during the spawning season, it significantly impacted on reproductive performances in comparison to a control undisturbed population with notably a reduction in fertilisation rate that correlated with increased egg cortisol contents. Overall, these studies confirmed, for the first time, that artificial noise mimicking anthropogenic sounds generated in marine land-based facilities trigger a typical acute stress response if a similar sound exposure is then applied in a chronic manner it resulted in reduced broodstock spawning performances. Overall this work provides novel evidence on the potential of anthropogenic noise to act as stressor in fish. The possible implications for both captive and wild stock are discussed. In chapter 4 the effects of light spectrum and tank background colour on Atlantic cod and turbot larval performance from hatch until the end of metamorphosis were investigated. In both species larvae exposed to shorter wavelengths (blue and green spectrums) showed significantly enhanced growth in terms of standard length, myotome height, eye diameter and condition factor in comparison to larvae exposed to longer wavelengths (red). Larvae performances in the colour background experiment differed between species. Atlantic cod larvae reared in a red tank background displayed the best growth and survival, while larvae in blue tank background had a significant positive effect on final survival rate. In contrast, turbot larvae survival rates were the highest in the red tank background colour with the lowest growth parameters, while larvae in the blue tank background displayed the best growth. In both species, white tank background colour resulted in the lowest final survival rate. These results highlight the biological relevance of light spectrum and background colour in marine larvae performance and survival, demonstrating the importance of considering the light composition of the light units used in the hatcheries for larval rearing. Subsequently in chapter 5 the effects of light spectrum in juvenile turbot growth, appetite, stress response and skin pigmentation were investigated. Two sets of experiments were performed with post-metamorphosed (1 g) and on-growing (100 g) turbot. Results demonstrated that short wavelength treatments had a significant positive effect on growth parameters (total length and wet weight), food intake and feeding response. Light treatments caused a positive correlation between plasma glucose and cortisol levels with significant differences between the short and long wavelength treatments. Skin pigmentation was affected by the light treatments, showing a relationship between wavelength and brightness (negative) and darkness (positive). Blue light treatment resulted in brighter and lighter skin colouration, while red light had the opposite effect: darkening of the skin. Overall these results confirm that turbot juveniles performance is enhanced by exposing them to a similar photic environment than the one from the natural ecological niche. Light spectrum intervenes in skin pigmentation and the possible mechanisms behind the variations are discussed. In general chapter 5 provides background knowledge of the possible implications of light spectrum in fish juveniles performance and possible commercial applications. The final two experimental chapters turned focus back on the optimisation of broodstock environmental management and subsequent effects on their productivity. In Chapter 6 the importance of crepuscular light simulation was investigated in Atlantic cod broodstock spawning performance. No significant impact could be observed in terms of egg production and quality in association with dawn/dusk simulation compared to abrupt lights on/off. This suggests, at least for Atlantic cod, that crepuscular light simulation is not a key factor affecting spawning performance during the spawning window. The possible implications of twilight on gamete quality prior ovulation are discussed. In Chapter 7 the effect of a “breeding nest” containing a substrate (i.e. sand) in turbot broodstock spawning performance was investigated. Behavioural observation recorded active occupancy of the nests with the suggestion of social structuring as specific individuals (females) occupied the nest preferentially. However no fertilised, naturally released eggs were collected from the overflow during the spawning seasons. This would suggest that the presence of a nest is not enough to induce natural spawning behaviour in turbot in itself however the elective occupancy suggests that nests and/or their substrate was a physical enrichment that was valued by the fish which should be explored further. Overall the studies contained in this thesis highlight further the importance of considering noise and light as crucial environmental factors in marine aquaculture. Results from the different chapters offer a possible application within the enclosed facilities that might contribute to the success of the industry. Present findings contribute towards the understanding of the effects of environmental signals in fish and provide further insight to guide further lines of research on the involvement of light spectrum on fish physiology.

Many studies have investigated the impacts of marine cage fish farming on seabed sediments. Most of these studies have focused on organic loading or toxic chemicals used for the treatment of disease, normally for a single or a small number of sites over short time periods. Only very rarely has there been the opportunity to use large data sets consisting of a large number of fish farm sites over a long time scale. In Scotland, localised nutrient impacts have been well documented for marine cage salmon farms, but mixed effects of nutrient and chemicals such as SLICE (the active ingredient of which is emamectin benzoate) have not been investigated in the long term. The aim of this project was to investigate the ecological impacts on sediments from farming activities using very large spatial and temporal data to investigate the long term effects of nutrient and chemical waste. This was achieved using a metadata set collected from 403 sampling stations at 31 fish farms on the west coast of Scotland over a 9 year period. Data consisted of sediment macrofauna, carbon and nitrogen levels, redox potential, particle size for sediment characterisation and sediment concentrations of SLICE. The data was analysed for trends using statistical and multivariate analysis to look for changes in sediment community and related conditions, and the relationships between these parameters were investigated. At sampling stations that were less than 50 metres from the sea cages, 72% of the macrofauna communities were correlated with regard to their species composition and abundance. A significant relationship between the concentration of SLICE and sediment characteristics was represented as: SLICE= 0.000644*(median size particle size) + 0.0311*(C %) – 0.00213*(redox potential) + 1.453. Annelids were the most sensitive to the presence of emamectin benzoate, with the sipunculid Phascolion strombi, the echinoderm Ophiura affinis, and the custaceans Iphinoe, Diastylis and Iphimedia also showing sensitivity. During the data period, there was a clear change in species composition associated with improved seabed conditions. This correlated with biomass changes at the relevant sites, where there was a consequent decrease in nutrient input and SLICE usage. The statistical comparison of the AMBI and ITI indices indicated a 68.9% correlation, but they differed in their ability to indicate levels of organic disturbance. AMBI was shown to correlate more closely with conditions and thus a more reliable index when working with large databases. Univariate and multivariate analysis indicated that a combination of abundance (N), Shannon Wiener (H’) and AMBI, as biological indices for describing the status of the ecological level associated with the carbon percentage and redox potential of sediments gave the most reliable representation of environmental change over a series of sampling stations. In conclusion, the overall results suggest that, in the long-term, sampling stations which contained significant levels of SLICE had a higher impact status than those affected only by nutrient inputs. The accuracy of multiple regression models were increased by adding biotic and abiotic parameters, though fish biomass at the sites were not considered be as important factor for the prediction of impacts. However, this model could be sensitive to natural environmental conditions and variations. In light of these results and conclusions, recommendations can be made both for updating the existed environmental regulation of marine fish farms and in the development of meaningful models to relate sediment conditions to accurate estimations of overall environmental impacts.

Small-scale fishing communities along Cambodia’s coast have relied on marine resources as a mainstay of their livelihood for decades. However, in the last ten to fifteen years, a confluence of shocks such as increased fishing pressure, the rapid rise of commercial fisheries in the Gulf of Thailand, illegal, underreported and unregulated fishing, climate change and, more recently, sand mining, have contributed to a progressive decline in catch. Such challenges demand that fishers harness social traits of adaptability, responsiveness, persistence, planning, inter alia. In other words, there is a need for fishers and their households to demonstrate resilience in the face of such challenges. Though a contested term, scholars working within human-environment relations have adopted the concept of social-ecological resilience, acknowledging that the social aspects of resilience have been relatively under-addressed. Relatedly, studies on fishers and fishing communities have shown the important contribution fishing plays in fulfilling social and psychological needs, i.e. wellbeing, and how fishing is more than ‘just’ a livelihood. While evidence for this connection between fishing and wellbeing has been shown across different regions, the nature of this relationship is not as clear for coastal communities in Cambodia. Meanwhile, Cambodia has exhibited rapid economic growth (and foreign direct investment) over the past decade. Part of this has been through the creation of Special Economic Zones (SEZs) across the country. The creation of the SEZs and thus, the resultant labour demand has catalyzed migration of Cambodians to secondary cities and to the capital, Phnom Penh. Unlike other parts of the country, the experience of the lives of people on the move from the coastal regions of Cambodia remains less understood. Through qualitative work done among three coastal fishing villages in Koh Kong province in southwest Cambodia, I aim to contribute to a better understanding of the social dimensions of resilience by using a multidimensional (material, subjective, and relational) social wellbeing framework to not only better understand how migration affects the wellbeing of those who leave and those who stay, but also the implications on fishing as ‘a way of life’. My research focuses on understanding the role fishing plays, and the degree to which it impacts the wellbeing of fishers and their households in coastal Cambodia, in the context of migration. My empirical findings problematize the notion that fishing as a way of life supplants other dimensions (e.g. material/income) as observed elsewhere by considering outmigration of villagers from the fishing village. I find that the draw of alternative economic opportunities outside the coastal village has resulted in shifting values and opinions towards fishing as a livelihood particularly by younger villagers and has catalyzed their out migration. As a livelihood strategy, migration plays a crucial role in supplementing income from fishing and, in some cases, forms a critical lifeline for the poorest households. I also show how life in the coastal fishing village is filled with trade-offs and difficult choices people must navigate and negotiate, including tensions between various aspects within subjective dimensions of wellbeing. My thesis reveals the important, and sometimes dominant, influence of subjective and psycho-social factors on coastal villagers’ resilience and how this changes the way some view fishing itself. As such this research shows that adopting a social wellbeing lens can not only result in a better understanding of the impact of migration on coastal fishing communities in Cambodia but also broaden understanding of social resilience, for villagers and migrants who are facing a sea of environmental and economic change.