One of the primary reasons for the high loss-rate of jewfish off The South End of the Kingscliff rocks in particular, is the power and speed of jewfish off the mark, from a stationary start. The almost incredible intensity of the action that immediately follows hook-set is to the fore in a list of contributors to why I became addicted to fishing for them in this location.
Jewfish are ambush predators. Textbooks on functional design in fish describe the advantages for this activity of a long bendy body and large surface area of tail for rapid acceleration from a resting position. The ‘full moon’ tail of jewfish is exceptional, even by comparison with closely related species, such as teraglin (for years known as ‘trag jew’) and white sea bass of the Pacific coast of North America (a closely related species that is extremely similar except for its crescent-shaped tail). It is relevant that the outline of a flathead tail is similar to that of a jewfish; they too are particularly effective from a stationary starting position. It is also particularly relevant that white sea bass readily take chrome spinners pulled quickly through the water; jewfish do not. White sea bass are capable ‘chasing’ predators; they have the tail for it. Jewfish rely far more heavily on ambush; they have the tail for that.
The overall design explains why jewfish are characteristically extremely difficult to hold when they are first hooked. They can at times be distracted by something like a hook through the tip of their snout. At such times the head shaking can take precedence over powerful acceleration, but power over short distances is the norm.
While collecting data for my PhD thesis at the University of Queensland on the comparative physiology of fish, I had numerous opportunities to compare the impacts of the functional design of jewfish with that of other species. One primary comparison I was able to make was with long-tail tuna.
I already had considerable experience with the difficulty of holding jewfish, even on a relatively short lead. I knew they were truly powerful from a standing start. But until my structured literature search and field work I had never had the opportunity to investigate the engineering, physiological and biochemical reasons for this.
Comparison of the total body shape of a jewfish with that of a tuna immediately exposes contrast. The jewfish’s long bendy body and relatively huge surface area of tail are obvious attributes for acceleration. In contrast, the rigid body of a tuna and sickle-shaped tail are the embodiment of rapid but low amplitude, tail beats that support sustained high speed. The height of a fish’s tail compared to the width is technically described as the ‘aspect ratio’. Highly mobile, fast-swimming species such as tuna have very high aspect ratios, while ambush predators, such as jewfish and flathead, have very low ones. Differences between species can be marked and obvious. But it is only when this relationship is combined with comparison of the muscle physiology and the blood and body chemistry of the two species that a bigger story begins to unfold.
Jewfish have predominantly white muscles, while tuna are famous for red ones. White muscle has evolved for short, sharp and strong bursts of activity. Hamstring muscles in humans are relatively white. The primary function of red muscle is continuous activity and repeated contractions. Heart muscle is the best embodiment of these attributes. Red muscle in tuna also has a partial liver-like function that helps the fish metabolise the by-products of extended periods of effort, thus facilitating continuity in high levels of activity.
Long-tail tuna are the classical shape of a constantly fast-swimming predator. Their relatively red flesh is rich in myoglobin and haemoglobin, the agents of oxygen storage, transportation and transfer. Their blood has virtually saturation levels of red blood cells. Sixty-two per cent of their blood is red blood cells; any higher levels would restrict the ability of the blood to be pumped around the body. For jewfish this figure is around 40 per cent. In dusky flathead it is 20 per cent. Long-tail tuna not only have more haemoglobin but what they have can take up oxygen from water and deliver it to tissues much faster than that of less active species. ‘Oxygen dissociation curves’ were a major part of my thesis.
The combined myoglobin and haemoglobin concentrations in the muscles of long-tail tuna average around 3000mg/100gm of tissue, whereas in jewfish the average is around 400mg/100gm. The levels in dusky flat-head are much lower again.
An additional feature of a comparison of the blood physiology of fish is the degree of variability within a species. The haematocrit (the percentage of red blood cells in the blood) in long-tail tuna does not vary greatly; from a high of 68.1 per cent to a low of 54.7 per cent (a variation of 19.7 per cent). At the other extreme, for dusky flathead the high is 36.0 per cent and the low, 12.0 per cent (a range of 300 per cent). Tuna are close to the maximum hydrodynamic and power limits for fish. An individual cannot afford to be seriously left behind. Consistency in sustained speed and power do not represent the same limitations for flathead.
What this degree of variability means for an angler is that there is very little variation in how hard individual tuna fight when hooked, but some flathead, and bream (a high of 41.8 per cent and a low of 15.8 per cent) can fight harder and for longer than others of the same species and size. I have found this variability most obvious in flathead but also readily apparent in whiting and brown trout. My observations may be biased by my use of 3-pound tippets for these latter two species. This allows individual variability to be more obviously expressed and noticed.
Comparison of the biochemistry of the muscle contraction and oxygen-carrying capacity between tuna and jewfish is not dissimilar to comparing the heart and hamstring muscles of humans. One is there for the long and continuous haul, the other for instantaneous strength and power for a relatively short time and specific task.
The functional design of the bodies of tuna primarily reflects the hydrodynamic excellence expected of a species that runs out of oxygen almost immediately it stops swimming. Their respiration is driven by moving constantly and relatively fast with their mouths slightly open to force water across their large and dense gills. Their external design includes not only a bullet-like shape but also small scales and grooves for their fins to fold into. The effectiveness of these attributes for high speed is surpassed only by the design of their tails and the high frequency and low amplitude of their tail beats. The sickle shape and taper of their tails is such that they cannot achieve maximum torque at low speeds. If they exert maximum effort by increasing tail-beat frequency while moving slowly, their tails are inefficient: they can actually cavitate. But, aided by the non-compressible nature of water, once they pass about half their maximum speed their efficiency and power increase dramatically. As a consequence, so can their acceleration, even without change to the rate of tail beats. The faster water passes over their tails, the greater the power generated by each tail beat. The faster they go, within broad limits, the more powerful they become; and they can, because of their blood and muscle biochemistry, maintain that power. The contrast with jewfish is stark.
I was most fortunate in having access to the University of Queensland’s research trawler for my sampling in Moreton Bay. In the 1960s long-tail tuna would come to prawn trawlers immediately they began to winch up their nets, particularly in the eastern side of Moreton Bay, offshore from Tangalooma. That was where I collected my long-tail tuna blood and muscle samples. My thesis work benefited from having blood samples from a minimum of six fish on each day I sampled. I quickly found that if I hooked 40-pound tuna on my 18-pound line each fish would take so long to land that I would struggle to get six in the time available. I would have up to 500 yards of 18-pound line out on a 40-pound tuna and more on the 70-pound ones we would occasionally hook. Furthermore, the blood chemistry that I was measuring was altered by the fish being played to exhaustion. In the early days of exploitation by commercial fishermen of tuna feeding behind trawlers, the fish would bite on very heavy lines, but the fish learnt quickly. By the time I fished for them regularly they commonly refused to bite on heavier lines. I was, therefore, forced to experiment with my fishing technique and 18-pound line. What I was learning about their body design and physiology helped in developing a strategy.
Provided we were in the right area, as soon as we began to sort the trawl catch and discard small ‘trash’ fish, the long-tails would gather. We would manipulate our discarding until we had them feeding right off the stern of the boat. With my 13-foot Sportex 3904 rod and 6-and-a-half-inch Alvey I would let out only a little more than one rod length of 18-pound line with a 6/0 hook and trash-fish bait. With this gear and a reasonable amount of practice I could hook a tuna up to at least 40 pounds and hold it with my rod up without giving it one inch of line. If I gave the fish more than about a yard or so of line, I would be unable to stop them. If I was to cast out more than about 20 feet, the principle of holding the tuna on a short lead was violated. People who handle horses are familiar with the advantage of a short rein. Even 30 feet gave long-tail tuna enough ‘rope’ to swing in a sufficient arc to generate a critical amount of speed and associated power.
To say the battle was intense, for the first few seconds at least, is an understatement. The tuna would swing around within the 20-foot range, but they could not generate the power necessary to get going properly. Normally I could pull them quickly to the surface and hold them there. We could clearly see their tails cavitate. Once their tails started to break the surface their power was shattered. Provided I held my nerve the contest was effectively over in just a few seconds.
Another feature that could be explained by biochemistry and physiology was that I did not have to hold the tuna long on the short lead before they gave in completely. Ten seconds or so would see their strength deteriorating markedly. The explanation for this is that tuna extract the large amounts of oxygen they use by swimming fast with their mouth open, thus forcing large volumes of water over their gills. When they are held so that they are exercising strenuously, but they are not moving quickly through the water, they quickly run out of oxygen. If a tuna is held stationary by the tail or restricted by a net while in the water it drowns very quickly, much more quickly than species such as mullet or bream, or jewfish, which have the functional design to pump water over their gills, even when stationary. So, holding the bucking bronco may have been extremely intense, but it did not last long.
The long rod played a critical role in cushioning any unexpected movements of the fish. But if I got the timing wrong, or lost my nerve, and gave them even as little as 4 or 5 feet of line, all bets were off. If I let them get going, it was common to have 500 yards of line out. Once they generated maximum torque it was complete folly to even contemplate holding them on 18-pound line.
But it was possible to hold a 40-pound tuna on a short lead from a slow start. There was no way I could anticipate holding a 40-pound jewie on 18-pound line from a complete standing start. I tried plenty of times! But by the time jewfish had taken 50 yards of line I could hold them rather easily, even on rather light lines: exactly the opposite to tuna.
My few successes with holding jewfish up short on relatively light lines were aberrations, or else fish that responded to being hooked in the tip of the snout by continuous head shaking, which jewies had the body design to do very effectively. But there was also no way a jewie was ever going to take 500 yards of even 12-pound line. The functional design of fish, including their biochemistry and physiology, makes a fascinating contribution to the study of fishing.
I accepted an offer to demonstrate the practicalities of this scientific knowledge to fishermen by accompanying Terry Russell and the late Tuck Fanning (who were at the time senior members of the Moreton Bay Game Fishing Club, President and Vice President from memory) on a fishing excursion in Moreton Bay, in, I think, 1968. Both of these gentlemen had been particularly helpful in getting me marlin samples for my thesis work. They had some difficulty believing what I had told them about holding tuna on a short lead with 18-pound line.
Even though we were successful in burleying up schools of tuna, the reality was they did not have any success with their short game-fishing rods. They hooked fish, but they could not hold them on light lines. It became obvious to me that a key advantage was the length and strength of my Sportex tailor rod, which, with the insert I had put in the butt, was over 13 feet. The advantage of this long rod was because first, it buffered any sharp movements of the fish. But more importantly, with it I was able to reach out much further over the gunwale. The result was that I was pulling the tuna vertically to the surface, where their tails would cavitate, whereas with their much shorter rods Terry and Tuck were attempting to pull them more horizontally towards the boat. With short rods they could not keep above their fish. The difference was obvious, painfully so to them.