Biology and ecology

Biology and ecology (research theme 1) consists of 4 projects that address key research needs for Snapper. These include:

• understanding the environmental factors that affect Snapper populations
• evaluating the potential influence of environmental change
• defining stock boundaries.

This research contributes to improved monitoring and assessment of Snapper stocks in South Australia.

Recruitment variability and climate change

Project commencing late 2023

Snapper populations are characterised by highly variable recruitment between years. Recruitment is the number of juvenile Snapper that are added to the population each year and, in most years, the number of juveniles that enter the population in the Spencer Gulf / West Coast and Gulf St Vincent has been recorded as low. In the past, the occasional strong recruitment event (for example, every 5 to 10 years) sustains the population through periods of poor to average recruitment.

This project involves 3 components:

• Continue to monitor the relative abundance of juvenile Snapper in Spencer Gulf and Gulf St Vincent as an early indication of recruitment. Juvenile Snapper are sampled in March and April each year using a small beam trawl, which is the same sampling method that has been used for the last 25 years in Port Phillip Bay, Victoria. These surveys were commenced in 2022 through an existing FRDC project (No. 2019-046).
• Investigate the relationships between Snapper recruitment and environmental factors – for example: temperature, wind, productivity. This will be done by comparing a time series of recruitment for each stock to the time series of environmental parameters for that region.
• The relationships between Snapper recruitment and environmental parameters will be used to assess the potential effects of environmental change on Snapper in SA. This will include modelling various climate change scenarios at a regional scale and developing spatial models for Snapper at different life stages – spawning, egg and larva, juvenile, and adult – to identify areas and life stages most susceptible to impact.

Contemporary stock structure of the West Coast population

Project commencing late 2023

The population of Snapper on the West Coast of Eyre Peninsula is a regional component of the Spencer Gulf and West Coast stock. It is hypothesised that in most years, the West Coast stock is replenished by local spawning and juvenile recruitment that maintain the population. However, in years of exceptionally strong recruitment in Spencer Gulf, the West Coast population is also replenished by fish that emigrate from Spencer Gulf to the West Coast.

Due to the prolonged period of poor recruitment in Spencer Gulf, it is unlikely that fish have emigrated from Spencer Gulf to the West Coast. As such, there is a need to understand the contemporary processes that maintain the population of Snapper on the West Coast to inform stock structure and identify the appropriate spatial scale for fishery assessment and management.

As such, this project will aim to understand the relative contributions to the population dynamics of Snapper on the West Coast of Eyre Peninsula of:

• local spawning and recruitment
• emigration from adjacent populations.

This will be investigated using a variety of approaches including otolith chemistry and population genomics.

Review of biological parameters

Project commencing late 2023

The biology of Snapper in South Australia has been studied over the past 40 years through regular sampling programs and targeted research projects. Over this time, SARDI has developed a database which contains biological information – capture date, location, length, weight, sex, reproductive stage, and age – for more than 27,000 Snapper, and length information for more than 75,000 individuals.

This project will investigate potential changes in key biological parameters for snapper in South Australia in response to changes in environmental conditions and stock abundance over time. These biological parameters, which include growth rates, maturation, and natural mortality, are fundamental inputs into the stock assessment model.

Habitat survey in Gulf St Vincent

Project commencing in 2024

Snapper use a variety of different habitats throughout their lives, ranging from soft sediments that are favoured by juveniles, to high relief structures that act as aggregation sites for spawning adults. As a result of the prolonged period of poor recruitment observed for Gulf St Vincent, there is particular interest in the distribution and abundance of habitats that act as nursery areas for juvenile Snapper, and whether the availability of these areas may have contributed to trends in recruitment.

This study aims to quantify the distribution and abundance of seafloor habitats in Gulf St Vincent, with particular interest in soft substrates that may act as nursery areas. The study will use towed underwater video and sediment analysis to quantify habitat types at approximately 150 sites that will be compared to previous surveys in the 1960s and early 2000s.

The results will be considered in terms of trends in recruitment and stock abundance for Snapper over this time and will also inform future restoration projects.