Image of yellowfin tuna swimming close to the surface

Bluewater Magazine Issue 123

Yellowfin Tuna are a highly prized species for both commercial and gamefishers alike. The majority of fresh tuna in sashimi bars across Australia is yellowfin tuna caught in Australia’s Eastern Tuna and Billfish Fishery (ETBF). Yellowfin tuna is the most valuable component of the ETBF and also an important gamefish, with specific tournaments targeting this hard fighting gamefish. Whilst both sectors target yellowfin tuna, there is little overlap in fishing grounds as the commercial boats typically target yellowfin tuna 30-80nm offshore, whilst the majority of gamefishing for yellowfin occurs within 30nm of shore.

Australia is almost unique in the Pacific Ocean in having a commercial longline fishery where yellowfin tuna is the main target species. The longline catch from the ETBF is a high value product typically sold fresh to Australian, Japanese and US restaurants and sushi bars.  The availability of yellowfin tuna off Australia’s east coast is highly variable between years and is probably related to conditions in the Eastern Australian Current, although this relationship is not well understood.

Most other longline fisheries in the Pacific Ocean target either bigeye tuna or albacore and only take small proportions of yellowfin. The vast majority of yellowfin tuna in Pacific Ocean is taken by purse seine boats and artisanal fisheries from Indonesia and the Philippines, with much of the catch ending up as much lower value canned tuna. Australia’s total commercial catch is less than 0.5 per cent of the Pacific wide landed catch.

Yellowfin tuna are sustainably managed in the ETBF under a quota system. Each year the Australian Fisheries Management Authority sets a Total Allowable Commercial Catch (TACC) based on the most up to date scientific information provided from the Tropical Tuna Resource Assessment Group (TTRAG). Each of the operators of the 35-40 commercial longliners in the ETBF are required to have uncaught quota for yellowfin tuna (and four other quota species) before they can go fishing. Many of the commercial operators own their own quota, but others are required to lease it in before they can go fishing. Each boat also has a satellite monitoring system and an e-monitoring system that included three – five camera’s to ensure they do not overcatch their quota, making it one of the most closely monitored fisheries in the world.

The management of yellowfin tuna in the ETBF has been recognised as meeting the highest level of sustainability when it was one of three species Walker Seafoods had certified as sustainable through the Marine Stewardship Council. Yellowfin tuna caught by Walker Seafoods boats is the only fresh tuna available to purchase in Australia certified by the Marine Stewardship Council.

Yellowfin tuna are also an important gamefish species, especially off NSW where the Eastern Australian Current brings them in relatively close to the coast. They are second only to black marlin in the number of fish tagged by the NSW DPI Game Fish Tagging program since 1974, with 37 998 yellowfin tagged and released up until 2015. 705 fish or 1.78 per cent have been recaptured by both recreational and commercial fishers during this period providing valuable information about movement and growth. For example, a 50-60kg fish caught by an ETBF longliner 80nm off the coast had been tagged nearly two and a half years earlier as a 4kg fish.

TTRAG has noted an unusual pattern catches in the commercial and recreational fisheries over the last couple of years. 2015 and 2016 saw some of the best catch rates of yellowfin tuna in the ETBF for the past 10 years. However, whilst these high catch rates were occurring in offshore waters, the inshore recreational fishery reported record low catches during both 2015 and 2016. Given the high abundance of fish offshore, TTRAG was unable to determine what was driving low inshore catch rates by game fishers. It has been suggested that environmental factors have led to the fish moving offshore over the last couple of years. To investigate this, TTRAG has developed a project to investigate how yellowfin tuna respond to environmental conditions. It is hoped that this project may gain funding during 2017/18 financial year and shed some light on the causes of the recent downturn in availability of yellowfin tuna to inshore waters off NSW.

One of the other most important questions about the management of yellowfin tuna in Australian waters is how many tuna move into and out of Australian waters. The current TACC for yellowfin tuna in the ETBF is 2 400 tonnes, but the total catch out of the Western and Central Pacific Ocean has been over 500 000 tonnes in all but 2 years since 2000.

With more than 99 per cent of the catch in the Western and Central Pacific Ocean occurring outside Australian waters, the most crucial information need for managing yellowfin tuna is to understand how many fish move in and out of Australian waters. To get a better understanding of this, AFMA and the Fisheries Research and Development Corporation (FRCD) have contracted CSIRO to use state of the art genetic techniques to help answer this question. This project started in July 2016 and sample collection is well underway and results are expected to be reported over the next two years.

AFMA and TTRAG will keep a close eye on yellowfin catches by both the commercial and recreational fishers over the coming years in effort to make sure that catches of yellowfin tuna will remain available to both sectors for years to come.