Fishy business: Genetic insights support sustainable fish management in Australia’s south west

Scientists have confirmed Australia’s west and southern coasts are home to three genetically distinct groups of pink snapper which has implications for fisheries management.

Led by a team out of Flinders University’s Molecular Ecology Lab, the study analysed more than 10,000 genomic markers from about 300 snapper samples and found the species could be grouped into three genetically distinct populations within its South and West Australian range.

The three populations range between Shark Bay and Lancelin, Fremantle and Albany, and the west coast of SA.

The findings published in Evolutionary Applications could provide insights as authorities seek to boost the numbers of Chrysophrys auratus to sustainable levels.

Western Australia recently decided to ramp-up recovery efforts for demersal scalefish like snapper and the endemic dhufish (Glaucosoma hebraicum) – both of which are important indicator species used to signify the health of neighbouring fish populations.

Pink snapper are particularly long lived – some records indicate lifespans of more than 40 years – and slow growing, meaning populations can be susceptible to overfishing.

On the flipside, snapper fishing is an important economic contributor for SA and WA, so ensuring sustainable levels of the species has both fiscal and conservation outcomes.

Currently, WA draws three management boundaries based mainly on environmental characteristics, so identifying two distinct, genetic groupings for the state’s snapper could provide authorities with a new edge in stock management, says the study co-author Professor Luciano Beheregaray.

“Our work actually contributes very clear guidelines about the boundaries of the different populations of snapper,” Beheregaray says.

“We have a much better idea about the range of each population.

“That gives government agencies the opportunity to focus their management on those units, and over the right, geographic area.”

There are plenty of fish in the sea but genetic sampling separates the ‘who’s who’

By analysing thousands of genetic markers, the researchers not only determined boundaries between groups, but also when one pink snapper ‘crossed the border’ into another population.

Although differences between the populations means that snapper rarely move outside of their geographical boundaries, one fish from the SA population was found to have swum a thousand kilometres to Busselton, just south of Perth.

This level of precision is made possible by using DNA markers as natural ‘tags’, allowing scientists to track individual movements over time and grouping individuals into single populations.

That saves time, money and delivers greater precision over manual tagging.

“[Manual] tagging requires a massive effort, and the reality is that you know you’re only going to recapture a small number, sometimes you don’t re-capture any at all,” says Beheregaray.

“But every individual has a genome, has DNA.

“So we can tell much more about individual movement, for instance whether it belongs to the population where it is caught by a fisherman, or whether it’s a migrant from another population.”

Like humans, fish manage themselves as distinct communities

Genetically distinct populations emerge due to restricted interbreeding and movement between groups of a species in a geographic range.

Even within a single species spread over a large area, these distinctions warrant consideration for conservation management because unique groupings may respond to fishing pressures differently.

A decision to stick with management approaches based on environmental characteristics (rather than tailoring them to suit genetic populations) means some individuals may slip through the cracks.

To put it in context, Beheregaray suggests it would be as if one country’s COVID-19 management strategy was applied to all human populations.

While it might be effective in some ways, individual nations – or populations – probably require tailored strategies for the best outcome.

It’s the same idea for snapper: unique populations might need unique solutions.

And scientists and managers involved in WA fisheries are considering the study’s findings to aid the management of pink snapper along its coasts.

“Many of the demographic processes that matter for fisheries management take place at the population level, not at the species level,” explains Beheregaray.

“Mortality, recruitment, growth, movement – these all take place within each population pretty much separately from another one.

Beheregaray told Cosmos different populations may need different types of protection measures, and “…different types of fisheries guidelines in terms of establishing quotas, for instance.”