As we’re putting pressure on ecosystems of all kinds, polar, alpine, tropical rain forests, dry-land areas. We’re of course, also putting tremendous pressures on our marine eco systems and the oceans.
We know that we’re changing basic ocean chemistry. We know that we are poisoning the oceans with the pollution of coming from huge oil spills and other disasters and we are also degrading the biodiversity in the oceans through human activities, especially through the over fishing and over harvesting of marine life.
The oceans cover three fourths of the Earth’s surface area. And we know, of course, as we discussed many times that, our huge cities around the world hug the oceans, depend on the oceans for trade, for economic activity, for our food supplies, for our proteins, and, Invaluable, nutrients such as omega-3 fatty acids from, our fish intake. Back in 1950, the estimate is that the total ocean catch measured, in total metric tons was somewhere, around, 20 to 30 million metric tons of fish catch. By 1990, that had become around 90 million metric tons that perhaps a factor of three or four increase globally in how much we were taking from the oceans.
And that is even an under estimate of the true effect, because those numbers, as conventionally reported, don’t measure what we discard and throw back in the oceans. When fishermen catch fish in the nets, they also bring in a lot of bi-catch, or unintended catch, of marine life that they don’t want. And that’s not counted in the, harvesting of the fish, but it is an absolutely core part of the actual, over harvesting of marine ecosystems. You’re looking here at a fascinating graph which has a very important message and reality to it. The blue area shown here is the capture from the oceans, it’s the amount of fish taken, and marine life taken, in metric tons year by year. And it rose sharply, as I said, up to the 1990s. And then more or less leveled off. You might say that’s a good thing. But in a way it was force majeure in the sense that, that leveling of reflects the collapse of many fisheries around the world that had increased the takes so much that they had driven the fisheries to depletion, to crisis.
So that the amount that could be taken out was, was limited, increases were no longer possible and in many cases such as the, near, my former home when I was a professor at Harvard university up in New England. A complete closure of the cod fisheries because of the collapse of the cod fisheries after so much heavy fishing for so many decades. So that leveling off is a reality that came from the enormous pressures being put on ocean fisheries. It doesn’t mean that we’ve reached an equilibrium because many fisheries around the world continue to be driven towards depletion. And our, in a situation of crisis. Now on top of that is another green area of rising production of aqua-culture. This is going to managed fisheries, not in the open sea catch, as in a traditional fitching, fishing, but in raising fish industrially either on the coasts in many cases or in inland areas that are suitable for growing fish. China is the world champion of aquaculture. And as the limits to the marine catch have intensified, the markets for aquaculture have expanded. And that has permitted a continuing overall rise in the metric tonnage of fish that are consumed. That’s a good thing overall, because, of course, this is, a reflection of the fact that, fish are highly desired in our diets, and highly nutritious as well. But it also poses a whole new chapter of risks, for us, because aquaculture itself has huge impacts on ecosystems. The cultivation of fish in managed locales at the coastline or in fish farms in in the interior Can lead to spread of disease, can lead to excessive nutrient flows of many kinds, can threaten the biodiversity of wild fish through escaped varieties from managed fisheries in aquaculture and so forth.
But what the diagram shows is that we are hitting limits of the open sea catch, and compensating in part and on the whole, in a desirable way, through aquaculture. But only if that aquaculture itself is operated in a responsible matter, and that is a complex challenge given all the things that can go wrong with aquaculture. Now, how did this massive increase of catch occur? It came from a massive increase of fishing activity. Shown here, comparing the intensity of fish fleets in different fisheries around the world in 1950 and in the early years of this new century. And what you see is a massive expansion in the magnitude of the fleet coverage in this period. There were huge technical advances in the use of massive long line nets, which allowed for much greater capture, in the use of all kinds of remote sensing, satellite imagery and other kinds of sensing to identify where the fish are located in the use of ocean bottom trolling. to, that just scrapes up the fish on the ocean floor and other marine life, often completely devastating those highly complex, highly bio diverse marine ecologies as a result of all of this. And so, the consequence is that technological advances, as is often the case, has not been the friend of biodiversity and of ecosystem sustainability.
It has led to a huge depletion of fisheries, a huge loss of biodiversity, and a huge threat to the productivity of these marine ecosystems. One measure of how big the catch is, is an innovative measure that has been developed, that looks at the amount of photosynthesis needed to produce primary food products for the amount of fish take that is being and marine catch that is being harvested from the oceans. And so, one looks at the amount of primary production implied by the fish take as a fraction of the primary production in that fishery area as an indicator of risk. In other words, how much photosynthesis is being appropriated for the fish catch. Just as we looked when Professor Vetusak asked how much of the terrestrial photosynthesis is being appropriated for the human species. And we found the shocking number that it’s 40 to 50% of the net primary production. Well, the same thing is true for the amount of fish that we’re taking, so this is, again, human appropriation. Of net primary production, but indirectly, in the form of the fish take, and what you can see in these red areas, shown on this map are fisheries where the amount of net primary production associated with that amount of fish capture is already an endangered zone. 30% or higher in many cases of the total net primary production being, taken, in fish catch each year, implying that we are harvesting at a rate that is completely unsustainable for these fisheries.
Now, one implication of this is not only are we driving the abundance of fish down to levels that threaten their very survival, but we’re also changing the structure of the ecosystems as well. It’s called fishing down the the trophic chain or fishing down the food chain. Because the first fish to go are the high trophic fish, the large blue fin tuna, and others that are the big prized carnivorous or pacivorous fish that eat other fish, that eat other fish, that eat the plankton. And the net primary producers weigh down the trophic level and what, the fish ecologists, have done is to measure the average trophic level of the fish that are caught. Meaning, are we mostly harvesting fish that are the first, on, on the first line of eating, the photosynthetic output or are we catching fish up the food chain that are the, predators of the fish lower down. And what we find in, from the evidence provided by, the ecologists, is that over time more and more of the catch is lower and lowered down the trophic chain. And the reason is that humanity is very good at eating those prized fish, way up the food chain.
The predators of the predators of the predators and we value those fish, we catch them, we deplete them, they’re smaller in number and they’re highly valued and then, later on, we go to smaller fish and lower down on the food chain. And this is shown by these two downward sloping lines which measure, over the years, the average trophic level of the catch that is brought from the fisheries. The top blue line in this chart is for the marine fisheries and the red line lower down is for fresh water fisheries. And what’s superimposed on this is aquaculture where we’re growing fish that are higher up the trophic level. Now that is also complicated.
When we grow, in agriculture, fish that are high up the fish chain. It means those fish have to be fed smaller fish. Or fish meal and that means that that kind of aquaculture requires massive open sea fishing to provide the fish meal. To feed the, the growing aquaculture, and so, in this way, aquaculture maybe doesn’t substitute for the open, open sea excessive harvesting, but actually can exacerbate it if we are feeding piscivorous fish in the aquaculture. To the extent that the aquaculture is for fish that are that, that eat photosynthetic output rather than other fish, herbivorous fish. Then we don’t have that phenomenon. And, those kinds of aquaculture. For instance, tilapia, us, is a substitute rather than, a, an amplifier, of the, the, pressures on the open sea fishing. Now, the, the basic framework that fisheries ecologists use is a framework that asks how much can be taken sustainably. And they calculate or try to calculate a complicated concept of maximum sustainable yield of a fish type. And the question that they’re asking is, how much tuna can be taken from this fishery or how much anchoveta can be taken from this fishery or how much cod can be taken from this fishery without depleting the fish stock? And the basic question is, at what natural rate is that particular species, for example growing, within this ecosystem?
So that if that amount is harvested, it’s leaving that amount of species, unchanged year to year, and therefore in a stable population. The basic idea of calculating the maximum sustainable yield is to try to determine what is a safe level of fishing. That concept has become more complicated necessarily in recent years, because ecologists came to understand it’s not good enough to ask, for an individual species, how much can be sustained.
We have to take an ecosystem-wide perspective, so now the ecologists are calculating a maximum sustainable yield, based not on a single species framework, but on an ecosystem wide sustainability concept. Now, the most essential point is that humanity continues to fish more than the maximum sustainable yield. And thereby drive more and more of the fisheries into danger of depletion, ultimate collapse, even extinction of, certain, fishes, that are, depleted, and, and then driven to extinction. What can be done about it? Well, the key point is clear. One has to put a limit on how much fish can be taken. And this has led to many kinds of policy innovations, none of which is foolproof by any means, because these market pressures are relentless. But to try to identify the maximum sustainable yield and then assign permits for that amount of fish catch. And in some cases, to allow those permits to be traded, among individual fishermen, in which case their individual fish quotas. Or among groups or companies. But a kind of tradeable permit system, where the total number of permits given is in correspondence with what the ecology tells us is a sustainable amount of fishing is the main policy direction that has been taken. But, with all of the lobbying pressures, more quotas, don’t tell us there are limits, with all of the illegality of unmonitored, and undocumented, and illegal fishing these systems have in some cases shown results. But in other cases have essentially been brushed aside by legal and illegal forces, political and economic that have meant that the depletion has continued despite the attempt to put on these kinds of limits. Well, if the oceans were troubled only by the extent of harvesting of marine life, we’d have trouble enough. But it’s important for us to remember that the kinds of assaults of humanity on marine ecosystems is coming from many, many different directions. This map is showing the corals at risk along the coasts of the world and emphasizing that the reasons for this risk are multiple, as usual. Tourism over fishing, over exploitation of the coral reefs. Harvesting of the corals themselves using dynamite for fishing, pollution sedimentation, human activities driving corals also to depletion to threat of extinction for many coral species because of climate change and direct impacts on the coral reefs all over the world. This map is showing what we’ve mentioned many, many times, and that is, the run-off of nitrogen and phosphorus, leading to eutrophication and to hypoxia, to dead zones. Depleted of oxygen along the coasts of the rivers. Look at the entire eastern coast of the United States and the Gulf of Mexico coast of the southern United States, especially where the Mississippi river enters the Gulf of Mexico, the massive amount of dead zones there. Similarly, we see that in the North Sea. We see it around China and Korea and Japan. We’re there’s a tremendous amount of eutrophication taking place. And this map, we’ve seen before, is the step by step acidification of the oceans as the high concentrations of CO2 dissolve in the oceans. Create H2C03, carbonic acid, that acid attacks the shellfish, the calcareous species in the ocean, threatening whole classes of marine life. We’ve got huge problems we have some tools to address these. But I think the fair summary is that our oceans are at profound and still growing threat because of the pressures of human activity. We depend on the oceans in countless ways for our well being, for our survival. If we don’t take care and face up to these multiple assaults. We will face a growing crisis in, the not so distant future.