Atlantic cod (Gadus morhua) from the eastern Scotian Shelf, 2002, shows physical signs of starvation


by Debbie MacKenzie

November 20, 2002, at the FRCC's public consultation in Halifax on groundfish stocks in the Scotian Shelf and Bay of Fundy region, I outlined my observations on unusual physical changes in Atlantic cod, provided the council with recent photographs to illustrate the changes, and submitted a written brief describing my concerns and recommendations (see text of my brief).

What struck me most at the meeting was that nobody registered any surprise at the malnourished and emaciated appearance of the cod, nor at the pattern of worsening fish condition that can clearly be seen as one moves toward the eastern side of the Scotian Shelf. As I described the codfish, council members, scientists and fishermen either said nothing, or nodded in agreement with me. It seems that they are accustomed to the sight of these sickly fish. Nobody challenged my claim that my photos accurately show the general condition of cod caught off the Nova Scotian coast today. Nor did anyone challenge my statement that the stomach contents of fresh caught cod now amount to little or nothing.

I tried to explain the significance of the unusually arched back and downturned head of the starving cod. This physical change in the fish provides an important clue to the source of the trouble. It is not news that cod (and virtually all other fish) are growing much more slowly now than they did in the past. Declining trends in weight:length ratios and size- and weight-at-age have often been dramatic. But explanatory hypotheses for the slowed growth of cod, for example, have generally not included a simple lowering of their normal food production on a systemic scale. Preferred hypotheses in the recent scientific literature have been the following three, each of which is contradicted by details of the physical appearance of the cod, and by the spatial (east-west) pattern of the occurrence of the changes.

(1) "Cold water" - On the eastern Scotian Shelf, a transient lowering of bottom seawater temperature in the late 1990's was thought to have a negative impact on the growth of cod, because cod feeding is inhibited if water temperatures are too low. Problem: If adult cod simply have their appetites suppressed by cold bottom water, they will presumably just decline to consume their normal prey items (small fish) from the water column. In this case, cod may become very lean but the "cold water" explanation provides no reason for the fish to be literally 'bent out of shape,' as they now appear to be. If cod have a normal appetite but are faced with a shortage of small prey fish, they will attempt to feed wherever they can. If the water column is empty they will be forced to consume food items at a lower trophic level, specifically bottom invertebrates. This rationale does provide a reason for the 'bent out of shape' appearance of the cod. (Furthermore, the "cold water" trend has been reversed in recent years while the decline in cod survival worsens.)

(2) "Size-selective culling effect of fishing gear" - Since much fishing gear is designed to catch only the larger individuals in the fish population, it has been thought that repeated use of these fishing methods over many fish generations may have had the unintended effect of selectively removing the genetically faster growing component of the stock. Since the survivors would then include more individuals genetically programmed for slower growth, it is thought that a genetic shift has thereby been induced in the population, that has resulted in slower-growing fish. Problem: Genetically slower growing individuals would be analogous to 'petite' humans. They should have the normal body proportions, with the only difference being a slower growth rate. The feeding struggle indicated by the altered shape of codfish today therefore also contradicts the "genetically slowed growth" hypothesis.

(3)  "Excessive predation by seals" - Although this has not been offered as an explanation for the slowed growth of individual fish, seal predation is a very common focus of the ongoing scientific investigation into the "failure to rebuild" of Atlantic cod stocks. One cannot read a media story about cod stocks without seeing the word "seals." Therefore, it bears mentioning that the current grossly starved appearance and condition of adult cod directly contradicts the hypothesis that these fish are being harmed by excessive natural predation. If so, the appearance of the surviving individual cod should be radically different: they should be unusually well-fed and plump.

THE MAJOR POINT - that I suggested (again) to the FRCC is this one:

The pattern of decline in Atlantic cod stocks can be explained by the theory that overall marine nutrient cycling (or "production") is declining.

If this statement is true, then all marine species must feel the effects, and one predictable general pattern will be this: Species which have historically expanded their ranges to the limits of their various physical tolerances under a higher marine nutrient-cycling regime, will necessarily contract their ranges occupied under a lowered nutrient-cycling regime. Range contraction forced by declining nutrient availability will increasingly limit marine species to the geographical areas that naturally enhance nutrient cycling, and where other environmental variables, such as temperature, are most conducive to the growth and survival of the particular organisms. Being well nourished is especially essential for survival of the 'fringe elements,' the fraction of the population that must tolerate the environmental extremes, of heat or cold, for instance. Therefore, a systemic drop in nutrition would first tend to cause the loss of both the northernmost and the southernmost components of temperate marine populations. An example of this can be seen in recent trends in the American lobster population. (In contrast, if range-shifting were forced directly by global warming, for instance, a general shift of many species toward higher latitudes would be expected. Occasionally this tendency has been seen, but it does not describe the major pattern of range contraction that has occurred in many marine species, including the Atlantic cod.)

The Atlantic cod lost the northernmost part of its former range first. It is now about 20 years since the end of the once-considerable commercial cod fishery off northern Labrador. And it is 10 years since the well-publicized failure of the stocks off southern Labrador and on the Grand Banks of Newfoundland, the infamous "crash" from which they now appear unable to recover. It is the pattern of spatial distribution of the surviving cod, however, as well as long term trends in growth rates and "condition factors" of these fish, that strongly suggest increasing food limitation as the ultimate cause of the decline (and the "failure to rebuild"). 

There still appears to be a few successful components of the formerly widespread Northwest Atlantic cod stock. They are located in the Bay of Fundy, on Georges Bank, and in inshore concentrations in a few large bays in Newfoundland. These are geographical areas that naturally enhance marine nutrient cycling, which seems to account for their continued ability to support better growth of cod than the vast areas from which the species has virtually disappeared (or where only a few starving remnants remain).

The overall lowering of system productivity is also suggested, however, in trends shown by these few "healthy" cod sub-populations. Although they are generally in fairly good body "condition" these cod populations too are growing more slowly than they did in the past in these prime locations. This suggests that areas such as the Bay of Fundy and Georges Bank once had levels or organic production far above the threshold needed to support healthy cod, and that the reduction that has occurred up to this point has not been great enough to exert severe nutritional stress on the species in these areas. However, if the negative trends continue, this will inevitably occur at some future point.

Evidence of declining marine productivity can easily be found in the Bay of Fundy. One telling example is shown by the diminished growth of barnacles in the area, which was once exceptional (for details see "The Barnacle Zone"). Along the open Atlantic coast of Nova Scotia a marked decline in barnacle growth is also evident. Where a high, heavy belt of barnacles thrived on the rocks at Peggy's Cove a half century ago, now the rock is bare except for the relatively few barnacles that survive in the crevices (the high flow/high food areas). This is a very significant indicator of declining marine production, and is the same pattern that is mirrored in the cod stocks: where cod once thrived across the entire Scotian Shelf, they can now only manage to do so in the "crevices" (high flow/high food production area, i.e. Bay of Fundy). This theme of marine life abandoning the parts of their historical ranges where nutrient availability is naturally lower, can also be seen in the dominant seaweed species on this coastline.

What can the FRCC be expected to do with this information?

As the body that recommends TAC's and other conservation measures to the Minister of Fisheries and Oceans, the FRCC plays a key role. With council objectives including these:

"To develop a more profound understanding of fish-producing ecosystems..."
"To review scientific research, resource assessments and conservation proposals..."

...and a mandate including:

"advise the Minister on research and assessment priorities"
"review DFO data and advise on methodologies"

...the FRCC clearly has a tremendous responsibility.    Maybe it's too much.

The increasing concern and frustration of the FRCC over the ineffectiveness of measures implemented to date to allow "stock rebuilding" is easily detected in their publications. One problem seems to be that implementing the TAC's that they recommend is a relatively simple bit of government business, but implementing the council's recommendations on scientific research priorities is a different game altogether. The Science Branch of DFO might (understandably, I suppose), resist accepting such direction from a group like the FRCC. (In part this may be because the majority of council members have no academic background in the marine sciences.) But it seems clear that DFO's Science Branch is entrenched in an approach that is simply ineffective. Evidence?...the vanishing fish, the great degree of "uncertainty" in the science assessments and their inability to predict future trends, summed up regularly in newspaper headlines such as yesterday's "DFO scientists can't explain cod problems" (The Canadian Press, November 25, 2002).

Since the FRCC at least has the ear of the Minister of Fisheries and Oceans, and since the Science Branch is obliged to respond to directives from the Minister, if these specific questions could somehow be conveyed through that route and transformed into "research priorities," some new light might be shed on the mysteries of "fish-producing ecosystems"...

1. Starvation must be assessed as a cause of unexplained adult mortality in fish stocks. This is certainly not unwarranted. 4VsW cod offers a prime example. These "slinky" cod are obviously starving, yet DFO officially professes to remain "baffled" by this. To be fair, I doubt that biologists can really fail to appreciate that the cod are starving, but what "baffles" them is the mismatch between their theoretical ideas about how much cod-food the ocean should be producing and the evidence offered by the cod itself. Disappointingly, recent scientific analyses* of 4VsW cod have not included looking at trends in cod stomach contents, nor has the physical change in adult cod body shape been described. These are two specific questions that require serious investigation before we fall back on the standard excuse that "the seals are eating too many cod."  (* DFO, 2002. Cod on the Eastern Scotian Shelf (Div. 4VsW). in Updates on Selected Scotain Shelf Groundfish Stocks in 2002. - and - Caihong Fu, Robert Mohn, and L. Paul Fanning. 2001. Why the Atlantic cod (Gadus morhua) stock off eastern Nova Scotia has not recovered. Can. J. Fish. Aquat. Sci. 58: 1613-1623 (2001))

2. The marine ecosystem must be assessed for indicators of a (previously unsuspected) long-term decline in marine primary productivity. This is almost certainly the key to the problems.

Besides the increasing signs of starvation in commercial fish species, I have described (on this website) concrete, observable long-term changes in species such as barnacles and seaweeds that support this hypothesis. When I wrote to the Hon. Mr. Thibault about the implications of the declining barnacles, he replied by reassuring me that DFO Science was competently assessing indicators of ecosystem productivity. Well, fish-producing ecosystems should also be barnacle-producing ecosystems...but my repeated attempts to draw this to the attention of DFO have been ignored. (The director at BIO finally just flatly stated that my barnacle article would not be reviewed by his department.)

Regarding the negative changes in seaweed, I got a bit farther, probably because I had managed to interest the Halifax Herald in printing a story about it. Subsequent to that, I actually had a meeting with DFO's seaweed specialist to discuss my concerns. But he declined to answer my questions on the physiology of the unusual breakdown pattern that I had noted in perennial seaweeds, stating that he is not an "algal physiologist." He recommended that I pose my questions to a professor at UNB whose specialty is this field. Twice I wrote to this professor (now many months ago), but I have received no reply.

The FRCC and the Minister of Fisheries and Oceans might not be as easily dismissed by the experts as I have been...

3. Understanding nutrient cycling and plankton dynamics is critical to fathoming the secrets of the "fish-producing ecosystem."

Hint: Do not accept measurements of elevated chlorophyll alone as evidence that nutrient cycling and primary production are occurring at high levels. The presence of chlorophyll (phytoplankton) alone is inconclusive evidence, partly (but not entirely) because the standing stock is closely related to the abundance of consumers (zooplankton). So, how can primary production actually be measured? Essentially, this refers to rates of carbon-fixation, but DFO does not have any time-series data on marine carbon fixation rates. If this data existed, the current assumption regarding the basic stability of marine primary production might be more plausible. If carbon fixation cannot be measured directly, some proxy measurement will have to be used to deduce it instead...and the truth is that fish production, or barnacle production, are as good as any other indirect measuring sticks.

DFO does have about 40 years of plankton abundance measurements, however, in the Continuous Plankton Recorder (CPR) data. Since the beginning of that time series, a significant increase has been recorded in chlorophyll ("greeness") and a significant decline in the zooplankton indices. This is incongruent with scientific expectations, since the standard view has been that "phytoplankton growth stimulates zooplankton growth." I found no discussion of possible reasons for the diverging trends in the SSR (SSR G3-02 (2000)). And my posing this question to the author of the SSR prompted only a (bizarre!) request that I refrain from sending him any further email.

4. When young adult cod are unexpectedly starving in the ocean, the very foundation of fishery science begins to look shaky.  My best hunch is that the fundamental flaw lies in the dogma that marine production is controlled by "physical forcing" (basically, weather patterns). Without rehashing the details of the argument here, I urge the FRCC to request that DFO Science address the specific knowledge gaps regarding the ecological role of zooplankton that I have described in this paper: Vertical Migration of Zooplankton: a bi-phasic feeding strategy that enhances new production? (I have also written an alternative holistic view of marine ecology that should be thought-provoking, and should suggest some appropriate new research questions: Challenging basic assumptions: a reassessment of marine nitrogen flux patterns, including biological controls on the availability of nitrogen in seawater, and finally, a Medical Diagnostic Model for a Starving Ocean ...but rather than suggest that the Science branch try to tackle all of that at once, I would recommend the previous migrating zooplankton question for an initial specific focus.)


I sincerely hope that this advice may be helpful to the FRCC, and wish you the best of luck,

Debbie MacKenzie

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