Harkerville area is fine to spear. as far as i know its not protected marine area. Ive done the 2 day hike twice and there are some really really nice spots to spear at. good entry and exit points. you'll obviously have to go off the trail to get to those. Most of the first day is spent hiking through the forest towards knysna, then its followed by a steep decent down the cliff and back towards plett along the coast. take extreme caution when hiking and spearing. there is no signal for your cell and if you fall or get injured in the water you'll have trouble getting help! the area is remote which can be a good and bad thing. if you maintain a good pace while hiking and start about 8am you should reach the hut where you will sleep after your first day by about 2.30pm. the hut is on a mountain which is preceded by your coastline hike. my suggestion is that you find a spearing spot just before the accent to the hut.when you start climbing to when you arrive at the hut should be about a 30min to 50min hike depending on how fast you walk. that should give you about 2 - 3 hours of spearing. Take note that there is no fresh water until you reach the hut where you should be able to get rain water. let me know exactly when you are here. i know a couple of short cuts in and out from the trail, early exits etc. if need be i know a road that goes to the hut where you will sleep mid hike. I've spent about 9 years fishing just about every section along the trail. Take care and good luck!!!
Pierre