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  • Mr Brett Crisafulli

    Researcher, Mr Brett Crisafulli, collecting biological data on oceanic Snapper (Chrysophrys auratus) in the Gascoyne.

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Variability and impact of released catch

Accurately quantifying the harvest (retained catch) of both the commercial and recreational sectors is vital for conducting stock assessments that support natural resource management. However, the impact of recreational fishing on fish populations and ecosystems is less understood than that of commercial fishing. In recreational fisheries, surveys of varying design are used to estimate the catch by number. To understand overall impacts on a resource, typically estimates of catch by weight are required, but collecting weight data presents numerous logistic and equipment challenges. An alternative is to impute fish weights from surveyed length data using length-weight relationships derived from biological studies. However, the accuracy of the imputed weights is dependent on the availability of suitable length-weight relationships. The trade-off between directly measured weights and imputed weights requires investigation.

The catching and releasing of fish are other sources of uncertainty requiring attention. Fish are often released due to management regulations and fisher behaviour, and a proportion of it may die. The biomass loss attributed to released fish that die needs to be considered as part of the overall harvest because it can be large enough to impact stocks directly. Quantifying the impact of releases is hampered by the additional uncertainty introduced by the need to convert the numbers of fish released to weight, requiring knowledge of the length or weight of released fish which is seldom collected by surveys, and to know the release rates and post-release survival of released fish.

This research seeks to evaluate the impact of uncertainties in the estimation of recreational harvest arising from variability in average weights of recreationally-caught finfish, variability in released catches and released rates, and the impact of released catches on estimating total harvest from boat-based recreational fishing using a major recreational fishery in Western Australia as a case study, namely the West Coast Demersal Scalefish Resource.

Funding agency

Department of Primary Industries and Regional Development (DPIRD)

Project duration

2018-2024, part-time PhD

Researchers

Mr Brett Crisafulli
Dr Johnny Lo
Dr Aiden Fisher
A/Prof. Ute Mueller
Karina Ryan, DPIRD
Dr David Fairclough, DPIRD

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