It's nice diving with sea lions, but if you are spearfishing they might be a hassle scaring the fish at the bottom before you actually get there.
I have fought many times with the sea lions that try to steal your fish from your hands, it's not nice, specially with the big ones that tend to be more agressive.:ko
The ''fight'' consist in slaping the water, making noise and ultimately, just floating on your back with the fish on your stomach while trying to swim to the buoy. If the agression happens at the buoy just make noise and aim at them with the speargun (but never shoot!), the sea lion will circle around and under you for a while and hopefully it will give up.:martial
Most common is that they will try to steal the fish from the stringer, in order to avoid this you will have to attach a bag (mesh-bag-style) to the buoy and put all the fish there (through the stringer first and then in the bag). This will help a lot.
As it was said, try to not to dive among them if it's the matting season, the big males are more agressive than ever and might consider the diver a threat.
Diving with the younger ones is really nice, they are very curious and tend to bite everything to see if they can play with it, just like a dog, so watch out for your fins, snorkel, speargun and lines.
The rest should be fun, just enjoy it!:t :t
I have attached pictures taken in the Palomino Islands in Peru, where there is a permanent colony of sea lions...and some good fishing too.
Cheers,
Roberto