Southern Bluefin Tuna command the attention and focus of many Victorian anglers from late summer through to winter every year along the Victorian coastline, with a particular focus upon the far south-west area near Portland. This year began like many others, with numbers of school fish and a smattering of ‘jumbo’ or ‘barrels’ frequenting catches to encourage even the serious and passionate game fishers to continue the quest for the ultimate Victorian tuna. However, from late July onwards and well into spring, the fishing accelerated to a level never encountered anywhere in the world, with catches of massive tuna over 80kg and up to 165kg almost every day and across the entire western coastal region of the state.
No one could have predicted the sheer numbers of huge southern bluefin that were spread along the coastline! Catches of massive tuna from central Bass Strait, all the way across to the South Australian border and beyond were the norm, with anglers spread across multiple ports and launching facilities at any one time. Huge concentrations of baitfish, seals, dolphins, whales, and of course tuna were amazing to witness and in levels never seen along the entire coastline in memory.
When it comes to baitfish, tuna behave in much the same way as humans do at a Saturday afternoon Bunning’s BBQ! Masses of baitfish were positioned along the coastline and while the ocean currents held the bait in productive water and in easy access to the coastline and boat ramps the feeding fest simply did not cease.
Maybe there were early signs of things to come that we missed or never thought would lead to the astounding fishing experienced. Let’s explore a few possibilities and reflect on a tuna bite that will potentially go down in history as the greatest ever seen.
In late June, the commercial trawler Costella Rosa operating from the Port of Portland hauled aboard a truly surprising by-catch of a 3t basking shark measuring 6.5m in length. The basking shark is rare and massive – the second largest shark on Earth – and this one was only the third specimen ever captured in Victoria on record. But how does a basking shark captured in a trawler net relate to the greatest tuna fishing ever witnessed in Victoria?
Basically, basking sharks are filter feeders. They feed exclusively on plankton through their enlarged mouth and gill system akin to a massive siphon that filters up to 6000L of water per hour. Plankton can generally be regarded as phytoplankton (tiny microscopic sized plant like organisms) and zooplankton (tiny microscopic sized animals) and are considered a key driver of ocean productivity. Think of plankton as the fuel for the environment and if there is enough of this fuel to have basking sharks around, there must be plenty of fuel for other marine life such as baitfish to feast on.
Logic dictates that if there are increased amounts of food around predators such as seals, whales, dolphins and tuna won’t be far away.
Significant numbers of southern right and humpback whales were seen along the western Victorian coastline during this winter and spring. While not uncommon, the frequency of sightings rose. The habit of whales hanging near baitfish schools reinforces the highly productive marine environment existing along the coastline. Across the world, whales and tuna are regarded to exist closely in the environment and one can assume it is no different here in Victoria. The sheer number of humpbacks encountered around the tuna fishing grounds was phenomenal.
‘Find the good water’ is a term often declared among game fishers and the good water never left the western Victorian coastline this year. Not the green or aqua looking water we often encounter close to the coastline, but the deep rich cobalt blue ocean that provides nutrients and life for the previously mentioned plankton communities and in turn delivers food sources such as whitebait, pilchards, squid, sauries and redbait for southern bluefin tuna to feast on.
The Portland area is known for being the central hub of a deep water ocean current cycle known as the Bonney Upwelling, created by south easterly trade winds from November to March that lift nutrient rich water to the surface from deep offshore and push it parallel to the coastline. This cycle creates a rich feeding environment for the entire ocean community and is renowned for attracting blue whales to the area during summer.
During other times of the year when the Bonney Upwelling is less effectual, the Victorian coastal ocean is influenced by the seasonal strength of the Leeuwin current from Western Australia. The Leeuwin flows southwards down the West Australian coast and then in an easterly direction across the Great Australian Bight. This current is used by southern bluefin tuna in their life cycle migratory routes across the oceans between feeding areas and to the only known spawning area in the world, situated in the Indian Ocean, south east of Java, Indonesia. This season, the offshore currents assisted greatly by blocking the productive water holding baitfish and tuna from dispersing. Instead, it funnelled parallel to the coastline and delivered the ultimate experience for many anglers with coastal towns reaping economic windfalls with the influxe of game fishers.
Amazingly, these tuna stayed in the close shore waters of the coast for nearly 3 months, generally in depths of 40-80m and around water temperatures between 12-15°C. This in itself is purely unbelievable, but with the sheer volume of food and activity these jumbo tuna saw no reason to leave. Locations of bite centres varied over the course of the season, but generally the tuna were spread across the entire western half of the state. Abundant reports came from the locations fished by the greatest number of boats.
The proximity of the fish near the coast for such a long time is astounding, as existing research has been accepted that southern bluefin tuna over the age of 5 years are seldom seen in the near shore surface waters of our oceans, spending the majority of their life in deeper waters well south of the mainland. After speaking with fisheries scientist Dr Sean Tracey and others, a general theory among several professionals was that the jumbo southern bluefin tuna along the Victorian coastline may be ‘feeding up’ prior to moving up the West Australian coast towards the known spawning grounds. Investigation of gonad state and spawning condition of these large mature fish may have assisted in adding to the knowledge base of current research.
Fisheries researchers have completed significant and highly relevant research on the migration patterns and behaviour of southern bluefin tuna. Cutting edge technology such as satellite tagging and stress recovery of recreationally caught tuna by scientists such as Dr Tracey assist in the knowledge base of the long term behaviour. This aims to continue the future recovery and growth of the entire bluefin population after being fished to the brink of collapse in the past.
Assistance from bodies such as the Fisheries Research and Development Corporation (FRDC), Victorian Recreational Fishing Trust (funded by recreational fishers), the NSW recreational fishing trust and Tasmanian Fishwise Community Grants have co-funded the project investigating how these bluefin tuna survive after capture and release, along with learning even more about the species. The initiative of anglers contributing back into science and research to ensure we have ‘fish forever’ is a fantastic and uplifting thing to see!
The standard approach to tackle southern bluefin tuna has been trolling a spread of skirted lures and hardbody lures. This season however, the vast majority of barrels were taken on lures significantly larger than regular. Previously, the standard length skirted lure trolled by most game fishers was around 6”(15cm), however this season saw a huge amount of 10”(250mm) and 12”(300mm) lures used to target jumbo bluefin. Many brands were a stand out, but Jaks, Marlin Magic, Billmark, Pakula and JB Lures asserted their stamp as ‘must have’ in your tuna tackle box during the season.
A logical conclusion that a bigger lure can be perceived as a more valuable meal to a large tuna is commonly assumed. However, inspection of the stomach cavities of large individual southern bluefin tuna indicated quite the opposite. The barrels were gorging themselves on small baitfish, generally under 50mm in length. Some fish contained up to 3kg of baitfish in various stages of digestion. So, were these tuna simply viewing these larger lure presentations as a more efficient and useful food opportunity?
Tuna fishers have experienced the greatest and longest run of jumbo southern bluefin tuna in history, and now the million dollar question is – will we see this again in future years?
Stepping back and taking a wider look at fisheries science, and the population dynamics leaves the southern bluefin tuna in a favourable position. Surveys published by the Commission for the Conservation of Southern Bluefin Tuna list that while the entire stock is still only at around 9% of its original levels, the population has made a significant improvement since the previous survey in 2011, up from 7%. The large increase of smaller school size tuna (2-4 years of age) in recent surveys, as well as an increase in the biomass numbers of mature breeding fish over 10 years of age in the population are two interesting and significant indications of a possible improvement into the future. Australian fisheries management practices, along with other nations involved with the southern bluefin tuna are to be congratulated for turning the fate of a species on the brink of collapse around.
Anglers can assist the long term future of the southern bluefin tuna – we all want to experience the thrill, power and beauty of these awesome predators. Obey the relevant local fisheries bag and size limits, but don’t use them to define your catches. Take only what you need, and respect the catch with the honour and privilege it deserves. Chill it immediately, prepare it properly and manage it effectively. Most importantly, there is nothing wrong with leaving one to catch another day. Let’s have more tuna and bigger tuna for our future generations!Reads: 1370