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Biology – Sailfish

Biology –  Sailfish

| On 30, Jun 2019

Darrell Mann

The Atlantic sailfish (Istiophorus albicans) is a world-record holding speed merchant twice over. Early measurements of the sailfish’s ability to move through the sea faster than any other marine vertebrate are currently the source of some challenge. What seems fairly clear, however, is that their short-burst top speed is indeed faster than any other fish. The initial view of the marine biologist community was that the capability was due to a pair of drag reduction features – one, the long, pointy snout, and the other, shark-like protrusions formed as part of the scales – and the fact that the enormous sail-like dorsal fin is retracted into a groove on the back of the fish so that it effectively disappears (an excellent example of both Principle 15, Dynamics, and 17, Another Dimension). The snout part of the story seems to now have been discounted from the drag-reduction equation and the growing consensus is that the biggest contribution to the high top speed record-breaking capability is the shape and musculature surrounding and just upstream of the tail fin. All in all, while we can see evidence of Principle 3, Local Quality in the scale-protrusions and caudal pedencies, what we’re really looking at is an optimizing improvement over the characteristics of other high-speed fish (tuna, sharks, etc). The high burst-speed capability, in other words, is not the result of a solved-contradiction, just the gradually evolution towards an ‘optimum’ configuration.

The second ‘high-speed’ characteristic of the sailfish is the more interesting one. It does involve a contradiction-solving step-change. To see it, we need to look in more detail at why the sailfish’s snout is so elongated: If the long, pointy feature has nothing to do with drag reduction, why has it evolved?

Sailfish eat primarily sardines and other types of shoal fish. Sardines have also evolved to swim at high speed. Because of their smaller size, they have the big advantage over the sailfish of being much more maneuverable. They can turn faster. So what does the sailfish do to overcome this relative lack of maneuverability speed deficiency?

Enter the snout. Quite literally. The main strategy of catching their prey involves the sailfish swimming up behind the shoal of whatever sardine-like prey it encounters. The narrow snout is able to ‘enter’ the shoal easily because it is long and thin. The snout enters the shoal. Some of the sardines at the rear, noticing a foreign object now swimming next to them, decide to change course. They dart rapidly in a direction away from the snout. The snailfish notices this deviation and immediately turns its head in the appropriate direction. In the time it takes for the sardine to move away, the sailfish can’t move its head by very much. But it only takes a small movement of the head to become, because the snout is rigidly attached to the head, a very large movement of the snout tip. The head turn rate has been measured at around 600degrees/second. Impressive in itself, but when we see the effect of this at the tip of the snout, it corresponds to a local speed of nearly 180m/s, or about 400mph.

So, in order to catch the maneuverable sardine, the sailfish needs to improve speed, and what makes that difficult are the forces required to do so. Here’s what the contradiction looks like when mapped on to the Contradiction Matrix:

Good to see Principle 17 high up on the list of contradiction-solving strategies. Another Dimension – i.e. evolve a long snout. Clever, sailfish-built Contradiction Matrix. Read more in this excellent paper: https://royalsocietypublishing.org/doi/pdf/10.1098/rspb.2014.0444

 

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