Dramatic shifting patterns in ocean life, and shifts in scientific thinking
…as DFO proposes a
new explanation for the codfish’s dilemma,
July 25, 2004
The Honorable Geoff Regan, M.P.
Dear Mr. Regan,
DFO scientists have recently recognized that a seal cull cannot possibly assist in cod recovery efforts on the Eastern Scotian shelf, because they have published their opinion that the cod are starving. (Choi et al., 2004) Strangely, they have implicated herring in this problem, but your scientists have also recognized that this starvation of cod has been the end result of centuries of fishing. And this changes…quite a few things…this new thinking about the nature of the trouble will have major implications for the future of DFO's "cod recovery efforts." Have you officially been made aware of this new development in Canadian fisheries science?
A group of scientists employed by the Canadian Department of Fisheries and Oceans (DFO) was assigned to do a comprehensive analysis of the groundfish crisis in Nova Scotia waters, on the Eastern Scotian Shelf - to finally get to the bottom of the problem. Two troubling facts, that Atlantic cod are not only now extremely few in number, but that the few remaining cod and other bottom fish are unusually poorly nourished, have been a great source of scientific mystery. To DFO’s working group, this situation remained “perplexing to the say the least” until late in 2003 (DFO 2003, Frank et al., 2003). But they thought that a grey seal cull might help.
Recently, however, DFO’s team of scientists has proffered a new explanation: Canadian cod are starving because their ocean environment is no longer providing enough food to support them, and an important cause of this food shortage has been centuries of fishing. Not citing “overfishing” in particular, but just the cumulative bulk “biomass removal” effect of fishing overall, scientists now suggest that this activity has ultimately damaged the ocean system to the point where medium sized bottom fish are starving, and large fish are virtually non-existent. This is the gist of the newest thinking on the groundfish crisis that has been published by DFO scientists (Choi et al., 2004). And this sounds remarkably similar to my own conclusions...it is not precisely the same, but DFO's thinking has clearly taken a step in the "starving ocean" direction, and away from the seal cull school of cod stock rebuilding.
Marine scientists are now moving toward an "ecosystem approach." In a departure from the standard single-species approach to fish assessment, DFO's team of scientists analyzed 64 different long-term scientific data sets pertaining to the Eastern Scotian Shelf, and they produced a detailed report describing various broad shifts that had occurred. Most striking was that virtually everything in this piece of ocean seems to have changed, and that similar changes affect non-fished bottom species as those that were affected directly by fishing. The scientists analyzed a wide range of information, from counts of fish, plankton and seals, to patterns in physical variables such as water temperature and salinity. After completing the first major analytical exercise, the working group reported the patterns they had found, which included a steep decline in groundfish numbers, a fall in the physical condition of many bottom fish, and a phenomenal ("500-fold") increase in certain of their smaller prey (especially the “small pelagic fish” group: herring, capelin, sand lance and mackerel). In two publications in 2003, the working group reported that they were considering three “key hypotheses” to explain the observed changing patterns (DFO, 2003, and Frank et al, 2003). These were:
(1) “’Top down’ or predator control of food webs…” (This is the hypothesis that had provided the rationale for using a seal cull to rescue cod from destruction by excessive predation. Significantly, it included the assumption that fish will grow if they are allowed to (i.e. not eaten by seals) because enough food exists in their environment to support greater fish growth.)
(2) “Physical changes associated with increasing stratification could favour the proliferation of a pelagic-based food web and limit the flux of nutrients to the benthos” (bottom life). (In which a weather-related decline in mixing of the seawater column is thought to somehow leave the food produced by plants in the surface water more under the control of herring-type fish, and these fish thereby intercept and tie up food that might otherwise have gone to feed the bottom fish. The exact dynamics of this hypothesis are vague, however, because much food in the ocean will reach the bottom simply by sinking, and the sinking tendency might actually be stronger in a stable, not-mixed water column.)
(3) “Cooling and increased advection were associated with colonization by sub-Arctic species, increases in abundance of snow crab and shrimp, and declining groundfish productivity.” (Colder water can depress feeding behaviour in some fish, and also the sub-Arctic species might presumably compete with the traditional species for food. As time goes on, however, this explanation for the missing groundfish becomes less plausible because (1) the cooling trend has not persisted, and (2) the increase in crab and shrimp does not compare to the decrease in fish, tonnage-wise (Choi et al., 2004).)
However, something important changed in the thinking of DFO’s Eastern Scotian Shelf ecosystem team during the winter of 2003-2004, because...
April 28, 2004: A third report was published on the Eastern Scotian Shelf ecosystem analysis, summarizing once again the broad changes in fish biomass and fish condition that were observed on the Eastern Scotian Shelf between the 1970s and the 2000s (groundfish are down and underfed, small pelagic fish are up). This article, titled “Transition to an alternate state in a continental shelf ecosystem,” was published as a “rapid communication” in the professional “Canadian Journal of Fisheries and Aquatic Sciences” (Choi et al., 2004). In this article, however, a significant change appeared in the key hypotheses, on “the causes of the transition.” No longer is “top down” control of the food web suggested as a cause of the changes. DFO scientists are now speculating that centuries of commercial fishing have had a “cumulative” effect in which the removal of “biologically useful biomass” has caused “energy depletion in the system.” Energy depletion in an ecosystem means generalized starvation for the larger animals. Choi et al. stated that they now consider this idea to be a “leading hypothesis” for what has gone awry on the Eastern Scotian Shelf. And this represents an important shift in scientific thinking.
Choi et al. have now offered a profoundly different interpretation of the level of damage that fishing might potentially inflict on an ocean, because fishing has never been thought capable of inducing starvation or “energy depletion” at the bottom of a continental shelf ecosystem such as the area under study. Indeed, the idea that fishing could NOT cause energy depletion in the ocean has been crucial to the conceptual foundation of “sustainable fisheries science.” DFO has not yet suggested that fishing might have induced a generalized energy depletion in the ocean system overall (as I suspect), but they have limited their conclusion to the lower water column, where the cod live and feed. So, we still disagree.
Nevertheless, in publishing this new hypothesis, I can see that DFO has taken an important first step in a direction that promises to ultimately dismantle the current “sustainable fishing” scientific paradigm. A radical shift in thinking about the ecological risk of fishing will inevitably entail a similar shift in the approach to fisheries management. For instance, if energy depletion (starvation) at the sea bottom has been caused by the bulk removal of fish (which Choi et al. describe as “biologically useful biomass”) could the current low energy problem then be worsened by the removal of more bottom fish, or by the removal of crustaceans, or of seals? Might not all of these be “biologically useful biomass” too? (Biological usefulness seems certain to be a multi-faceted attribute of the individual elements that make up ecosystems...)
The scientists have now suggested that not only physical changes in the water column ("increased stratification"), but also the cumulative physical removal of groundfish biomass, has contributed to the hypothetical "proliferation of a pelagic based food web" (herring dominance) and thereby induced the starvation of cod. The most definite part of this diagnosis, however, is the conclusion that the cod and other groundfish are now food-deprived...for some reason.
Choi et al. (2004) acknowledge that the weight of evidence from the Eastern Scotian Shelf supports the following conclusions:
(1) Marine biomass removal "without replacement" (primarily bottom fish) has had a broad unanticipated energy depleting effect on ocean bottom life in general, and this has been a cumulative effect.
(2) Non-targeted species sharing the ocean bottom habitat, including smaller invertebrates eaten by the groundfish, appear to have declined in abundance along with their predators. Overall, the benthic system (bottom) is now energy poor.
(3) Slowed growth of fish has resulted from a deficiency in their food supply. (Different hypotheses for slowed fish growth were commonly proposed before: a growth slowing effect of cold water, and a genetic shift towards smaller fish body size that could have been induced by the size-selective culling effect of some fishing gear (fishing was thought to weed out the fastest growing fish and leave behind a slower growing group). However, both of these hypotheses for small, stunted fish seem to have been discarded in the light of the sum of recent evidence.)
It is an important realization that a lack of energy flow (food) to the bottom is now limiting cod growth, and this will undoubtedly have an impact on DFO’s “cod recovery efforts.” What should be done now? Which factors tend to increase the energy flow to the sea bottom, and can we affect any of them?
While DFO and I now agree that cod are starving because their food supply is shrinking, we still disagree about other associated changes in the wider ecosystem and the ecological function of small pelagic fishes, the herring-types…What are the implications of the small pelagic fish in this story, whether they are now at unusually high abundance (DFO’s idea) or whether they are not (my hunch)?
Choi et al. speculate about a “self-stabilizing” dominance of small pelagic fish now prevailing on the Eastern Scotian Shelf, describing an unusual hypothetical situation that has somehow thrown the bottom dwelling fish into poverty. Just how this might be working, however, is difficult to imagine.
DFO suspects that the herring-type fish are causing starvation and poor recruitment of the groundfish, through two feeding-related dynamics, by intercepting food produced at the surface that might otherwise have fed bottom fish, and by eating too many of the floating eggs released by cod. By this logic, lowering the numbers of herring should work to the greater advantage of the bottom fish. There seems to be too many herring, eating too much. One significant implication of this line of thinking is that any increased activity by the natural predators of herring would be a good thing, because reducing herring numbers will tend to divert energy flow back down toward the starving groundfish. Important herring predators include seals, and if this hypothesis is true, then DFO’s “cod recovery efforts,” which are currently based largely on the removal of seals (DFO, 2004a), are scientifically unsound and may backfire. Further culling of seals is clearly scientifically inadvisable. Although Choi et al. did not state this management implication specifically in their article, they did refer to other marine scientists who have advanced precisely this rationale to warn against seal culling (Swain and Sinclair, 2000).
When there was assumed to be adequate food for cod, killing seals seemed as if it might logically tend to increase cod survival, but under a scenario of inadequate food for cod, this cannot be true: killing seals in this situation carries a real risk of being counterproductive and it can therefore not be recommended by scientists. (I have made this argument before, based on a cod food shortage resulting from a systemic fertility decline. But it works either way: cod starved by “too many herring” or cod starved in a generally starving ocean…in either case, killing seals can be expected to worsen the starving fish problem.)
What if DFO is right? If there has been a great explosion in the growth and abundance of herring and other small pelagic fish, then how do these fish “limit the flux of nutrients to the benthos?”
It is difficult to imagine the dynamics of the ecosystem as DFO now describes it. How did the bottom fish in decades and centuries past ensure that energy flowed to the bottom? Was this done by lots of big cod always eating lots of herring? By keeping the potentially dangerous herring biomass cropped down? Instead of an ocean with a large swimming biomass tied up in mature groundfish who maintained control over the herring, do we now have an ocean where the bulk of fish biomass is tied up instead in a lot of herring, who have reached such a level of dominance that they can now effectively keep food away from groundfish? Does this accurately describe the "transition" that has occurred in the Eastern Scotian Shelf ecosystem?
In the absence of the big cod, as we see today, how do the herring manage to prevent food from sinking to the bottom (because any sinking organic bits will add energy to the bottom system, not just pieces big enough for cod to eat)? DFO seems to be suggesting that a 100-fold (or greater) increase in herrings is now intercepting, eating and hoarding all of the newly formed ocean food (plankton), plus they are consuming a dangerously high fraction of the floating fish eggs released by the groundfish.
However, herring cannot effectively “juggle” the general seafood resource and retain it at higher levels in the water column, because food flows naturally to the bottom from herring. One pathway for this downward food “flux” can be seen in sinking herring eggs. Unlike the majority of ocean fish, including cod and other bottom fish, that release buoyant free-floating eggs, the eggs of herring, capelin and sand lance sink to the bottom and stick to whatever they touch.
Just the shower of spawn that settles to the bottom from today’s small pelagic fish outweighs yesterday’s entire small pelagic stock biomass (if DFO is right). A 100-fold increase in herring biomass implies a 100-fold increase in the quantity of food they deliver to the sea bottom in the form of eggs.
Consider that 10% by weight of adult herring is released annually as their spawn (in reality, this fraction can be higher than 10%, but for the sake of round numbers I will use 10. Also, this 10% of the live herring by weight represents more than 10% of their total food value, since fish roe is more protein-dense and calorie-rich than the fish that produces it – but again, to keep it simple, I will assume that roe represents 10% of the food locked up in herring.) Herring mature at a three or four years of age and some have been estimated to live for up to 20 years, spawning each year. Some herring spawn in spring and others in fall. Sticky sunken herring eggs then become a food that is available to virtually every type of bottom fish and other benthic animal, from large groundfish to tiny invertebrates.
The flow of herring-derived food to the sea bottom today, approximately 10% of the adult herring biomass, must therefore now be about ten times greater than was the entire herring biomass pre-groundfish collapse…if herring have increased 100-fold. Fewer groundfish today (less than 10% of previous numbers) are now starving on a sea-bottom that is receiving a 100-fold increase in herring spawn, with the food value of these fish eggs being greater than the entire previously existing herring biomass, that was thought to exist during the days of better groundfish growth…can we really believe that the starvation of bottom life is occurring today due to the effects of herring? The hypothesis seems to become untenable, not least because “biomass” estimates of anything do not reveal the rate of energy flow, whether of plankton, pelagic fish, or groundfish…
The casual observer might simply wonder why the starving cod do not swim up a bit and eat some of the overabundant herring. And that is a good question too…
Food and energy in the ocean cannot be tied up and sequestered away from the hungry cod by the herring. Besides paying a tithe to the bottom life in the form of their eggs, herring frequent the upper parts of the seawater column, where they excrete a bodily waste, ammonium, that acts as a fertilizer to stimulate greater plant growth. Herring eat plankton, but they also “regenerate” this fertilizer in parts of the water that are affected by sunlight, and therefore herring naturally induce greater plankton growth. Some portion of this additional food will inevitably sink and contribute to the energy flow to the bottom.
The nature of the disconnect between cod and herring, the “benthic pelagic decoupling” that DFO scientists are struggling to understand on the Eastern Scotian Shelf, cannot be clearly delineated and explicitly stated, because this is not a real possibility for these fish species that have long co-existed in the sea. That is not the nature of what is happening now, nor has it ever been before.
What if the herring are not there? If herring are not dominating the coastal ocean and preventing the flux of energy to the bottom, then an energy poor bottom suggests the possibility of an energy poor ecosystem throughout, a "starving ocean." And this is a far more serious development.
My stance on the herring question is that the dramatic biomass increase estimated by DFO most likely represents mainly an error in their assessment technique. My criticisms were detailed in an earlier article. Essentially, the flaw in DFO’s calculation has resulted from estimating the abundance of herring-type fish living at higher levels in the water column only by examining those that were caught in a bottom trawl. The apparent increase in herring biomass may be related to a shift in herring distribution and “catchability” by the bottom trawl, rather than to a genuine substantial increase in herring numbers. (See: baitfish error.)
Included as evidence of the increase in herring biomass is a mention of the development of a new herring fishery on the Scotian Shelf:
“Current pelagic biomass estimates are approximately two orders of magnitude higher than those of the 1970s. This is attributable primarily to the increased abundance of herring (Clupea harengus) in the west, capelin (Mallotus villosus) in the east, and sandlance (Ammodytes dubius) throughout. These increases in abundance were accompanied by the development of a large offshore herring fishery on the outer banks of the central Scotian Shelf where none had existed before 1996 (DFO 2003).” (Choi et al., 2004)
The last statement is potentially misleading on two counts. First, what is a “large” herring fishery? The herring fishery that developed on the offshore Scotian Shelf post-1996 has never approximated the catches made by the Nova Scotia inshore herring fishery. In its first few years, this offshore fishery netted about 12,000 tons of herring yearly, but catches declined after 2000, dwindling to less than 1000 tons in 2003 (DFO, 2004b). In comparison, the Nova Scotia inshore herring fishery has recently landed about 90,000 tons per year. This new offshore herring fishery has also never met catch levels that were made previously in the same area, because “a foreign fishery during the period 1963-1973 is estimated to have removed as much as 60,000t in a single year from the offshore Scotian Shelf banks” (DFO, 2000). (CJFAS peer reviewers appear to have missed this factual inaccuracy in the article by Choi et. al.)
The scientists charged with assessing the herring stocks specifically (as opposed to diagnosing the whole ecosystem) have placed more faith in acoustic (sonar) surveys than they have in any evidence of herring found in the bottom trawl surveys. For herring, acoustic surveys “form the foundation for evaluation of the stock status” (Melvin et. al., 2003). A recent report from the outer Nova Scotian banks includes these observations:
“Fleet activity/catch in the spring/early summer fishery on the offshore banks of the Scotian Shelf diminished in 2002. Acoustic recorders were activated on a few occasions but insufficient quantities of fish were observed to warrant analysis. Consequently, no acoustic biomass estimates were available from the Scotian Shelf in 2002. The fall herring survey (Oct 22 – Nov 2), which covered a large number of the outer banks, documented very little fish…The largest aggregation of herring was observed on the “Patch” and no herring were captured in any fishing set southeast of Halifax, excluding the Patch.” (Melvin et. al., 2003)
There is reason, therefore, to suspect that herring might actually be declining on the offshore Scotian Shelf. Also, a “deterioration in the state of the herring stock” has been reported for the inshore component (DFO, 2004b). The hypothesis that the coastal ocean ecosystem is now heavily dominated by small pelagic fish seems to be contradicted by a lack of direct evidence of high herring abundance.
Increasing bottom trawl counts of a common small baitfish, the sand lance (Ammodytes dubius), have been considered to be an important part of the evidence of the transition of the ecosystem to dominance by "pelagic fish," which have been speculated to be preventing the flow of food to the bottom. "Pelagic fish" tend to swim in schools and stay away from the very bottom water. The sand lance, however, is only a semi-pelagic fish. While it does swim in pelagic schools, the sand lance is more accurately described as "semidemersal" (Anon.). Besides releasing sinking eggs at maturity, the sand lance is often found in very close association with the sea bed. In fact, it commonly buries itself. Sand lance therefore seem most unlikely to have any capacity to prevent the normal flux of food to the bottom. Sand lance are regular food for larger bottom dwelling (demersal) fish. For instance, haddock, a fish which roots through the soft sea bottom for food, is a common consumer of sand lance.
"Sand lance, as the name implies, are found on sandy bottom, both inshore and on the banks; they avoid rocky bottom. They occur in large schools and burrow in the sand at times to a depth of several inches; sometimes they remain buried in sand when the tide leaves the area...Over half of the food of haddock on the Sable Island Bank consists of sand lance." (Liem and Scott, 1966)
Therefore, DFO's hypothesis that a great biomass of pelagic fish - largely herring, capelin, and sand lance - is currently causing the starvation of bottom fish by preventing the flux of food to bottom, seems to be contradicted by known aspects of the biology of these "pelagic" fish species.
If the "small pelagic fish" are not causing the starvation of the bottom fish, then what is causing it? Is the ocean itself now "starving?"
Might the upper region of the ocean water column also now be relatively “energy poor” compared to its previous condition, as is the lower region where the codfish live? The truth is that overwhelming evidence suggests exactly this, from declining zooplankton counts across the Eastern Scotian Shelf to a “coherent community-level reduction” in shoreline marine animal life. Barnacles, mussels, and other small animals and fish living near the shoreline have demonstrated a broad general decline in size and numbers, echoing and coinciding with the trends that scientists have described in groundfish. Seaweeds provide direct evidence of declining plant fertility at the ocean surface, of being “energy poor” today in comparison to seaweeds that grew here decades ago. The long-term decline in the availability of Irish moss on the Nova Scotia shoreline provides but one piece of such evidence. This broad scenario of declining life at the sea surface cannot be plausibly explained by pollution or by climate change, no more than the starving cod on the sea bottom can be. However, the larger changing picture, of the erosion of vitality of an ocean overall, can be explained by the cumulative effect of fishing, by the progressive removal of “biologically useful biomass.”
Mr. Regan, five years ago, in 1999, I sent copies of my self-published book, "Wake Up and Feed the Fish! A new insight into the causes of the collapsing fisheries," to DFO Science and to the office of the Minister of Fisheries and Oceans. Then minister, Herb Dhaliwal, replied to me that this was of definite interest to him and that he would direct DFO Science to respond to me. I was told by scientists that my diagnosis of the cod problem - an inability of cod to find enough to eat - was simply wrong. I was naive, and I did not understand how the ocean works. Marine scientists at that time had alternate ways of interpreting the various data that I thought supported my conclusion. But it seems now that I was right. I had argued that cod are starving today because of centuries of fishing, because of cumulative bulk biomass removal from the ocean. Five years later, DFO has arrived at a remarkably similar conclusion.
It is interesting that Choi et al. mentioned the problem of bulk biomass removal "without replacement," because this was also what I saw. I thought that perhaps we could help reverse the situation by "replacing" some of the missing biomass/food on the fishing banks, and that maybe we should try scattering edible human food wastes where fish or other sea creatures could eat them. I wanted to "feed the fish." This might help somewhat, but I now realize that it would be a delicate and risky venture, because the risk of depleting oxygen from the water by letting organic materials rot on bottom would be a serious hazard in many places. Carefully done, however, this strategy might help a bit. The most obvious intervention that we need to make, however, is to stop removing living biomass from the ocean. A catastrophe for the fishing industry, for sure, but the ramifications of causing greater starvation in the ocean are serious global ones; they affect even the stability of the atmosphere, the carbon cycle.
Mr. Regan, I offer you a prediction today that over the next few years DFO scientists will discover new insights and will publish new papers describing the subtle specifics of the nature of the “biological usefulness” of “biomass” that swims in the ocean as fish. It will eventually be shown that an important part of the natural usefulness of fish is to enhance the fertility of the ocean ecosystem itself, and that this is why centuries of fishing caused the ultimate starvation of cod on the Scotian Shelf. Those big old bottom-dwelling cod did more that was "biologically useful" than to just eat a lot of herring: they also sent untold billions of their own excess eggs floating up to fertilize the surface water, and those fish thereby helped to ensure that more food would grow and sift down through the water column later, feeding everything. It will be further realized that all marine animals exert this same positive effect on ocean health and fertility, from small pelagic fish and groundfish, to seals and whales, and including all of the tiny forms of animal plankton. Unfortunately, however, this realization will signal the end of the prevailing “sustainable fisheries” scientific paradigm. But this establishment is teetering already…that much can be easily appreciated, and it is not too difficult to guess which way it will fall.
There will soon be a major revolution in scientific thought about the ecological role and significance of all animals living in the ocean.
Once DFO makes a more accurate assessment of the trends in small pelagic fish biomass, and it is crucial that they do this, the Eastern Scotian Shelf science team will be very close to seeing the big picture clearly. And they will see something that they were never taught to see before: that fishing has ultimately eroded the energy of the overall ocean ecosystem, because all fish, and all marine mammals and seabirds, naturally contribute to the health and enhance the fertility of the ocean itself. Humans have simply killed far too many of these creatures, by centuries of fishing, and we have thereby now dangerously lowered the energy of the ocean ecosystem itself. We have run up a huge debt. Important organic reserves in the sea, that we did not appreciate as such, have been significantly drained. It will eventually be realized that the ocean health enhancement provided by abundant large marine animal life extends even to helping ward off such modern ocean ills as “dead zones,” bacterial domination in coastal waters, and toxic algae blooms.
The only real remedy for the problem of generally weakened ocean health will be for people to protect whatever is left alive in the sea and to allow marine animals to regain strength, and to rebuild ocean fertility, together: we will need to leave all marine life alone for some time. Impossible? Maybe, but this will soon be the objective scientific truth of the matter. I realize that admitting this to the Canadian public will be rough work for a Minister of Fisheries and Oceans. However, the sooner we bite this bullet, the better, because the health of the environment that our children inherit depends heavily upon our action – or our inaction - today. And a healthy ocean is crucial to all else; this is true beyond any doubt.
As the Minister of Fisheries and Oceans, you need a well-informed, honest and impartial ocean science watchdog. As for myself, I find now, after years of being able to support my marine research independently, that I can no longer afford to continue to do so. Might I be able to help you? I will soon need to find a way to generate income. Any practical help or financial support would be greatly appreciated.
P.S. Following up on a couple of issues we discussed at our meeting in April: Thank you for ensuring that DFO scientists will finally give me at a hearing at the Bedford Institute of Oceanography. This has been arranged in a seminar format for September 15, 2004 - please let me know if you would like to attend this meeting or to send someone from your office. Also, did you or your assistant discover any signs of activity by MACO, the Minister’s Advisory Council on Oceans?
Copyright © Debbie MacKenzie, 2004
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