The elusive big eye tuna
11 August 2015
The bigeye tuna is the most elusive tuna in the South Pacific but as Al McGlashan explains a change of techniques might just see you hook up to this deep water trophy.
The reel exploded into life, taking everyone by surprise. The fact that we were busy on the other side of the boat filming a mahimahi for the camera crew only heightened our excitement further. Vic Levitt was on the rod in a flash and pushing the drag up to sunset on the 80 pound Daiwa only made the fish run faster.
The burst of speed was impressive enough but what really excited us was the fact that this fish had struck a bait set some 330 metres below us, that meant one of two things in my mind - a swordfish or a bigeye tuna.
The fight was like nothing I had ever seen before. The fish traversed the water column in its bid to escape, in fact at one stage it almost seemed to breach the surface. Initial thoughts were pointing towards a swordfish due to the erratic behavior, but then as the fight continued it changed to a typical ‘slug-it-out’ tuna style. It took 45 minutes on 80 pound gear to get the fish up, but seeing it break the surface beside the boat with all its golden flanks is something I will never forget. At 65kg it was an impressive bigeye.
The bigeye tuna is the most elusive member of the tuna family. With a distinctly large eye and barrel-like body the bigeye is a true barrel of a tuna. With yellow fins and a yellowish flank the bigeye can be hard to distinguish from the yellowfin tuna especially in immature models. There are numerous cases of anglers tagging yellowfin which they noted as ‘fat’ on the tag card only to discover later that they were in fact a bigeye tuna.
Left - Dolphins can be a good sign that bigeye are around. Right - make sure you are prepared with high-quality gear.
Found throughout the world’s major oceans, the bigeye is present throughout the Indo-Pacific and the Atlantic oceans. Despite being found in tropical and temperate waters, bigeye actual favour cooler waters and as a result spend a majority of their lives down deep. Satellite tagging has revealed they spend a lot of their lives at an average depth of around 300m. Interestingly, in tropical waters bigeye tuna, especially immature fish, will often congregate around flotsam or seamounts and stay near to the surface for a majority of the time.
Due to their cold water preference, bigeye are a relatively slow growing species. Like most game fish they enjoy a growth spurt in their first year, reaching 7-9 kilos and then doubling it in their second year. This is a lot slower than their cousins the yellowfin tuna who can reach 15kg in their first year and 25-30kg by the age of two.
At 45kg a bigeye would be around five years of age and more than 1.3m in length. However while the yellowfin has a short
lifespan, a bigeye can live for more than 15 years and reach potentially 200kg in weight. Having said that, fish over 100kg are rare. Shane Ralph, a commercial fisherman, recent caught his biggest bigeye which weighed well in excess of 150kg. Ironically, it wasn’t hooked at all but had gagged on a black snapper. In Australia, longliners catch a lot of bigeyes in the 40-80kg range, but there is no such data for New Zealand.
Larger bigeyes are often male, which is the complete opposite to most other game fish species like marlin where the females are always larger. However, similar to striped marlin, bigeye are believed to spawn in the spring and summer months in the Coral Sea, northwest of New Zealand.
There have not been a huge number of bigeye tagged in the South Pacific but some interesting results have come from New South Wales Gamefish Tagging Program. One small bigeye tagged off Eden was recaptured by a longliner wide of South East Queensland. Initially estimated at just 7kg it weighed just over 40kg when recaptured more than three years later. This highlights that immature bigeye as well as adult fish travel south into the Tasman Sea. There is also evidence that the species migrate up and down the coast with the East Australian Current.
As with any tuna, bigeye put up a good scrap and demand good gear and patience.
Bigeye are a wide ranging species but their preference for depths makes them difficult to target. While they are common throughout tropical waters, the bigger fish are more common at the extremities of their range in temperate waters.
Places like New South Wales, the Hudson Canyon off New York and remote spots like Madeira and the Accession Islands all produce heavyweight bigeyes at times. In New Zealand the bigeye is still largely an unknown quantity but with the right conditions the waters off the North as well as East Cape offer serious potential. To the north the seamounts around the Three Kings also hold potential. However there have been reports of bigeye caught all the way down to the Kapati Coast near Wellington.
Bigeye can handle an extreme variation in temperature but are most comfortable in 18-20 degree water on the surface. Satellite tagging has shown that bigeye make regular vertical movements throughout the water column diving to more than 500 metres. During these vertical migrations, bigeye can handle as much as 20 degrees variation in temperature from 25 down to a nippy 5 degrees.
This is very different to the yellowfin which rarely dive to water that is more than 8 degrees cooler than the surface layer.
The bigeyes movements through the water column follow the deep scatter layer (DSL) which they extensively exploit for food, although like swordfish they will rise up periodically to the surface layer to warm their muscles after feeding deep at times. At night they follow the DSL to the surface. It appears that like most tuna species, their movements up and down through the water column mirror that of prey species.
Water colour is also important to bigeyes who prefer clean blue water. The addition of birds or toothed whales are also good signs for the presence of bigeyes. Mature yellowfin and albacore often favour similar conditions so if you encounter these species higher in the water column then there is a good chance bigeye are also presence. These three species are often caught together.
n tropical waters, immature bigeye tend to congregate around flotsam and can be caught jigging or deep live baiting. The problem is that commercial factory ships are also targeting these flotsams and are smashing bigeyes along with other tuna species and there is some concern that these foreign fleets are depleting bigeye stocks to unsustainable levels.
The bigeye’s elusiveness isn’t because it’s rare, instead its due to their preference to live deeper in the water column out of reach of traditional fishing techniques. Trolling and even cubing have little hope of reaching these deepwater inhabitant so in most cases anglers are simply driving straight over them. In recent years, more and more anglers are pushing the boundaries and experimenting with new techniques to probe the depths and suddenly bigeye are becoming more frequent.
In the North Atlantic anglers have had good success trolling at dawn and dusk. However the peak period is the first and last hour of light which doesn’t give anglers much fishing time. For some inexplicable reason this technique has not yet been employed in Australia or New Zealand but it certainly has merit. In fact some anglers have gone one step further and have been catching bigeyes by trolling at night.
Satellite tagging has revealed that bigeye spend a vast majority of their time at a depth of around 30m. This is vital information and highlights that this is the depth you need to focus on. It was this information that was vital and dictated why we set the bait at that precise depth to catch that 65kg bigeye off Sydney.
The technique basically entails rigging up a hardy live bait like a yellowtail and then sending it into the depths.
A cheap line counter is essential to get the bait down to the correct depth and in most cases anglers employ low stretch braid lines as opposed to conventional monofilament.
The rig I have developed is very simple. A 14/0 circle hook rigged on a 150kg leader with the bait bridled to the hook. However where the finesse comes in is how the sinker is added. To get the bait down fast the sinker is attached directly to the hook which means you can free spool the bait into the depths at speed without any chance of tangles. However, having the sinker attached direct to the hook is not ideal and may impede the hook up in some cases.
Another approach which has been adopted from deepwater daylight swordfishing is to let the bait out without any weight on it and then when it is the desired distance out the weight is added to the line by way of a snap swivel. The snap swivel runs down the line and at the same time the line drags the bait down to the desired depth. The advantage with this technique is that it does it slowly, allowing you to fish your bait down through the water column, potentially presenting it to any predator on the way down.
Deepwater fishing is most effective when it is calm and the current is minimal. On rough days it is near impossible to fish this technique. In the right conditions you can combine deep drop with other techniques like cubing and live baiting the surface layer to double your odds.
The idea of fishing baits during the day is a relatively new technique but it has proved highly effective and really it is simply a matter of anglers spending more time on the water refining the method to get more consistent results. In Florida, anglers chasing swordfish are setting baits at more than double this depth so it is definitely achievable to start fishing the depths for bigeye.
While on the subject of new techniques, another Sydney boat Tantrum caught a sizable bigeye trolling at midnight on its way to Lord Howe Island. Trolling at night has worked for swordfish in places like Kenya but it is a completely new technique for a species like bigeye. Again it is simply a matter of experimenting to refine the technique.
In the Coral Sea, bigeye along with yellowfin and even billfish congregate when the Lanternfish spawn over remote seamounts. When this occurs, anglers can enjoy some amazing action where the fish can be caught trolling or jigging.
The problem however is that the phenomenon can happen one year only to be a non event the next, so it is impossible to predict. At other times, jigging around flotsam and fish aggregating devices will produce immature bigeye tuna.
At the end of the day bigeye tuna are the perfect fish to go and try something new on. They are an exciting species that is wide open to new techniques so get there.