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

Related research

All research
research
Environment
Industry
PROJECT NUMBER • 2023-085
PROJECT STATUS:
CURRENT

Snapper Science Program: Theme 1 - Biology and Ecology

1. Quantify the abundance of age 0+ Snapper in northern Spencer Gulf and Gulf St Vincent to provide relative estimates of recruitment for 2024, 2025, and 2026. Examine the otoliths of these fish to improve the understanding of early life history processes.
ORGANISATION:
Flinders University
People

Modelling environmental changes and effects on wild-caught species in Queensland

Project number: 2019-013
Project Status:
Completed
Budget expenditure: $257,459.05
Principal Investigator: Jerzy A. Filar
Organisation: University of Queensland (UQ)
Project start/end date: 19 Nov 2019 - 30 May 2021
Contact:
FRDC
TAGS
Stock Assessment
Reproduction
Remote Sensing
Rac Qld
Population Dynamics
SPECIES
Snapper
Spanner Crab
Pearl Perches

Need

A better understanding of the impacts of environmental drivers on the population dynamics and abundance of key fishery species can inform flexible management decisions that pre-empt both risks of overfishing under adverse environmental conditions and opportunities for increased harvest under favourable conditions. This is increasingly important as shifting environmental dynamics drive geographical shifts in fish stocks.

This project will identify environmental variables influencing the abundance of three priority fishery species, quantify those relationships to enhance their stock assessment models, and develop a forward projection tool to inform adaptive management of each fishery. Target species - Spanner Crabs, Snapper and Pearl Perch – were selected based on key interest to management of fisheries in Queensland and NSW. Some associations between these species and certain abiotic environmental factors are already known, but there is yet to be a rigorous and comprehensive approach to this work, with the explicit goal of incorporating abiotic influences into Queensland and NSW stock assessments.

The project has three key objectives: (1) Find indices of association between measures of abundance and key environmental drivers; (2) Use these indices to enhance the existing stock assessment model for each species; and (3) Enable forecasting of environmentally driven fluctuations in targeted species’ abundance, including enhancing Management Strategy Evaluations (MSEs).

In particular, environmental correlates will be valuable to fisheries managers by: (a) reducing the uncertainty in biomass estimates, (b) explaining fluctuations in abundance, and (c) characterising what is a “bad year” for each species. Such information can be incorporated into MSEs.

The “Queensland Sustainable Fisheries Strategy 2017-2027” identifies several challenges to fulfilling its mission of ensuring the sustainability of fisheries and the economic viability of fishing sectors. The first of these is “gaps in monitoring and research, which limit the ability to make timely, evidence-based decisions”. This project will close some of these gaps and assist in formulating measures for promoting stock recovery and adaptive management.

Objectives

1. Find indices of association between measures of abundance and environmental drivers.
2. Improve stock assessment models, for targeted species, by incorporating environmental drivers.
3. Enable forecasting of environmentally driven fluctuations in species’ abundance, including enhancing Management Strategy Evaluations for targeted species with the help of a rapid adaptive projections tool (RAPT).

Final report

ISBN: 978-1-74272-356-3
Authors: J. A. Filar A.J. Courtney L. J. Gibson R. Jemison S. Leahy Y. Lei M. Mendiolar J. Mitchell B. Robson C. Steinberg S. Williams W.-H. Yang N. Ye.
Final Report • 2021-12-31 • 12.89 MB
2019-013-DLD.pdf

Summary

This project studied environmental factors which may be influencing the recruitment, catchability or productivity of Snapper, Pearl Perch, and Spanner Crab stocks in Queensland. Two environmental variables: GSLA and Chl-a were found to have strong associations with either abundance or catchability across the three target species. These associations occurred at spatio-temporal scales relevant to each species’ biology. A third variable, SST, also had strong associations with Snapper.

 

Importantly, all three of these environment variables, GSLA, SST and Chl-a were found to have certain consistent long-term trends, with rates of change depending somewhat on the region under consideration. We demonstrated that incorporating these environmental variables into simple surplus production stock assessment models results, under some scenarios, in delays in stock recovery. This assumed that the above trends of GSLA, SST and Chl-a are sustained and the direction and strength of the identified associations are maintained.