To me, sustainability is the management of a resource that allows for it to be used over an extended period rather than being immediately exploited. Management is necessary in order for this to work, and planning ahead for the future is imperative as well. I agree with Solow in that the idea of sustainability is a vague idea that doesn’t have a clear path to achieving. It’s impossible to plan for the future and get it perfectly right because there are so many variables to consider, but this doesn’t mean that we should throw our hands up and harvest resources without considering if the action is sustainable.
Though I don’t necessarily agree that sustainability always hinges on the availability of substitutes, I do think that substitutes can help foster sustainability in some cases. The example of aquafarming compared to wild salmon is a tricky example. In theory, aquafarming should take pressure off of wild stocks since many people who consume salmon (at least outside of Alaska since we’re more aware of what salmon we’re eating) don’t know or care if it is farmed fish or wild fish, as long as they’re eating salmon. However, this way of thinking only encompasses the usefulness of a resource to humans. Just because it’s working out for us, it doesn’t mean that it’s a suitable option for ecosystems. Ultimately, if one species is eliminated then the ecosystem will suffer because species depend on each other to survive. Saying that something is sustainable just because there is a substitute waiting for us when the original resource runs out is irresponsible. However, if substitutes are implemented before the original resource is depleted, then sustainability can be achieved through the use of substitutes.