A fundamental challenge, it seems, is that the systems we might try to manipulate are so complex and dynamic as to be largely unpredictable. With all those different species, each with its own idiosyncratic natural history, each somehow linked with so many others, it's awfully hard to be sure that pressing any given circle, and thus tugging certain threads, is going to have exactly the predicted effects. You might set out to support cod or crab, and end up bouncing something else altogether. After all, no one had much idea what bearded gobies could do until they overcame the Benguela.
Another challenge is that the instruments with which we press and tug on the web are awfully blunt: trawls, vast nets, mile-long lines with hooks dangling below. Such tools cannot be used to trim a single circle in the diagram; rather, they harrow whole neighborhoods. As a result, to get that annual 160 billion pounds of seafood we keep, we scoop out fully twice as much. So manipulating an oceanic ecosystem might be like doing cat's cradle tricks while wearing boxing gloves.
And we haven't given a thought to the ecological effects that are not depicted in our diagram. Remember that success story of restoration in Yellowstone? It turns out the wolves helped repair riverine woodlands not so much by killing deer as by terrifying them, and thus keeping them from lingering lazily riverside, browsing down their favorite herbage. What ecologists call "the landscape of fear" is now known to be important in seascapes, as well. And the implication is that we cannot stand-in, ecologically speaking, for the predatory fish we take out, even if we also catch the prey they would have eaten. Sophisticated as we may be in our understanding of the trophic web, we can't pull off a good impersonation of tuna.
For all these reasons, Management 505: Advanced Oceanic Biomanipulation is maybe a harder course than we'd like to enroll in. But unfortunately, we may have little choice in some cases—when things have gone desperately awry, for instance, as they have in the Benguela; or when an ecosystem is just now wobbling between different paths, and even conservative management—keeping the recent status quo—represents a momentous choice. Ironically, on the Scotian shelf, where the prospect of oceanic manipulation was brought to the fore by the stubborn collapse of cod, it is now being raised, once again, by the cod's belated and surprising recovery. Kenneth Frank has recently shown how one regime shift may eventually give way to another: The herring population, having gained ascendancy over its predators, became so abundant that it overshot its own food supply. Fluctuations of the population have ensued, and in the deeper dips, the cod may just recover—provided people aren't fishing for it. And so the top-predator, it seems, may soon reclaim its name.
That is, if we let it. And this raises what is, perhaps, the hardest challenge for a program of intentionally tilting ecosystems into arrangements that maximize value. As is often the case in economic arguments, "maximize value" is a phrase that sweeps an awful lot of complexity under a semi-technical rug. The really tough question is: value to whom? After all, cod fishermen and shrimp fishermen are not the same parties. And you cannot decide what to do simply by summing the total price fetched or profit garnered by a season's shrimp and comparing it with that of cod, because the different kinds of fishing entail different sorts of workforce, different distributions of wealth in the community, different ways of life. Deciding to manage for groundfish or shellfish is effectively to make choices in all of these arenas at once. And yet, the dynamics of the ecosystem dictate that, like it or not, a decision will be made.
In Bahía de los Ángeles, too, I have glimpsed what complications may hide behind pesos and pounds, the simpler measures of a fishery's value. The Humboldt squid—that creature my students hoisted from the deep—supports what is, by weight, the Gulf of California's largest fishery, amounting to about a quarter of a billion pounds per year. In view of such scale, it is surprising to realize that, prior to the late 1970s, no one in the northern gulf ever fished for squid, because there were hardly any there. What fishermen pursued instead were large fish, such as tunas and jacks. But then, in yet another variation on the ecological theme, the tunas and jacks were fished down, and their rarity helped open the way for squid. And since squid are voracious predators of just about everything, it is likely that their consumption of young tunas and jacks has helped maintain the new regime.