Macroalgae farms can be used to remove excess nitrogen, phosphate, and trace minerals from coastal marine waters. Genera such as Asparagopsis have been highlighted through previous research as efficient biofilters of wastewater from salmon farms, in the context of Integrated Multitrophic Aquaculture (IMTA). Despite recent interest in Asparagopsis-derived products and the promise shown by IMTA, macroalgae cultivation is still a minor industry in Australia, with its bioremediation potential relatively untested.

Our project will use utilize previous research on the physiology of Asparagopsis and other valuable native macroalgaes genera (including Macrocystis, Ecklonia, Lessonia, Porphyra and Ulva) within an established model of macroalgae growth, to assess the bioremediation potential of these genera across a broad range of environmental conditions. The model will be calibrated and validated using data from previous field trials involving targeted species where possible. We will construct scenarios that assess how farm arrangement influences nutrient remediation efficacy, providing valuable insights for optimizing cultivation strategies including cultivation depth, harvesting frequency and seasonality, and the possibility of multiple partial harvests. We will also test the robustness of key results to changes and uncertainties in species’ parameterisation.

We will then apply the model within a wide range of environmental conditions representative of different growing regions in coastal Australian waters. This approach will allow us to identify and address challenges specific to bioremediation across different states and macroalgae genera, contributing to a comprehensive understanding of the feasibility and implications of this innovative and low-impact approach to nutrient remediation. This research will not only inform practical cultivation strategies but also provide knowledge of environmental impacts and tools for future regulations and research.

Furthermore, the project serves as a catalyst for interdisciplinary collaboration and knowledge exchange, engaging stakeholders from scientific, industrial, and regulatory domains. By disseminating findings and facilitating dialogue, we aim to inform policy decisions, and empower stakeholders with the knowledge needed to best support innovation in this field.

Given the significant management changes that are likely to be made, there is a critical need to ensure that, model assumptions and knowledge gaps are addressed to predict recovery trajectories more accurately, and more effectively evaluate management strategies. These actions should be taken with the values and aspirations of recreational fishers at the forefront.

Implementing new management settings, which will be significantly more restrictive than current catch and size limits, will require a coordinated and collegial engagement and awareness program to minimise loss of social licence and political risk. Stewardship is a recognised component of improving societal practices across a range of areas. Improving stewardship through knowledge brokering has great potential to complement and enhance regulatory initiatives designed to protect ecosystem function through sustainable resource management. The strength of stewardship over regulatory initiatives is the genuine drive of individuals to contribute to improved societal norms through a learned and shared understanding of the benefits of the activity that is being advocated for. On the other hand, regulatory approaches can be met with a degree of skepticism and resistance due to a lack of understanding of the purpose of the regulations and a natural resistance of being ‘told what to do’. However, with increased marine literacy, compliance to and acceptance of regulatory policies can be increased. Effective communication, engagement and stewardship programs are increasingly recognised as mechanisms to enhance marine literacy and deliver positive behavioural change through engaged and interactive programs. This project will include a sector led stewardship program and a suite of communication and engagement initiatives by all co-investigator agencies (Government, Recreational Fishing Peak Body and research) with effective management and delivery of these initiatives facilitated by coordination groups.

Objective 1. Model development

Methods to assess sand flathead population status (biomass relative to limit and target reference points) and fishing pressure (fishing mortality relative to natural mortality) have recently been advanced through FRDC project 2020-005. These methods now include a combination of classic assessment approaches (e.g., the von Bertalanffy growth model and catch curve analyses) as well as more recent methods to estimate relative biomass (e.g., LBSPR and LBB estimation approaches). However, all assessment approaches developed to date are equilibrium-based. Here, the size-frequency distribution of a sample is compared to a theoretical prediction of the species’ size frequency distribution’ in the absence of fishing. These equilibrium-based models assume that populations are at a stable state and do not change significantly over time. They are also based on the principle of maximum sustainable yield and are used to determine the maximum number of fish that can be harvested sustainably. While equilibrium-based models are useful for setting sustainable harvest limits, temporal models are more appropriate for evaluating the long-term impacts of management strategies and predicting future changes in fish populations by explicitly considering the progression of cohorts from small to large size classes.

Temporal models are based on the idea that populations are constantly changing over time in response to various biological and environmental factors, including fishing pressure. These models simulate the dynamics of the population over time and can be used to evaluate and monitor the impacts of different management strategies. Evaluating fisheries management strategies using temporal population dynamic models involves building mathematical models that simulate the population dynamics of the targeted fish species over time. These models incorporate various biological and environmental factors that influence the population, such as growth rates, mortality rates, and fishing pressure. By manipulating the input parameters, the models can simulate the effects of different management strategies on the fish population, allowing for the evaluation of various scenarios. These models can provide valuable information on how different management strategies might impact the population, enabling managers to make informed decisions to achieve desired conservation or 'value maxima' objectives. Overall, temporal population dynamic models are the best tool for evaluating fisheries management strategies and for supporting sustainable management decisions.

Objective 2. Understanding spatial connectivity of population

It is likely that sand flathead are relatively resident (Tracey et al., 2020), but effective spatial management and understanding of stock recovery rates will require a better understanding of stock connectivity. This will be used to assist the spatially explicit components of the models proposed in this project. To understand sand flathead movements and space-use, we will use population genetic tools as well as passive tagging. There is some evidence that sand flathead move into deeper water during spawning season (Tracey et al., 2020). Through a tagging study, this project seeks to better understand spawning migrations as well as get a better understanding of the location of important spawning areas.

In addition to tagging, a genetic assessment will be undertaken to determine if Tasmanian sand flathead populations are genetically distinct. Processes such as genetic drift can lead to significant divergence of genetic signals between demographically isolated groups (i.e., stocks). This component of the study will test a number of possible stock scenarios for sand flathead across Tasmania to determine the level of connectivity between regions. Stock scenarios will be tested using Next-Generation Sequencing technology and single-nucleotide polymorphism (SNP) markers.

Objective 3. Understanding phenotypic variability and potential impacts of fishery-induced evolution.

The identification of phenotypic variability both within and between sand flathead populations has added significant complexity to the sand flathead rebuilding strategy. Despite an overall decline in mean individual size, populations of both large and fast-growing individuals remain (Bani and Moltschaniwskyj 2008, Fraser et al 2022). This represents a unique opportunity to determine the impacts of fishery-induced evolution and identify the factors that influence individual growth rates, performance and vulnerability to catch. This information will be necessary for a potential fisheries enhancement program and in parameterising assessment models that predict species recovery. The proposed study will therefore assess several physiological and behavioural parameters relevant to energy use and uptake between individuals from ‘high’ and ‘low’ performing populations. It’s likely that variations in physiological traits like metabolism and swimming performance may translate to different capture vulnerabilities between phenotypic groups.

Individual sand flathead will be collected from multiple populations and measured for a range of physiological parameters such as metabolic rate, aerobic scope, appetite, growth, digestive efficiency, thermal tolerance, swimming performance, recovery rate, capacity for acclimation and behavioural traits like boldness/aggression. Through this assessment, we aim to gain a better understanding of specific traits that have contributed to the decline in overall performance observed in fish from some regions and identify associated impacts from fisheries induced evolution.
The findings of this study will therefore be used to inform sustainable fishing practices that contribute to the conservation and restoration of depleted populations of sand flathead in Tasmania. This understanding may also allow us to identify desirable traits for promotion in potential stock enhancement programs to enhance the recovery and future sustainability of this species and also included as a variable in stock assessment and MSE models.

Objective 4. Education, Communication, Engagement and Stewardship initiatives

DNRET, IMAS and TARFish are all currently contributing to education, communication and engagement around Sand Flathead research and management. DNRET have developed the ‘Flathead For the Future’ education, communication and engagement program and will continue to evolve and deliver this initiative as an in-kind contribution to this broader application. IMAS have been working with both DNRET and TARFish to develop publicly available and digestible material explaining the current research and knowledge of Sand Flathead and the need for management intervention.

Part of the funding requested through this application will facilitate the development of a stewardship program led by TARFish with a coordination group comprising stewardship subject matter experts, two TARFish board members and two members of this project team to ensure continuity and linkages with the wider project (one from DNRET and one from IMAS).

All the education, communication, engagement and stewardship initiatives will be guided by the results/outcomes of the initial research findings of Objective 6, outcomes of FRDC project (2021-116: Recreational fishers in Tasmania: understanding experiences, behaviours, drivers, communication needs and change factors) and the IMAS project (DNRET funded) which is currently being finalised titled ‘Understanding flathead fishers to develop acceptable management options and maximise the effectiveness of stewardship initiatives’. The DNRET project aims to better understand flathead fishers to 1) develop management settings that are widely acceptable; and 2) inform the development, promotion and targeting of engagement and outreach activities. The stewardship program will also be guided by insights from the success of the Tuna Champions program (FRDC projects: 2017-123 & 2021-086). The TARFish stewardship program will complement the DNRET ‘Flathead for the future’, which focuses on increasing marine literacy on the needs for the proposed/implemented management regulations (policy acceptance). The stewardship program will be a sector led initiative focusing on an outcome of societal behavioural change (social norms) to enhance the welfare of the fish and fish stocks.

Objective 5. Experimental testing of communication, engagement and stewardship program outcomes

An important component of this study is testing the effectiveness of the education, communication, engagement and stewardship initiatives. This will be done using a range of metrics but the central assessment method will be a field framed behavioural experiment run by staff at the Utas Behavioural Sciences Laboratory. The objective of the framed field behavioural experiment is to comprehensively test and analyse the behavior patterns and decision-making processes of recreational fishers in order to gain a deeper understanding of their actions, motivations, and potential impact on fish populations and ecosystems but also understand how their values can be incorporated into effective fisheries management. Through this experiment, we aim to gather valuable insights into the factors that influence fishers' behavior, such as catch preferences, angling techniques, adherence to fishing regulations, and environmental considerations. The findings from this research will inform evidence-based fisheries management strategies and contribute to the sustainable conservation of aquatic resources while promoting the recreational fishing experience.

We will subject the different outcomes of the stewardship program to rigorous scientistic testing to ensure their effectiveness. Candidates for testing include all outcomes including website and video content, messaging for print and social media and branding elements. The purpose of the education, communication, engagement and stewardship initiative research is to develop audience-appropriate and targeted messaging and content. These outcomes are promising candidates for effective interventions. However, the effectiveness of these outcomes is an empirical question. Adoption requires establishing an appropriate evidence base for their effectiveness. In particular, any proposed interventions need to be tested in the specific environment in which they are to be deployed, including the context of their use and the demographics and characteristics of the targeted population.