One bothersome point in this debate is the fact that some species that are in severe decline seem not to thrive even the presence of what appears to be abundant stocks of their “normal” prey. Atlantic Canadian groundfish seem not to benefit at present from the relatively abundant capelin and shrimp in the area. Why not?

“It’s a little hard to see how cod could be short of food when the shrimp resource seems to be exploding -- likely (in part) because of the release of predatory pressure.”


Here’s part of a debate (excerpted from email exchange) with a marine biologist that includes this issue...

The (scientific data avilaible) deals only with exploited groundfish, ‘not’ with the species that current dogma predicts should increase in biomass to replace depleted, over-exploited types. Thus, their data cannot indicate whether the "SUM TOTAL OF LIFE" (my phrase that means ‘total marine biomass’) is declining or staying steady.

You are right of course. The data does not exist to calculate the "sum total of life" - but it's still a valid concept and missing numbers don't convince me that a significant portion of the marine biomass is not also missing. I am challenging "current dogma" because I just do not see evidence of species replacement as predicted.

However, to support your argument, you will need to show that nothing else is replacing them. I doubt that you can do that

You "doubt that I can do that?" Maybe not, but I can certainly ask the question. Can you prove that they are in fact being replaced as predicted? It is not long since we were told that "skates and dogfish are thriving where cod once reigned." In your note you acknowlege the disappearance of the dogfish:

“...the weight of evidence suggests that heavy fishing leads to species replacement (such as skates replacing the dogfish that replaced cod on Georges Bank) but not to any major change in total biomass.”

...which leaves me looking for the skates. I only found the one SSR on skate, "4VWS Winter Skate" on the groundfish-depleted and dogfish-depleted Scotian Shelf - no reliable abundance estimate but "total mortalities have doubled since 1995." How many skates are there on the Grand Banks? Are survey trawls full of them now that the fish are missing? Or are they just theoretical skates? I know you'll say that it's not just "skate," it's all sort of little things that we take no notice of, but I'm just not seeing "lots" of anything much.

OK...there are populations of "feed" that are at high levels now, one example being the abundant capelin currently on the Scotian Shelf. And most people seem to agree that it's a rebound effect from the drop in predation. Which raises the question, however: why don't the groundfish take advantage of this abundant food supply? (like you said: “though it is a little hard to see how cod could be short of food when the shrimp resource seems to be exploding -- likely (in part) because of the release of predatory pressure.”) I agree that this does present a conundrum. If their "prey" is now unusually abundant, then what is their problem? Why don't they just eat it, grow fat and prosper? A biologist at BIO asked me the same question. Here's what I wrote back but he's very busy and hasn't yet replied to me - so, feel free to criticize...

“I'll try to answer the question. Anyone who does this is speculating...but this is what I think...

First of all, describing the cod-capelin relationship as predator-prey might be a tad simplistic. Is it not likely that capelin also eat cod larvae while munching on the zooplankton? This partly reverses their relationship. With the balance of species tipped the way it is today, large capelin stocks could eat enough larvae to have a negative impact on the recovery of the groundfish. (Actually, you also mentioned this idea.)

But - the ones that survive the larval stage - why don't they grow fat on capelin? It's because a lot more species than capelin and shrimp matter to the cod. The abundance of cod doesn't reliably follow the abundance of capelin anyhow. (Here's a link to one article that I read - does this look fairly accurate to you? http://www.stemnet.nf.ca/cod/role.htm) A quote from that article:

‘For example, in the Barents Sea, the growth rate and condition of cod decline when capelin are scarce, but here and in Iceland the evidence on this point is not clear. Here, the abundance of capelin has been highly uncertain in recent years. However, we know that in the 1970's, when capelin were definitely scarce, there was no obvious decline in the condition of cod.’ (...suggesting that cod eat a variety of things. Also in the article “here” means Newfoundland.)

In the 1970's the cod had a lot more "neighbours" around in the form of all the other groundfish stocks. No doubt at different stages they ate a lot of the young of these neighbours as well as cannibalized their own. Now, especially in a spot like the Eastern Scotian Shelf, there are a lot less of all these fish. How much has the rate of cannibalization increased since the decline in groundfish in general? There could have been/probably has been a big change even in the last 10 years. How frequently is the diet data collected? I think the cod need the usual variety in their prey, and the usual concentration of their traditional neighbours, at certain ages/sizes capelin might not be the easiest thing to catch.

Cod cannibalism must be ‘way’ down on the eastern Scotian Shelf. It takes a big cod to eat a small cod and there just aren't many big cod in that area any more.

There could have been/probably has been a big change even in the last 10 years. How frequently is the diet data collected?

Very rarely. And such studies as have been done have not been able to capture all of the subtleties: Cod have such variable diets that it would take enormous numbers of samples to sort it all out.

So: You are acknowledging that prey is relatively plentiful, at least in this one area. And you are suggesting that the cod are starved, despite this abundance of prey, because capelin is an unsuitable prey item, at least at certain times? And that despite capelin being a known major food of cod in other times and places?

I guess the idea just about holds together. However, before anyone could take it very seriously, you would need some evidence that the cod 'are' starving. If prey was scarce, that might be indication enough. However, to postulate starvation in the presence of prey, you really need some independent indicator of the starvation. (Skewed RNA/DNA ratios might do it. Low fat content might also.) Simply low weight-at-age won't be enough: The observed low temperatures on the eastern Scotian Shelf in recent years will have slowed the cod down, including reducing their feeding and so slowing their growth.

So: Do you have any evidence that the fish are starving -- or even food-deprived? Without it, I think we have to assume that fish do not starve when prey are available.

RNA/DNA ratios I do not have. I do have a recent quote from DFO regarding the Eastern Scotian Shelf cod stock (the directed fishery has been closed since 1993):

"Condition is the relative weight of the fish for their length, i.e. their plumpness. Up to 1989, there was a highly significant negative relationship between population biomass (age 3+) and the condition of the fish in July. This suggested that in periods of high abundance the condition of the fish was reduced. As the population biomass declined in the early 1990s however, the condition index continued to fall and remained low until 1995. Although higher, there is greater uncertainty in the 1996 and 1997 estimates due to relatively small sample sizes. These condition observations are consistent with the widely reported loss of weight seen by the industry and the presence of "slinky" fish in the catch. Investigations into the cause and significance of low condition in fish have suggested that low temperatures can induce poor condition and that reduced survivorship and reproductive success can result. This is also consistent with the appearance of colder waters on the eastern scotian Shelf since 1986."

"Slinky" has been described to me by fishermen in terms that suggest "emaciated". Regarding the colder water, has it not been recorded that this temperature trend has in fact been reversed in recent years? You suggested that cod cannibalism must be very low due to the absence of large ones. That makes sense. But despite warming conditions, no fishing and "abundant prey" this stock is doing very badly. From the latest SSR: "Surveys indicate that since the mid-1990s, there has been an increase in mortality of cod, other than that attributable to fishing, and which has persisted even after the closure of the fishery...The biomass is projected to decline 5% to 20%, even in the absence of any fishery."

So, are the low condition "slinky" codfish evidence?...Enough to take the "starvation" idea seriously?

You also pointed out another troublesome finding:

For the Scotian Shelf, groundfish condition factors generally rose during the years of the great foreign fishery (roughly 1960s), as simple theory said they should. (Fewer fish were expected to mean more food for each one and so better condition.) If I remember correctly, average condition then began to fall as biomass started to recover in the later 1970s (as was expected) but continued to fall once biomass tended down from the early or mid-1980s onwards. That was remarked on and documented at the time. The guys at BIO have now been struggling with the issue for more than a decade and I am not in the least surprized that they agreed with you that it is important. It is (for the particular area and species).

So beyond the mid-1980s the "simple theory" failed? I am aware of this trend and wonder if it has ever been seen before or observed to be reversible. When condition and abundance decline at the same time, I think you are seeing something that might not have occurred before (please correct me, I don't have all the facts), in any case it now looks to me like a completely different ball of wax - not at all like the story of the "downturn" in the 1960s.

Exactly (as to the ball of wax being different).

(In the 60s our favorite groundfish were overfished but their "neighbours" were virtually untouched, and I believe that is why the survivors were able to maintain good "condition.")

Belief is a risky basis for scientific conclusions. You seem to be suggesting that cod were able to maintain condition because they had unspecified and unexploited competitors (wolffish perhaps?). As discussed above, you have accepted that they still have available prey. I'm not clear why a lack of competitors should cause a cod to grow slowly. That is certainly a novel hypothesis that need some support before it can be accepted scientifically.

Yes, it’s a novel hypothesis, but you yourself said that “cod have such variable diets.”

Also regarding "low abundance + low condition" - I believe this is also being seen in the declining Pacific salmon stocks. (I can't say exactly that it's "condition" but they have seen a steady decline over at least the last couple of decades in the average size of salmon (including dropping weight-at-age).

If you want to speak only of the northwest Atlantic but to extrapolate from the known declines in groundfish and to suggest that the region has seen a decline in total biomass, I would be happy to take that idea on board as one hypothesis (alongside the notion that species replacement is maintaining a constant overall biomass).

[As Gary Sharp will no doubt point out, marine biomass is ‘never’ stable. A general stability, subject to cyclical and irregular environmental change, remains a useful abstraction against which the effects of other driving forces can be discussed -- though not as a standard against which anything can be measured.]

...I'd agree that the northwest Atlantic ‘seems’ to be showing decreased total biomass.



I have been told as a criticism that “Anyone who looks for anything can usually find it.” This is referring to scientific research, and of course it is true -- our bias always shows, mine and everyone else’s. (Look for what you are hoping to find, ignore information that appears to refute your pet theory, and juggle the statistics in the end if necessary...choose the “level of significance” that suits you.) What is really needed is an objective look at the data and a serious consideration of all possible explanations, including those that are not the “favorites” of the researcher. Believe it or not, that is what I have tried to do.

“What is your affiliation? Where do you get your funding from? Why are you involved in this issue?”

Some wonder what is my “real agenda,” what is it that I am really “promoting?” I have been suspected of ulterior motives. Is it an end to fishing, and am I funded by an “animal rights group?” “WHY” am I doing this...why am I so interested in this problem? Do I eat fish?

I am wondering about your interest in this subject. What is your background/affiliation? I ask this directly, because some of my colleagues who are interested in your hypothesis are beating around the bush and wondering. Please tell me "where you are coming from" with regard to your affiliation and scientific background.

I eat fish and I go fishing. I grew up and still live in a fishing village, and count many fishermen among my friends and family. My interest in this subject is because it is so important. My "scientific background?" I have a nursing degree, am an engineering school dropout, an inventor, a very interested student of many different things, and for a long time the problems in the ocean have been on the top of my list. I read constantly, lately including scads of marine biology research documents, I'm always "looking around" at things, and I ask a lot of questions. (Re: “funding” and “affiliation” - I have neither.)

Unfortunately, my lack of "formal education" in this field ruins my credibility with many. Someone wrote to fishfolk yesterday "Most marine scientists do specialize in something particular. They are not general practicioners"...maybe that's what I am trying to be, a marine GP... Actually marine biologists resemble a lot of speciality doctors who are intently studying the intricate details of the problems that have been identified. That’s fine, but who is doing the “nursing” part? They can “doctor” the ocean but can they “nurse” it? (They are two distinctly different jobs and it is generally the nurse who takes care of routine details like “feeding” the patient...)

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