(Part two of “a fish story.”)

by Debbie MacKenzie


June 8, 2001. The author of DFO’s mackerel stock status report has sent me the updated version for this spring. (The document can be read online, in a pdf file on DFO's website.) Here are my comments to Francois Gregoire.

Dear Francois,

Thanks for sending me your updated mackerel SSR, that was very thoughtful. And thank you for drawing my attention back to the mackerel. I’ve been busily juggling many other things (by chance, did you read beyond the original mackerel story on my website?), but really, I must take the time to update the mackerel story now.

Regarding your report, SSR B4-04(2001), here are my comments and concerns. (You must realize that I’m not criticizing any scientist or group of scientists as such...it’s just that everything seems to be falling apart, following some rapidly changing and “unpredictable” downhill course.) You may think that I am “over-reacting” but my impression after reading your latest mackerel report is that I FEAR THIS FISH IS HEADING TOWARDS EXTINCTION. I find the changes alarming, though not unpredictable. It fits far too well with the larger pattern of decline.

Mackerel catch at age, 1973-2000 The most remarkable change in mackerel in 2000 was the prevalence of small fish, 63% of the catch being taken from the 1999 year-class. I am afraid that I agree with the fishermen in the Gulf of St. Lawrence who worried that this indicates a collapse of the stock rather than the advent of a “dominant year class.” This trend towards small fish echos the pattern demonstrated in other collapsing stocks, northern cod for instance...lots of juveniles appear but they just don’t pan out into “dominant year classes” like they did in the past. Today their "bubbles" seem to burst very quickly.(The graph at right above is Fig. 8 taken from the SSR. It illustrates "Canadian catch at age (%) for the period between 1973 and 2000 (the largest-ever catch of one-year-old fish was recorded in 2000; the dominant year-classes are also shown)").

The biggest alarm bell that I see in your new SSR is the disappearance of the bigger, older fish. WHERE DID THE BIG MACKEREL GO?

Your statistics show the maximum age of mackerel caught between 1973 and 1994 to consistently be 10 years (from Fig. 8), but between 1995 and 2000 this maximum age at capture dropped rather abruptly to 6 years. This is an ominous sign! (Your Fig. 2 (which I was unable to copy)shows length and weight at age measurements for mackerel up to age 18, which implies that mackerel were once known to live for 18 years. The age contraction in this stock may therefore have started to occur well prior to 1973?)

The fact that large MACKEREL are missing is very worrisome. For other commercial fish stocks, fished more heavily than mackerel, we are told that the bigger fish have disappeared because they have been selectively targetted by the fisheries...and the predominance of small fish in those stocks is said to be a sign only of “overfishing.” Implied in this explanation is the idea that the smaller, younger fish would grow bigger and older if they were give a chance to do so. But mackerel have not been “heavily exploited” for decades, so how do you account for the contracting age structure of this stock?

The disappearance of the big mackerel therefore offers an important clue regarding what’s changing in the marine ecosystem as a whole.

The lesson is that the change in the fish stock is not the direct result of the fishing pressure that has been applied to that specific stock. In some other fish stocks, it’s possible to believe that the fishermen caught all of the big ones, but not so with the mackerel! “Something” in the sea is now selectively killing bigger, older fish...and whatever that “something” is, it causes them to become leaner than ever before just prior to their disappearance. The force acting in the overall marine ecosystem now, the one that is driving these changes, is food limitation/starvation.

Temperature, for instance, does not selectively affect the feeding habits of bigger, older fish - temperature effects would more reasonably be expected to affect all stock members.

Whatever today’s trouble is, it presents a much more severe problem for fish living at higher trophic levels, and that is an important clue. The system still supports the smaller individuals in many fish stocks, but when they get bigger and need to feed at a higher level, they start to grow very slowly and their numbers become very few. This common theme is found in countless fish stock reports today.

The mackerel report, showing a lightly exploited fish stock falling into line with all the others, by losing its older members, nicely illustrates that “the thing that is forcing these mackerel stock changes is a bigger thing than the mackerel fishery.” Merely controlling the mackerel fishing pressure will not alter this downhill course, it’s ALL-FISHING that’s causing this picture, which is a systemic weakening and loss of life. Vulnerability of fish stocks today is more related to their trophic feeding level than to the fishing pressure to which they are subjected individually. (For other examples of this theme see “cod vs. haddock” and “why are there so many lobsters?” And it is discussed in detail in “the marine nutrient cycle” and “fisheries research priorities.”)

Atlantic cod and Arctic charr have relatively good data sets. Both of those show long-term declining trends in growth, beginning first in the older age groups and the older the age of fish, the steeper the drop. (See DFO's data tables reproduced in the article on this website on “fisheries research priorities.”) Weight-at-age and condition factor in the youngest age-cohorts remains unchanged for the longest time. The little ones are the last ones to feel the pinch. The growth data on your mackerel stock seems to be limited, but perhaps this theme is underlying there as well? As I mentioned in my “mackerel story” written last year, the length of an 8 year old mackerel appears to have dropped significantly since the 1960s (and most recently the 8 year old mackerel has apparently disappeared). Checking that same older reference (Leim and Scott, 1966) against your latest SSR, I find no real difference in the length reported for yearling mackerel then vs. now. So, has the higher end of the mackerel stock been gradually diminished until the point of disappearance.....like the cod and the charr...and like the many other crashing fish stocks worldwide?

A look at the mackerel SSR-2001 in a bit more detail, these are my comments on your findings.

1. Trends in condition factor.

Fig. 4 indictates that condition factor remained low for mackerel in 2000. Seemingly, condition factor in mackerel was synchronized with variations in water temperature of the “cold intermediate layer,” but these two trends diverged in 2000. CIL temp went up and condition shifted down....another “unexpected” finding. Unfortunately, condition factor is not reported by age group, rather it seems to be averaged for the whole stock. Condition of mackerel is at an annual low following spawning, yet from the catches we know that the bulk of the fish in 2000 were pre-spawners. One year old fish should not have had their condition factor reduced by the demands of spawning. (Are we to believe that the class of 1999 had low condition because there were so many of them there competing for food? A density-dependent effect? No longer credible, density-dependent effects on condition of fish seem to be a thing of the past - abundant or scarce, essentially all fish are now thin.)

2. Trends in GSI (gonadosomatic index) - age/size at maturity not factored in.

Illustrated in Fig. 9 of the SSR, the curve for GSI in 2000 more closely resembles the 1973-1997 average than did those of 1998 and 1999. The comment in the text is that “the situation returned to normal in 2000.” Gonadosomatic Index graph“Normal” might be an overstatement, however, since the curve in 2000 appears to have dropped more sharply than the long-term average. But of course that detail might not be significant. One thing that definitely was not “normal” in 2000 was the age structure of the spawning fish that were measured. What effect does age and size of spawner have on GSI? Does a 12 inch reproducing mackerel normally attain the same GSI as an 18 inch long spawner? Or is it higher or lower? This sort of unknown reduces the usefulness of comparing this sort of data from year to year - in the context of a stock that is undergoing such a dramatic shift in composition, many variables are shifting together, and attempts to compare measurements with the stock that existed in the past may be deceptive.

3. Trends in egg abundance.

“The abundance of mackerel that spawn in the southern Gulf of St. Lawrence is calculated on the basis of a biennial egg survey.”

Counting a wild fish like mackerel presents a huge challenge. Since they do not stick to one area that can be sampled in a consistent manner (like groundfish), nor do they swim up a river where their abundance can be guessed at as they pass a counting station (like salmon), highly migratory pelagic fish like mackerel are extremely hard to count.

Trying to estimate the number of spawning fish by looking only at the abundance of their eggs is impossible, however. It is naive to think that a constant, possibly linear, relationship exists between these two variables. Like all fish, mackerel produce an abundance of eggs far in excess of the number that usually survives. Most mackerel eggs are eaten by their natural predators in the sea. The abundance of these natural egg-predators is therefore a more important controlling factor in egg abundance than is the number of spawners. So, any conclusions derived from egg abundance surveys must find a way to account for the activity of the natural predators. The natural predators of mackerel eggs are also in steep decline; this includes larger mackerel as well as herring and many other species that consume floating fish eggs at various life stages. It is not apparent that this variable has been accounted for in the spawner estimates that have been derived from the egg abundance surveys - therefore, we in fact have NO IDEA how many spawning mackerel are in the sea! The egg survey reveals how many EGGS are in the sea...period. Similarly, the abundance of one-year old mackerel is also a reflection of the abundance of their natural predators....again the many predators that normally eat small mackerel (including big mackerel) are in steep decline, and this is the main conclusion that can be derived from the presence of an abundant mackerel class of 1999.

Regarding Fig. 12, and the different approaches to estimating the biomass of mackerel, it must be re-emphasized that to count mackerel, you must find a way to count mackerel....not just their eggs.

4. An unusually large year class for 1999 was noted in the summer of 2000 - is this a good sign or a bad sign? Is this the advent of a “dominant year class” in the style that was observed in the past?

As the class of 1999 is depicted in Fig. 8, it does not seem to be following in the footsteps of earlier dominant year classes. For instance, the classes of 1974, 1982 and 1988 did not appear as large “bubbles” at the age of one year.

From the text: “All fish in dominant year-classes, like those of 1959 and 1967, in which growth was slower, reached maturity at age five and a length of 330 mm.” -- This next point will be easy to test...I predict that a relatively high proportion of the class of 1999 will be sexually mature in the summer of 2001 (if they are still alive). Rather than following the slowly-maturing pattern of the earlier large classes, these fish are much more likely to display another widespread pattern in the sea today: markedly smaller size and age at sexual maturity. Analogous to “bolting,” which occurs in stressed garden vegetables such as spinach, the rush to reproduce is a survival mechanism for tough times. When the “window of opportunity” in the environment is closing, many species will switch their energy to reproductive efforts rather than somatic growth, at an earlier stage than usual. The crashing fish stocks seem to react to the loss of the high end of their populations by the young ones reproducing earlier than ever.

5. The value of information from fishermen.

DFO scientists are increasingly considering the opinions and observations offered by the fishermen. This is very good. I also maintain contact with the fishermen, it is important to have these “reality checks.” Fishermen in my area are now puzzled and worried, they cannot understand why they are unable to catch mackerel this year like they have in the past. WHERE IS THE CLASS OF 1999? Two year old mackerel should be unusually abundant this year...no? Has that last "bubble" burst already? The horribly noisy mackerel pump sits on the wharf this spring, as it has in all recent years...but this year the miserable thing is quiet...is this how the story ends?

But a few mackerel have been caught this year. I’ve not seen them yet, but I have been told that the fish look very poor, thin, even “wormy” by one fisherman’s account. No fancy math is needed to draw conclusions about the “condition” of these fish. Nor about their true abundance.

It’s very helpful and can be enlightening when we are able to get a glimpse into the past. Here’s a look at the “condition factor” of the Atlantic mackerel during the 1930s, these observations were recorded in my father’s memory.

Mackerel were so fat then. Nobody cut fillets from mackerel, they were all split for the salt fish market - opened like a “butterfly.” The first deep cut was made from the back, parallel to the spine, (in the same manner as one approaches removal of the first fillet today.) But in those days it was impossible to spread open the fish after making that first cut and pulling out the guts and gills....the belly flesh of the mackerel was so rounded, thick and tight, that forcibly bending it open would always result in the splitting of the flesh. The rips would be irregular, so the method of preparing these fish included a making a second cut before laying the fish open. It was necessary, and routine, to score the flesh to the skin by means of another inside cut or two, before spreading out the mackerel to be salted. After about the 1940s, mackerel were never that fat again, and that technique of scoring the flesh was no longer necessary.”

The "take home message" from this story is that the feeding success of Atlantic Mackerel has been undergoing a gradual decline for many decades, DFO's "condition factor" graph only illustrates the very last chapter of the story. The fishermen today do not believe that there is a "very large biomass" of Atlantic mackerel in the sea...and on this point, I believe that the fishermen are right.

6. Uncertainties and the Precautionary approach?

The one thing that is multiplying the most quickly in fisheries science these days is the “uncertainties.” The theory that “overall biomass depletion in the sea” is at the root of these stock changes is very easy to justify. The “precautionary approach” should demand at this point that, in the name of caution, all fishing be halted until a proper assessment of the health of the marine ecosystem can be made.

Based on the latest mackerel report, SSR B4-04 (2001), and the early indications of the mackerel fishery for this year, moves should be made immediately to have the ATLANTIC MACKEREL listed as an ENDANGERED SPECIES. And it should then receive the appropriate legal protection. The “essential fish habitat” for the mackerel is very large, it takes in the bulk of the Northwest Atlantic ocean fishing areas. This is the area that needs to be protected to save this species, and the “protection” needs to mean the relief of ALL-FISHING/ALL BIOMASS EXTRACTION in the area. Merely stopping mackerel fishing alone will not suffice to protect this fish. This is the essence of the “ecosystem approach” which marine scientists have been struggling to define. It all fits together, right whales in recent years have been described by scientists as “emaciated,” groundfish are gone, crustaceans are booming, Atlantic salmon are nearing extinction...all of these things are relevant...the thing that is “endangered” is the marine ecosystem as a whole.

Designate the whole thing as a “marine protected area?”


No, not at all... “desperate times call for desperate measures.”

One of the largest obstacles to this, of course, will be the economic impact on fishermen. But they all sense that fishing is coming to an end anyhow...is it better to let the industry (and ecosystem) die a “natural” death, or to make a last-ditch effort to save it? We may still have the choice. A conscious, “precautionary” decision to stop fishing now is the most prudent course of action. Assistance will need to be provided to people currently dependent on the fishing industry (this is not a new concept), but some of them can be employed in creative approaches to restoring health to the ocean. I have suggested all along that we should try “feeding the fish,” and I still believe that a cautious investigation into this idea should be made. A project like that one would also offer useful employment to out-of-work fishing boat owners.

The fishermen have children, the scientists and politicians have children, and so do I. This is really about the future. We MUST save something for our children...too much is riding on this, and the problem extends FAR beyond mackerel.

WHEN do we blow the whistle, and call a halt to the destruction of life in the sea?

Does DFO and the FRCC have the nerve to “tell it like it is?” To “pull no punches,” and “mince no words?”

Is “precautionary approach” simply the jargon of the day, or does it reflect our true intentions? And WHOSE needs take priority and determine the urgency of applying “precautions” - the immediate economic concerns of fishermen or the continued existence of their prey? (...or perhaps the quality of our CHILDREN'S future "habitat?")

As a society we can make a conscious decision now to help fish and fishermen both...or we can wait a while longer, and “face the music” in the very near future when self-termination of the fishing industry occurs. The problem is that the casualty list at that time is going to include a lot more than “fish” and “fishermen.”


Copyright © 2001, Debbie MacKenzie

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