Many of us probably tend to take fish for granted, as it’s a fairly sustainable resource—at least, that’s what we’d like to believe. It’s difficult to imagine that we could even come close to depleting what seems to be limitless; after all, the earth is mostly covered in water. But as Ray and Ulrike Hilborn discuss in an excerpt from their book, Overfishing: What Everyone Needs to Know, there is reason for concern in our flippancy towards our complex ecosystem.
Overfishing is harvesting a fish stock so hard that much of the potential food and wealth will largely slip through our fingers. Yield overfishing is the most common. It prevents a population from producing as much sustainable yield as it could if less intensively fished. The population will typically be less abundant, but it can and often does stabilize in an overfished state. However, with extreme overfishing, in which the forces of decline are consistently greater than the forces of increase, the population would continue to decline and could become extinct.
Economic overfishing occurs whenever too much fishing pressure causes the potential economic benefits to be less than they could be. Many fisheries simply have more boats than needed to catch potential yield, and seasons have become shorter and shorter as more boats enter the fishery and catch the allowable harvest more rapidly. Far more money than is needed to catch the fish is spent on boat repairs, maintenance, fuel, and insurance. For example, governments may have subsidized vessel construction and fuel expenses or large fleets may have developed rapidly when the fisheries first began.
Related to any form of fishing is the ecological or ecosystem impact. Yet in that context there is no “optimal” level because, obviously, the actual number of fish in an ecosystem will decline continuously with increased fishing pressure; thus any amount of fishing can be said to be “ecosystem” overfishing, and to achieve the least possible impact means no fishing whatsoever. In some cases the total number of fish may be higher in a fished ecosystem if we remove important predators. However, any fishing is ecosystem overfishing to those with a focus on natural ecosystems.
But since we need to eat, let’s look at abundance.
There is a relationship between the abundance of fish in an ecosystem and fishing pressure, sustainable yield, profit, and ecosystem impacts. When there is little or no fishing, there is little sustainable yield and precious little profit. As fishing pressure keeps increasing, first the profit peaks and then at higher fishing pressure the sustainable yield peaks. As fishing pressure further increases, both profits and sustainable yield decline. And when that happens we are said to be in a state of biological or economic overfishing. Normally we would expect profits to be highest when the fishery takes less than the biological yield.
Overfishing has been with us since man first started fishing. Even with pre-industrial technology, natural resources could be overexploited, and we know that when humans first arrived in new parts of the world some of the more easily captured species were hunted to extinction. The historical record for fish is not as reliable as it is for land animals, but it is safe to assume that the most vulnerable species bore the brunt of first contact.
The concept of overfishing was already widely discussed in scientific circles in the second half of the 19th century. The British scientist Sir Norman Lockyer used the word in the journal Nature in 1877: “Nor does it seem to me quite worthy of my friend, in discussing the probabilities of overfishing in the sea, to try to prove his case by bringing forward an instance of overfishing in the rivers leading to a smaller supply of food.” That overfishing involves taking too large a portion of a population was well understood by 1900, when Walter Garstang of Oxford University wrote:
We have, accordingly, so far as I can see, to face the established fact that the bottom fisheries are not only exhaustible, but in rapid and continuous process of exhaustion; that the rate at which sea fishes multiply and grow, even in favorable seasons, is exceeded by the rate of capture.
The biology of overfishing is always a question of the “rate at which sea fishes multiply and grow” compared to their “rate of capture.”
As fishing technology got better, our ability to catch fish did, too, but the ability of the fish to multiply and grow stayed the same. Steam- and then oil-powered fishing vessels were the most important technological innovations. Trawl nets, which are dragged through the sea and were small when fishing boats still had sails, got ever larger as the fishing fleets switched to boats with ever more powerful engines after World War II. Other technological advances were made in fishing nets, especially cheap monofilament gill nets that almost anyone could afford. They are made of a near invisible mesh that traps fish behind their gills when they swim into the net. As these nets cost just a few dollars, their use spread around the world. Electronics such as global positioning systems (GPS) and fish-finders allowed fishermen to repeatedly find the same best fishing spots associated with reefs and rocks on the bottom and to do so in the fog.
We now have the technology to overfish almost every imaginable marine resource. The question is, do we have the political will and the social and cultural institutions to restrain ourselves?
Image Credit: Photo by stickfish. Public Domain via Pixabay.