Having read through the Min Of Env document, the only mention of spear gun use being banned is when using compressed air - ie scuba diving
Article (52)
It is forbidden for diving hobbyists to:
5- Use fishing guns while using diving equipments (compressed
oxygen).
So looks OK for freediving spearos.
However, the document also states (Article 45)that
It is forbidden to... possess...atheistic materials used for fishing
So ensure your speargun is of the true believer type! 
