Spear fishing is far more harmful than hook and line fishing since the 'hunter' almost always kills the biggest prize he (or she)can find. Especially commercial fishermen.
The biggest fish are the most important ones since they produce so many more eggs and are proven survivors. Fact; A 10 kg grouper produces 97 times more eggs than a 1kg grouper.
Missed shots damage coral too.
This is utter BS!
Since others have already answered the lack of spearfishing bycatch issues I'll just address the rest of the lack of knowledge here.
1. Commercial spearfisherman: First of all this is an extremely tiny niche business, that is shrinking faster than any other form of commercial fishing. I've spearfished all my life and know a few of these guys. They stick to the high percentage shots on average fish most of the time, because they are the sure thing, they don't break or lose equipment like they do trying for bigger fish.
2. The big fish produce no eggs at all, because they have switched from female to male. Yes, many larger species are equally important as males, but many people wrongly think that trophy fish are the master breaders, when in fact these fish are past their prime. Fish are similar to many animals in this capacity.
3. Spearfisherman are excellent divers. They don't crash onto reefs like rookies. They have a deep respect for all marine life and understand the importance of preservation of coral reefs. They don't pollute the ocean with any monofilament line, tackle or nets.
4. Responsible H & L fishing is an environmentally sound method of fishing, but still the recreational sector of spearfisherman is minute in comparison to that of the anglers. Fewer fishermen means less consumption, pure and simple.
5. Which brings up the real issue... unsound fishing practices. Presently over 80% of the fish population are being taken by commercial longline boats with many miles of lines with thousands of hooks. Nothing survives... the catch is dwindling and the bycatch is huge!
BTW, the Gulf of Mexico regulations I spoke about above have been voted on and it looks like we are facing a 45% reduction in fishing both recreational and commercial in 2008.
Before you come onto a spearfishing section of a diving forum and blast spearfisherman, you better do your homework!
Here's a good place to start!
The FRA Fishing Rights Alliance
Chad