Tim Dempster

Understanding how farmed salmonids sense and respond to their environment is key to securing animal welfare and efficient production. However, hearing has rarely received attention, despite the omnipresence of underwater sound and its potential effects. We describe how and what salmonids hear, and explore how hearing may differ between wild and farmed conspecifics. We then conduct two systematic reviews, to: (1) understand the existing soundscapes experienced by farmed salmonids; and (2) identify potential short‐ and long‐term impacts of sound on salmonid behaviour and physiology. Sound can be measured via pressure changes or particle motion; pressure levels are commonly reported, whilst particle motion is rarely measured due to logistical challenges. Salmonids have an open, physostomous swim bladder, relying primarily on their lateral line to sense sound via particle motion. Because of this, they are most sensitive to low frequencies, with startle responses most apparent between 7 and 400 Hz. Few studies have tested for effects of sound on salmonid physiology, although there is evidence that some sound exposure regimes lead to chronic stress, whilst very loud sounds (e.g., cumulative sound exposure level > 216 dB re 1 μPa ² a) can cause fatal injuries. Quantifying salmonid aquaculture soundscapes, their potential welfare impacts, and strategies to mitigate these impacts should form a new frontier in salmonid aquaculture research. We make a series of recommendations, specifically: (1) conduct targeted research to fill knowledge gaps; (2) develop a standardised protocol to measure and report sound in salmonid aquaculture; and (3) apply mitigation strategies to reduce impacts of noise.

Introduction: The flat oyster Ostrea angasi previously formed extensive reefs throughout temperate regions of Australia. These reefs were overharvested and destroyed after European colonization and have been functionally extinct for >150 years. While large‐scale subtidal O. angasi restoration has occurred, there are no intertidal restoration attempts despite historical occurrence. Further, while facilitative relationships with subtidal foundation species have been explored, intertidal species have received little consideration. Objectives and Methods: We investigated the feasibility of intertidal restoration by testing O. angasi survival and growth across intertidal elevations spanning the shallow subtidal to low intertidal across three sites in Victoria, Australia. Further, we tested if co‐occurring foundation species—seagrass ( Zostera muelleri ) and mangroves ( Avicennia marina )—can facilitate O. angasi survival and growth. Results: Oyster survival varied between sites and elevations. At one site, survival probability increased with decreasing elevation. Mangroves facilitated oyster survival at one site, likely through reduced temperature and light conditions. However, all oysters at this site died within 5 months post‐deployment. At another site, only oysters deployed under mangroves survived the entire duration of the experiment. We found no evidence of seagrass facilitation on growth and survival. Conclusion: This study provides the first evidence that O. angasi can survive in the intertidal. While shallow water restoration appears feasible, survival will likely depend on underlying site conditions. Exploring novel restoration strategies for functionally extinct shellfish ecosystems can help bring these ecologically, culturally, economically, and socially important ecosystems back into coastal areas.

Global declines in marine shellfish have resulted in widespread efforts to restore populations. Previous research has predominantly focused on substrate‐limited rather than recruitment‐limited systems, yet given increased use of aquaculture‐produced stock to restore marine bivalves, there is a need to understand differences in the survival of hatchery‐produced and translocated wild stock. We conducted a systematic review and synthesis of studies that quantified the survival of outplanted marine bivalves. The systematic review identified 893 unique stocking events across 111 studies for 29 species across 10 families. Most research has occurred in temperate regions (73%), across four bivalve families (Ostreidae 37%, Pectinidae 20%, Veneridae 16% and Mytilidae 11%). More stockings have outplanted hatchery‐produced (66%) than translocated stock (34%). We conducted quantitative analyses for five species to determine how stock origin, size at outplant, outplant density, substrate co‐deployment, predator exclusion and time since outplant influences survival. Survival consistently decreased through time across all species. Substrate co‐deployment, stock origin and size at outplant did not influence survival, while predator exclusion and outplant density affected some species. Synthesis and applications. Our analyses broadly demonstrate variability in the survival of outplanted bivalves through time, however predicted survival was poor after 2 years (<3%). Generally low survival highlights difficulties associated with conducting scalable restoration in recruitment‐limited systems. Based on our findings, using hatchery‐produced stock, mitigating predation and outplanting epifaunal bivalves at high densities may increase survival probabilities when outplanting stock for restoration. Further exploration is needed to understand whether use of aquaculture‐produced stock results in similar ecosystem structure, function, and service provisioning to natural and restored shellfish reefs in recruitment‐limited systems.

Formulated diets are a critical driver of the productivity and effectiveness of commercial abalone aquaculture. As a major component of production costs, the industry is always searching for new dietary ingredients that can improve production performance. Asparagopsis armata is a species of red macroalgae entering commercial scale production with potential as an additive to formulated abalone feeds. Here, we tested the effects of the inclusion of Asparagopsis (0, 1, 3 and 5% dry weight) in formulated feeds on the growth and production characteristics of abalone. The inclusion of Asparagopsis increased growth of the hybrid abalone (Haliotis rubra x H. laevigata) by up to 10% over 3 months but did not alter the growth of greenlip abalone (H. laevigata). Dry weight inclusion of 3% of Asparagopsis produced the greatest growth increase. Colour of new shell growth differed in the 3% and 5% inclusion diets compared to 0 and 1%, but at levels that are likely imperceptible to consumers. Our results demonstrate that Asparagopsis is a promising new feed ingredient for abalone diets pending further testing over longer time scales, abalone sizes and in differing environmental conditions.

Understanding spatio-temporal variability in the production of drift macroalgae is useful for monitoring and assessing the influence of local anthropogenic nutrient sources on coastal ecosystems. In this study we: (1) assessed how the drift macroalgal community composition and biomass have changed over a 22-year period in Port Phillip Bay (a large coastal embayment in Victoria, Australia); and (2) measured the amount of accumulated nitrogen in drift macroalgae and the contribution of anthropogenic nitrogen sources through isotopic analysis. The surveys revealed little overlap in species composition ( 17‰ and ~ 3% N content) at depths and locations close to nutrient sources, particularly at times of the year when large wastewater discharges occur. Harvesting of drift macroalgae could be a cost-effective solution for offsetting nitrogen inputs from anthropogenic sources, but it will be important to first investigate whether harvesting results in negative impacts to associated fauna or nutrient cycling.

Aquaculture creates ‘aquatic foods’ such as fish, shellfish, and seaweeds that are critical for food security. Gene editing using CRISPR‐Cas9 has the potential to transform aquaculture by improving animal welfare, nutritional attributes, and farming efficiency, with benefits for environmental sustainability. However, gene editing also poses risks of harm via side effects on other important traits or genetic introgression into wild populations. Public acceptance of gene edited aquatic species will rapidly erode if risk mitigation is ineffective or not applied. Here, we review the benefits and risks for gene editing in aquaculture. A general framework for risk–benefit analysis of gene editing in aquaculture is proposed, incorporating nine key considerations: genetic impacts, ecological impacts, disease risk mitigation, nature of edit, supply chain environmental footprint, animal welfare, human nutrition, ethical business implications and impacts on local communities. When applied on a case‐by‐case basis, the framework will help identify how gene editing of a farmed species can most enhance production and nutritional benefits while minimising harms to animal welfare, the environment, and society.

As aquaculture expands, ensuring the sustainability of practices requires a focus on minimising environmental effects. At the same time, where fish are cultured, their welfare needs to be secured to ensure compliance with legislation and gain social acceptance of farming practices. However, clear conflicts exist between protecting the environment and protecting welfare where either environmental or welfare outcomes are traded off against each other. We document 5 cases in aquaculture where environmental sustainability and welfare principles are antagonistic. If knowledge or management of environmental sustainability or welfare is weak in a specific setting, the best outcome may not be achieved. We contend that identifying conflicts between desired environmental and welfare outcomes as early as possible will allow for knowledge-based consideration of trade-offs using the best available evidence. Further, where different departments of regulators are responsible for different outcomes, targeted collaboration focused on identifying conflicts should reduce instances of unconscious trade-offs. Reducing conflicts between the 2 goals of good welfare and environmental protection should promote both ecologically and ethically sustainable aquaculture.

Disease and parasitism cause major welfare, environmental and economic concerns for global aquaculture. In this review, we examine the status and potential of technologies that exploit genetic variation in host resistance to tackle this problem. We argue that there is an urgent need to improve understanding of the genetic mechanisms involved, leading to the development of tools that can be applied to boost host resistance and reduce the disease burden. We draw on two pressing global disease problems as case studies—sea lice infestations in salmonids and white spot syndrome in shrimp. We review how the latest genetic technologies can be capitalised upon to determine the mechanisms underlying inter‐ and intra‐species variation in pathogen/parasite resistance, and how the derived knowledge could be applied to boost disease resistance using selective breeding, gene editing and/or with targeted feed treatments and vaccines. Gene editing brings novel opportunities, but also implementation and dissemination challenges, and necessitates new protocols to integrate the technology into aquaculture breeding programmes. There is also an ongoing need to minimise risks of disease agents evolving to overcome genetic improvements to host resistance, and insights from epidemiological and evolutionary models of pathogen infestation in wild and cultured host populations are explored. Ethical issues around the different approaches for achieving genetic resistance are discussed. Application of genetic technologies and approaches has potential to improve fundamental knowledge of mechanisms affecting genetic resistance and provide effective pathways for implementation that could lead to more resistant aquaculture stocks, transforming global aquaculture.

Amoebic gill disease (AGD) is a significant health issue for Atlantic salmon farmed in a marine environment. While the disease is currently managed using freshwater or hydrogen peroxide baths, there is a need to develop other treatments. The aims of this study were to examine the effect of salinity (0 ppt and 35 ppt) and temperature (3 °C and 15 °C) on attachment and survival of Neoparamoeba perurans in vitro over short exposure times (15 min and 2 h) and to assess the efficacy of reduced temperature (3 °C) as treatment for Atlantic salmon affected by AGD. In vitro freshwater 3 °C was at least as effective as freshwater 15 °C and the attachment was significantly lower after 2 h in freshwater 3 °C than freshwater 15 °C. In vivo there was no difference between the fish treated with freshwater 15 °C for 2 h or freshwater 3 °C. This study showed that despite exposure to low temperature reducing attachment of N. perurans to their substrate in vitro, 15 min cold-water bath treatment was not more effective at reducing AGD in Atlantic salmon than current commercial 2 h freshwater bath.

Dispersal is a critically important process that dictates population persistence, gene flow, and evolutionary potential, and is an essential element for identifying species conservation risks. This study aims to investigate the contributions of dispersal syndromes and hydrographic barriers on patterns of population connectivity and genetic structure in fishes occupying the particularly rugged and fragmented landscape of the Kimberley Plateau, Western Australia. We assessed population genetic structure between three neighbouring catchments (the Mitchell, King Edward, and Drysdale rivers) in three congeneric groups of freshwater fishes that exhibit varied dispersal syndromes within and among groups: (1) Melanotaenia australis and M. gracilis; (2) Syncomistes trigonicus and S. rastellus; and (3) Hephaestus jenkinsi and H. epirrhinos. Within each species we sampled the upper, middle, and lower reaches of each catchment and assessed patterns of gene flow between and within catchments using microsatellite markers. Our results suggest that contemporary connectivity between catchments is greatly limited or absent in all study species, regardless of their dispersal syndromes. However, gene flow within catchments varied in line with predicted dispersal potential, with poor dispersers exhibiting limited gene flow and significant genetic structuring. We conclude that the rugged landscape and historical habitat isolation has contributed to patterns of population fragmentation among fish populations from different river catchments. However, it appears dispersal syndromes influence connectivity and gene flow within catchments, where landscape constraints are not as pervasive. This study presents a comparative population genetic analysis of freshwater fishes with differing dispersal syndromes and colonisation ability. Our findings provide new insights into factors shaping patterns of biodiversity on the Kimberley Plateau, and the evolutionary uniqueness of fish communities from different river catchments draining the plateau. More broadly, they highlight the importance of accounting for dispersal‐related traits when planning management and conservation strategies.