Storms and fog can slow and delay rescue efforts. You may be difficult to locate. Be self reliant, carry and know how to use a first aid kit, and consider consequences before taking action. Cell phones work on the islands, although not from every location. There are no public phones.
Rangers carry radios.
The park is a pretty safe place as far as theft, robbery, etc. is concerned. But it can always happen - take normal precautions. Some, not all, rangers carry law enforcement commissions and have powers of arrest. First, be prudent and avoid trouble in the first place. You are on an island 26 miles in the ocean.