9. Biomass, productivity, their economic analogs and sustainability Some resources are nonrenewable: When people exploit them, they don’t regenerate. As humans deplete nonrenewable capital stocks, our survival and prosperity therefore depend increasingly on renewable ones. But some renewable resources have such low resilience that our consumption essentially makes them nonre-newable, at least over time scales of human lifetimes. The lower their productivity or resilience, the more important it is for people to exercise self-restraint because resource biomass and produc-tivity drive economics that, in turn, are crucial to the prospects for sustainability.
One can gage prospects for sustainable use of renewable resources with a simple 2 2 table (Table 3). Its two dimensions are related because a fish stock’s biomass generates production of new biomass, just as capital generates interest or dividends. But biomass and productivity are also critically different. Species and ecosystems occur in all four quadrants, and their position in these quadrants determines economic incentives for human behaviors that, in turn, determine prospects for sustainability.Location, depth, biomass concentration (which all feed into the cost of fishing) and per unit value all affect whether a population is profitable or unprofitable to exploit, which largely determines whether people want to extract a resource. As Sethi et al. succinctly summarize, ‘‘Taxa with higher potential profit are targeted first, followed by progressively less economically attrac-tive alternatives [122].’’ Although deep-sea fishes are more expensive to exploit, those having sufficiently high biomass concentrations make tempting targets.In the deep sea there are some areas where biomass density, hence potential catch per unit effort, is high. These generally occur
where currents advect food, usually zooplankton, from larger areas. Such transported production is filtered by seamount invertebrates (e.g., corals) or captured by fishes such as orange roughy, which hover near seamount crests. But thesesi tuations are unusual in the deep sea; most high-biomass areas and fisheries have occurred shallower, on continental shelves and in epipelagic upwelling zones, where high productivity feeds the high yields of resources that would be sustainable if only our fisheries were well-managed.Whether a population can be sustainably fished is determined by Clark’s Law. It can be interpreted, for all practical purposes, to mean that people can only sustainably take living resources that exceed a productivity threshold, the percentage of annual biomass increment that exceeds prevailing annual interest rates. An insuf-ficiently productive fish stock cannot, in practice, be exploited