Why take out insurance?
When we know a lot about a system, it still seems sensible to guard against the unpredictable: natural disasters, human error, accidents and other unknowns. For example, supermarkets are very well understood systems, but a good supermarket manager, despite all the detailed knowledge, will have:
All of these cost real money, yet none of them have an exactly-foreseen function. They are a protection against potential hazard. Of course, there are smoke detectors, fire extinguishers, staff training, fire walls, inspections, etc. but there is also fire insurance. It is a sign of good management to not assume that one can foresee everything in precise terms, and to take general precautionary action as well. Furthermore, there will be no complaints from the owners if, after many years, no fires occurred and all the fire insurance money could be said to have been unnecessary! The owners also understand the need to cover against human error, natural disasters and other labels for hazard.
Oddly enough, when we know very little about a system, reasons for sensible precautions are not yet predictable. Compared to supermarket systems, where there are books about the best arrangement of the shelves, we know very little about any of the systems in the sea. But in the sea we tend to be satisfied with little or no insurance.
If we are told that a fisheries management program is the best practical option for the particular stock or species, we tend to say "Fine, no problem!" rather than "What are the risks and how can we guard against them?" It seems that if ignorance is both great and widespread, we lose sight of the need for precautionary principles just when we need them most.
Even when attempts have been made to measure the risks in fisheries and other marine management systems, we tend to accept very high risk levels. Warned of impending dangers, politicians and the public tend to worry about false alarms rather than the price to be paid if the warning is accurate. This is partly because of communal ownership of marine resources, but mainly because everyone has great difficulty in assessing the risks, or even imagining their nature. In the marine field, the "experts" are those who realise how ignorant they are - the others don't even know that much.
In the sea we tend to say, "What harm is it doing?" and challenge someone to produce clear evidence before we will even consider precautions or controls. We fail to notice that even the measurement of "harm" will be difficult if our "management" is general and our knowledge poor. What sounds like a sensible "If it's not broken, don't fix it." is really more like "We will take out insurance only when we can see the flames".
Marine reserves are not a substitute for careful and intelligent marine management, but they are a sensible part of it. At the very least they are a useful precaution against the unforeseen hazard. Every citizen knows this is wise even when we have good understanding and a high level of control. You put more oil in your car before you can "prove any harm". You keep a straight edge in the workshop so you can measure kinks and bumps. You keep some savings in the bank in case of unforeseen developments. You insure your property against fire, theft , and natural disasters.
But in the sea, we just "go for it" with a single management plan for each activity. When some reservation is suggested, we say "What exactly will this achieve?"