A slender oceanic shark, usually about 2.5 m (8 ft) and up to 3.5 m (11.5 ft), metallic bronze-gray above and white below, with sickle-shaped pectoral fins and a tiny second dorsal fin drawn out into a long trailing tip. The name is literal: the denticles covering the skin are unusually fine and closely packed, and the animal feels smooth where other sharks feel like sandpaper.
It hunts by ear. Low-frequency pulses - the irregular thumping made by fish struggling or by a feeding frenzy - carry for kilometers underwater, and this shark is tuned to them, homing in from far outside visual range. That sensitivity is why silkies appear within minutes around anything that makes a commotion on the surface, and why they follow schools of tuna, which do the finding for them.
The same instinct is killing the species. Industrial tuna fleets fish around drifting artificial rafts, which attract tuna and everything that follows tuna, and this is the shark that arrives. It is the most commonly caught shark in tropical purse-seine fisheries on Earth, taken in hundreds of thousands per year as bycatch, and it is now Vulnerable with regional declines above 85 percent.
In the water it is curious, persistent and difficult to discourage, and it appears out of blue water rather than off the reef - usually several at once, usually at a safety stop, usually already close before anyone notices.
The species. Carcharhinus falciformis (Bibron 1839) - falx (L.). ETYFish
- skin noticeably smooth to the eye, without the usual rough texture
- small first dorsal fin with a curved rear margin
- tiny second dorsal fin drawn out into a long trailing tip
- metallic bronze-gray, appears out of open water rather than off the reef
