Blaasop... they had to choose a cutoff point.
The kob we get around cape town and up to Henties, is the silver kob. Same as in the pictures. These are sexually mature at 31cm or something. East of augulhas they are offshore and they come into the surf zone west of augulhas and up north. This is also why East of Augulhas you are allowed 5 from the boat if not mistaken, and it's also 50cm in stead of the usual 60 from shore, same as our usual shore based fishing west of augulhas but just one over 110. This is because the fish over 110cm is likely to be a dusky kob.
The dusky kob is usually the one caught from shore east of augulhas. They only mature at 95-110cm. Because every angler east of augulhas would start a small riot if they were only allowed to keep kob if it's over 110cm and the guys in the western cape could keep fish of 50cm, it seems the authorities made it 60cm, and you only allowed 1, in an effort to minimize the damage.
Hope that makes sense.
Silver west of augulhas, mature at 31cm = breeds quicker vs Dusky/daga kob east of augulhas mature at 95-110cm = breeds slower = can take less = taking big fish out the estuaries like the breede & Gouritz = serious damage