A big part of the reason why there’s so much confusion around their upper size is the predominance towards juvenile (and usually male) sharks in almost every coastal aggregation known around the world, including Ningaloo Reef (Meekan et al. 2006, MEPS; Norman & Stevens 2007, Fish Res) and off Mexico (Ramirez et al. 2012, JFB).

The 12 m shark was a stranded specimen measured with a tape measure, by a scientist, and remains the largest physically measured by a scientist to my knowledge. However, a 20 m specimen was reported in the scientific literature from the Taiwan fishery in the 1990s and an 18.8 m specimen was reported from the Indian fishery (summarised by Rowat & Brooks 2012, JFB).

There are predictable sightings of thumping big live ones in the Eastern Pacific every year. This area is the only place where the genuinely enormous 15 m+ females are regularly seen by divers. Two of the sharks tagged by Eckert and Stewart (2001, Env Biol. Fish) off Mexico were visually estimated at 15 and 18 m apiece.

Though not much is known about the size of female maturity (the smallest, and only, pregnant female was 10.6 m), male maturity appears to vary between around 7.5-9 m through their distribution, suggesting that there probably isn’t huge variation in maximum size throughout the world. The big sharks are out there somewhere – they’re just not often being seen!