Pacific Bluefin Tuna Confirmed in Victorian Waters

A significant discovery has led to the first confirmed records of recreational catches of Pacific bluefin tuna (Thunnus orientalis) in Victorian waters.

The breakthrough came after two large tuna caught off Bass Strait in July 2026 were genetically tested and confirmed as Pacific bluefin tuna, a species rarely recorded by Australian recreational fisheries.

The fish were caught just days apart by Victorian anglers fishing wide off Western Port Bay in 50-60m depth. One fish weighed approximately 165 kg and measured 2.12 m, while the second weighed 131.6 kg and measured 2.02 m. Initially, both fish were assumed to be southern bluefin tuna (Thunnus maccoyii), a species commonly targeted by recreational game fishers in Victoria and more commonly associated with Australian waters.

However, Tuna Champions Scientific Ambassador Jonah Yick and experienced fisher Dave Standing, along with a few other fishers noticed several unusual features on the fish that raised questions about their identity.

"The fact that these two fish were caught in close proximity, literally on Melbourne's doorstep, within 10 kilometres of the shoreline, is an amazing catch and story," Jonah said.

"The Pacific and southern bluefin tuna look very similar to the naked eye but there are subtle differences which can be used to distinguish between the two species, which includes anal and second dorsal fin length, markings on their skin, body shape, and average size."

Pacific bluefin tuna have been known to be caught by long liners (or commercial fisherman) in Victorian waters but they are usually in very deep water, a long way from shore.

Recognising the potential significance of the catches, Dave quickly contacted the anglers involved in both catches and coordinated the collection of muscle samples for genetic testing. The samples were then sent to Jonah, who subsequently passed them on to Principal Research Scientist Dr Peter Grewe - the lead geneticist working on tuna genomics at CSIRO in Hobart.

Dr Grewe ran an initial DNA screen using a rapid tuna species identification test developed at the CSIRO labs. The results indicated both fish were Pacific bluefin tuna. This was an exciting and significant finding, as these captures represent the first genetically confirmed Pacific bluefin tuna caught by recreational fishers in Victoria.

"I'm extremely confident in these results following a secondary forensic grade sequencing analysis further confirming our initial quick species ID test," Dr Grewe said.

In a remarkable development, months later anglers off Lakes Entrance, Victoria, began catching large numbers of tuna weighing between 130 and 217 kg. Preliminary assessments based on external features suggest these fish may also be Pacific bluefin tuna. Samples have been collected from some of these fish from local recreational fisher Simon Webster, and testing is now underway by CSIRO to determine their identity.

News of the recent catches has travelled fast through the Victorian recreational fishing community.

"There's a huge amount of interest among Victorian fishers at the moment. I was told there were over 150 boats out off Lakes Entrance, Victoria over the weekend," Jonah said.

A majestic species

Pacific bluefin tuna are among the largest and most powerful tuna species in the world, capable of growing to almost three metres in length and approaching 450 kg in weight. They are also one of the world's most valuable prized fish, especially in high-end restaurants in Japan. There have only been a handful of Pacific bluefin tuna caught by recreational anglers in Australia, and the species has never been confirmed by recreational fishers in Victoria until now.

More commonly found in the Northern Hemisphere, Pacific bluefin are also present among recreationally caught fish in New Zealand waters. In their first year of life a large proportion of Pacific bluefin tuna have crossed the Pacific Ocean, a journey of over 8000km from the two known spawning grounds near the southern end of Japan (Nansei Islands between Japan and Taiwan and also in the Sea of Japan between Japan and Korea). Some also swim south from Japan to New Zealand traversing close to 5000km. On maturing the adults return to their birthplace to spawn in warm waters (24-28'C) between late May and early July. Once spawning has completed the adults once again return to the rich feeding grounds found in the cooler waters off both California and New Zealand.

The first two Victorian fish tested at CSIRO, although substantial catches in their own right by recreational fishing standards, were well below the upper size range for the species. The discovery is important because it suggests Pacific bluefin tuna may occur in southern Australian waters more regularly than previously recognised.

The need to scientifically confirm and the summer ahead

The finding also highlights how difficult it can be to distinguish between bluefin tuna species based on appearance alone. Without genetic testing, both fish would almost certainly have been recorded as southern bluefin tuna.

Jonah said some fish are able to be easily identified in photos, while others can be difficult. Of the first two fish caught near Melbourne, one was a substantially large size which was not commonly seen in southern bluefin tuna, while the second fish had subtle distinguishing characteristics such as the length of their second dorsal and anal fins and markings on the bellies.

Dr Grewe said given the recent rebuilding of southern bluefin tuna stocks, tuna fishing has increased in popularity, resulting in more vessels seeking tuna across southeastern Australian waters. He believes the likelihood of encountering and capturing rare species such as Pacific bluefin tuna may have increased due to greater fishing effort and more anglers spending time on the water.

Perhaps most importantly, this discovery highlights the power of collaboration between recreational fishers, charter operators and scientists. The finding was only possible through a collective effort: recreational fishers recognised unusual characteristics in the fish and coordinated sample collection from fellow anglers; charter operators provided timely reports to Jonah Yick and helped facilitate the collection of biological samples; and researchers at CSIRO undertook the genetic analyses required to confirm species identification. Together, these contributions demonstrate the value of citizen science in advancing our understanding of Australia's marine environment and underscore the important role that fishers can play in supporting scientific discovery.

"Information from people out on the water every day is invaluable to scientists," Dr Grewe said. "Fishers are a wealth of knowledge, they see unusual things, they tell great anecdotes. Sharing that information and knowledge with each other is a very human thing to do. It's like sitting around a campfire sharing stories that pass wisdom down through the generations."

Without that cooperation and quick action, these fish would likely have gone down as just another pair of impressive tuna captures. Instead, they have provided confirmed evidence of Pacific bluefin tuna in Victoria's recreational fishery and opened an exciting new chapter in our understanding of these remarkable fish.