(in which I tackle a fairly large subject and follow a few tangents
....but do my utmost to make “sense” out of this puzzle
...and finally propose a link between fishing and (gasp!) the rise in atmospheric CO2...)

Copyright © 2001 Debbie MacKenzie
February 3, 2001

My theory states that the living ecosystem in the ocean has experienced a significant loss of overall biomass as the cumulative result of human fishing. (“All take and no give,” our parasitic relationship with the sea in recent centuries has had the effect of causing a huge deficiency of organic material.) This offers a plausible explanation for the many changes that we are seeing today in marine life. Nutrient depletion has been insidious and continuous, and the effect is noticeably worse in ocean areas farther from the mainlands. At first not noticeable, now “food shortage” has reached a critical level for many ocean dwellers and signs of “nutritional stress” are everywhere...possibly since many of today’s sea creatures evolved to live in a “thicker broth” than the one they find themselves in today.

I have engaged a number of marine scientists in debate on this point and invariably the first objection that I get is this one:

“The nutrients that are being poured into the sea from land-sources are at an all time high, and they are of a magnitude much higher than the nutrients humans are removing by fishing. Therefore there cannot be a nutrient deficit in the sea. On the contrary, humans are contributing to the destruction of sea life by overloading estuaries and coastal waters with nutrients.”

The first and last statements are doubtless true. The mistake lies in the conclusion “therefore there cannot be a nutrient deficit in the sea.” Of course there can be. That’s rather like concluding that a farmer cannot be suffering from a drought since overall precipitation rates are very high and there is a problem with flooding in some places.

“Fixed” nitrogen is the most common limiting nutrient in marine systems, including the North Atlantic, so a close look at the “fixed nitrogen cycle” is warranted. I have been reassured by the scientists with the numbers that “total fixed-N in” exceeds “total fixed-N out”. These estimates are necessarily rough but their conclusion may well be technically true, more organic nitrogen is flowing into the ocean than is being removed by fishing or natural processes. But questions remain: (1) What is the fate of the organic nitrogen that flows into the sea? Where does it end up? (with a specific look at the likelihood that it might become incorporated into the body of a codfish swimming around on one of the offshore banks). (2) How much fixed nitrogen is “created” and “lost” normally in the ecosystem, especially offshore?

A significant amount of work has been done in this area, so answers to these two questions can be given with reasonable certainty.

First, what becomes of the huge quantities of nitrogen that are now entering the sea via rivers? (The contributors are human sewage, agricultural runoff of fertilizers and manure, increased input due to erosion, and nitrates arriving there via aerial deposition/fuel burning.) One effect is very well known, called “eutrophication” it’s a syndrome wherein the oversupply of nutrients stimulates overgrowth of algae, which then die and sink to the bottom where they undergo decomposition by bacteria which depletes the water of oxygen, killing fish and being generally unhelpful. But the nutrients in this scenario don’t get very far, they become part of the nearshore bottom sediment rather than effectively stimulating production in the food web as a whole or moving offshore to become “food” for fish on the offshore banks. Another thing that happens in the polluted rivers is that they become much more effective as functioning septic systems - i.e. conditions of high nitrates and low oxygen stimulate higher rates of denitrification by the bacteria that normally carry out that function. (It has recently been discovered that some “nitrifiers” will actually switch over and function as “denitrifiers” in these conditions, amplifying the nitrogen-removing effect.) This bacterial activity has the effect of changing much of the organic nitrogen into the inorganic form, which then no longer qualifies as a “nutrient.” Actually denitrification is a well-known process that occurs in the seabed, both nearshore and offshore, so it represents one of the normal “sinks” but it is greatly accelerated by the practice of dumping large quantities of concentrated, liquid nutrients into estuaries and coastal waters.

So, incorporation into the bottom sediment or denitrification...that describes the fate of the major portion of the nitrogenous “nutrient input” into the ocean. It never gets an opportunity to “feed the fish.” Nutrient pollution is commonly blamed for negative impacts on estuarine and coastal ecosystems, never offshore ones. That’s because it just doesn’t reach that far. Good research and references on these points are not difficult to find. Two sources on the internet are “Human Alteration of the Global Nitrogen Cycle: Causes and Consequences” by Peter M. Vitousek et. al. and “Ocean Sources and Sinks” by Fred Mackenzie et. al.

When I try to visualize the marine nitrogen/nutrient cycle, I can only see the ride in the fishing boat as being a “one way ticket” to land. There’s no way back to the offshore fishing banks for those “marine derived nutrients,” even if they are eventually flushed into the sea. No physical process provides the “horizontal” or “lateral” movement required to complete the loop. So that’s where the break is, unfortunately and unwittingly, through fishing, we have diverted a significant amount of nutrients/nitrogen that once cycled through the offshore ecosystem to the land and the margins of the sea. (“Vertical mixing” of seawater has been well researched and described as an important and continuous loop in marine nutrient cycling....the “horizontal” loop needs to be somehow completed as well, or the system may “accidentally” be drained of life.)

Doubtless some minor fraction of the organic nitrogen runoff is taken up and used by the nearshore food web, but it seems certain that this effect does not extend to the offshore areas. They are out there “on their own” ...offshore ecosystems must find their own way of replacing the building blocks for fish...

Off the coast of Atlantic Canada the continental shelf is relatively wide - and an exceptionally rich fishing ground once existed far from shore, the famous “Grand Bank” of Newfoundland. There the cod stock seemingly replenished itself for many years, “fishing removals” were somehow always replaced with more codfish. How did that happen? Was the offshore ecosystem actually “fixing” enough new nitrogen to do the job or is there (was there?) a vast pool of “extra” nutrients in the ocean that could easily and conveniently be tapped to replace what the fishermen caught? Or did the neighbours all “chip in” and allow the “exploited” cod to continue to flourish for as long as possible?

(1) Nitrogen-fixation - this method is just too slow, counteracted normally by denitrifying microbes on the seafloor, this process of the blue-green algae accounts for only a very small net annual gain. Scientists agree with me on this point: nitrogen fixation does not function at a rate sufficient to replace organic nitrogen removed by fishing. On an annual basis it’s contribution is trivial.....over many millions of years however, nitrogen fixation is the process responsible for the rich accumulation of life that was once in the sea.

(2) The pool of “extra” available organic nitrogen? Does something like this exist offshore? Like a food bank? I rather doubt it for these reasons - certainly there exists an ambient level of dissolved nitrates in the sea, and it is one of the many parts/key players of the living system in dynamic flux with all the others. This stuff represents the very bottom, available only to the phytoplankton, but nitrates need to find their way into the photic zone to enter ‘into the game’. Vertical mixing is one key physical process making the nitrates “available” and when the conditions are right, phytoplankton will reliably respond by “blooming” until they manage to deplete the nitrate level to the point that limits their own growth. So...if “extra” nitrates were really “available” in the would just stimulate an burst of phytoplankton growth and be consumed...if there really was a huge “vast pool” of extra “available” nitrates in the open sea...the result would be the same murky, hypoxic mess that we have in the estuaries - eutrophication. And that’s certainly not the case offshore. So, it looks like a lot of “available spare parts” there may not be in the open sea. The “vast pool” of nitrates that exist in the sea...for the most part they are in areas where they remain inaccessible to the phytoplankton (like the depths of the abyss), so for the purposes of this argument and the investigation into the “marine nutrient cycle” that number should be left out of the equation. It’s not “available” nor is it likely to become “available” for a very long time...all of the “available” parts are already in use. If organic nitrogen is “available” then it is promptly used by the phytoplankton, there is no system of “making withdrawls from a nutrient reserve” on an as-needed basis to replace human fishing removals. In other words the ecosystem never did “respond” to our fishing by “producing” more organic biomass.

(3) So, did the neighbours “chip in” and support the cod during it’s many years of “exploitation?” Yes, that’s actually the most likely explanation...supporting their “neighbours” turns out to be one of the “ecological services” commonly provided by sea creatures.

If so - how so?
What happened during the great offshore cod fishery?

Reproduction in fish differs remarkably from reproduction in other animals. Individual parents produce literally millions of viable eggs in excess of their replacement requirements. The vast majority of these offspring are destined to die very young, many consumed before they hatch, many more shortly thereafter. That is why a direct relationship between the number of parent fish in a stock and the number of surviving young has never been dependable, a likely source of some frustration for mathematical modelers. It’s also why many believed that “recruitment overfishing” could not be accomplished...although that’s another notion that has been retracted lately.

During the great cod fishery, the cod stock seemed almost invincible...since the annual dent in their “spawning stock biomass” (SSB) caused by fishing removals, was not apparently translated into decreased survival of their young...that outcome depended on other variables anyhow, those things affecting egg/larval survival, like weather patterns. If cod eggs were a bit less concentrated than usual, then a smaller number would be eaten by their predators since all “unexploited” groundfish species for instance, would have released their usual number of eggs. The fish that consume cod eggs or larvae, for instance, can only graze them down to a certain level anyhow - it’s not possible for them to locate and eat the last egg or larvae - the fish eggs’ protection kicks in when they become relatively scarce and their predators can no longer find many of them - (Predator-prey theory states that predators cannot eliminate their prey, they cannot chase down the last one, they can only lower prey abundance to a certain (approximately constant?) level - Therefore if fishing removed 30% of the potential cod parents (SSB), for instance, and as a consequence cod eggs started out at only 70% of the concentration that they would have been if no fishing had occurred....those eggs would just be grazed down to the same base level as before, “dilution” eventually protecting the usual number of survivors in the usual manner, and cod recruitment would appear to be as healthy as ever.

The effect of the cod fishery on the cod stock? Initially, it really didn’t appear to be much - hence, perhaps, the idea that “fishing doesn’t affect fish stocks.” The annual oceanic buffet of “fish eggs from all species” just started out containing somewhat fewer than before in the “cod section.” After the buffet and the consumption of the majority of all the fish eggs...the number of survivors left to hatch contained the same number of cod juveniles as would have been there if the starting number of cod eggs had been higher.

...So cod survival, specifically, was not clearly affected by cod fishing - recruitment in fish stocks is not easily related to the size of the “spawning stock biomass” that much is well known in fisheries science. So at first the loss - be it ever so slight - would have been felt by the consumers of fish eggs (as a group, no one species in particular taking the whole hit) - there was a bit less “food” available to this group since a portion of the adult cod had been removed from the system. This is one illustration of how the marine ecosystem as a whole would bear the brunt of fishing imposed on only one or a few “exploited” species. A very subtle effect, spread between many potential consumers...not noticeable for quite a long while in a system so large and rich...And the result of this? All fish egg consumers made do with slightly less to eat, and so as a group they also provided slightly less nourishment to their own predators, and so on...

So...beyond missing out on the potential to consume a few fish eggs and larvae, how else would the ecosystem feel the loss of the adult cod that were removed by fishing? What other “ecological function” will they no longer be performing? Well, their contribution to continued nutrient cycling would be gone - the normal function of constantly excreting phyto-fertilizer - and their natural ultimate fate would have been consumption by some other member or members of the marine ecosystem - so each fish removed by fishing does represent “missing nutrients” for some sea creature at some point... even for the phytoplankton that would have taken up and used the ammonia excreted from it’s gills...

These aspects of the life and death of fish and other marine life can be described as parts of the “ecological service” that they provide - their contributions to keeping the whole thing going. And in a system relying on an efficient recycling program, all participants continue to play an important role after death. Recently several research studies have concluded that the now-missing corpses of formerly abundant marine species represents a significant loss of nutrients that once were very valuable to the species that previously consumed them. Two examples are now fairly well known. The first is the Pacific salmon (the role is now recognized that their corpses played in providing nutrients to the stream ecosystem as a whole, their own juveniles included. This is very interesting, scientists are now trying to improve the situation by tossing dead salmon into the streams. That sounds dangerously close to what I believe needs to be done in the open ocean...). Secondly there are the “whale falls” (studies have shown that natural death in whales, with their corpses resting on the seafloor, provides important nutrients to a whole range of sea life). Here is an interesting quote from Ron Huber, part of his expression of protest of the Makah whale hunt:

“Numerous federal and academic researchers have noted the importance of deceased whales in local marine food chains. Gray whale bodies on the seafloor have been found to host very large aggregations of marine life, including numerous commercially exploited invertebrate species. See Smith, C.R. 1992. Whale falls. Chemosynthesis on the deep seafloor. Oceanus 35(3):74-78.

As a NOAA press release on February 17 2000 noted:

"Dead whales may tell no tales, but they are an undersea encyclopaedia to scientists who believe they may provide the building blocks for a variety of deepwater creatures.:

Craig Smith, a biological oceanographer at the University of Hawaii, is quoted in that press release as follows: "We are able to observe the three stages of ecological succession, or community change, that the falls pass through," Smith said. "The first attracts scavengers, such as crabs, sharks, and fish that strip most of the soft tissue from the carcass in as little as four months." - end of excerpt

While much of the research on whale falls has focused on whale corpses found in abyssal waters, it is reasonable to conclude that gray whales that have died and settled to shallower sea floors near the coast also provide critical nutrients and habitats. NOAA should determine the importance of whale falls from resident gray whale populations on the ecosystem of the waters off Washington State before concluding there will be little if any impact from a Makah whaling program.”

(This quote was taken from Ron Huber's webpage)

(One quick observation of mine: When dead marine mammals “foul” the shorelines, people often cart them away to be buried in landfills or incinerated...perhaps not a very intelligent thing to do with “the building blocks for a variety of deepwater creatures?”)

These realizations of the far-reaching importance of species to their ecosystems after death...this principle cannot apply only to salmon and whales. It must similarly be true for all of the others. (If whales, etc., are “nutrients” and the sea is depleted of whales, etc., then is the sea depleted of “nutrients?” I think so.) One point worth mentioning in the salmon-hungry streams and in the study of the fate of the whale falls, is how it seems to be significant that the food is a SOLID FOOD. “Bioavailability” is far wider (as in “available to whom?”) when the nutrients arrive in solid form. This is also nature's way. Pouring liquid fertilizer as a replacement in either example would obviously be far less valuable and more likely to be damaging to the system, so why do we think that it’s somehow OK in the larger picture?

(Idle justifying the continued killing of whales, the Japanese point out that whales are related to cattle...elsewhere “whale falls” are recognized as now-rare sources of essential nutrients in the sea...Europe is now in a panic over “mad-cow” disease and faces a huge disposal challenge for unwanted dead cattle....marine fish are fewer and thinner, often found with empty guts....I’m willing to bet that the prion could never leap from mammals to fish, in any case the question could be experimentally tested first...)

Another piece of evidence that suggests that the “neighbours” helped to bear the brunt of fishing exploitation is this: “exploited” and “unexploited” species are dropping together...we have just recently noticed this but it cannot be new, it must have been happening all along. The “unexploited” ones were the buffer, the great “biodiversity” ensured that each had only to give up a little bit to allow the continuation of the cod......we just never noticed it, the effect was too subtle, but everything has been gradually slipping down together.

Regarding the importance of “neighbours,” the significant thing competition-wise is the trophic’s the biomass of one’s trophic level as a whole that matters, not just one’s own species...and regarding prey the same thing is true. Today we are perplexed by the presence of apparently very poorly nourished cod on the “East Scotian Shelf,” partly because the area contains a higher than usual biomass of shrimp and capelin, known prey of cod. For the East Scotian Shelf cod, however, it’s not just the biomass of shrimp and capelin that’s the “all prey biomass” that is significant, and for codfish that once included the younger members of many other now-severely-depleted neighbouring groundfish species. So the cod are experiencing a prey shortage, as is well attested to by their current pathetic, “slinky” condition. The disruption that we have caused has imbalanced things in favor of “lowly” crustaceans for now. This is clearly temporary.

I describe the problem as a “nutrient” shortage. WHAT EXACTLY IS A “NUTRIENT?”

When I say nutrient depletion I do not just mean dissolved nitrates....I mean all fish and other marine life, all life stages, because all are ultimately nutrients for the others, constantly recycled and nourishing the ecosystem as a whole...a barometer that only measures “dissolved nitrates” or “phytoplankton level” just doesn’t “get it”’s the view of the carnivorous fish....“if you have a heartbeat, then you are a nutrient...or a potential nutrient.” From their point of view, and mine, there is not a shred of doubt that the ocean is suffering from “nutrient” depletion.

A few more thoughts on the “ecological functions” of fish, including those bigger, older ones who...well, what did they do? Growing “too slowly,” taking up space in their stock, fisheries management theory long held that the best thing to do was to fish them down, to remove “older slower growing components of the stock,” and supposedly to thereby provide more scope for rapid growth and “production” in the younger, faster growing components. (This kind of tuning taken too far however, would theoretically lead to “growth overfishing.”) I’m really not sure that approach was ever logical. How meaningful is a concept like “cod stock” and what, if any, relationships - mathematical or otherwise - can be assumed to exist between the bigger and smaller ones? The “removal of the old to allow more growth in the younger segment” idea...seems to rest upon an assumption that there is a bin of seafood somewhere, labeled “food for the cod stock” and if the big ones are not around to eat out of it, that then the little ones will profit and experience better growth.

Thinking that there must be some set amount of seafood reserved for “the cod stock” which would more “profitably” be fed to younger, faster growing fish, this is an example of how people think, not of how ‘Mother Nature’ thinks. We want to group all of the “cod” together, she seems more inclined to group fish together (at least for the purpose of parceling out the food) by their size, an imaginary bin of seafood would more likely be labeled “food for fishes that are approx. 6 inches long.”

One big problem with “our” approach is the fact that older and younger members of the same “fish stock” do not share the same diet; it evolves (to ever higher trophic levels) as they grow and age. Big cod are not in direct competition for food with little cod. Prey size, as a general rule, increases with body size. The juvenile, plankton-eating versions of cod actually share more in common with small fish like capelin than they do with adult cod - perhaps that might suggest a more useful way to assess, and classify, and think about them, than simply adding up all ages of cod in a single “stock biomass” measurement. Speaking in defense of the “unproductive” big fish...besides the fact that they did not steal food from the mouths of smaller fish, I would like to point out that one thing that the big fish did do was LIVE in the sea, and part of that involved constant excretion of ammonia which has the effect of constantly fertilizing the phytoplankton.....usable nitrates don’t only reach the photic zone via upwelling or physical vertical mixing of water layers. How significant was this ongoing contribution of the living, moving fish? Who knows? I tend to mention this repeatedly because I suspect that it might once have been fairly important to the “big picture.”

The interdependency of marine life is more circular than we seem to generally visualize it, we intuitively understand the dependence of the bigger things (fish) on the littler things (plankton) but maybe forget that the little stuff (plankton) equally depends on the presence of the big stuff (fish) - it’s a nice, if complex, symbiosis...”you feed me and I’ll feed you.” That’s why I characterized human entry and participation in the marine scene as being “parasitic” in my opening paragraph. (We like to describe ourselves as a “top predator” in the sea, but all that we really do is kill and carry away fish.) The real “top predators” that naturally evolved in the sea have been replacing nutrients appropriately all along. Their approach “works” and does not degrade or diminish the system. Our nutrient replacement program, on the other hand, leaves rather a lot to be desired.

I also wonder if the bottom-to-top mixing in the shallower areas might not have been enhanced when there were large herds of active bottom-feeding whales keeping things stirred up (maybe I like this idea, maybe I don’ sounds a bit like one of the effects of draggers, digging up the seafloor...although whales are/were a natural part of the living marine system - like the gray whales that once inhabited the North Atlantic - they would have selected the appropriate bottom areas for their grazing...the softer areas, no doubt, it’s very hard to imagine whales using their heads to smash apart the hard coral formations like the draggers have done ...but I digress...)

The preceding discussion was an attempt to understand the effects on a dynamic living system of removing fish from the sea - how it is that “the dominos fall both ways”, i.e. it’s not just the natural predator of the adult cod who misses a meal when she’s gone...the effect ripples through the whole living system, down to the phytoplankton and affecting ...if only ever so slightly...every level in between. One part of the sad joke is that there are not, nor have there ever been, any “unexploited” marine species...we have exploited them all by stealing away their food.

A tiny little, subtle draining effect like the one I have long would it take puny human fishing efforts to put a serious dent in the vast wealth of the living sea? ...Probably a couple of hundred years or more....check the history books, how long has it been since we started intense fishing and whaling?

Another way to look at it is this: Every year “Mother Ocean” shuffles the deck, finds that she has a few less “cards” (organic nitrogen that is actively in the game), distributes what she has left in a balanced manner among the current players...of course if she runs seriously short it’s the higher creatures that must do without first...they are more “expendable” in the system as a whole than are the lower trophic levels - if the lowest levels are not maintained the entire web necessarily collapses. Last in, first out...over the billions of years during which she built up the accumulation of life in the sea, Mother Ocean developed a rich and elaborate collection of “low” feeders before she could allow herself the luxury of adding the upper trophic levels, and the “apex predators.” Now she is forced to unravel her project. Mother Ocean was always careful to recycle her most precious building blocks, it was one of the secrets of her success, but sadly she has fallen victim to a land-based parasite that has no comprehension of this. Like any good mother she still places the highest priority on feeding her little ones. Therefore the “food bin” designated for “fishes approx. 6 inches long” will be emptied last. This abstraction may or may not “work” for you, but the trophic level of life in the sea is clearly being forced down. And maybe this explanation accounts for the widespread and progressive disappearance of the bigger fish today...

To sum up at this point, I may have rambled a bit in my discussion, but my objective was to discover how it is that fishing removals are now or were ever replaced on the offshore banks. Fixed nitrogen limits the growth of the phytoplankton so it seems reasonable to try to pinpoint it’s source - as the key replacement building block for the new fish that are “expected” to grow and replace the ones we have taken away. Terrestrial runoff and nitrogen fixation do not provide enough fixed nitrogen to replace what has been (and still is being) removed from the offshore marine ecosystem. I therefore considered the possibility that the impact of the loss is spread throughout the system as a whole, and described the scenario in some detail. I do not see another potential source for the replacement organic nitrogen. And I have yet to encounter another really plausible answer to these two questions

“How is it that the offshore banks accommodated very large fishing removals in the past, stocks seemingly rebounding or “rebuilding” easily year after year...and why is that resiliency not still there?”

“Why are there so many exceptionally small and lean fish among those that still survive in the supposedly ‘over-fed’ ocean?”

My theory could turn out to be right or wrong, I’s just that rather a lot of direct evidence seems to support it. However, alternate conceptions of the workings of the ecosystem and scientific models and theories of “sustainable fishing” need to find the answers to these questions if they are to be believed. **Here is where many will offer “fluctuating environmental conditions” as the driving force behind all the declines - sorry, that one just doesn’t cut it, at best it only offers part of the answer, part of the time. (see list of references at bottom of page)

Another scientific protest to my complaint about the depletion of marine biomass, is this one:

“The amount of biomass removed by fishing is such a minute fraction of the annual ‘productivity’ of the system, that the overall simply could not be depleted in this way. There is a vast reserve of organic nutrients contained in the sea in the very lowest levels of the web - fishing might contribute to altering the species mix but will never bring down the system as a whole, and the sum total of life in the sea will remain quite stable.”

Recent research, however, seems to refute this idea, the thinking that the marine biomass at the lower end is “orders of magnitude” greater than at the high end, as was once commonly believed.

Here is a very interesting paper by William Silvert: titled “Size-aggregation in Models of Aquatic Ecosystems” July 2000, a quote:

“The Eltonian pyramid does not apply to pelagic aquatic ecosystems, but little was known about the size structure of these systems until the pioneering work of Sheldon et al. (1972). Based largely on a series of plankton measurements collected during the 1970 circumnavigation of the Western hemisphere by CSS Hudson and supplemented by data from other sources on macrofaunal stocks, Sheldon and his co-workers showed that over a size range of almost seven orders of magnitude in linear dimension, which is a range of approximately 20 orders of magnitude in mass, the particle concentration varies by only a single order of magnitude when expressed as the volume of particles per logarithmic size range (in simpler terms, the volume of particles in the size range 1-10 um is roughly the same as the volume of particles in the size range 1-10 cm). Thus although there is a pyramid in numbers, with 10 um plankton being roughly 1,000,000,000,000 more numerous than 10 cm fish, the biomass pyramid looks more like a vaguely Tuscan column, as shown in . Although there is a slight taper to the column, the ratio of biomasses at the top and at the bottom of the food chain is remarkably constant, so much so that primary production is considered by many a good predictor of fisheries production (Nixon 1988, Iverson 1990).”

“Figure 1a” and “Figure 1b” in the article illustrate the two concepts, pyramid vs slightly tapered column. If “primary production is considered by many a good predictor of fisheries production”...might not “fisheries production” equally be considered a good reflector of “primary production?”

Along the same lines: current dogma holds that “fishing at lower points in the food web should result in higher yield (tonnage) of many interpretive puzzles today being why this is not so. Overall biomass depletion offers a good explanation.

We are still given reassurance that today’s trends only reflect changing climatic conditions, although it is often hard to elucidate exactly how...and that we need not worry about a decrease in the global tonnage available to us.

“Thus, and most importantly from the perspective of this report, while past changes in ocean climate on a decadal scale and through NAO and ENSO events have resulted in changes in distribution, survival rates, and growth rates of fish, there is at present no clear basis to forecast what future climate change will do to these variables (IPCC 1996). Because of the differences among regions of the oceans in responding to climate change, the IPCC (1996) report concludes that there will not likely be major changes in total global biomass of fish stocks. However, there may be some effect on regional spatial distribution of fish populations, which may in turn affect the relative abundance and species composition of fish communities in some areas. In this context, Frank et al. (1990) speculated that long-term climatic change would lead to a general warming and freshening of coastal Atlantic waters and predicted northward shifts in spatial distribution of some groundfish stocks, changes in migratory behavior of some pelagic fish species, and a trend towards replacement of groundfish communities with pelagic fish communities. These changes would have significant implications for those human communities that rely on local groundfish stocks. However, the uncertainty in the prediction of such future changes is large.” (Paul deYoung et al. “Canadian Marine Fisheries in a Changing and Uncertain World” 1999)

“Uncertainty” is the key word here. Rather than a northward shift in spatial range, some groundfish stocks are simply contracting their ranges, or moving inshore. The northernmost stock of Atlantic cod (Labrador) seems to have disappeared. Some crustaceans are moving southward, like the snow crab in Atlantic Canada, and the total global harvest of wild fish is dropping. The “climate change” explanation is getting very shaky.

Finally, I have been told by scientists that: “There is no proof that the ‘total marine biomass’ is being lowered.” Of course a comment like that doesn’t prove that the “total marine biomass” is stable, rather it probably just proves that the question has never been asked. Along this theme, a major new research endeavor was announced in the year 2000, called the “marine census,” my understanding is that it will be the first ever scientific attempt at actually quantifying the total amount of life in the sea. Good idea, but rather late in the game...

I see evidence that the “total marine biomass” has been lowered. Some scientists point to the (relatively stable) levels of dissolved nutrients and phytoplankton offshore as proof that “productivity” and “food levels” there are as healthy as ever. What does it mean, a measurement of phytoplankton (or chlorophyll) density, for instance? Well, it provides a snapshot of one part of a dynamic system, but drawing conclusions about the health of the system as a whole from a peek at one a very dicey business. Records kept off Atlantic Canada over the last 40 years actually show somewhat of an increasing trend in phytoplankton levels A good sign? Maybe, maybe not. Phytoplankton are able to respond very promptly and dramatically to the availability of nutrients and sunshine. This of course is well known. I have read that, under favorable conditions, the “standing stock” of phytoplankton can increase by 100% in a single day. But they are constantly being grazed down by their consumers, the zooplankton. It is therefore a moving picture. Interpretation of the significance of a measured phytoplankton level can only be done in the context of the co-existing zooplankton level, since “the phytos do the growing and the zoos do the mowing” simultaneously. It’s tricky. Anyhow, data over the same 40 years in Atlantic Canada show a significant declining trend in the abundance of zooplankton What does the phytoplankton “produce?” Does it “produce phytoplankton” or does it “produce zooplankton,” or does it perhaps “produce fish?” Interpretation of “production” in the ocean can become fuzzy. If we are going to look at snapshots, at least we should put them all on the table together before we try to draw conclusions about the big picture... “cod stock” snapshots, “whale stock” snapshots, etc...(Satellite pictures?...the most important lesson about the sea that we can learn from them is that the ocean is the major feature of this planet, and it has “everything” to do with sustaining life here.)

The recorded drop in zooplankton abundance in the Northwest Atlantic is not an isolated incident. A steep drop, a decrease of 70% over a few decades, has been recorded in parts of the North Pacific. Major changes have occurred in the Bering Sea ecosystem, a dramatic shift in the picture occurred in the late 1970s, largely triggered (probably - I don’t dispute the idea) by a relatively quick shift in climate (El Nino). There has been a lot of interest and investigation into what is termed the “carrying capacity” of the Bering Sea - it seems to be dropping. There have been a couple of El Nino/La Nina cycles there since the 1970s, which should be bouncing the “productivity” alternately up and down - a bit simplified, but that more or less seems to be the theory. Some of the plankton consumers keep their own records, however. And what they have experienced, since before 1970, is nothing but a steady downward trend in food availability. They are the northern plankton-feeding whales, the “bowheads.” Although an endangered species, they are the targets of an aboriginal hunt, and therefore bowhead whale specimens have been available for study by biologists. Here’s a quote from Donald Schell:

“The story it tells is amazing because the whale baleen reflects phytoplankton productivity quite well. The record shows that from 1946 to 1963 everything went along fairly smoothly at a relatively high rate of productivity. And then in the mid-1960s it increased and peaked at around 1965. Then ocean plankton productivity began to decline, and since the mid-1970s it has gone down and down and down. The last samples we have from 1994, 1995 and 1996 show the lowest primary productivity in the Bering Sea over this 50-year period."

So this has been the feeding experience of the bowhead whales in the Bering Sea, despite a recent increase there in “gelatinous zooplankton” - I can only presume that that stuff must be “too watery” for a whale to derive much benefit.

Dear Reader, You have read this far, thank you. That was the tame bit, not so very radical, now here’s where I really stick my neck out...we’d might as well follow this story to its natural conclusion... “to the bitter end?” your mind just a bit wider and consider this:


Looking backward, trying to imagine a time when the big cod were so numerous on the Grand Bank that they slowed the progress of John Cabot’s ship...what an incredible, awesome mass of living fish!...they inhabited the ocean year round, in constant motion, fins and tails, bursts of speed in the endless drama of predator and prey, action packed, “mix it up”...a multitude of fishes of all sizes, all exhaling ammonia from their gills, forever stimulating the growth of the phytoplankton, thereby constantly adding fuel to the fire of life. Keeping the web of sea life pulsing and humming at a high pitch, “revving it up” the whole time. The great schools of living fish accomplished this by their very existence, it was a part of their “ecological function.” Those fish are all but gone now...and the sea life is much quieter than before. There’s not much going on, little fish only, remnants of the formerly great stocks are what is left, and it’s far too silent. Eerie...I find it, in dreams I try to remember what it was before...such a racket above, millions of screaming seabirds, the noises of the great colonies of marine mammals and the whales...just imagine the great whales! ...and such a frenzy of silent activity below the surface of the water....was a sea like that ever real?

Can we understand the implications of what we have unknowingly done? Can we allow ourselves to even contemplate the dreadful possibility? (To understand the scale of the destruction, I cannot recommend highly enough that you read Farley Mowat’s “Sea of Slaughter.”)

He wrote: "Our understanding of the present and our ability to plan with wisdom for the future rest on possession of sure knowledge of the past...perhaps with luck, this record of our outrageous behaviour in and around the Sea of Slaughter will help us comprehend the consequences of unbridled greed unleashed against animate creation."

An amazing book, shocking and depressing, if you have not read it, you must. You are missing important information. Looking back at this story is the first step in “comprehending the consequences...” And just how serious might those consequences be?


Atmospheric carbon dioxide levels are rising sharply on this planet, starting with a relatively abrupt upswing two hundred years ago. This coincides well with the mushrooming of human population and technology, and most people believe the two are connected. Most also believe that the rising CO2 is causing “global warming” and we are starting to worry. Predictions for future instability (possibly rapidly accelerating) in the climate are becoming more and more convincing. How has human activity and technology caused the rise in atmospheric carbon dioxide? CO2 is a byproduct of burning fossil fuels, which is now a widespread practice of, “case closed”...that’s what’s primarily causing it. Or is it? The “burning fossil fuel” theory is very appealing, but a close look indicates that the data does not fit as well as it might be expected to. The time frame is not quite right, and there are a couple of other little glitches as well...

First look at the earth, it may be easy for us to forget this, but by far the largest feature on the planet is the ocean. One early astronaut labeled earth “the blue marble,” and it’s easy to see why. If you turn the globe so that you get a view of the south Pacific, practically the whole thing is blue. And we do realize that life started in the sea, and that the sea life as it developed determined the composition of the atmosphere, that was favorable for us all. We acknowledge the importance of the ocean as a moderator of temperature and as holding large amounts of the atmospheric gases in solution. That is the passive function of the water, and it’s basically unchanged. But the thing that actively impacted the atmosphere in such a life-enhancing way (increased oxygen and decreased carbon dioxide) was the LIFE in the sea, not the water alone. The growth of sea LIFE, starting with the action of phytoplankton, has the effect of removing CO2 from the air. The health of the atmosphere on this planet (especially the maintenance of CO2 and O2 levels) is therefore largely a function of the health of the sea life.

As I have explained in my earlier discussion, the reason that sea life is not growing particularly well at the present time is because such a great quantity of organic matter has been physically removed by fishing. Land plants have responded to the increase in atmospheric CO2 by increasing their growth - but strangely, the phytoplankton (the most “atmospherically” important vegetation on the planet) has not. This might seem strange until one realizes that the problem is simply a lack of fertilizer (organic nitrogen mainly, although iron may also enter into it). Where did the fertilizer go? Well, it was originally contained in the bodies of the fish that we caught. When land plants react to higher availability of CO2, the “aerial fertilization effect” results in a greater accumulation of plant growth, taller, thicker trees, for instance, and this is recognized as a place that CO2 then becomes sequestered from the air (a “carbon sink”, a good thing). Phytoplankton are small however, and they stay small. They don’t store the extra CO2 - that they would absorb if they could - by growing to larger sizes. In the open ocean phytoplankton to a large extent is “grazed down” by the zooplankton (of course some of it dies and sinks) so accelerated plant growth at sea would translate ultimately into more fish flesh rather than more plant matter (as in a forest, for instance.) The carbon sink that is triggered on land takes the form of more and bigger plants, but in the ocean the carbon sink would be or “should be” more and bigger FISH. So...stimulate the growth of a forest by increasing atmospheric CO2 and you will see bigger trees, stimulate growth of phytoplankton in the ocean and you will see a greater accumulation of fish...a carbon “sink” that “swims!”

If I am right in speculating that the entire marine ecosystem has borne the brunt of fishing and whaling removals, and there is just a smaller quantity of organic nitrogen in the system now to be recycled, and I think that the effect could be described as a lowering of the “metabolic rate” of the oceanic system as a whole. Static measurements of absolute chlorophyll or phytoplankton levels may not necessarily show a drop, but less “stuff” may be being processed through the system all the same. I keep thinking about the hordes of codfish once exhaling all that ammonia, stimulating little bursts of phytoplankon growth that supported the higher density of zooplankton...I just suspect that the “turnover rate” or “primary production” was once much, much higher thanks to all the fish that were there. With less to work with in recent years, Mother Ocean has had to ease back on the throttle, scaling back production...

What fishing has done, the cumulative and increasing effect, is to hamper the ability of the phytoplankton to remove CO2 from the air as it would normally do, it has been “undercut”...and the result of this has been the steady rise in atmospheric CO2 levels. Since there never really were any “spare parts” in the ocean, whatever was removed was missed...and it has gotten to the point where our best atmospheric buffer does not work very well anymore. Fishing and whaling technology underwent a rapid expansion and then were sustained at a high (and increasing) rate thereafter - that’s exactly what’s been observed about the “burning of fossil fuels” and “CO2 emissions.” But look at the graphs (this one was taken from and decide which potential trigger fits best with the evidence...

The record shows today’s climbing CO2 level starting a good two hundred years ago, around the turn of the nineteenth century. A quick look at the burning of fossil fuels shows this: coal, peat and firewood were used for many centuries before that for home heating and cooking, so they cannot be implicated. This fuel burning practice did not undergo a dramatic or sudden expansion at any point. The steam engine was invented in the 1700s, lots of experimental designs were tried, but there was not a great proliferation of the technology in that century. In 1807 the first internal combustion engine was designed by Francois Isaac de Rivaz (he made a vehicle that used a mixture of hydrogen and oxygen!) The first gas engine was built in the 1860s and the first diesel engine in the 1890s. Cars only became a commercial success after the turn of the twentieth century. Sure, a lot of factories sprang up during the “industrial revolution,” but whatever it was that triggered a measurable increase in the GLOBAL concentration of CO2 had to be well “in gear” and established considerably before 1800. Did fishing and whaling undergo a dramatic expansion before that time? Most definitely they did, which makes removal of life from the sea a very plausible explanation as the trigger for the rising CO2 level. It is probably safe to say that wholesale involuntary physical removal of sea creatures to the land - is an unprecedented event in the history of the planet.

Look a little closer, this is interesting... In “Carbon Dioxide and Global Warming” Idso and Idso rightly state: “The observation that two things have risen together for a period of time says nothing about one trend being the cause of the other. To establish a causal relationship it must be demonstrated that the presumed cause precedes the presumed effect. Furthermore, this relationship should be demonstrable over several cycles of increases and decreases in both parameters.” A significant expansion of whaling and fishing activity did precede the start of the current CO2 rise, the “industrial revolution” by and large did not.

“Demonstrable over several cycles of increases and decreases in both parameters?” That will be fairly tough. However, in an article titled “Atmospheric Carbon Dioxide” Vincent R. Gray writes:

“Between 1935 and 1945 the atmospheric carbon dioxide concentration was constant, or even declined slightly. The reason for this is unknown.”

So there was a little leveling off in the midst of the otherwise steadily rising trend. What happened then? World War II, of course! Not a time for a cutback in the burning of fossil fuels, but WWII was a time of a SIGNIFICANT DECREASE IN FISHING EFFORT! Yes, in wartime our "give and take" relationship with the sea briefly looked quite different. Besides taking much less out, we put more in...transatlantic movement of people, and discharge of raw sewage into the open sea, was at an all time high, as was the number of men lost at sea...remember the "Battle of the Atlantic?" I remember reading somewhere about the remarkable increase in the North Sea fish stocks during the wartime. Proof? No...but getting quite close to a “demonstrable increase and decrease in both parameters.” It goes without saying that intense fishing resumed after the war, as did the rising trend in the atmospheric CO2.

Gray makes another comment later regarding the records kept of CO2 levels:

“Also the measurements are deliberately biased. The New Zealand results, for example, are only registered when the wind comes from the sea. The figure from the land is lower, but they do not want to know...”

Wow! Atmospheric CO2 is higher over the sea than it is over the land? Very strange, indeed...

The potential atmospheric benefit of increased phytoplankton activity has certainly been considered by others. Proposals to add liquid fertilizer (or particulate iron in one case) offshore are too risky, and this is acknowledged. Either one would probably trigger an unnaturally high phytoplankton response with the potential of unforeseen negative consequences for other life, although they would draw some CO2 out of the atmosphere. (It would be safer to provide solid food, some approximation of “dead fish” and “dead whales.”) “Tech-fixes” proposed for the atmosphere have included using the ocean as a CO2 sink, someone wanted to pump liquid CO2 down to the seafloor. Horrible, that would kill life locally, and then potentially make a sudden rise to the surface and asphyxiate any nearby airbreathers while causing an increase in the CO2 in the atmosphere. The “marine carbon cycle” is naturally coupled to the “marine nitrogen cycle,” we know that, so let’s take advantage of it. The safest route to improving the CO2 situation is going to be to STOP FISHING AND WHALING, and then turn around and FEED THE FISH!

"Education, I fear, is learning to see one thing by going blind to another."
- Aldo Leopold

Aldo Leopold was a renowned ecologist, but unfortunately for the creatures of the sea he lived inland. Brilliant, however, he also wrote:

"Conservation is a state of harmony between men and land. By land is meant all of the things on, over, or in the earth. Harmony with land is like harmony with a friend; you cannot cherish his right hand and chop off his left. That is to say, you cannot love game and hate predators; you cannot conserve the waters and waste the ranges; you cannot build the forest and mine the farm. The land is one organism. Its parts, like our own parts, compete with each other and co-operate with each other. The competitions are as much a part of the inner workings as the co-operations. You can regulate them--cautiously--but not abolish them.

The outstanding scientific discovery of the twentieth century is not television, or radio, but rather the complexity of the land organism. Only those who know the most about it can appreciate how little we know about it. The last word in ignorance is the man who says of an animal or plant: "What good is it?" If the land mechanism as a whole is good, then every part is good, whether we understand it or not. If the biota, in the course of aeons, has built something we like but do not understand, then who but a fool would discard seemingly useless parts? To keep every cog and wheel is the first precaution of intelligent tinkering."

THE "OUTSTANDING DISCOVERY" OF THE TWENTY-FIRST CENTURY HAD BETTER BE THE "COMPLEXITY" OF THE OCEAN-PLANET ORGANISM!...rather than some utter irrelevancy such as the composition of the moons of Jupiter...


(*You may wonder at the connection between some of these references and the article above, although I did not refer to every aspect directly, for example the deep-sea fisheries and the Antarctic fish stocks, this is a representative list of the literature that I have read in an attempt to explore the current scientific understanding of the marine nutrient cycle and in search of evidence that contradicts my theory.)

J. Boreman, B. S. Nakashima, J. A. Wilson, and R. L. Kendall, Editors “Northwest Atlantic Groundfish: Perspectives on a Fishery Collapse” American Fisheries Society: 1997

Cushing, D.H. “Climate and Fisheries” London: Academic Press, 199?

deYoung, Brad, et al. “Canadian Marine Fisheries in a Changing and Uncertain World - A report prepared for the Canadian Global Change Program of the Royal Society of Canada” Ottawa: NRC Research Press, 1999

Duhamel G. and J-C Hureau “Biology and Status of Exploited Antarctic Fish Stocks: A Review” Cambridge, England: Scott Polar Research Institute, 1985

Embree, Harland D. and Harold J. DeBey. “Introduction to the Chemistry of Life” Menlo Park, California: Addison-Wesley Publishing Company, 1975

Gomes, Manuel do Carmo “Predictions under uncertainty” St. John’s, Newfoundland, Canada: Institute of Social and Economic Research, Memorial University of Newfoundland, 1993

Gordon, John D. M., Nigel R. Merrett, Richard L. Haedrich. “Environmental and Biological aspects of Slope-dwelling Fishes of the North Atlantic” in Hopper, Alan G. (ed) “Deep-Water Fisheries of the north Atlantic Slope” the Netherlands: Kluwer Academic Publishers, 1995 (pp1-26) And from the same book: “Structure over time of an Exploited Deep-water fish assemblage” by Richard L. Haedrich (pp27-50)

Howarth, Robert, et al. “Nutrient Pollution of Coastal Rivers, Bays, and Seas”

MacKenzie, Debbie. “Wake up and Feed the Fish! A new insight into the causes of the Collapsing Fisheries” self published, Yarmouth, Nova Scotia, Canada: 1999

Mackenzie, Fred, Karen vonDamm, Dave DeMaster, Tom Church, Billy Moore. “Ocean Sources and Sinks”

McLeod, Guy C. and John H. Prescott (eds) “Georges Bank: Past, Present, and Future of a Marine Environment” Boulder, Colorado: Westview Press, 1982

Merrett, Nigel R. and Richard L. Haedrich “Deep-Sea Demersal Fish and Fisheries” London: Chapman and Hall, 1997

Mills, Derek, (ed) “Salmon in the Sea and new enhancement strategies” Fishing News Books, 1993

Mowat, Farley “Sea of Slaughter” Toronto: Bantam Books, 1984

Nixon, Scott. et al. “Study Reports Human Impact on Global Nitrogen Cycling greater than originally believed” University of Rhode Island oceanography professor, - I have lost the URL for the full document which I originally found online, here’s a link to a press report on it:

Rounsefell, George A. “Ecology, utilization, and management of marine fisheries” Saint Louis: The C. V. Mosby Company, 1975

Vitousek, Peter M., John Aber, Robert W. Howarth, Gene E. Likens, Pamela A. Matson, David W. Schindler, William H. Schlesinger, and G. David Tilman. “Human Alteration of the Global Nitrogen Cycle: Causes and Consequences”

______Canadian Department of Fisheries and Oceans, online publications, too numerous to list but here’s the link to their index:

______Fisheries Resource Conservation Council, publications online, here is their index: (these are large “pdf” files but the FRCC gives out paper copies on request, you can contact them through their website)

______”Joint Global Ocean Flux Study”

______ “Proceedings of the NATO Advanced Researach Workshop on Deep-Water Fisheries of the North Atlantic Oceanic Slope” Hull, U.K.: Kluwer Academic Publishers, 1995

______“The Fish Resources of the Ocean” FAO, 1971

**Also, I have been greatly helped and enlightened by the scientists and others who have debated this theory with me online, thanks to “FISHFOLK” and “FISHSCI” members ;>)

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Copyright © 2001, Debbie MacKenzie


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