Nature’s Torpedo

Nature’s Torpedo

"You can tune a piano, but you can’t tuna fish."

REO Speedwagon; 1978 album

The above quotation needs a little extra information. As a musical experience, it was one of the 70’s defining LP records (remember LP records?), but as a literary and artistically creative masterpiece it was definitely found wanting: both its cover (an upright tuna fish with a tuning fork in its mouth, no kidding ) and its title, as quoted above, garnered ‘Worst of…’ awards from the wincing music industry.

Which is unfortunate for the tuna, because it is one of nature’s most magnificent creatures. The problem these days is that humans tend to think of animals (and here we include birds and fish) in terms of “Can we eat it?” Mention tuna, and most people think of delicious tunny steaks, or, worse, round cans of tuna fish that are easy to open and make quick meals. At Waterfront Charters we see things differently: the tuna swimming beneath our vessels are worthy of much closer examination and admiration. True, they aren’t the type of fish that you will see sporting about when you are relaxing aboard a luxury catamaran, but we know they are there, and the sea is a better place for that knowledge.

A school of Tuna in their natural environment. An active and agile predator, the tuna has a sleek, streamlined body, and is among the fastest-swimming fish reaching speeds up to 75km/h. - Photography by OAR/National Undersea Research Program (NURP).

Tuna, or tunny as they sometimes known, are members of the vast ‘bony fish’ category (as is the snoek, as any person who has eaten one will attest to), and they tend to populate the more shallow areas: that’s where the plankton, their food of choice, is densest. But shallow waters are more dangerous too, so tuna have evolved countershading camouflage with a light underbelly and darker colouring on top, making them harder to spot against the background. When viewed from side on their silvery scales reflect light too, and this can be confusing for a hungry predator. But that’s not the only protection. Sharks are often cited as the meanest kids on the watery block, but tuna are actually – pound for pound – much more capable. With a bony skeleton and scales; a flap covering their gills and adjustable fins, they have the design edge over cartilaginous sharks. A well-known marine scientist, Dr Ellen Prager, sums up the tuna perfectly: “The shape of the tuna is the most hydrodynamic shape possible. And one that humans have sought go emulate in submarines and torpedoes. Some call the tuna torpedo-shaped, but really the torpedo is tuna-shaped.”

Their fins are marvels of efficiency; they can be folded into specialised grooves in the body at speed, making them even more hydrodynamically efficient, capable of averaging 45kph when swimming quickly. The yellow-fin tuna can power through the water at over 75 kms per hour – a human going downhill on a bicycle will understand just how quick that actually is. At slower speeds, those fins are equally impressive. They are infinitely adjustable and this makes manoeuvring an acrobatic exercise in finesse. Imagine an aeroplane with wings that could be adjusted to suit any flying conditions and you’ll get an idea of the advantages. Behind the tuna’s dorsal fin are a row of ‘finlets’; researchers liken their effect on reducing drag to that of dimples on a golf ball. Then there is the tuna tail: it’s powerful side-to-side thrust is extremely powerful, and at the base of the tail are two peduncle keels, which also reduce turbulence and drag. All in all, the superb tuna is an underwater F1 machine.

But it’s not only speed that sets the tuna apart: they are long-distance champions as well as sprinters. Tuna can easily cover 15 km in a night’s swim (possibly for feeding, but that is not known for sure); one well-travelled tuna tagged and studied by scientists covered a mind-boggling 10 000 kilometres in 50 days. As Dr Prager puts it, the tuna has evolved a circulatory system and muscle structure that human athletes can only dream of. Their name says it all: ‘tuna’ derives from Middle Latin thunnus, derived from Ancient Greek thýnō, to ‘rush or dart along.’

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Their biggest problem is that they taste good too. Tuna are being fished in the millions of tons each year; currently in excess of four million tons per annum globally. As a species they cannot survive this over-fishing; although upper limits have been set by commercial fishing watchdogs, it is impossible to enforce and measure the amounts taken in the oceans. According to a recent BBC documentary, if Japanese and European tuna fishing continues at current levels, population of all tuna species will collapse within five years. Think about that the next time you are considering a piscatorial meal; make sure the fish you is a sustainable species.

Waterfront Charters supports all sensible fishing limitations; we also know that knowledge is the greatest weapon that conservationists can utilise. We visit the ocean on a daily basis; tuna and all other fishes live there permanently – we need to respect their right to life. Join us on an Eco-cruise and see the ocean in a new light; it’s beautiful, it’s a human playground, but it is also a biosphere that we need to cherish.

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