Sand flathead stocks are being managed for recovery in Tasmania and stock enhancement with hatchery reared fish has been proposed as a strategy to accelerate recovery and improve recreational fishing opportunities going forward. There are a range of possible enhancement strategies as part of the flathead recovery strategy including using enhancement to recover faster growing genotypes in the population, or enhancement of alternate species such as blue-spot flathead, snapper or kingfish.

There is some indication that flathead enhancement is technically feasible although many questions remain on the economic viability and ecological effects. Flathead enhancement is underway in NSW using hatchery reared juvenile dusky flathead. Similarly, Victoria has a hatching rearing program for dusky flathead, and have conducted an investigation into the feasibility of flathead enhancement (Ingram 2019). Similarly, snapper and bream have been enhanced elsewhere. Snapper are one of the most developed species for enhancement operations with over 500 million juveniles released in Japanese commercial scale operations over the last 50 years.

Determining the feasibility of enhancement operations tends to be complex and vastly different outcomes (cost / benefit) can occur depending on factors like size of release, hatchery production costs, and post-release survival. This complexity means that responsible enhancement should include testing of feasibility. Feasibility modelling also helps to identify and focus attention on issues most critical for the viability of operations.

This project will be a critical first step in scalefish enhancement in Tasmania. It will conduct enhancement modelling using existing knowledge where possible (e.g. known growth data) and plausible estimates for other aspects (e.g. hatchery parameters). Given there has been significant research on local species of (sand, blue spot) flathead (Coulson et al. 2022; Fraser et al. 2022) much of the required information on physiological and population level traits are available. Likewise there is interstate hatchery information on similar species (Dusky Flathead) which is required for inputs of hatchery information to estimate production costs.

We will use a specialist model ‘EnhanceFish’ (Medley and Lorenzen 2006) that is designed for this exact purpose. It also helps managers consider other possible impacts of enhancement, such as the effect of genetic drift that may occur with larger scale enhancement operations, as well as economic costs based on hatchery production.

We will examine the feasibility of enhancement of sand flathead, blue spot flathead, snapper, black bream, and estuary perch.