Abundance, population modelling, and potential biological removal estimates for Common Dolphins in Spencer Gulf: implications for the South Australian Sardine Fishery

Project number: 2019-063
Project Status:
Current
Budget expenditure: $380,000.00
Principal Investigator: Simon D. Goldsworthy
Organisation: University of Adelaide
Project start/end date: 2 Feb 2020 - 9 Dec 2021
Contact:
FRDC
TAGS
Sustainability
Stakeholder
Rac Sa
Population Dynamics
Observer
SPECIES
Sardines

Need

This project is needed to assess the impacts of the South Australian Sardine Fishery (SASF) on the common dolphin (Delphinus delphis). The SASF is Australia’s largest volume fishery and is critical to providing a supply of feed for the ranching of southern bluefin tuna. Operational interactions between common dolphins and the SASF have been persistent since the development of the fishery. Common dolphins occasionally become encircled in purse seine nets during fishing operations, which can lead to their injury and death. Observations of high interaction rates from an initial observer program, led to the temporary closure of the fishery in 2005 while an industry Code of Practice (CoP) to reduce dolphin interactions was developed. Since then, the CoP has been reviewed and refined to increase its effectiveness in preventing dolphin interactions, and improve release procedures. An independent on-board observer program has operated in the fishery since July 2006. It collects information on dolphin interaction and mortality rates, as well as data relating to the application of the CoP, and this information is provided in annual assessment reports. Since the introduction of the CoP, dolphin encirclement and mortality rates have declined, however, concerns about the level of interactions and mortality have persisted, with industry facing sustained pressure to demonstrate that steps taken to manage and mitigate dolphin interactions represent World’s best practice, and are sustainable.

This project is needed to address Marine Stewardship Council Fishery Assessment recommendations for the SASF to collect adequate and sufficient quantitative information to assess the consequences of interactions with common dolphins on their populations. This project is needed to provide an important Australian fisheries test-case for meeting new US Government legislation, requiring nations importing seafood to demonstrate that they have a regulatory program for reducing marine mammal bycatch that are comparable in effectiveness to US standards.

Objectives

1. Estimate the abundance of common dolphins in core fishing areas of the SASF
2. Collect critical life history (longevity, age specific mortality) information from museum specimens
3. Develop population models to evaluate bycatch limits of common dolphins and assess the sustainability of interactions with the SASF

Related research

All research
research
Environment
Environment
Environment

Cost-effective, non-destructive solutions to developing a pre-recruit index for Snapper

Project number: 2019-046
Project Status:
Current
Budget expenditure: $541,804.00
Principal Investigator: Troy Rogers
Organisation: University of Adelaide
Project start/end date: 19 Jan 2020 - 30 Dec 2022
Contact:
FRDC
TAGS
Survey
Stock Assessment
Resource Access And Allocation
Reproduction
Rac Sa
SPECIES
Snapper

Need

The population dynamics and fishable biomass of Snapper in South Australia are fundamentally driven by high inter-annual variation in recruitment, i.e. the numbers of 0+ juveniles that recruit to populations. Throughout the 2000s, SA’s Snapper stocks experienced different trends in recruitment that led to extraordinarily different trends in fishery catches. For the Spencer Gulf/West Coast Stock successive poor year classes led to the significant decline in fishable biomass, and a ‘depleted’ stock status. In contrast, the Gulf St. Vincent Stock increased to unprecedented levels due to numerous strong recruitment year classes, but since 2015 has also experienced considerable declines in fishery catches. In 2019 it was classified as ‘depleting’. From 2018, concerns about both stocks prompted a comprehensive review of the fishery management approach. This resulted in significant changes to the management strategy including a spatial and long-term fishery closure. Despite this, there remains the need to monitor the stocks and demographic processes. Given the significance of variable recruitment for Snapper, the need for regional, annual estimates of recruitment as an indicator of future trends in fishable biomass has re-emerged. Between 2000 and 2010, recruitment surveys were done in Northern Spencer Gulf, for which the sampling methodology, i.e. otter trawling, was non-selective and destructive of benthic and demersal biota. One need here is to develop a cost-effective, non-destructive sampling strategy for future annual sampling. Also, there is the need to develop a better understanding of larval ecology, connectivity, and the causes of variable recruitment. Combined benefits from addressing both needs would significantly enhance predicting future trends in fishable biomass.

Objectives

1. To develop our understanding of the processes that regulate recruitment based on finalising datasets from previous research projects that relate to the early life history, and larval and juvenile ecology of Snapper, as well as the annual variation in environmental factors
2. To undertake an empirical study to compare the utility and effectiveness of several potential sampling methodologies to provide a relative recruitment index for Snapper and to develop a sampling strategy for future surveys
3. To apply the sampling strategy as developed in Objective 2 in the following two years, to provide relative estimates of the recruitment rates for Snapper in NSG and NGSV