Understanding population structure and dynamics of Victoria’s developing Octopus fishery

Project number: 2019-031
Project Status:
Current
Budget expenditure: $561,140.00
Principal Investigator: Jayson M. Semmens
Organisation: University of Tasmania
Project start/end date: 31 Dec 2019 - 30 Dec 2022
Contact:
FRDC
TAGS
Sustainability
Stock Assessment
Rac Vic
Rac Tas
Population Dynamics
SPECIES
Octopuses

Need

In Victoria, Octopus spp. are predominantly a byproduct species caught across various fisheries. Pale Octopus is not differentiated from other octopus species in catch and effort reporting in Victoria, making it difficult to apply stock assessment methods or catch rate indicators. Maori Octopus (Octopus maorum) are likely caught in the Victorian Rock Lobster Fishery (VRLF); whereas Pale Octopus and Gloomy Octopus (Octopus tetricus) are caught within the Inshore Trawl Fishery, Ocean Access Fishery (OAF), Corner Inlet Fishery (CIF) and Port Phillip and Westernport Bay Fishery (PPWPBF). Targeting octopus using 'shelter traps' within the OAF off Lakes Entrance has significantly increased in 2016 and 2017. The average catch during this period was ten times greater compared with the average catch taken from 2006–2015. With the potential for a developing fishery, management is lacking fundamental information to assist in guiding and building a sustainable fishery. For example, there is no requirement to identify and report quantities of species caught. This makes any sort of assessment impossible. Presently, two license holders actively fish for octopus with a capacity to have many more within the OAF.

Objectives

1. Species identification: * Develop identification keys to ensure octopus are identified to at least the three main species and to ensure collection of accurate catch and effort data.
2. Biological characteristics:* Determination of age, growth and reproduction information.* Determine population structure to inform appropriate spatial scale for management.
3. Development of appropriate biomass indicators and analysis for assessment:* Implement pot sampling regime to enhance the understanding of fishery impact particularly at relatively small spatial scales.* Development and assessment of performance indicators to monitor biomass and stock status.
4. Development of fisheries management tools: * Identify appropriate spatial management tools based on stock structure defined in objective 2a. * Identify an objective approach for setting limit and target reference points for the indicators developed in objective 3. * Provide an overview of possible management tools and their suitability for the Victorian octopus fishery given the identified biological characteristics in objectives 1 and 2.* Using a process identified by VFA develop one or more harvest strategy proposals.

Related research

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research
Industry
Environment
Industry

Estimating the biomass of fish stocks using novel and efficient genetic techniques

Project number: 2019-016
Project Status:
Current
Budget expenditure: $494,794.00
Principal Investigator: Meaghan Duncan
Organisation: Department of Primary Industries and Regional Development (NSW)
Project start/end date: 3 Nov 2019 - 29 Sep 2024
Contact:
FRDC
TAGS
Stock Assessment
Rac Nsw
Population Dynamics
Fishing Gear
Fisheries Management
SPECIES
Mulloway
Murray Cods

Need

The effective management of fisheries resources implicitly requires accurate abundance estimates. But, even after more than a century of effort, this prerequisite need remains one of the greatest challenges facing fisheries scientists. Traditional methods of estimating abundance include parametric and empirical approaches that often rely on extensive time-series of size-at-age data (e.g. from otoliths). Acquiring these data can be expensive and therefore restricted to species that are most economically important or of conservation concern. Due to the cost of independent sampling, indicators of abundance usually involve fishery-dependent data, which have numerous biases that can affect accurately quantifying population trends.

The clear need for accurate and rapid stock assessments is increasingly apparent in the current climate of competing commercial, recreational and conservation interests. Specifically, marine protected areas have been implemented across all NSW coastal bioregions and are a source of political and public contention as a result of perceived inequalities in access to (and allocation of) fisheries resources, particularly among species shared by commercial and recreational fishers. Also, recent fish kills in NSW due to hypoxic water have sparked debate over the cause of poor water quality and longer-term effects on freshwater habitats. Rapidly quantifying existing and/or changing stock abundances of key species will be essential to inform recovery actions, and advise on the sustainable exploitation of commercial and recreational species. Sampling eDNA could meet these needs by directly facilitating cost-effective biomass and/or relative abundance estimates for population assessments in NSW where fishery-dependent data are scarce or unavailable.

Objectives

1. Assess the species-specific precision and importance of key influencing abiotic and biotic factors for determining abundances of mulloway and Murry cod using eDNA under controlled conditions.
2. Compare the utility of eDNA against directed fishery-dependant methods for assessing relative abundances of mulloway and Murray cod across appropriate spatio-temporal scales in the wild.
3. Based on results of phase 2, determine what additional factors affect concentration of eDNA such as depth of eDNA water sampling.
4. Assess if eDNA of other selected species collected from samples obtained during 2 above, correspond to routinely collected catch-and-effort data in New South Wales.

Final report

ISBN: 978-1-76058-824-3
Author: Meaghan L. Rourke and Matt K. Broadhurst
Final Report • 2024-09-30 • 23.46 MB
2019-016-DLD.pdf

Summary

This project represents the first detailed study exploring the relationship between eDNA concentrations and the biomass and/or abundance of some economically and ecologically important (primarily freshwater) fish species in Australia. The work was conducted over four-and-a-half-years as part of a collaboration between the New South Wales Department of Primary Industries and Regional Development (NSW DPIRD), the University of Canberra (UC) and the Australian Museum. Broadly, the project concept was to address a critical need for accurate and timely non-lethal population assessments involving environmental DNA (eDNA) to compliment and/or eventually replace fishery-dependent monitoring methods. Justification for this concept was based on positive outcomes from recent and ongoing international efforts. 

The literature review identified 63 relevant papers investigating relationships between eDNA and biomass and/or abundance, with biases towards salmonids and cyprinids, and mostly from the United States and Japan. These studies predominantly utilised species-specific detection methods and reported positive correlations for various fish species in the field (60% of publications), controlled environments (25%) or a combination of both (14%). However, the review also highlighted uncertainties regarding absolute biomass or abundance estimates due to environmental factors affecting DNA dynamics in freshwater and marine ecosystems—emphasising the need for controlled pilot studies to address these limitations. Consequently, the design of phase-2a aquaria experiments assessed the importance of key factors such as water temperature on eDNA concentrations.

During the phase-2a aquaria work, species-specific assays were developed for Murray Cod, Mulloway, and Golden Perch. The results indicated there was a significant quadratic relationship between biomass and eDNA concentration for Murray Cod, whereby eDNA increased in tanks containing up to 180 g of Murray Cod, but then decreased as Murray Cod weights exceeded 200 g. This outcome was attributed to excessive variability in DNA shedding rates among individuals and possibly exacerbated by a species-specific response to confinement. In contrast, promising findings were observed for Golden Perch and Mulloway, with significant positive relationships between eDNA concentrations and biomass, despite some variability in shedding rates among the latter species.

Phase-2b field trials further validated the potential of eDNA as an indicator of fish biomass, and in some cases, abundance. Notably, experiments with Golden Perch revealed a useful significant positive quadratic relationship between eDNA concentration and biomass, while the Mulloway trials showed a significant positive relationship between eDNA concentration and biomass and an almost significant positive relationship with abundance, but (for both) only during autumn. Bony Bream also had useful positive linear relationships between their eDNA concentration and biomass and abundance and a significant negative relationship between eDNA and flow. Similarly, and despite few attributable impacts detected in aquaria, in their natural environment Murray Cod biomass (but not abundance) was characterised by a significant (but weaker) positive linear relationship with eDNA concentration, as well as a significant but weak negative relationship with flow. 
Final Report • 2024-09-30 • 23.46 MB
2019-016-DLD.pdf

Summary

This project represents the first detailed study exploring the relationship between eDNA concentrations and the biomass and/or abundance of some economically and ecologically important (primarily freshwater) fish species in Australia. The work was conducted over four-and-a-half-years as part of a collaboration between the New South Wales Department of Primary Industries and Regional Development (NSW DPIRD), the University of Canberra (UC) and the Australian Museum. Broadly, the project concept was to address a critical need for accurate and timely non-lethal population assessments involving environmental DNA (eDNA) to compliment and/or eventually replace fishery-dependent monitoring methods. Justification for this concept was based on positive outcomes from recent and ongoing international efforts. 

The literature review identified 63 relevant papers investigating relationships between eDNA and biomass and/or abundance, with biases towards salmonids and cyprinids, and mostly from the United States and Japan. These studies predominantly utilised species-specific detection methods and reported positive correlations for various fish species in the field (60% of publications), controlled environments (25%) or a combination of both (14%). However, the review also highlighted uncertainties regarding absolute biomass or abundance estimates due to environmental factors affecting DNA dynamics in freshwater and marine ecosystems—emphasising the need for controlled pilot studies to address these limitations. Consequently, the design of phase-2a aquaria experiments assessed the importance of key factors such as water temperature on eDNA concentrations.

During the phase-2a aquaria work, species-specific assays were developed for Murray Cod, Mulloway, and Golden Perch. The results indicated there was a significant quadratic relationship between biomass and eDNA concentration for Murray Cod, whereby eDNA increased in tanks containing up to 180 g of Murray Cod, but then decreased as Murray Cod weights exceeded 200 g. This outcome was attributed to excessive variability in DNA shedding rates among individuals and possibly exacerbated by a species-specific response to confinement. In contrast, promising findings were observed for Golden Perch and Mulloway, with significant positive relationships between eDNA concentrations and biomass, despite some variability in shedding rates among the latter species.

Phase-2b field trials further validated the potential of eDNA as an indicator of fish biomass, and in some cases, abundance. Notably, experiments with Golden Perch revealed a useful significant positive quadratic relationship between eDNA concentration and biomass, while the Mulloway trials showed a significant positive relationship between eDNA concentration and biomass and an almost significant positive relationship with abundance, but (for both) only during autumn. Bony Bream also had useful positive linear relationships between their eDNA concentration and biomass and abundance and a significant negative relationship between eDNA and flow. Similarly, and despite few attributable impacts detected in aquaria, in their natural environment Murray Cod biomass (but not abundance) was characterised by a significant (but weaker) positive linear relationship with eDNA concentration, as well as a significant but weak negative relationship with flow. 
Final Report • 2024-09-30 • 23.46 MB
2019-016-DLD.pdf

Summary

This project represents the first detailed study exploring the relationship between eDNA concentrations and the biomass and/or abundance of some economically and ecologically important (primarily freshwater) fish species in Australia. The work was conducted over four-and-a-half-years as part of a collaboration between the New South Wales Department of Primary Industries and Regional Development (NSW DPIRD), the University of Canberra (UC) and the Australian Museum. Broadly, the project concept was to address a critical need for accurate and timely non-lethal population assessments involving environmental DNA (eDNA) to compliment and/or eventually replace fishery-dependent monitoring methods. Justification for this concept was based on positive outcomes from recent and ongoing international efforts. 

The literature review identified 63 relevant papers investigating relationships between eDNA and biomass and/or abundance, with biases towards salmonids and cyprinids, and mostly from the United States and Japan. These studies predominantly utilised species-specific detection methods and reported positive correlations for various fish species in the field (60% of publications), controlled environments (25%) or a combination of both (14%). However, the review also highlighted uncertainties regarding absolute biomass or abundance estimates due to environmental factors affecting DNA dynamics in freshwater and marine ecosystems—emphasising the need for controlled pilot studies to address these limitations. Consequently, the design of phase-2a aquaria experiments assessed the importance of key factors such as water temperature on eDNA concentrations.

During the phase-2a aquaria work, species-specific assays were developed for Murray Cod, Mulloway, and Golden Perch. The results indicated there was a significant quadratic relationship between biomass and eDNA concentration for Murray Cod, whereby eDNA increased in tanks containing up to 180 g of Murray Cod, but then decreased as Murray Cod weights exceeded 200 g. This outcome was attributed to excessive variability in DNA shedding rates among individuals and possibly exacerbated by a species-specific response to confinement. In contrast, promising findings were observed for Golden Perch and Mulloway, with significant positive relationships between eDNA concentrations and biomass, despite some variability in shedding rates among the latter species.

Phase-2b field trials further validated the potential of eDNA as an indicator of fish biomass, and in some cases, abundance. Notably, experiments with Golden Perch revealed a useful significant positive quadratic relationship between eDNA concentration and biomass, while the Mulloway trials showed a significant positive relationship between eDNA concentration and biomass and an almost significant positive relationship with abundance, but (for both) only during autumn. Bony Bream also had useful positive linear relationships between their eDNA concentration and biomass and abundance and a significant negative relationship between eDNA and flow. Similarly, and despite few attributable impacts detected in aquaria, in their natural environment Murray Cod biomass (but not abundance) was characterised by a significant (but weaker) positive linear relationship with eDNA concentration, as well as a significant but weak negative relationship with flow.