Seals in the Marine Ecosystem
Grey seals and cod in the marine ecosystem
Grey seal. Photo by Andrew Vaughan, Canadian Press 2005
In October 2012, the Standing Senate Committee on Fisheries and Oceans presented a report that called for a cull of 70,000 grey seals in the Gulf of St. Lawrence in order to assist the recovery of the North Atlantic cod. The report, "The sustainable management of grey seal populations: A path toward the recovery of cod and other groundfish stocks," was produced after several months of hearings in which Canadian fishing industry represenatives pleaded their case, government scientists working for the Department of Fisheries and Oceans presented their data, and independent scientists provided data and criticism of this proposal.
Adept at observing changes in marine life, we see fishermen around the world over-simplifying explanations and jumping to conclusions. "If certain species of seals or other marine mammals eat target fish, and if the population of these marine mammals is increasing, this must be why their catches of fish are decreasing," they reason. And then they proceed to the corollary: "It would be beneficial for the fish stock to cull the marine mammals."
Ignored in this is the complexity of the marine food web, the effect of climate change, and the effect of ocean pollution, among other factors.
In his testimony to the Senate panel, biologist and marine scientist Dr. David Lavigne asserted, "While clearly bits and pieces of the science can be selected to support a grey seal cull, when all the scientific evidence is considered, any apparent support vanishes."
Dr. David Lavigne
Dr. Lavigne offered the following explanation:
- Grey seals have undoubtedly increased in recent decades as they recover from near extirpation in the late 1940s . In some circles this recovery is actually regarded as a conservation success story.
- Cod populations off eastern Canada were seriously depleted by over-fishing in the late 1960s, and further in the mid-to late 1980s, which resulted in the imposition of a moratorium on the cod fishery in 1992.
- Since then, cod populations have been slow to recover but a number of stocks are now showing positive signs of recovery, even in the presence of a number of seal species.
- Nonetheless, the question remains whether their recovery has been or is being impeded by seals, in particular by grey seals in the Gulf of St. Lawrence and on the Eastern Scotian Shelf.
- Recently, much scientific attention has been directed to the issue of grey seals and cod. Most of the resulting papers conclude that grey seals have little impact on cod stocks. A recent manuscript suggests, however, "that seals have contributed to both natural mortality increase and lack of cod stock recovery". That claim has been publicized in the press, most recently, yesterday. What the media has not reported is that the "Model predictions [in that paper] are not consistent with recent observed cod increase in trawl surveys". This admission by the authors of the paper – O'Boyle and Sinclair – seems to suggest that there are problems with their modeling. Instead, the authors suggest that the observations, rather than their models, "need to be confirmed". I have to say that is not the way science is normally conducted. Elsewhere in the paper, they are more circumspect.
- Regardless, taken at face value, the conflicting scientific results highlighted in the DFO Science Advisory Report (2010) and O'Boyle/Sinclair manuscript, simply remind us that marine systems and interactions between seals and fisheries are complex and difficult to study. As always there is scientific uncertainty in the data and analyses associated with trying to figure out what has really been going on with grey seals and cod, and how that relationship will unfold in the future.
- Of course, as soon as one mentions the future, I am reminded that we are in the midst of a period of environmental uncertainty – resulting from climate change and global warming – that is already having an impact on ice-breeding seals across the North Atlantic. Some grey seals reproduce on ice and, if that ice fails to form in the coming years, it may have implications for them as well. To the uncertainties mentioned previously, we must therefore add environmental uncertainty.
- All of this uncertainty has not resulted in any noticeable abatement in calls for undertaking a massive cull of grey seals.
- Nonetheless, undertaking a cull of grey seals at this time is a risky business. Scientists have repeatedly said over the past three decades that it is impossible to predict the effects of increasing or decreasing the size of a seal population on exploited fish stocks and future fishery yields from them. More uncertainty.
- After more than 30 years of trying to understand the impacts of culling seals it would be fair to ask why the scientists still can’t provide definitive answers. Of course, the answer to that question brings us back to the issue of complexity.
- And, as noted previously, scientists – including DFO scientists – have also warned that culls can have unintended consequences. Science tells us, for example, that culling a predator like grey seals could actually result in a reduction of preferred fish stocks, the antithesis of the intended outcome. It all depends on the complex (that word again) interactions in a particular marine ecosystem.
- All of the uncertainty associated with interactions between grey seals and cod, environmental change, and the various uncertainties associated with culling, call for the rigorous application of the precautionary approach.
Dr. Lavigne, along with four Dalhousie University scientists, Dr. Sara Iverson, Dr. Lindy Weilgart, Prof. Hal Whitehead, and Dr. Boris Worm, as well as Dr. Sidney Holt of Paciano, Italy, wrote an open letter to the Fisheries Minister in 2011, which further explains why a cull would be reckless.
In the letter, they expose the flaws in the way a workshop was organized to discuss and debate the issue of a seal cull. "The process by which we arrived at the present situation represents the antithesis of how science should function in the fishery management process."
The Fisheries Minister first directed the DFO to "ensure the targeted removal of grey seals". The DFO then organized a science advisory workshop in which attendees were directed to consider the negative impacts of grey seals on fisheries while ignoring the positive impacts they have.
Read the full text of this open letter here.
For more information, read Dr. Lavigne's chapter in Hindell and R, Kirkwood
(eds.), Marine Mammals: Fisheries, Tourism and Management Issues: CSIRO
Publishing, Collingwood, Victoria, Australia 2003, "Marine Mammals and Fisheries: The Role of Science in the Culling Debate," pp. 31-47
Another scientist who testified before the Canadian Senate committee convened to discuss a proposal for a grey seal cull is Dr. Jeffrey A. Hutchings, Professor of Biology at Dalhousie University in Halifax, Nova Scotia, Canada. Dr. Hutchings also chaired a panel that was convened in 2010 and reported on the sustainability of Canada’s marine biodiversity in 2012.
In his testimony before the Senate committee, Dr. Hutchings criticized the DFO's mismanagement of the oceans:
"Marine fishes in Canada’s oceans are estimated to have declined by an average of 52% from 1970 to the mid-1990s and have remained stable thereafter. Most commercially fished stocks remain well below conservation targets. When compared to other developed fishing nations and jurisdictions, such as the US, Norway, Australia, New Zealand, South Africa, and increasingly in the EU, Canada’s record at achieving long-term sustainability in its fisheries has been less than stellar."
He went on to say, "Fishery-induced changes to predator-prey interactions might be responsible for significantly retarding, or even preventing, the recovery of depleted marine fishes. At least three species in the southern Gulf of St. Lawrence, for example, are experiencing unsustainably high levels of natural mortality, meaning that they will be extirpated, or lost, from the southern Gulf if mortality rates do not decline." These species include white hake, winter skate, and the North Atlantic cod.
Dr. Hutchings testified that the "increase in abundance of species that cod formerly preyed upon, such as mackerel and herring" may contribute to the failure of the cod to recover because now these species are preying upon cod eggs and larvae. Although there is some evidence that grey seals may be contributing to the "unsustainably high mortality of some fish in the Southern Gulf, including cod," Dr. Hutchings testified that, "the culling of grey seals, by whatever means, might not be sufficient to allow for the recovery of Atlantic cod, and other depleted fishes, in the Southern Gulf." One reason for this is that there is a complex food web with incompletely understood interactions.
Dr. Hutchings then addressed the question of whether a grey seal cull would be justifiable:
"In my view, a cull of grey seals for the purpose of 'improving fisheries productivity' would represent an insufficient reason for initiating such a cull because:
- the effects of such a cull on the recovery of cod, or of other species, cannot be credibly predicted from a science perspective;
- and the deliberate killing of one species native to Canada because of the human-induced depletion of another native species -- ultimately caused by politically expedient but scientifically unjustified management decisions -- would be difficult to defend from a variety of perspectives.
Dr. Hutchings full statement may be downloaded here.
In the following paragraphs, Dr. Hutchings answers three questions that Harpseals.org posed to him.
1. What would you recommend the DFO do as part of a recovery plan for the North Atlantic cod?
"As part of a recovery plan, I would urge DFO to:
(i) establish a science-determined (as opposed to science-based) target reference point
for all of its cod fisheries, but most notably for Southern Gulf cod and Eastern Scotian Shelf cod;
(ii) establish harvest control rules for each of its cod fisheries; and
(iii) fully implement its Sustainable Fisheries Framework policy, which in essence articulates the point that stocks that fall below their respective limit reference points should not have any targeted or directed fisheries for cod (bycatch would be the only permissible catch, which should also, of course, be kept to a minimum). (I should note that, at present, there are no directed fisheries for cod in either the Southern Gulf or Eastern Scotian Shelf.)
2. Would you recommend banning all fishing for the species including recreational fishing and the Sentinel fishery?
I would not advocate a ban on recreational fishing for two reasons:
(i) it is unlikely that these fisheries are contributing substantively to the
death of cod at present; and
(ii) a ban on recreational fishing seems verylikely to have just the opposite reaction than what would be intended, i.e., an increase in fishing mortality. That is, I strongly suspect that
the illegal catch of cod would increase (and a ban would be exceedingly difficult to enforce).
3. Would establishing protected nurseries help?
And I don’t think that a nursery (in the sense of protecting young cod)
would have much effect, given that the survival of young cod is not
currently of major concern; rather, it is the unusually high natural
mortality of larger, older cod that is the problem.
Harp seals and cod in the marine ecosystem
Did harp seals cause the collapse of the North Atlantic cod fishery? Are harp seals preventing the cod population from recovering? This debate has raged since the Grand Banks cod fishery collapsed in 1992, though, as evidenced from the speech reproduced above, the effort to brand marine predators, such as seals, as destructive competitors to fishermen existed many years prior to this.
In fact, overfishing and excessive killing of marine mammal species has been altering and destroying marine ecosystems for centuries. The main difference in modern history has been the introduction of industrial-scale fishing, made possible by technological developments such as large-scale purse seining, long-lining, bottom trawling, and factory freezer trawler ships.
Harp seal pup. Photo: AP
In 1995, then Canadian Prime Minister Brian Tobin increased the harp seal kill quota to 250,000, and in one of his most famous lines, claimed that there was one primary reason for the failure of the cod population to recover. "There is only one major player fishing that stock," he said. "His first name is harp, and his last name is seal."
But this assessment ignores the complexity of the food web and of the ecosystem itself. Seals eat not only cod, but predators of cod. The cod population was depleted so much that many scientists question whether recovery is possible.
Links for more information on the interactions between seal and cod populations
Click here for more on the seal-cod relationship.
Click here for a pictorial of myths and facts about seals as part of the marine ecosystem.
Here are articles on marine fish population collapses and how they recover,
the DFO scientists' article on grey seal impacts on the cod recovery,
and research showing that initial recovery of the cod is in progress.
Captain Paul Watson Speech on Seals as Part of a Marine Ecosystem
Captain Paul Watson, founder of Sea Shepherd Conservation Society and cofounder of Greenpeace, gave a speech in Vancouver, Canada, on February 4th, 1985, to the Royal Canadian Commission set up to investigate the seal hunt. Here, we reprint this speech:
"Those who support the theory that seals are destroying the fish are only exposing their ignorance of ecological systems. The reasoning that less seals will result in more fish or that more seals will deplete existing fish populations is an unscientific belief because it is a belief not backed by observation or data.
Seals are essential
element in maintaining a state of ecological stability. The ocean is a complex, living environment that has evolved since the beginning of the planet. In our present state of evolution, the natural world we live in has found a key role for marine mammals in marine habitats. The issue of harp seals cannot be separated from the issue of the long-term future health of the oceans.
The seal slaughter
is a contributing factor to the overall ecological crises now taking place. Other major factors directly damaging the marine environment are destruction of spawning areas; over fishing by commercial trawlers, especially vessels of foreign registry; waste dumping of oil, chemicals, and sewage; and the slaughter of other marine mammals such as whales and dolphins. The synergistic, or combined, effects of all these different sources of ecological disruption are having a catastrophic impact.
The life that thrives in the oceans has a critical influence on the overall health of the ocean system. The great herds of seals are a life force whose influence on the health of the ocean can be recognized once the complexities of the food chain are investigated and understood.
When harp seals eat in herds, the return massive amounts of nutrients in the form of fecal material, which feeds the plankton, which feed the fish, which in turn feed the seals. The removal of this nutrient base would be critical to the health of plankton and fish populations.
The migrating seal herds, and other marine mammals, move nutrient wealth in a way no other force can: in giant north-south loops
and from great depths to the surface. By going through regular periods of gorging and feasting, seals provide large amounts of nutrients at key times of the year. The combination of the seal supplied nutrients in the area where the Labrador Current meets the Gulf Stream of Mexico is responsible for the great fish grounds of the Grand Banks. Reference to the logs of captain Jacques Cartier, Samuel de Champlain, and John Cabot illustrate that at the time of the greatest number of seals prior to European exploitation, the fish were so abundant that Cabot described the Grand Banks as "so swarming with fish that they could be taken but in baskets let down with a stone."
Plankton, the smallest animals in the ocean, require organic matter and sunlight to grow. Once the sun reaches a high enough point in the sky in the northern latitudes so that sufficient sunlight is available to the plankton, the seals arrive and begin to eat and defacate, releasing the needed supply of nutrients. Plankton cannot eat fish, but they can consume fecal material as it is broken down into nutrients. The plankton then provides for krill and up the food chain through the fish and back to the seal.
that helps to understand the role of the seal herds in the ocean is that of trees in a forest. A healthy forest can be viewed as being dependent on a healthy soil. The soil is made up of minerals that come from rock, and organic material from trees. Without the rocks or the trees there would be soil and no forest. The impact of clear-cuts is well known. Once the trees are taken away, a desert is left behind. In a similar manner, taking seals out of the ocean environment takes away an important source of organic material to the plankton, and thus leaves a relatively sterile environment behind.
To suggest that seals threaten the ocean is to suggest that trees threaten the forest."
*In the usual political manners and traditions, this explanation, of course, was dismissed by the commission...
* (Excerpted word for word with permission from Paul Watson and the
Sea Shepherd Conservation Society from the book entitled "Seal Wars-
Twenty Five Years on the Front Lines with the Harp Seals"- Firefly Books, Copyright 2003, Paul Watson)