Dispersal and assimilation of an aquaculture waste subsidy in a low productivity coastal environment

Relationship between in feed drugs, antibiotics and organic enrichment in marine sediments at Canadian Atlantic salmon aquaculture sites

The presence of in-feed anti-sea lice drugs and their relationship with organic enrichment is poorly understood in sediment surrounding salmon farms. Using data from an aquaculture monitoring program (2018-2020), we describe this relationship at ten sites in four Canadian provinces. Three anti-sea lice pesticides (lufenuron, teflubenzuron, emamectin benzoate and metabolite desmethyl emamectin benzoate), and one antibiotic (oxytetracycline) were detected. Concentrations were often below limits of quantification. Values are also lower than those reported in other aquaculture salmon-producing countries. Highest concentrations, along with organic enrichment, were observed ~200 m of cages with lower concentrations detected up to 1.5 km away. Most samples had at least two drugs present: 75.2 % (British Columbia), 91.4 % (Newfoundland), and 54.8 % (New Brunswick/Nova Scotia) highlighting the potential for cumulative effects. Emamectin benzoate and oxytetracycline were detected four and three years respectively after last known treatments, demonstrating the need for research on overall persistence of compounds.

Organic contaminants in imported salmon feed and their effects on reef ecosystems in New Zealand

Organic matter from salmon farms has been shown to be assimilated by soft sediment and rocky reef communities within the ecological footprint of salmon farms. Given these findings, another question arises - What other chemicals in salmon feed may be assimilated into wild communities via organic waste from salmon farms? Here we measured a suite of organic contaminants in salmon feed, in organisms used in a controlled feeding experiment, and in reef species collected within the depositional footprint of salmon farms. Gas Chromatography-Tandem Mass Spectrometry was used to quantify trace concentrations of polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs) and current-use (CPUs) and historic-use pesticides (HUPs) in salmon feed imported to New Zealand. The effect of assimilation of farm-derived organic matter on contaminant profiles differed among species during the controlled feeding experiment and demonstrated that migration of individuals to a farm-associated site has the potential to increase or decrease organic contaminant concentrations. Concentrations of PCBs in Parapercis colias (blue cod), a highly resident, long-lived fish, were significantly higher at farm sites than at reference sites. While these concentrations were relatively low in a global context, this result presents blue cod as an important candidate for future monitoring of organic contaminants around point sources. PCBs and PBDEs measured in wild marine species were all below limits set by the European Union, whereas concentrations of certain HUPs, specifically dichlorodiphenyltrichloroethane (DDT) and its degradation products and endosulfan, may be of concern as a consequence of alternative anthropogenic activities. Overall, feed imported to New Zealand had relatively low levels of most organic contaminants that, at current levels, are unlikely to result in significant ecological effects to wild communities in adjacent habitats.

A quantitative analysis of organic matter inputs to soft sediment communities surrounding salmon farms in the Marlborough Sounds region of New Zealand

Local differences in trophic structure and composition of organic matter subsidies can influence the capacity of soft sediment communities to assimilate recycled organic matter from processes such as salmon farm enrichment. The present study combines biochemical analysis with biomass density information on soft sediment taxa collected within the depositional footprint of salmon farms and at reference sites in the Marlborough Sounds, New Zealand. Distinct biochemical signatures confirmed that the flux of organic matter from salmon farms was an important subsidy for soft sediment communities. Isotopic modelling demonstrated that the proportion of biomass supported by farm-derived organic matter did not change in a consistent pattern along the 300 m gradient from each farm site, whereas the average trophic level of communities decreased with increasing proximity to farms. High variability in both the total biomass and the distribution of biomass across trophic levels occurred among sites downstream of farms and among individual farms. Consequently, estimates of basal organic matter assimilation per unit area by communities differed by several orders of magnitude among sites. Total organic matter assimilation tended to decrease with increasing proximity to farms due to a shift towards a more detrital based community. Differences in basal organic matter assimilation among farms did not appear to be directly related to local flow regime, but instead was closely linked to differences in the soft sediment community composition likely influenced by an array of anthropogenic and environmental factors. The results presented here highlight the importance of considering local variability in basal organic matter source pools, and the potential for synergistic and cumulative effects to drive changes in food web trophodynamics when assessing the impacts of aquaculture on soft sediment communities.

Influence of aquaculture waste on fatty acid profiles and gonad maturation of wild fish aggregations at fish farms

Wild fish belonging to four species belonging to different trophic groups were captured at three distances from fish farm facilities: long distance (>5 Km), medium distance (1.5 Km) and close to sea-cages. Flesh, brain, liver and gonads were sampled for fatty acid analysis. Fish aggregated near sea-cages showed accumulation of fatty acids of vegetable origin in the studied tissues, due to surplus feed consumption or via predation of fish that consumed the feed. Gonads accumulated vegetable fatty acids in different manner in the different species, and the species least and most influenced by fish-feeds were selected for gonad histological examination. Results showed an acceleration of the final stages of the oocyte development in fish aggregated near fish farms compared to fish captured at long distance. Differences in oocyte development were more acute in the species which incorporated higher quantities of vegetable fatty acids.

Sociodemographic Variation in Consumption Patterns of Sustainable and Nutritious Seafood in Australia

National dietary guidelines (DGs) consistently recommend consuming seafood for health benefits, however, the sustainability of increasing seafood consumption is often challenged. Seafood products vary in environmental performance as well as health benefits, yet there is no information integrating the health and ecological impacts of different seafood choices. The first step in optimising improved health and environmental outcomes is to examine more closely the types of seafood being consumed at population and individual levels, to develop the means to increase the intake of seafood that is optimal for human health and the environment. The purpose of this analysis was to better understand the specific types and amounts of seafood consumed by the Australian population, and by socioeconomic subgroups within the population, to determine the relative nutritional content and sustainability of seafood consumed by these groups. Secondary analysis of the Australian Health Survey (AHS) (2011-2013), which reached 32,000 people (25,000 households) was undertaken. The majority of respondents (83%) did not consume any seafood on the day of the survey. Results indicated the proportion of seafood consumers was lowest among adults who were unemployed, had the least education and were the most socio-economically disadvantaged. Crustaceans and farmed fish with low omega 3-content, such as basa and tilapia, were identified as the least nutritious and least sustainable seafood categories. These two categories constituted a substantial amount of total seafood intake for the lowest socio-economic consumers, and over 50% for unemployed consumers. In contrast, consumers in the highest socio-demographic group consumed mainly high trophic level fish (moderate nutrition and sustainability) and farmed fish with high omega-3 content (high nutrition, moderate sustainability). Fewer than 1% of adults or children reported eating seafood identified as both more nutritious and less resource intensive, such as small pelagics or molluscs. Opportunities exist to increase seafood intakes to improve health outcomes by varying current seafood consumption patterns to maximise nutritional outcomes and minimise environmental impacts. Initiatives to promote the health and environmental benefits of seafood should be promoted at the population level, with targeted interventions for specific groups, and should encourage consumption of highly nutritious low resource intensive types of seafood.

Biogeochemical markers across a pollution gradient in a Patagonian estuary: A multidimensional approach of fatty acids and stable isotopes

A combined approach merging stable isotopes and fatty acids was applied to study anthropogenic pollution in the Río Negro estuary. Fatty acid markers of vegetal detritus indicated considerable allochthonous inputs at freshwater sites. Correlative evidence of diatom fatty acids, δ¹³C, chlorophyll and particulate organic matter suggested the importance of diatoms for the autochthonous organic matter production at the river mouth. Low δ¹⁵N values (~0‰) and high fatty acid 18:1(n-7) concentrations in the suspended particulate matter, in combination with the peaks of coliforms and ammonium, indicated a strong impact of untreated sewage discharge. The ¹⁵N depletion was related to oxygen-limited ammonification processes and incorporation of ¹⁵N depleted ammonium to microorganisms. This work demonstrates that the combined use of lipid and isotopic markers can greatly increase our understanding of biogeochemical factors and pollutants influencing estuaries, and our findings highlight the urgent need for water management actions to reduce eutrophication.