Factories owned by one of the world’s largest seafood suppliers have been using children on production lines, locking workers inside buildings and threatening workers with violence.

The three major Australian supermarket chains – Coles, Woolworths and Aldi – have each acknowledged they sell prawns or other seafood supplied by Thai Union (the seafood company at the centre of the scandal), and are now investigating their supply chains.

Associated Press reporters uncovered evidence of forced labour in Thai factories, and their investigation led today's news on the Sydney Morning Herald as Fairfax reporters found that frozen prawns stocked in major Australian supermarkets are sourced from Thai Union. As each supermarket chain pledged to review their suppliers and Thai Union president Thiraphong Chansiri committed to take action, Fairfax reporters raised the prospect of a prawn shortage this summer.

While many Australians will hopefully use this news to pressure retailers to withdraw imported frozen prawns from shelves or seek out locally farmed prawns, sadly, this is not an isolated case. What went unreported in most media this week is that as recently as 2012, thousands of “guest” workers from Cambodia and Myanmar revolted after their passports were seized by their employers at a Thai fish processing plant.

Most fresh prawns sold in delis (even supermarket delis) are local, but given CSIRO estimates that around half of all prawns eaten in Australia are imported, and most from south-east Asia, it can be hard to determine whether your seafood has been ethically or sustainably sourced.

Worldwide certification programs such as the Marine Stewardship Council and Global Gap are working to improve both environmental and ethical standards of seafood harvesting, and all prawns sold at major supermarkets in Australia must be labelled according to the country of origin. As reported by The Conversation in 2013, in some states such as the Northern Territory and South Australia, compulsory labelling extends to all seafood retail outlets, including restaurants.

Australia is recognised as having some of the world’s best managed fisheries, so buying local is an obvious start. That said, whether farmed or wild-caught, prawns still come at a significant cost.

When farmed, the feed used for prawns is often made from wild-caught fish, and while the CSIRO is working with prawn farmers to develop less intensive prawn-food, it is by no means perfect yet. Wild caught prawns account for most of Australia’s locally-harvested prawns (around 80 per cent). Unfortunately, prawn-trawling is often cited as generating the highest amount of by-catch (accidental catching and wastage of other species) of all fisheries.

So what to do? The simplest answer is to eat less prawns, but if you're committed to seafood this Christmas, then head for the amazing Cleanfish Australia Market in Banksmeadow on Saturdays. Other suppliers who make an effort to sell ethically and sustainably sourced fish in Sydney include DeCosti Seafoods, Annandales' Fish & Co seafood cafe (where you can also buy fresh fish and seafood by the kilo) and LoveFish in Rozelle.

For more information, including specific sustainably-certified suppliers, see GoodFishBadFish, SustainableSeafood, and the Australian Conservation Foundation’s Seafood map.