"Four Fish" by Paul Greenberg is a mostly balanced and thoughtful book addressing the issues involving wild fisheries and aquaculture. There is one suggestion by the author that I find troubling though: the idea that wild fisheries can be managed much as a shepherd manages her flock.
The fallacy of this suggestion is that one cannot manage wildlife like one manages domesticated livestock. With domesticated animals we control the genetics of the animals, their range, what they eat, how we manage their waste and how many we raise and harvest. Wild species simply cannot be managed this way. Wild species are part of an ecosystem and when we tinker with one element of the system we can cause untold consequences elsewhere in the system.
The image of the fisherman-herder may be a romantic one that appeals to the author's nostalgia for fishing the way it was, however, it has no validity in wild fisheries management.
The 2020 North Sea cod quota was recently cut by nearly 70%. The reason given was that the original assessment of the species was wrong and that "new science" has shown that both spawning biomass and recruitment were significantly lower than estimated. Of course, intensive lobbying by industry and our elected representatives certainly helped in the ready acceptance of the "old science" that supported an artificially high quota level in 2019.
So how is it possible that the estimates for a marine fish population can be so terribly wrong? The simple reason: marine fisheries science is based on flawed assumptions, incomplete models and supported by inaccurate and incomplete sampling methodologies.
This fact is the 800-pound gorilla in the closet of marine fisheries management. The basic science underlying fisheries management was memorialized in treaties after WWII- the often-cited "maximum sustainable yield" ("MSY"). This concept was at the time a hypothetical assumption based on the centuries-old perception that the oceans were a limitless resource. In fact, the resource was vast but certainly limited as we now know. Unfortunately, the hypothetical MSY was already the treaty established standard in international marine fisheries management; and no one has been willing to change what has turned out to be the best possible formula for the commercial fishing industry.
Thus, for decades marine fisheries managers have been justifying and tweaking MSY to support the various fish quotas set-mostly with poor results. The mathematical models have gotten better for sure, however, the ability to sample and evaluate fish populations in the wild has not improved nearly as much. As we all know from basic computational science: "garbage in; garbage out." So that is where we are at with fisheries management- we are plugging in inaccurate and often blatantly wrong numbers into models that are incomplete and never fully validated. Result? Fishery science is largely guesswork that is only truly verifiable when a species disappears.
Disappearing, by the way, can happen on two levels when it comes to fish- ecologically and biologically. Ecological extinction has already occurred with bluefin tuna, that is, bluefin tuna no longer fulfill their role in the ecosystem as a dominant apex predator. Biological extinction has yet to catch up with bluefin tuna as evidenced by the fact that fishermen are still catching the fish and shipping it off to grace our sushi bars.
To illustrate the difference between biological and ecological extinction, imagine there being five lions left in all of Africa- so there are still lions left, but are they performing their expected role in the ecosystem? My guess is many a zebra family will sleep easier if there were only five lions remaining that want them for dinner- in fact, they will do more than just sleep!
By overfishing apex predators we dramatically alter the marine ecosystem in ways that overfishing prey fish would never do. And yes, as you probably recognize, most of our favorite fish to eat are higher up the food chain with the resulting disproportionate effects on the entire marine ecosystem. The chart above highlights the effects overfishing of predatory fish has on the entire ecosystem. This graphic, while helpful in visualizing the effects of fishing, is not so easily modeled and even harder to quantify which is why marine fisheries managers have an impossible job.
Thus, the effects that marine fishing has is nearly impossible to model on a single species basis- which is exactly what marine fisheries managers attempt to do every day. There is no mystery then as to why marine fisheries management is a doomed enterprise and as a result, our oceans will never be able to rebound from centuries of overfishing without a dramatic cessation of industrial fishing.
I note that fishing down the food chain is also problematic. It is not as simple as saying let's skip the tuna fishing and go for the sardines. In so doing we essentially flood the oceans with planktons and their jellyfish friends as the previously referenced chart highlights. This is not so good. Jellyfish are wreaking havoc in many local ecosystems with increasingly negative impacts. As for plankton, while at one level they absorb CO2 (good) they also increase ocean acidity (bad). This acidification of the ocean along with increasing water temperatures resulting from global warming will have devastating effects on many species- including many planktons! Furthermore, as plankton populations grow they will eventually transition from CO2 sinks (good) to CO2 emitters (bad). So overfishing has a link to global warming- who knew?
In sum, my guess is that we will continue to see wild fluctuations in quotas for wild fisheries worldwide based on "revised" data or poor science. I pray that soon we will recognize and address the urgent need to cease industrial-scale fishing of the planet's most precious resources.