Something is Rotten in the Gulf of St. Lawrence:
Eco-logical reasons to abolish the Canadian harp seal hunt

By Debbie MacKenzie
February 11, 2005

 Cod stocks cannot “rebuild” where life at the sea bottom is increasingly stifled by rot, as in Canada’s Gulf of St. Lawrence, early in the 21st century. Modern “ocean ecosystem managers” must realize that dead seals increase the ominous environmental problem of “rot,” while live seals act to curtail it.

A silent killer: the oxygen content of the bottom water has been steadily falling for decades in vast regions of the Gulf of St. Lawrence (1). While the reason for this is officially unknown, the ill effects of oxygen loss on the health of cod (and other fish) are well understood by scientists. It can kill them (2). This mounting problem signals, in essence, the advance of rot in the very ecosystem. A dying ocean, a thing starting to decompose.

(click to enlarge)

"In the northern Gulf, cod avoided areas with less than 30% oxygen saturation, which is close to the incipient lethal threshold (28%) determined in the laboratory. However, a large proportion of the stock was found in waters with 30-70% saturation in 1991 and 1995..." (Dutil et al, 2003 (ref 2))  DFO's authors went on to explain that cod feed, grow and swim more efficiently in the presence of more oxygen - up to 70% oxygen saturation, above which there is no further positive effect. Between 70% and 30%, cod health declines as oxygen declines. Below 30% oxygen saturation, cod begin to suffocate and die. The area affected by lethal hypoxia is expanding in the Gulf of St. Lawrence, threatening "nothing less than an environmental disaster" in the region (1).


Oxygen-depletion (“hypoxia”) has recently reached levels that can sicken or kill cod in large areas ("more than 1000 km2") of the Gulf of St. Lawrence, and no live cod have been found in these areas in recent surveys done by The Canadian Department of Fisheries and Oceans (DFO) (2). (see map at right - click on map to enlarge)

Why a shortage of oxygen? Bacterial decomposition (rot) of dead organic matter (animals or plants) exerts a severe oxygen-draining effect on seawater, and this process is widely recognized as a primary cause of “hypoxic” seawater. This is how ocean “dead zones” are being formed in various other parts of the world ocean (e.g. the Gulf of Mexico, Chesapeake Bay, Baltic Sea and others) (3).

Any dead organic matter in the ocean will undergo bacterial decomposition, unless it is instead eaten fairly promptly by an animal. The metabolism of animals, while using oxygen, does not severely drain this crucial substance from the water, as does bacterial metabolism. Uneaten dead plants or animals on the seafloor can aggravate any existing problem of hypoxia, because the tiny nibbles taken by crabs and starfish, for instance, will seldom consume the bulk of a larger corpse before oxygen-draining rot (bacterial decomposition) becomes established.

Large, “toothy” predators are therefore crucial to ocean ecosystem health in part for this reason: they have a unique ability to quickly devour substantial chunks of dead flesh, before it can begin to rot. Animals like large sharks, called “apex predators,” perform a crucial “ecosystem hygiene” service by efficiently consuming large marine animals that are dead or dying, and thereby denying bacteria an opportunity to become sufficiently established to consume all the oxygen in the area. (Note that this anti-bacterial service in the ocean is not performed by sharks alone: all other animals contribute too, each from its own “niche,” eating what it can. Many people will easily accept the logic of this, but marine scientists might argue the point.)

The fearsome “biting” ability of sharks allows them to consume very large prey, even including whales. In contrast, the majority of other ocean fish, living at “lower positions in the food web,” have no real ability to “bite” their prey, and these fish are therefore limited to eating items that they can engulf and swallow whole. The well-known pattern is that “bigger fish eat littler fish,” but it is important to note that this rule is broken by the big sharks, positioned at the “apex” of the food web. Too few sharks patrolling the ocean might realistically result in an increase in the presence of their de facto natural “competition” in the sea, which is actually microscopic bacteria, or “rot.”

A drastic decline in numbers of large sharks in North Atlantic waters, including the Gulf of St. Lawrence, has occurred in recent decades (4), as seawater oxygen levels have fallen, and bacterial counts have risen. One predictable consequence of the great loss of sharks is that efficient animal consumption of dying post-spawning fish may no longer occur, and that these mature fish, who have essentially lived out their lives and run out of energy, might instead rot after death, and thereby contribute to sickening the environment for both their offspring and for food potentially eaten by their offspring. (For example, hypoxia will kill worms too, and various other small bottom creatures that might have served to feed young cod…and a cascade of negative consequences can occur.) For reasons like these, it is far preferable for an exhausted mature fish to be eaten by a shark, or a seal, than for it to simply die and rot.

Adverse environmental conditions in the Gulf of St. Lawrence, including episodes of low temperature, hypoxia and starvation, are thought to have caused undetected mass mortalities of cod in recent years, while the "productivity" of these stocks has been uncharacteristically low (2). If uneaten by seals, or other "predators," those dead cod will have rotted.

An unacknowledged flaw in DFO's extensive efforts to "quantify" the "effects of seal predation on cod stocks" has been the implied assumption that all cod flesh digested by seals is the result of seals having killed otherwise-viable cod. The insinuation is always that the "tonnage" of cod eaten by seals represents a "loss" to commercial fishermen, and that these beleaguered souls could otherwise have ultimately taken those fish to market - hence the perpetuation of the "seals are destroying the cod fishery" myth (9). Fishermen may honestly not know any better than this, but DFO Science should. Unfortunately, DFO has publicly played along with the naive arguments offered by the fishing industry, giving them "scientific credibility" in the eye of the public, and great numbers of Canadian tax dollars have been spent by DFO, raising the false alarm of the "threat" of seals.

Seals in Atlantic Canada have recently been observed to be eating larger cod than they did previously (5), suggesting that individual cod fish that are exhausted, dying, or perhaps already dead, are now being cleaned up by seals rather than by larger fish, such as sharks. This is a good thing, although seals are sometimes only able to eat the bellies from larger fish (6). In this way, seals are somewhat less efficient than sharks. The average seal is not as “fearsome” or as “toothy” a predator as a large shark.

Shark - click to enlarge image
(from www.animalyawns.com )

Large sharks are vanishing from the ocean en masse today, and they are reappearing only on endangered species lists. This human-induced change in the ocean, unprecedented for millions of years, may soon cause profound negative effects on the entire ocean food web - especially if other predators, like seals, are hampered in their efforts to step into and maintain the large animal "apex predator" role. Removing more of these animals does not tip the "natural balance" of power to small fish, as the fishing industry naively hopes, but it deals the upper hand to bacteria and "rot" instead...the most "fearsome" predator of all, from the perspective of all animals, including humans.

Young harp seal - click to enlarge
(image © IFAW www.ifaw.org /S. Cook)

Believe it or not, this animal can go, and can function efficiently, where sharks "fear to tread" - i.e. where seawater oxygen has been dangerously depleted. Note that seals possess nostrils, which is better than having the biggest teeth in some situations...

(DFO often describes seals as "important" predators of fish. Well, that much is right.)

Ailing Atlantic Cod - click to enlarge
(from www.fisherycrisis.com )

This cod was caught (alive) on a baited hook, but its emaciated condition is reason to think it may have been on the verge of succumbing to "natural mortality" instead. DFO has found cod in the Gulf of St. Lawrence, which scientists classify as "deceased-like," and with "extremely low chances to recover and survive." (2) Only a few cod fit this classification, but this seems certain to reflect the short survival time of a fish in this condition, rather than implying rarity or insignificance of the problem. A dramatic unexplained increase in adult natural mortality now affects all Canadian cod stocks. If "deceased-like" cod are being eaten by seals, this is a good thing, but DFO wrongly construes all such "consumption" (9) as "damage to cod stocks" perpetrated by seals. Ridiculous. The current "management" strategy threatens to replace cod and seals both with a rotting dead zone.

While seal numbers in Atlantic Canada have increased in recent years, they have not expanded nearly enough to fully compensate for the adverse ecosystem effects of the massive disappearance of large fish (7). For this reason alone, to ensure the continued provision of natural predator/scavenger services in an oxygen-stressed marine environment, seal hunting should be immediately banned in the Gulf of St. Lawrence.

It is worthy of note, and of particular value in this situation, that, unlike sharks and other fish, seals draw no oxygen from the seawater, since they are air-breathers. Along with whales and seabirds, the value of living seals today increases because they conserve ocean oxygen. This characteristic also renders seals immune to being overwhelmed and asphyxiated themselves when swimming through hypoxic waters, a risk faced by all predatory fish, whose subsequent deaths can then cause a snowballing of the “dead zone” effect, as they, too, rot. Sometimes, massive fish-kills are triggered by this dynamic. From this perspective, it can be appreciated that seals are somewhat more efficient than sharks, because they are less dependent on the oxygen content of the immediate water column. Ideally, of course, as was evident in the robust, fish-filled ocean ecosystem of several centuries ago, both sharks and seals should exist in substantial numbers.

"Why don't the sharks get 'em? I just figure with all the predators out there, a nice big piece of meat wouldn't last long." 

- excavator operator hired to bury beached gray whales in California

"Ernest Hemingway wouldn't have been able to catch marlin without them being covered by shark bites."

- Ransom Myers

The Canadian harp seal hunt is doubly injurious to the health of the ecosystem in the Gulf of St. Lawrence because, not only are large numbers of important predator/scavengers prevented from performing their natural ecosystem-cleansing role, but massive numbers of seal corpses are dumped in the Gulf yearly and allowed to rot on bottom. There is nothing living in this region today that is capable of consuming thousands of tons of dead seal flesh…that is, there is nothing there that can do this job except oxygen-greedy bacteria. This presents a second compelling eco-logical reason* for imposing an immediate ban on seal hunting in the Gulf of St. Lawrence.

(*But one immediate objection to this particular suggestion can be anticipated: it may be claimed by some that the dead seals - even thousands of tons of dead rotting seals - would be but a trivial bit of pollution in comparison to the vastness of the Gulf of St. Lawrence, and that dumping dead seals (the current practice) would therefore be inconsequential from an environmental water quality/oxygen perspective. Scientists should not be quick to dismiss this warning, however, and they should carefully consider events in another dying cold water ocean inlet, in Hood Canal, in the state of Washington, U.S.A. In that case, a 60-mile long ocean inlet, a fjord, has lately become severely hypoxic, and massive fish-kills have occurred where marine life once thrived. Investigators have determined that a significant amount of the hypoxia (15%) can be accounted for by the practice by chum salmon fishermen in the area of stripping the eggs for market and discarding the fish carcasses in the fjord. About 24 tons of dead salmon have been discarded in Hood Canal yearly, and efforts to ameliorate the hypoxia problem now include the banning of this practice. (8) The parallel to the ecological stupidity of skinning seals and dumping their corpses (not to mention those of untold thousands of "struck and lost" seals) in the hypoxic Gulf of St. Lawrence should be obvious.)

The continued wholesale removal/destruction of fish predators from an environment like the Gulf of St. Lawrence, where fish stocks are crumbling, and are known to be suffering accelerated attrition due to hypoxia, starvation, and temperature stress (2)…this practice, of killing seals by the hundreds of thousands and transforming them into "pollutants," as the Canadian harp seal hunt blindly forges ahead into the 21st century; this is beyond eco-logically unjustifiable. Refusing to blow the whistle and to end this bloody seal hunt, as DFO and the Government of Canada continue to do (10), is pathetically gutless and outrageously irresponsible.

Copyright 2005, Debbie MacKenzie


Marine scientists may argue with my premise that sharks, seals, and other animals tend to decrease the strength and dominance of bacteria in the sea. This is because scientists have long been operating on the assumption, essentially, that everything ultimately rots anyhow.

If a dead cod is eaten by a seal, it is now generally assumed that seal feces, or perhaps the dead seal, will rot eventually, before the original broken-down organic matter from the cod ever becomes available to fertilize new plant growth in the surface water. Bacteria, the "decomposers," have been classically imagined by marine scientists as a bottleneck through which all dead organisms must pass before they can be recycled into new life.

However, the integrated web of ocean animal life can be shown to be working in direct competition with bacteria, and to be carrying out its own oxygen-sparing "decomposition" process.

Dead cod flesh eaten by a seal may fall to the sea floor as feces. Seal feces (food passed through one digestive system) are typically eaten by invertebrates, such as starfish. Starfish, like a great many other related bottom species, divert a large fraction of the food they eat into the production of billions of tiny eggs. Their innards become filled with roe. Starfish eggs, among countless others, float to the surface, where they release chemicals into the water that work directly to fertilize the growth of plants and other new sea life. This describes one nutrient cycling "loop" in which a series of animals effectively works to bypass bacterial decomposition of dead animals in the ocean. Many other similar "loops" can be described, and it soon becomes clear that the more established and diverse the animal web in the sea, the stronger will be its inherent, self-sustaining "anti-septic" property.

This concept I have not found described in the mainstream scientific literature - but that does not serve to disprove it. Am I right? ...well, do fish eggs float?...do sharks bite? ...does uneaten food rot on the seabed?

Is not the finding of increasing hypoxia in the Gulf of St. Lawrence alarming enough to prompt Canada to take any possible corrective action? If so, the harp seal hunt must be stopped.

Elsewhere on this website, I have often described the natural anti-hypoxia and "biological forcing" role of ocean animals, but it has been very difficult to engage scientists in serious discussion of the issue. But I've tried...last September I explained to an audience of DFO scientists that I hoped they would  soon reach the point where a seal cull proposal would be rejected because they realized that the oxygen content of the seawater was falling, and because they understood how to "connect" these two "dots"...

An uphill battle.

by Debbie MacKenzie


1. Anonymous. "Hypoxia in the Gulf of St. Lawrence"
( www.eps.mcgill.ca/~sundby/MarineGeochemistry/hypoxia.html ). Also: "There is no doubt that the oxygen levels in the bottom waters of the lower St. Lawrence Estuary are low, and that they have been decreasing over the last 70 years or so. The reasons for the decrease are not certain..." (Dr. Bjorn Sundby, pers. comm.) And from DFO: "The deep waters of the Gulf of St. Lawrence have low dissolved oxygen concentration. The prevailing saturation levels in the Laurentian Trough are so low that they can affect various aspects of the biology and ecology of populations and communities. In certain areas, they can even lead to the death of organisms. This information has rarely been integrated in research on distribution, migration, growth and production." (From "Experimentation and Innovation - Experimental Biology" online at: www.osl.gc.ca/exp_innov/en/bio_exp/intro.html ) ......My conclusion: this type of "information" should be immediately "integrated" into an "innovative experiment": into a switch to a DFO-led practice of protecting seals in the Gulf of St. Lawrence.

2. Dutil, J.-D., J. Gauthier, Y. Lambert, A. Frechet, and D. Chabot. 2003. Cod stocks rebuilding and fish bioenergetics: low productivity hypothesis. Canadian Science advisory Secretariat Research Document 2003/060

3. Mark Clayton, 2004. 'Dead zones' threaten fisheries. http://www.csmonitor.com/2004/0527/p13s01-sten.html Widely reported in the scientific literature and, lately, in the public media, is the mounting problem of hypoxia in marine waters. This article is typical of many, and the blame is laid primarily on human-caused "pollution." However, "natural" dead-zone-type incidents are on the rise in the ocean too...

4. Michael Hopkin, 2004. Sharks suffer population crash. http://www.eurocbc.org/sharks_suffer_population_crash  Reporting on scientists who have lately raised the alarm about the massive global loss of sharks.

5. The observation of a shift by harp seals toward eating bigger, older cod is included in this report of the "Independent Seal Panel" to the "Council of Canadian Professional Fish Harvesters"  http://www.ccpfh-ccpp.org/e_dbViewer.asp?cs=policy&id=33   "The Northern Cod Stock Status Report also found that not only are harp seals travelling further south to feed on cod, they are also eating older fish ... From 1986 to 1996, cod up to one year old were the predominant age found in harp seal stomachs. In 1997 and 1998, older fish (aged 3-5 years) were the dominant age group and fish as old as age 7 were found in seal stomachs more frequently than in previous years." References are readily found in the scientific literature to support the claim of the CCPFH.

6. DFO, 2003. Northern (2J3KL) cod Stock Status Update. DFO Can. Sci. Advis. Sec. Status Report 2003/018.

7. Bundy, A. 2004. Mass balance models of the eastern Scotian Shelf before and after the cod collapse and other ecosystem changes. Can. Tech. Rep. Fish. Aquat. Sci. 2520: xii + 193 p.

8. Christopher Dunagan. 2004. "Hood Canal: Salmon plan may help fix oxygen problem"
( www.thesunlink.com/redesign/2004-09-17/local/200409179872.shtml ) Excerpt: "What's the problem? Salmon carcasses dumped into Hood Canal consume oxygen as they break down and decompose. One study suggests that salmon carcasses might be responsible for up to 15 percent of the low-oxygen problem in the waterway. Other sources of nitrogen, including septic tank effluent and fertilizers, trigger the growth of plankton, which consume oxygen when they die and decay."

9. Stenson, G. B. 2004. Quantifying uncertainty in estimates of Atlantic cod (Gadus morhua) consumption by harp seals (Phoca groenlandica). Canadian Science Advisory Secretariat Research Document 2004/089

10. Consider this sampling of relevant Canadian government publications:

DFO, 2004. Cod recovery efforts since the 2003 closure. http://www.dfo-mpo.gc.ca/media/backgrou/2004/hq-ac43a_e.htm

DFO, 2003. Why the cod stocks haven’t recovered. http://www.dfo-mpo.gc.ca/media/backgrou/2003/cod-3_e.htm

DFO, 2003. Seals. http://www.dfo-mpo.gc.ca/media/backgrou/2003/hq-ac01b_e.htm

DFO, 2003. Objective-Based Fisheries Management (OBFM). (for harp seals) http://www.dfo-mpo.gc.ca/media/backgrou/2003/hq-ac01a_e.htm

DFO, 2002. Canada’s Oceans Strategy (backgrounder) http://www.dfo-mpo.gc.ca/media/backgrou/2002/hq-ac77a_e.htm

DFO, 2003. Understanding Seals & Sealing in Canada - the Atlantic Seal Hunt Management Plan.
( http://www.dfo-mpo.gc.ca/seal-phoque/reports-rapports/mgtplan-plangest2003/mgtplan-plangest2003_e.htm )
The introduction to this piece states that "Seal management is founded on sound conservation principles..." and that "The report of the Eminent Panel on Seal Management, along with consultations with more than 100 stakeholders at the 2002 Seal Forum in St. John's, greatly assisted in the development of this plan." Unfortunately, publicly available records from both the "eminent panel" and the "stakeholder consultations" indicate that no consideration was given by either group to the mounting problem of bottom water oxygen depletion in the Gulf of St. Lawrence. Have the experts not considered this....might they be "sleeping their heads into train oil?" (Report of the Eminent Panel on Seal Management: http://www.dfo-mpo.gc.ca/seal-phoque/reports-rapports/expert/repsm-rgegp_e.htm )

Many groups are raising protests in an effort to stop the Canadian harp seal hunt in 2005. For more information see:

Sea Shepherd Conservation Society http://www.seashepherd.org

Humane Society of the United States http://www.hsus.org

International Fund for Animal Welfare http://www.ifaw.org

Harpseals.org http://www.harpseals.org

ProtectSeals.org  http://www.protectseals.org


P.S. May 2006 - Canada has found seal meat difficult to market... Little Wonder!!


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